Acta mater.49(2001)
1051–1062
https://www.doczj.com/doc/3f15991131.html,/locate/actamat
SINGLE-CRYSTAL LASER DEPOSITION OF SUPERALLOYS:
PROCESSING–MICROSTRUCTURE MAPS
M.GA ¨UMANN§,C.BEZENC ?ON,P.CANALIS and W.KURZ?
Department of Materials,Swiss Federal Institute of Technology Lausanne,1015Lausanne EPFL,
Switzerland
(Received 29September 2000;accepted 27October 2000)
Abstract —In order to extend the life cycle of modern single-crystal (SX)high-pressure high-temperature gas turbine blades,repair of cracked or worn parts is of great interest.The success of the repair technique depends critically on a close process control in order to ensure SX repair.Based on solidi?cation theory a process called epitaxial laser metal forming (E-LMF)has been developed.This paper presents the important concepts necessary for any process control for SX repair based on processing maps which relate the expected solidi?cation microstructures and growth morphologies to the processing conditions.These maps are obtained in two steps.Firstly,the relationships between local solidi?cation conditions and the resulting solidi?cation microstructures,i.e.columnar or equiaxed,are formulated.Secondly,the local solidi?cation conditions as a function of the laser processing parameters are calculated with an analytical heat ?ux model.By a combination of both approaches,processing–microstructure maps are obtained which de?ne processing windows for SX generation and repair by laser deposition.?2001Acta Materialia Inc.Published by Elsevier Science Ltd.All rights reserved.
Re
′sume ′—La re ′paration locale d’aubes monocristallines (SX)de turbines a `gaz,apportant la possibilite ′d’aug-menter le cycle de vie de ces e
′le ′ments,est de grand inte ′re ?t.A?n de garantir une re ′paration monocristalline des parties endommage ′es,un proce ′de ′permettant le contro ?le des microstructures de solidi?cation est ne ′ces-saire.Un tel proce
′de ′,epitaxial laser metal forming (E-LMF),a e ′te ′de ′veloppe ′sur la base de the ′ories de solidi?cation.Cet article pre
′sente les concepts importants pour le contro ?le de la microstructure lors de de ′po-sition par laser,et propose des cartes de proce
′de ′,reliant la microstructure de solidi?cation et la morphologie de croissance aux parame
`tres du proce ′de ′.Ces cartes sont obtenues en deux e ′tapes.Premie `rement,la relation entre les conditions locales de solidi?cation et la microstructure de solidi?cation re
′sultante,i.e.colonnaire ou e
′quiaxe,est e ′tablie.Deuxie `mement,les conditions locales de solidi?cation sont calcule ′es en fonction des parame
`tres de proce ′de ′laser,par un mode `le analytique de ?ux de https://www.doczj.com/doc/3f15991131.html, combinaison des deux approches donne des cartes de microstructure/proce
′de ′,permettant l’e ′tablissement de fene ?tres de proce ′de ′pour une re ′par-ation monocristalline,par rechargement laser.?2001Acta Materialia Inc.Published by Elsevier Science Ltd.All rights reserved.
Zusammenfassung —Die Einkristallreparatur von defekten Einkristall-Turbinenschaufeln kann zu einer betra ¨chtlichen Erho ¨hung der Lebensdauer fu ¨hren.Der Erfolg der Reparatur ha
¨ngt kritisch von der Prozesskon-trolle ab,durch die das Einkristallgefu ¨ge wiederhergestellt wird.Aufgrund von erstarrungstheoretischen U ¨ber-legungen wurde ein Prozess entwickelt,der Epitaxiales Laser Metall Formen (E-LMF)genannt wird.Fu ¨r dieses Verfahren werden Prozesskarten in zwei Stufen ermittelt:(1)Beziehung zwischen den lokalen Erstar-rungsbedingungen (G ,V )und den Gefu ¨gen (gerichtet/globulitisch);(2)Beziehung zwischen lokalen Erstar-rungsbedingungen und Laserprozessparametern.Durch Kombination beider Beziehungen konnten Prozess–
Gefu ¨ge-Karten aufgestellt werden,die es erlauben,eine Einkristallreparatur hoher Qualita
¨t zu realisieren.?2001Acta Materialia Inc.Published by Elsevier Science Ltd.All rights reserved.Keywords:Ni alloy;Single crystal;Solidi?cation;Laser treatment
1.INTRODUCTION
One way to raise the overall ef?ciency of a gas-tur-bine is to increase the operating temperature.In mod-?To whom all correspondence should be addressed.Fax:?41-21-693-5890.
E-mail address:wilfried.kurz@ep?.ch (W.Kurz)
§Presently with Calcom SA,1015Lausanne,Switzer-land.
1359-6454/01/$20.00?2001Acta Materialia Inc.Published by Elsevier Science Ltd.All rights reserved.PII:S 1359-6454(00)00367-0
ern aircraft engines and power generating systems this is obtained by the use of single-crystal (SX)high pressure–high temperature (HPT)turbine blades and vanes [1,2].The life of these high value components is limited by defects such as platform cracks or blade tip erosion.A repair/reshaping technique is therefore of great economic interest in order to extend the life cycle of these components.As the SX alloys do not contain grain boundary strengtheners,it is necessary
1052
GA
¨UMANN et al .:SINGLE-CRYSTAL LASER DEPOSITION OF SUPERALLOYS that the reshaping technique also generates a single
crystal and a deposit which is epitactic with the sub-strate.
Laser metal forming (LMF),a rapid prototyping technique related to cladding,has been developed in recent years to produce shaped components [3].Simi-lar processes with various names have been developed by other groups (for example,[4–6]).In this process,metal powder is injected into a molten pool formed by controlled laser heating of the sub-strate [Fig.1(a)].By the superposition of laser traces,a three-dimensional object can be formed which has,under controlled conditions,a reasonably good sur-face quality.The local solidi?cation conditions which are encountered during LMF and also in the related process of laser surface remelting [Fig.1(b)]lead generally to a dendritic microstructure with columnar or equiaxed growth morphology.
Epitaxial laser metal forming (E-LMF)[7]is a LMF-type process where epitaxial growth of colum-nar dendrites is achieved during the solidi?cation
of
Fig.1.Schematic representation of (a)the LMF process (?rst two deposits only are shown)and (b)the laser surface remelt-ing process.
the melt pool by a careful selection of the processing parameters through (i)partial remelting of the sub-strate to ensure epitaxy between substrate and deposit [Fig.2(a)],and (ii)avoiding the CET (columnar to equiaxed transition),i.e.nucleation and growth of equiaxed grains [Fig.2(b)].A close process control based on recent solidi?cation theory (e.g.[8])is a prerequisite for any successful SX repair.In this way the crystal orientation of the substrate is reproduced in the newly formed solid which shows,due to higher solidi?cation rates,a ?ner columnar dendritic struc-ture.With this process,SX repair has been performed locally on damaged turbine blades [9].Single crystal-line solidi?cation was also obtained in electron beam and pulsed laser welds of Fe–Cr–Ni alloys and Ni-base superalloys when the substrate was itself a single crystal [10–12].
The aim of this paper is to present the basic con-cepts for the determination of relevant laser pro-cessing windows for a controlled SX repair of SX turbine components.After describing the experi-mental conditions,a microstructure selection criterion for the CET of complex alloys is developed and a microstructure selection map for the superalloy CMSX-4is established.The local solidi?cation con-ditions (thermal gradient,G ,and solidi?cation velo-city,V )during the laser process are calculated.The in?uence of the processing parameters such as laser power,P ,beam velocity,V b ,beam diameter,D b ,
or
Fig.2.Schematic representation showing (a)?ne epitaxial col-umnar dendritic growth on a SX substrate with coarse den-drites,(b)defects to be avoided in E-LMF:loss of epitaxy and columnar to equiaxed transition (CET).The lines represent a
speci?c crystal orientation such as [001].
1053
GA
¨UMANN et al .:SINGLE-CRYSTAL LASER DEPOSITION OF SUPERALLOYS Table 1.Nominal composition,in wt%,of SX alloys,CMSX-4and PWA 1480[15]Co
Cr Al Ti W Ta Re Mo Hf Ni CMSX-4
9.0 6.5 5.6 1.0 6.0 6.5 3.00.60.1bal.PWA 1480
5
10
5.0
1.5
4
12
–
–
–
bal.
preheating temperature,T 0,on the solidi?cation microstructures is shown in the form of processing–microstructure maps.Such maps are instrumental for the control and optimisation of the E-LMF process.
2.EXPERIMENTAL
Laser metal forming and laser remelting (Fig.1)are related localised solidi?cation processes.The lat-ter may be seen as LMF with a powder feed rate equal to zero [13].Laser remelting represents a simpler form of the more complex LMF process and allows rapid analytical calculation of the local solidi?cation https://www.doczj.com/doc/3f15991131.html,ser remelting is therefore used here for the modelling of the solidi?cation phenomena of the E-LMF process and to connect the processing para-meters with the relevant parameters for microstruc-ture control.
Substrates for laser remelting experiments were machined from single crystalline cast ingots,fully heat treated (solutionized and aged [14])with the ?001>orientation normal to the surface.The alloy CMSX-4(Table 1),a typical commercial SX Ni-base superalloy,was selected for the experiments.
For all experiments a 1.7kW cw CO 2laser was used.The beam intensity pro?le was a near top hat mode (TEM 00?TEM 01)with circular polarisation.Six surface remelting experiments of SX substrates were undertaken under different processing para-meters (Table 2).Three conditions (samples A–C)will be discussed in more detail.Preheating was done with an induction coil.In all experiments a laminar ?ow of Ar was applied for oxidation protection of the melt pool.The shape and microstructure of the laser trace was observed with optical and electronic micro-scopes.Sections were polished with diamond paste and an acidic alumina suspension was used for ?nal polishing.
The volume fraction f of equiaxed grains after laser resolidi?cation is obtained by electron back scattering diffraction (EBSD)analysis of transverse
Table 2.Processing parameters (preheating temperature,T 0,laser beam rate,V b ,nominal laser power,P )and volume fraction of equiaxed grains,
f ,after laser remeltin
g (laser beam diameter,D b ?0.75mm)Internal No.Sample T 0(°C)V b (mm/s)
P (W)f (%)
GA186A 2013405GA187B 20108209GA184C
10001082080GA1831000134027GA1851000100150032GA188
20
100
1500
3
sections of the traces.(EBSD is a technique for the analysis of the local crystal orientation and therefore the grain-structure of materials [16–18].)
Cracked SX HPT blades removed from an aircraft engine were used to show the feasibility of a SX repair of real parts by laser generation.The cracked platform was cut,polished and repaired by E-LMF by eight successive laser traces with a laser beam rate,V b ?4mm/s.The powder and substrate materials consisted in this case of PWA 1480,a ?rst generation Ni-base superalloy (Table 1).The feeding powder was produced by atomisation in a protective atmos-phere.
3.MICROSTRUCTURE SELECTION
Prediction of solidi?cation microstructures requires the modelling of the nucleation and growth of all possible phases.Nucleation will,in many cases,play a critical role in the phase selection process [19,20].In other cases,growth behaviour controls the selec-tion of the microstructure [21].In a more general approach,however,as is necessary for the columnar to equiaxed transition (CET),both nucleation and growth have to be considered simultaneously [22].During solidi?cation of the melt pool obtained by laser treatment,the solid acts as a heat sink and solidi-?cation is mostly directional,at least locally.The heat ?ux is opposite to the growth direction and the rate of advance of the isotherms constrains the solid–liquid interface to grow at an imposed velocity.If the feed-ing material is similar to the substrate,initial solidi?-cation will show an epitaxial growth when the sub-strate is slightly molten.If nucleation and growth of equiaxed grains in the liquid ahead of the columnar front are avoided,an epitaxial,columnar and SX structure is achieved throughout the deposit.A close control of the CET is therefore a necessary condition for successful processing.
The CET occurs when nucleation of suf?ciently numerous equiaxed grains takes place in the consti-
1054GA¨UMANN et al.:SINGLE-CRYSTAL LASER DEPOSITION OF
SUPERALLOYS
Fig.3.Microstructure selection map for superalloy CMSX-4 under the experimental conditions described in the text,show-ing the expected solidi?cation morphology as a function of temperature gradient,G,and solidi?cation velocity,V.The dot-ted line represents the critical condition for E-LMF given by equation(5),with K?2.7?1024(K3.4/m4.4s).The rectangular insert shows the range of conditions which is typical for the LMF process.The squares represent average G and V values for laser processing conditions A,B and C.?T n?2.5°C,
N0?2?1015/m3,f c?0.0066.
tutionally undercooled liquid adjacent to the columnar dendritic front.Once nucleated,a certain volume frac-tion of equiaxed grains,f,will form,depending on the temperature gradient in the liquid,G,on the sol-idi?cation velocity of the columnar front,V,on the nuclei density of the alloy,N0,etc.This will eventu-ally lead to the CET.This phenomenon has been modelled in different ways[22–24],the most recent and complete of the analytical models being that of Ga¨umann et al.[25].Results of this model applied to superalloys trough a database for superalloys[26]is shown in Fig.3for a nuclei density,N0?2?1015/m3and a nucleation undercooling,?T n?2.5°C.This microstructure selection map shows the ?nal solidi?cation microstructure,i.e.columnar or equiaxed,for a range of G and V values.An increase in N0,or a decrease in?T n extends the equiaxed regime to higher G and lower V values,respectively. The model’s use for superalloys with10components such as CMSX-4is,however,limited by the avail-ability of the thermodynamic data and the long calcu-lation time required.Therefore another approach based on a modi?cation of Hunt’s model[22]will be presented here.
By assuming that all the grains nucleate at the same critical undercooling?T n,the radius of the equiaxed grains is given by integrating the growth velocity from the time that nucleation starts until the time that the columnar front reaches the grains.After substitut-ing(for steady state conditions)time by undercooling [(d(?T)/d t??VG],a relationship can be derived between the temperature gradient,G,the volume frac-tion of equiaxed grains,f,the nucleation undercoo-ling,?T n,the number of nucleation sites,N0,an alloy parameter,n(see below),and the dendrite tip undercooling,?T.
G?
1
n?1
·3??4p
3ln[1?f]
N1/30·?T·?1??T n?1n n?1?(1)
Calculation of the CET requires the determination of the dendrite tip undercooling?T,i.e.the difference between the equilibrium liquidus temperature of the alloy and the tip temperature.Under normal dendritic growth conditions,the total tip undercooling is the sum of three contributions:a constitutional,a curva-ture and a thermal undercooling.Since for solidi?-cation of metallic alloys,the tip curvature and the thermal contributions are much smaller than the con-stitutional undercooling[8],only the constitutional contribution will be taken into account in the calcu-lations.Moreover,by neglecting the thermal undercooling,a unique relationship can be used for columnar and equiaxed growth.
In a multicomponent model considering an inde-pendent solute?eld of each component(q elements) [27,28],the constitutional tip undercooling?T c is given by
?T c??q j?1m j(C0,j?C?l,j)(2)
where,for each solute element j,m j are the slopes of the liquidus,C0,j the nominal concentrations of the alloys and C?l,j the concentration at the tip in the liquid.
The concentration C?l,j is calculated by the IMS (Ivanstov–Marginal stability)dendrite growth model [29],by assuming a constant Gibbs–Thomson coef-?cient of1.8?10?7(m K)and equal diffusion coef-?cients for the alloying elements of3?10?9(m2/s). This calculation was coupled with a ThermoCalc dat-abase for superalloys developed by Thermotech[26], allowing an evaluation of the distribution coef?cients, k j,and the liquidus slopes,m j,for each element as a function of the temperature for the alloy CMSX-4. In order to simplify the calculations,the consti-tutional tip undercooling,?T c,for columnar and equi-axed dendritic growth is given,approximately,by
?T??T c?(a·V)1/n(3)
where a and n are material dependant constants.
In Hunt’s original work n was equal to2(linearised binary system,hemispherical dendrite tips,and low Peclet numbers).Here,a more realistic evaluation of the parameters a and n have been undertaken by?t-ting equation(3)to the dendrite tip undercooling cal-culated with the IMS dendrite growth model.A good correlation of?T c with equation(3)can only be obtained for a limited range of solidi?cation velo-cities,and gives,for the window of conditions met
1055 GA¨UMANN et al.:SINGLE-CRYSTAL LASER DEPOSITION OF SUPERALLOYS
during laser treatment(insert of Fig.3),n?3.4and
a?1.25?106(K3.4/m s].
Substituting equation(3)into equation(1),
G?
1
n?1
·3??4p
3ln[1?f]
·N1/30·(4)
?1??T n?1n(a·V)(n?1)/n?·(a·V)1/n
For solidi?cation under high temperature gradient G,the nuclei density,N0,plays the important role and the nucleation undercooling,?T n,can be safely neg-lected?[22,25].As in laser surface treatment con-ditions,the thermal gradient G is high(105–107K/m),?T n can be set to zero and the following relationship is obtained
G n
V
?a?3??4p N03ln[1?f]·1n?1?n(5)
This equation is useful for V of the order of cm/s and G of the order of106K/m.
The number of nucleation sites N0of CMSX-4has been evaluated experimentally by laser remelting of SX samples,as described previously.Figure4shows EBSD patterns of samples with(a)high and(b)low G n/V ratios.The?rst remelted trace(sample A)resol-idi?ed with a mostly columnar dendritic morphology (f?0.05)while the second(sample C)showed a large fraction of equiaxed grains(f?0.8).For
N0?constant,f depends on G n/V.The measured volume fractions f have been plotted as a function of the calculated G3.4/V ratios in Fig.5.A good corre-lation between equation(5)and the experimental measurements can be obtained when N0?2?1015/m3.
Hunt proposed that fully equiaxed growth occurs if the volume fraction of equiaxed grains f>0.49, whereas the structure is assumed to be fully columnar if f?0.0066.By setting f to the latter lower critical value,f c,in equation(5),a criterion based on the G n/V ratio can be derived which states that the micro-structure is columnar when the following condition is satis?ed everywhere in the melt pool:
G n
V
>K(6)
In the present case K?2.7?1024(K3.4/m4.4s)and n?3.4.This relationship is crucial for a successful E-LMF process.It is represented by the dotted line in the microstructure selection map of Fig.3.As can
?Note that under solidi?cation conditions of investment casting of SX blades the situation is opposite:the tempera-ture gradients are much lower and the principal alloy para-meter controlling the CET is?T n[30].be seen,this criterion is more restrictive than the tran-sition calculated with the more complete analytical model.The processing conditions for E-LMF must lie on the right-hand side of this limit.
The avoidance of equiaxed growth is a necessary condition for successful SX deposition.Another necessary condition is suf?cient remelting of the sub-strate to ensure epitaxy between substrate and deposit. This will be treated in the next section.
4.PROCESSING PARAMETERS
The temperature gradient,G,and the solidi?cation velocity,V,under laser processing conditions are the most important parameters which govern the solidi?-cation structure of a given alloy.For instance,the CET transition can be characterised by a critical G n/V ratio.However,in the practice of laser processing one controls the processing parameters P,V b,T0or D b, which show complex relationships with the local sol-idi?cation conditions G and V.The thermal gradient is given by the temperature?eld generated by the laser source and the solidi?cation velocity is related to beam velocity and the melt pool shape.Therefore, the heat transfer from the moving laser source into the material and the resulting melt pool geometry must be considered in more detail.
LMF is a rather complex process which is con-trolled by mass transfer(powder)and heat and?uid ?ow in the melt pool.It will be simpli?ed in order to obtain approximate values for G and V as a func-tion of the processing parameters.As stated before, only heat diffusion will be taken into account and the in?uence of the mass feeding and of convection will be neglected,leading to the simpler case of laser remelting.The mass feeding and the convection have clearly an in?uence on the melt pool shape[31,32] and consequently on G and V.Their effects will be discussed in Section6.
The thermal gradient was calculated by solving the heat diffusion equation with a modi?ed Rosenthal approach.Rosenthal proposed a solution for the tem-perature?eld in the metal for a moving point heat source[33],assuming a semi-in?nite body with con-stant physical properties and no latent-heat release. This model was modi?ed for a gaussian laser inten-sity pro?le[34,35]and was adapted for the top-hat mode of this laser(see Appendix A).
The melt pool shape was assumed to be given by the liquidus isotherm.The position of the solid–liquid interface,as represented by the dendrite tips,deviates from that of the liquidus isotherm by the dendrite tip undercooling(which is a function of velocity).As the thermal gradients are high,the in?uence of?T on the exact position of the solid–liquid interface may be neglected.The velocity of the solid–liquid interface is therefore considered to be equal to the rate of advance of the isotherms V iso.The normal velocity of the liqui-dus isotherm is linked geometrically to the heat source velocity,V b,by the angle between the solidi-
1056
GA
¨UMANN et al .:SINGLE-CRYSTAL LASER DEPOSITION OF
SUPERALLOYS Fig.4.EBSD maps of the transverse section of two laser surface remelted samples showing (a)an epitaxial
and mainly columnar structure (sample A)and (b)equiaxed grain structure (sample C).The colour scale shows the misorientation angle between the crystallite direction and the crystal coordinate system of a reference point
(black
spot).
Fig.5.Determination of the nuclei density N 0by correlation
between the measured (Table 2)and the calculated [equation (5)]volume fractions of misoriented (equiaxed)grains as a function of the average G 3.4/V ratio [for a ?1.25?106
(K 3.4/m s)].
?cation front normal and the beam direction,q ,as shown by equation (7).
|V iso |?|V b |·cos q
(7)
V iso increases rapidly from zero at the bottom and at the side of the melt pool to a value close to V b at the rear of the melt pool surface [36].The orientation of the substrate will be taken into account in our cal-
culations as the dendrites of cubic crystals grow gen-erally along the ?001>direction which is closest to the heat ?ow direction.Therefore,the dendrite tip velocity V hkl ,where hkl represents the growth direc-tion,is given by the following relationship [10]:
|V hkl ||V b |?cos q
cos y
(8)
where y is the angle between normal to the solidi?-cation front and the dendrite trunk axis de?ned by [hkl ].
These equations are solved numerically and enable the computation of the temperature gradient and the solidi?cation velocity of the dendrites for laser remelting conditions.Figure 6(a)and (b)show the evolution of V and G at the solid–liquid interface,as a function of the melt pool depth z ,for processing condition C.These have been calculated in the median plan (plan of symmetry)of the melt pool,where y ?0(the physical parameters used for com-putation are reported in Table 3).The laser beam moves along a [100]direction with the [001]direction normal to the surface.The arrows in the ?gure show the time evolution of solidi?cation:the beginning of
1057
GA
¨UMANN et al .:SINGLE-CRYSTAL LASER DEPOSITION OF
SUPERALLOYS Fig.6.Evolution of the local solidi?cation variables,as a func-tion of depth z ,calculated in the plane of symmetry of the melt pool (y ?0);(a)velocity of the isotherm,V iso ,and dendritic velocity along the [001]and [100]directions for processing conditions C (if it would produce columnar grains);(b)tem-perature gradient,G ,for conditions C;(c)G 3.4/V calculated for conditions A,B and C.The arrows show the time evolution of the solidi?cation conditions and the squares represent depth
averaged values.
solidi?cation occurs at the bottom of the melt pool and the solidi?cation ends at the melt pool surface,i.e.z ?0.It may be seen that the dendritic velocity is greater than or equal to the isothermal velocity.The [001]dendritic velocity is zero at the bottom of the laser trace and rapidly increases until it reaches the
Table 3.Values of the physical and thermal properties of CMSX-4used in the calculations of processing parameters and processing maps Melting temperature of Ni 1726(K)Speci?c heat C p
690(J/K kg)Liquidus isotherm T l
1660(K)Heat conductivity ?22(W/m s)
Absorption coef?cient b 13(%)a
Thermal diffusivity a 3.66?10?6(m 2/s)
Alloy density r at 20°C
8.7?103(kg/m 3)
a
The mean absorption coef?cient b for CMSX-4melt and CO 2laser radiation was determined experimentally by a calorimetric technique [38].
[100]dendritic velocity (in the direction of and equal
to V b )where a 90°growth direction transition is observed.The growth orientation with the smallest velocity,i.e.lowest undercooling or highest tempera-ture is selected [10,37].
Figure 6(c)shows the evolution of the G 3.4/V ratio with respect to melt depth for processing condition A,B and C.The maximum depth of the melt pool,z max ,is a function of the processing conditions,but the three ratios are highest at the bottom of the laser trace and decrease when z approaches zero (in the particular case of sample A,the ratio is not at its minimum at the top of the trace,due to the particular behaviour of the thermal gradient).
In these diagrams only columnar dendritic growth is calculated as only this type of dendrite growth per-mits judging the possibility of a CET (even if the ?nal result lies completely in the equiaxed range as is the case in example C in Fig.6).
In order to facilitate the comparison of the in?u-ence of various sets of laser processing parameters on the solidi?cation morphology,characteristic values
V
ˉz and G ˉz will systematically be calculated as an average over the depth z of the trace along the liqui-dus isotherm,in the median plan of the pool.For G this is
G
ˉz ?1
z max ?
z max
G ·d z (9)
The mean value of the G n /V ratio can be calculated
correspondingly:
?G n
V
?
z
?
1
z max ?
z max
G n
V
·d z (10)
These values are reported in Fig.6as squares,and are characteristic for a given set of processing con-ditions.For instance,it can be shown that the charac-teristic temperature gradient G
ˉz drops when the laser power P increases.
Figure 7shows the evolution of the solidi?cation conditions for processing conditions A,B and C (Table 2)superimposed on the microstructure selec-tion map for CMSX-4(inset of Fig.3).The arrows show the direction of the evolution from the begin-
1058
GA
¨UMANN et al .:SINGLE-CRYSTAL LASER DEPOSITION OF
SUPERALLOYS Fig.7.Evolution of the solidi?cation condition G and V during
melt pool solidi?cation for the process window of Fig.3.Pro-cessing condition and average values (square)for condition A,B and C (Table 2).The ?gure also shows the region of a fully columnar growth (grey zone)and the criterion corresponding
to equation (5)for the CET (dotted line).
ning to the end of solidi?cation.The squares represent the average values for each processing condition,as given by equations (9)and (10).The columnar to equiaxed transition is calculated with the more com-plete analytical model [25]whereas the dotted line is the more restrictive criterion presented above [equ-ation (6)].In the case of processing conditions with-out pre-heating (A and B),the higher thermal gradi-ents give rise to a higher G 3.4/V ratio.Therefore it becomes obvious that solidi?cation under processing condition C ,with preheating to 1000°C,leads pre-dominantly to equiaxed grains whereas for processing condition B,the CET is reached only at the end of solidi?cation.By reducing the beam velocity and the power (sample A),the average V value is lowered and the CET may be avoided during the whole process.
5.PROCESSING–MICROSTRUCTURE SELECTION
MAPS
The critical G 3.4/V ratio may be used as a safe cri-terion for producing purely single crystalline struc-tures.Therefore,G 3.4/V values are computed as a function of the laser processing parameters.This allows an appropriate choice of process conditions to be made.Figure 8shows,for instance,the
in?uence
Fig.8.In?uence of the laser power P on the average ratio (G 3.4/V )z for different preheating temperatures T 0(V b ?
10mm/s,D b ?1
mm).Fig.9.Processing map showing the dominant microstructure,for two laser scanning speeds,V b ,as a function of laser power P and preheating temperature T 0(D b ?1mm).SX ?
single crystal,PX ?polycrystal.
of the laser power P on the average G 3.4/V ratio for different preheating temperatures T 0.It can be seen from this ?gure that an increase in preheating tem-perature and of the laser power lowers the average G 3.4/V ratio,so that the tendency to form equiaxed grains increases.If the increase in preheating tem-perature is accompanied by a decrease in laser power,columnar structures might still be obtained.
In order to visualise the effect of a combination of several processing parameters,it is instructive to compile processing maps for the critical value
G 3.4c /V ?2.7?10
24
(K 3.4/m 4.4s).Figure 9shows poss-ible processing conditions for various sets of P ,T 0and two V b values.P must be reduced when T 0is increased in order to achieve columnar growth during solidi?cation of the melt pool (grey zone).This is mainly due to the thermal gradient,as G decreases when T 0is increased and must therefore be compen-sated by a decrease in P .A higher scanning speed,i.e.V b ?20mm/s,is accompanied by a displacement of the CET to lower preheating temperature T 0.An increase in V b increases V ,leading to smaller values of G 3.4/V .
Other processing maps with D b ,P ,T 0or V b can be computed in a similar way.Figure 10shows the combined effects of P ,V b and two T 0values as para-meters.The transition curve is C shaped.The shaded zone at the top left of the ?gure represent
conditions
Fig.10.Processing map showing the dominant microstructure,for two preheating temperatures T 0,as a function of laser power
P and beam scanning speed V b (D b ?1mm).
1059
GA
¨UMANN et al .:SINGLE-CRYSTAL LASER DEPOSITION OF SUPERALLOYS for which the heat input is insuf?cient to melt the
surface,leading to a loss of epitaxial growth.For the set of conditions given in Fig.10,scanning speeds of the order of 20mm/s have a greater probability of forming an equiaxed morphology than scanning speeds of either 1or 100mm/s.At low velocity,an increase in V b increases V without a major effect on G ,leading to a decrease in the G 3.4/V ratio.At high velocity,the melt pool becomes smaller,leading to a higher temperature gradient.Hence,even if V is increased,the ratio G 3.4/V may increase.However,a treatment with high V b will be critical with respect to surface melting.With some preheating (T 0?200°C),the remelting of the surface is easier but the CET line moves to lower P .This leads to a smaller window of processing conditions where the substrate is remelted and where solidi?cation results in a columnar mor-phology.
The in?uence of P and D b is shown in Fig.11.Clearly,as shown by the shaded zone,large beam diameters are dif?cult to work with since the reduced beam intensity rapidly limits the process.Thus,when a large D b is desired,it is necessary to increase P in order to control a suf?cient remelting of the substrate to insure epitaxial growth.It is also clear that this might eventually lead to CET.Increasing preheating slightly facilitates melting at larger diameters,but sig-ni?cantly reduces the processing window,as it shifts the transition line to lower laser powers.
These processing microstructure maps are useful for process control and development.As an example,the repair of a modern SX blade containing platform cracks [Fig.12(a)]is presented.After having machined off the edges of the platforms,a SX plate was deposited by E-LMF onto the edge [Fig.12(b)].An EBSD grain-structure map of a transverse section of the repaired zone [Fig.12(c)]shows that the deposit of eight successive traces is epitaxial with the substrate and that the columnar growth of dendrites is well controlled during the process.Equiaxed grains are only present on the top of the last trace,due to non-remelted powder particles.This equiaxed layer has to be removed by a ?nal machining
operation.
Fig.11.Processing map showing the dominant microstructure,for two preheating temperatures T 0,as a function of laser power
P and laser beam diameter D b (V b ?10mm/s).
6.DISCUSSION
The processing–microstructure maps described above permit conclusions to be drawn concerning possible processing conditions for a successful SX turbine blade repair,i.e.to ensure the complete absence of grain boundaries in the repaired part.The microstructure selection and the laser process have been simpli?ed and modelled in such a way that the processing maps can be calculated in a relatively short time.The critical steps in the overall model are discussed below.
6.1.Microstructure modelling
The microstructure analysis is based on dendrite models which have been extended to multicomponent alloys.These models give reliable semi-quantitative results so far as good thermodynamic data are avail-able.This latter point is critical.Much work is still needed before such data can be obtained for alloys of the complexity of superalloys with some 10elements.The use of a single diffusion coef?cient is another important simpli?cation.
The CET model is approximate,as it does not take into account the real composition pro?le of a colum-nar dendritic growth front.The differences are how-ever suf?ciently small so as not to produce important errors (see discussion in [25]).Under typical con-ditions for laser processing (high V and G )nucleation undercooling has a negligible effect on the CET and the complex equation (4)may be simpli?ed substan-tially without loosing precision.The result is the criti-cal parameter set,G n /V ?K ,which permits the com-putation of solidi?cation conditions which safely lead to SX growth.The two unknown alloy parameters are:(i)the nuclei density,N 0,which can be determ-ined for any alloy in simple separate remelting experi-ments (N 0seems to be constant and characteristic for a given alloy);(ii)the equilibrium liquidus/solidus range of the alloy which appears in the constant “a ”and exponent “n ”of equation (3).The model is valid for concentrated solutions (something which is sel-dom the case in solidi?cation modelling).
The microstructure selection model also takes into account the important fact that dendrites grow along ?xed crystallographic directions,generally [001]in cubic crystals,and that this introduces modi?cations in the solidi?cation path and leads to abrupt (90°)changes of the growth direction when the undercoo-ling of the dendrite trunk tip is equal to the dendrite branch tip.
6.2.Process modelling
Computation of the relevant solidi?cation para-meters,G and V ,from laser process control variables is complex and tedious as it involves numerical FE calculations of 3D heat and ?uid ?ow in a surface tension stabilised melt pool.In order to make these calculations tractable and rapid enough for practical use the LMF process has been simpli?ed in several
1060
GA
¨UMANN et al .:SINGLE-CRYSTAL LASER DEPOSITION OF
SUPERALLOYS Fig.12.Single-crystal repair of a damaged SX turbine blade.(a)cracked platform,(b)platform repaired by E-LMF,(c)EBSD grain-structure map of transverse section of repaired zone.
ways.Remelting is assumed to represent suf?ciently well the melt pool geometry of LMF to make sensible predictions possible.The 3D thermal ?eld of the plate geometry is modelled by a semi-in?nite substrate geometry of a modi?ed Rosenthal solution.This sol-ution for the temperature ?eld assumes constant ther-mal properties,no latent heat release and no convec-tion in the liquid pool,as well as no powder injection.Several authors have proposed models which show that convection [39,31]signi?cantly in?uences the shape of the pool.Fluid ?ow will ?atten the melt pool when the surface tension decreases with temperature,or will make the pool deeper in the opposite case.It has been observed experimentally that with small laser beam diameters,the remelted laser trace differs substantially from the calculated trace.It is expected that a high energy density leads to high thermal gradi-ents in the liquid surface and therefore to strong con-vective ?ow.When larger laser beam diameters are used the melt pool becomes smaller than the beam diameter and the melt pool shape is reasonably well described by Rosenthal’s model.The variations of the melt pool geometry directly affect the transitions of the growth direction and slightly affect the solidi?-cation velocity.
Moreover,the ?uid ?ow induced by convection may promote dendrite fragmentation and the transport of dendrite arms which can act as nucleation sites for equiaxed grains.As N 0is determined by experiment in the presence of convection,neglecting convection for the thermal model should not have an in?uence on the prediction of the CET and the calculated microstructure selection maps.
Powder injection has an important in?uence on the melt pool shape,on the depth of the remelted layer in the substrate and on the CET.Powder injection tilts the melt pool by an angle related to the height of the clad and the length of the pool [32],therefore affect-ing,under others,the solidi?cation velocity.The glo-bal absorption of the laser energy is given by the energy absorbed by the powder and the energy absorbed by the irradiated substrate [39].Frenk et al .showed that the powder injected into the deposit
absorbs energy when crossing the laser beam and that the global absorption may be enhanced by powder feeding (depending on laser polarisation).Therefore,the unremelted zone shown in the processing maps of Figs 10and 11will be reduced and the processing window for epitaxial deposition will be enlarged.Similar to dendrite arm fragments,undissolved powder particles will increase the nuclei density.This effect will depend strongly on the powder particle size distribution,larger particles producing more equiaxed grains.Moreover,solid powder particles may sinter to the surface of the deposit without remelting,leading to a randomly oriented layer at the surface [Fig.12(c)].
Due to these assumptions only qualitative relation-ships between processing parameters and solidi?-cation variables can be expected.
The laser treatment of Ni-based superalloys is often limited by their high susceptibility to solidi?cation cracking.One way to overcome this critical phenom-enon is to preheat the part [11].These superalloys show a minimum of ductility at approximately 700°C [40].Therefore,preheating has to be undertaken well above this temperature to be effective.The processing maps of Figs 8and 9show,however,that SX struc-tures can only be produced with no or little preheat.Therefore,under the experimental conditions described,preheating of CMSX-4should be avoided when a SX structure is required.Fortunately,due to the absence of grain boundaries,the SX material is less hot crack sensitive than the directionally solidi-?ed (DS)or polycrystalline material of the same alloy.Therefore,it is possible to generate crack-free SX parts without preheating,even if polycrystalline parts have to be preheated above 1000°C for crack-free welding.
7.CONCLUSIONS
Processing windows for SX laser deposition of superalloys have been determined through (i)theor-etical modelling of microstructure formation,(ii)
1061 GA¨UMANN et al.:SINGLE-CRYSTAL LASER DEPOSITION OF SUPERALLOYS
experimental measurements of alloy parameters and (iii)heat-?ux calculations of the laser process.
A model of the columnar to equiaxed transition (CET)has been developed for solidi?cation of multi-component alloys under high temperature gradients (G?106K/m).A microstructure criterion,predicting columnar growth when the G n/V ratio is greater than a system constant K,is obtained.This alloy constant, essentially a function of the solidi?cation interval and the nucleation site density,has been experimentally determined for CMSX-4.The nuclei density has been evaluated as2?1015/m3,n?3.4and the critical
G3.4/V?2.7?1024(K3.4/m4.4s).
The complex laser metal forming process has been simpli?ed in order to compute the characteristic value of the G n/V ratio as a function of a set of processing parameters(T0,V b,P,D b).By calculation of the characteristic ratios for several sets of processing parameters as compared with the microstructure cri-terion,processing–microstructure maps have been obtained.They show the resulting microstructure (columnar or equiaxed)and the zone of unremelted substrate(leading to loss of epitaxy)as a function of the laser process parameters.It is only under both simultaneously achieved conditions,i.e.suf?cient remelting for epitaxial growth and columnar dendrite growth,that a SX deposit can be produced.Those SX-processing windows allow some important con-clusions about the laser processing conditions for a successful SX deposit:
?The temperature of the substrate should be as low as possible(preheating has to be avoided).
?The laser beam power should be reduced as this increases the temperature gradient.
?The laser beam diameter should be small in order to ensure suf?cient remelting for epitactic growth. By the use of the processing–microstructure maps presented in this paper,cracked platforms of SX gas turbine blades have been successfully repaired with a SX deposit.
Acknowledgements—The authors would like to acknowledge various contributions to this paper by Franc?ois Cle′ton,Ste′-phane Dobler,Anders Engstro¨m,Jeremy Green,Olivier Hun-ziker and Milton Lima.Speci?c thanks are due to Jean-Daniel Wagnie`re for the carefully performed experiments.This work has been achieved within the Swiss Priority Program on Materials Research(PPM)with the?nancial support of the Board of the Swiss Federal Institutes of Technology.The con-tinuous support and interest of all industrial partners,ABB, Calcom,Sulzer-Innotec and Swissair,is sincerely acknowl-edged.
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APPENDIX A
Modi?cation of the Rosenthal solution for a Gaussian laser intensity pro?le and derivation of thermal gradient G
The intensity pro?le I for a laser with a TEM 00(gaussian)mode is well described by Geissler [35].
I [x ,y ]?
2b ·P p ·D 2b ·exp ?
?2(x 2?y 2)
D 2b
?
(A1)
where P and D b are the power and the beam diameter of the laser.It can be adapted to a near top hat mode (TEM 00?TEM 01)by summing up several gaussians.The associated temperature ?eld can be obtained by integrating Rosenthal’s solution over the intensity pro?le
T [x ,y ,z ]?T 0??T
(A2)
with
?T [x ,y ,z ]?
(A3)
2ab P
?p 3/2
·?
?
exp ??2
(x ?V b t )2
?y 2
D 2b ?8a t
?
z
2
4a t ?
√a t ·(D 2b ?8a t )
·d t
The temperature gradient G is then given by (G x ,G y ,G z )and can be derived as
G [x ,y ,z ]?√G 2x ?G 2y ?G 2
z
(A4)
G x ,y ,z ?
?T
?x ,y ,z
?g x ,y ,z ·?T (A5)
with
g x ??4·x ?V b ·t
D 2
b ?8a ·t
(A6)
g y ??4·y
D 2
b ?8a ·t
(A7)
g z ?
?z 2a ·t
(A8)
The temperature ?eld T and temperature gradient G can be calculated numerically.Unfortunately,equa-tions (A3)and (A8)are unde?ned at t ?0.These singularities can be set aside by a proper change of the integration variable t .For T ,g x and g y ,this change is
m ?
2√2a ·t D b
(A9)
and for g z it is
m ?z ·
D b
2√2a ·t
(A10)
where m is the new integration variable.
1 铺粉 国外选区激光熔化成形技术在航空航天领域应用现状 董鹏 陈济轮 （首都航天机械公司，北京100076） 摘要：选区激光熔化成形技术具有制造精度高、表面质量好以及能够实现悬空、复杂内腔和型面等复杂构件的整体制造等特点，是满足航空航天领域中复杂薄壁精密构件高精度、高性能、高柔性与快速反应的理想制造方法。本文对国外选区激光熔化成形技术在航空航天领域的应用以及技术发展方向进行了分析。 关键词：选区激光熔化成形；航空航天；应用现状 Current Status of Selective Laser Melting for Aerospace Applications Abroad Dong Peng Chen Jilun (Capital Aerospace Machinery Company,Beijing 100076) Abstract ：Selective laser melting can manufacture complex geometries structures with thin walls and hidden voids or channels without tools or mould,for difficult-to-machine materials.It provides a high efficiency,high-quality,flexible manufacturing technique for manufacturing components in aerosapce fields.The current status and the trends of of selective laser melting for aerospace applications in abroad were analysed. Key words ：selective laser melting ；aerospace ；current status of applications 1 引言 金属材料增材制造技术是在航空航天领域关键件研制需求的牵引下诞生的，由于其特有的技术优势，使得各国政府和研究结构投入大量的人力、物力、 财力进行该项技术的研究。近些年在航空航天领域迫切需求的牵引以及计算机技术、激光技术以及材料科学等相关基础技术快速发展的推动下，增材制造技术发展十分迅速。 图1选区激光熔化成形基本流程[4] 作者简介：董鹏（1983-），工程师，光学工程专业；研究方向：激光焊接与增才制造。 收稿日期：2014-03-06 CAD 模型 分层切片 铺粉 激光按分层形状熔化金属粉末 基板下降 完成零件制备
金属零件激光选区熔化3D打印装备与技术随着科学技术日新月异的进步，机械加工行业不断发展。而快速成型技术，尤其是激光3D打印技术在机械加工行业中起到了越来越大的作用，并渐渐在制造业得到了广泛应用，成为了如今机械制造业中不可或缺的一部分。3D打印技术正在快速改变我们传统的生产方式和生活方式，不少专家认为，以数字化、网络化、个性化、定制化为特点的3D打印制造技术将推动第三次工业革命。 金属零件3D打印技术作为整个3D打印体系中最前沿和最有潜力的技术，是先进制造技术的重要发展方向。按照金属粉末的添置方式将金属3D打印技术分为三类：（1）使用激光照射预先铺展好的金属粉末，即金属零件成型完毕后将完全被粉末覆盖。这种方法目前被设备厂家及各科研院所广泛采用，包括直接金 属激光烧结成型（Direct Metal Laser Sintering,DMLS）、激光选区熔化（Selective laser melting,SLM）和LC（Laser Cusing）等；（2）使用激光照射喷嘴输送的粉末流，激光与输送粉末同时工作（Laser Engineered Net Shaping，LENS）。该方法目前在国内使用比较多；（3）采用电子束熔化预先铺展好的金属粉末（Electron Beam Melting,EBM），此方法与第1类原理相似，只是采用热源不同。 激光选区熔化技术是金属3D打印领域的重要部分，其采用精细聚焦光斑快速熔化300－500目的预置粉末材料，几乎可以直接获得任意形状以及具有完全冶金结合的功能零件。致密度可达到近乎100%，尺寸精度达20－50微米，表面粗糙度达20－30微米，是一种极具发展前景的快速成型技术，而且其应用范围已拓展到航空航天、医疗、汽车、模具等领域。 目前SLM设备的研究和开发也成为了国内外快速成型领域的热点。本文对SLM设备的组成和成型原理进行了一个概述性的介绍，对比了国内外SLM设备的参数，并对SLM设备和技术的发展进行了展望。 SLM成型设备 SLM设备一般由光路单元、机械单元、控制单元、工艺软件和保护气密封单元几个部分组成。 光路单元主要包括光纤激光器、扩束镜、反射镜、扫描振镜和F-?聚焦透镜等。激光器是SLM设备中最核心的组成部分，直接决定了整个设备的成型质量。近年来几乎所有的SLM 设备都采用光纤激光器，因光纤激光器具有转换效率高、性能可靠、寿命长、光束模式接近基模等优点。由于激光光束质量很好，激光束能被聚集成极细微的光束，并且其输出波长短，因而光纤激光器在精密金属零件的激光选区熔化快速成型中有着极为明显的优势。扩束镜是对光束质量调整必不可少的光学部件，光路中采用扩束镜是为了扩大光束直径，减小光束发散角，减小能量损耗。扫描振镜由电机驱动，通过计算机进行控制，可以使激光光斑精确定位在加工面的任一位置。为了克服扫描振镜单元的畸变，须用专用平场F-?扫描透镜，使得聚焦光斑在扫描范围内得到一致的聚焦特性。
第２７卷第３期２００７年５月 ＪＯＵＲＮＡＬ 孝感学院学报 ＯＦ ＸＩＡＯＧＡＮ ＵＮＩＶＥＲＳＩＴＹ ＶＯＬ．２７Ｎ０．３ ＭＡＹ．２００７ 激光无线通信光发射与接收电路的设计 鲁德初，吕 昊，吴迪 （孝感学院物理与电子信息工程学院，湖北孝感４３２０００） 摘要：提出了一种为半导体激光器的调制驱动电路，能够在大气激光通讯中稳定工作。还研究了大气信道的特点，并讨论了大气信道对信号的吸收、散射和湍流影响，给出了衰减的因子。结合信道编码定理，讨论了适于在大气中传输的码型，特别是Ｒｓ码，得出了适合大气信道的编码码长和码率的选择依据。 关键词：无线激光通信；大气信道；码型分析中图分类号：ＴＮ９２９ 文献标识码：Ａ 文章编号：１６７１—２５４４（２００７）０３—００３８—０４
激光无线通信又称为自由空间光通信（ＦＳＯ），它以大气作为传输介质进行通讯¨也１，与传统的通信方式相比，有着许多优势，如传输速率高，光束方向性好，保密性高，不需无线电频率使用许可，不影响市政建设，成本低，结构轻巧，通信频带宽，尤其是激光特性中具有高度的定向性，发射波束纤细，在短时间内能够传输大量数据，通信时间短，具有高度的保密性和抗干扰性，能有效地防止窃听和侦测¨“ｏ。 ． １．１激光器的直接调制电路 图２是数字式直接调制电路图，图中晶体管ＢＧ２和ＢＧ３为发射极耦合对，组成非饱和电流选择开关。当ＢＧ：基极电位高于ＢＧ３基极电位时，ＢＧ２导通，恒流源的驱动电流Ｉ。全部流过ＢＧ：，故流过ＬＤ的电流为零；反之，当ＢＧ２基极电位低于ＢＧ３基极电位时，ＢＧ３导通，所有驱动电流都通过ＬＤ。电流开关的转换过程由输人数字信号转换成ＥＣＬ电平来控制，ＥＣＬ电平为“ｌ”码时，输出为一１．８Ｖ，为“０”码时，输出为＋０．８Ｖ，经过ＢＧｌ和Ｄ１电平移动后加到ＢＧ２基极，而ＢＧ３基极电平固定在一２．６Ｖ，它由温度补偿的参考电平Ｖｂｂ经ＢＧ。和Ｄ２电平移动得到。Ｖｂｂ＝一１．３ｌ是“ｌ”码和“０”码电平的中间值。 选择适当的输入电压，使晶体管不驱动到饱和状态，就能起到快速开关作用，同时恒流源可使开关噪声很小。１．２调制发射电路 图３是调制驱动电路图，主要由ＭＡＸＩＭ公司的１５５ＭＨｚ的ＭＡＸ３２６３芯片和内部带有监视二极管的激光器ＬＤ构成。ＭＡＸ３２６３内部的主偏置电源提供温度补偿偏置和参考电压输出Ｖｒｅｆｌ和Ｖｒｅｆ２，通过电阻Ｒ２５、Ｒ２６、Ｒ２７和Ｒ２８对内部的高速调制驱动电路、激光器和监视二极管进行编程。ＭＡＸ３２６３的输出电流都被内部的镜像电流 Ｖ
《快速成型技术Ⅰ》课程论文 针对熔融挤出成型(FDM)技术的表面粗糙度分析讨论 学院机械与汽车工程 专业机械一 学生姓名廖政泰 指导教师杨永强王迪 提交日期年月日
表面粗糙度及影响因素 表面粗糙度影响零件的耐磨性。表面越粗糙，配合表面间的有效接触面积越小，压强越大，磨损就越快。 2）表面粗糙度影响配合性质的稳定性。对间隙配合来说，表面越粗糙，就越易磨损，使工作过程中间隙逐渐增大；对过盈配合来说，由于装配时将微观凸峰挤平，减小了实际有效过盈，降低了联结强度。 表面粗糙度 表面粗糙度 3）表面粗糙度影响零件的疲劳强度。粗糙零件的表面存在较大的波谷，它们像尖角缺口和裂纹一样，对应力集中很敏感，从而影响零件的疲劳强度。 4）表面粗糙度影响零件的抗腐蚀性。粗糙的表面，易使腐蚀性气体或液体通过表面的微观凹谷渗入到金属内层，造成表面腐蚀。 5）表面粗糙度影响零件的密封性。粗糙的表面之间无法严密地贴合，气体或液体通过接触面间的缝隙渗漏。 表面粗糙度 表面粗糙度 6）表面粗糙度影响零件的接触刚度。接触刚度是零件结合面在外力作用下，抵抗接触变形的能力。机器的刚度在很大程度上取决于各零件之间的接触刚度。 7）影响零件的测量精度。零件被测表面和测量工具测量面的表面粗糙度都会直接影响测量的精度，尤其是在精密测量时。 此外，表面粗糙度对零件的镀涂层、导热性和接触电阻、反射能力和辐射性能、液体和气体流动的阻力、导体表面电流的流通等都会有不同程度的影响。 选择性激光熔化技术的基本原理 SLM技术是利用金属粉末在激光束的热作用下完全熔化、经冷却凝固而成型的一种技术。为了完全熔化金属粉末，要求激光能量密度超过106W/Cm2。目前用SLM技术的激光器主要有Nd-YAG激光器、Co2激光器、光纤(Fiber)激光器。这些激光器产生的激光波长分别为1064nm、10640nm、1090nm。金属粉末对1064nm等较短波长激光的吸收率比较高，而对10640nm等较长波长激光的吸收率较低。因此在成型金属零件过程中具有较短波长激光器的激光能量利用率高，但是采用较长波长的Co2激光器，其激光能量利用率低。在高激光能量密度作用下，金属粉末完全熔化，经散热冷却后可实现与固体金属冶金焊合成型。SLM 技术正是通过此过程，层层累积成型出三维实体的快速成型技术。根据成型件三维CAD 模型的分层切片信息，扫描系统(振镜)控制激光束作用于待成型区域内的粉末。一层扫描完毕后，活塞缸内的活塞会下降一个层厚的距离;接着送粉系统输送一定量的粉末，铺粉系统的辊子铺展一层厚的粉末沉积于已成型层之上。然后，重复上述2个成型过程，直至所有三维CAD模型的切片层全部扫描完毕。这样，三维CAD模型通过逐层累积方式直接成型金属零件。最后，活塞上推，从成型装备中取出零件。至此，SLM金属粉末直接成型金属零件的全部过程结束. 在制造过程中，铺粉装置按设定的层厚将金属粉末均匀地铺设在基板上，激光在振镜控制下对需要熔化的区域进行扫描熔化；然后，基板下降一个层厚，重复下层的加工，如此往复，金属零件一层层地被加工出来。SLM激光快速成型技术非常适用于复杂零件的快速制造，它可以极大地缩减产品开发周期，降低设计与制造成本，具有广阔的研究与应用前景［1～8］。在这种逐层加工过程中，前一层水平面的表面质量直接影响到下一层的铺粉均匀性，如果前一层的表面粗糙度值很大，甚至存在球化现象，则可能导致下一层的铺粉过程无法完成，从而使得成型加工无法继续；另外，垂直面、倾斜面的表面粗糙度作为成型零件表面粗糙
GH3536合金选区激光熔化成形行为及高温性能研究 GH3536合金是一种典型的固溶强化型镍基高温合金,具有良好的高温强度以及抗氧化性能,主要用于制作航空发动机燃烧室部件和其他在高温环境下服役的零部件。出于轻量化要求,高性能航空发动机对零部件结构的复杂程度要求越来越高,这给传统制造工艺带来了很大的困难。选区激光熔化(Selective Laser Melting,SLM)技术作为一种典型的金属3D打印技术,在难加工、结构复杂高温合金零部件的加工成形方面具有极大的优势,因此被广泛地应用于航空航天领域。SLM成形过程中,粉末层局部区域经历快速升温/降温过程,存在较高的温度梯度和热应力,容易产生孔隙和微裂纹等缺陷,制约了材料的成形效果和服役性能。同时SLM成形过程中凝固冷却速率极快,区别于传统工艺零部件,SLM成形件晶粒更为细小均匀,残余应力更高。因此有必要对SLM成形件内部孔隙、微裂纹缺陷控制以及组织性能进行研究。为研究GH3536合金SLM成形过程、优化成形工艺、减少成形件内部孔隙和微裂纹缺陷、评估SLM成形GH3536合金服役性能,本课题基于体能量密度研究不同工艺的成形效果,并选择致密度、孔隙和微裂纹数量作为衡量标准;分析薄壁管状成形件显微组织、微裂纹和维氏硬度分布;测试成形件常温力学性能以及高温力学性能,分析高温蠕变行为,并与热轧GH3536合金棒材相应性能进行对比;同时采用有限元方法模拟成形过程温度场、熔池形貌尺寸以及凝固组织。主要结论为:SLM成形件内部孔隙随体能量密度的增加逐渐减少并消失,微裂纹随体能量密度的增加出现并逐渐增加,微裂纹沿晶扩展,整体扩
展方向垂直于扫描线方向和平行于成形方向,并同时跨越相邻扫描线和多个沉积层;SLM成形件显微组织形貌呈现为熔池组成的鱼鳞状形貌,熔池内部存在跨越多个沉积层的柱状晶,晶粒间距约为0.6~1.5μm;SLM成形件硬度和强度高于棒材,塑形低于后者;SLM成形件的蠕变抗力高于棒材,其蠕变裂纹沿熔合线及柱状晶晶界形成并扩展,断口 可见明显扫描线痕迹,SLM成形件和棒材具有相近的蠕变应力指数 6.4~ 7.4;ANSYS模拟熔池形貌尺寸、凝固组织与试验结果吻合较好。
(19)中华人民共和国国家知识产权局 (12)发明专利申请 (10)申请公布号 (43)申请公布日 (21)申请号 201910326782.0 (22)申请日 2019.04.23 (71)申请人 阳江市五金刀剪产业技术研究院 地址 529533 广东省阳江市高新区福冈工 业园科技五路科技企业孵化中心大楼 首层 申请人 阳江市高功率激光应用实验室有限 公司 (72)发明人 路超 张瑞华 屈岳波 肖梦智 赵超 栗子林 康平 刘燕红 邱桥 (74)专利代理机构 北京市邦道律师事务所 11437 代理人 薛艳 温雷 (51)Int.Cl.B22F 3/105(2006.01)B33Y 10/00(2015.01)B33Y 30/00(2015.01)B33Y 40/00(2015.01) (54)发明名称一种选区激光熔化成型的方法(57)摘要本发明属于选区激光熔化成型技术领域。为了解决采用现有选区激光熔化成型方法获得的成型件存在内部有气孔以及表面精度差的问题，本发明公开了一种选区激光熔化成型的方法。该方法具体包括以下步骤：步骤S1，进行铺粉操作；步骤S2，采用第一热源对粉末层进行扫描处理；步骤S3,采用第二热源对粉末固态层进行扫描处理；步骤S4，重复步骤S1至步骤S3，进行逐层的粉末铺设和扫描操作，直至完成零部件的制备；其中，第一热源的能量密度小于第二热源的能量密度。采用本发明的方法进行选区激光熔化成型操作，可以避免成型件内部出现气孔，提升表面精度， 获得高质量的成型件。权利要求书1页 说明书5页 附图5页CN 110064756 A 2019.07.30 C N 110064756 A
５０，０８００２５激光与光电子学进展ｗｗｗ．ｏｐｔｉｃｓｊ ｏｕｒｎａｌ．ｎｅｔ基于选区激光熔化快速成型的自由设计与制造进展 宋长辉１，２ 杨永强１，２ 叶梓恒１ 王 迪 １（１华南理工大学机械与汽车工程学院，广东广州５１０６４０；２广州有色金属研究院，广东广州５１０６４１ ）摘要 随着机械系统复杂性的不断增加，在现代结构理论模型的设计中，设计者需要统筹考虑结构新颖性、性能优 良性和制造可行性，但传统的制造方式对设计约束很大。选区激光熔化（ＳＬＭ）是快速制造中最有发展潜力的技术之一，在理论上可以实现任意复杂的计算机辅助设计（ＣＡＤ）理论模型到金属功能件的直接制造。针对ＳＬＭ自由 制造的特点，结合华南理工大学在该技术方面的研究基础，研究了具有免组装、功能集成和轻量化特点的复杂金属 功能件自由设计与直接制造的工艺，为航空航天、医疗、汽车等领域的产品创新设计与个性化制造提供参考。 关键词 光学制造；选区激光熔化；自由设计与制造；免组装机构；轻量化构件 中图分类号 Ｏ４３６ 文献标识码 Ａ ｄｏｉ：１０．３７８８／ＬＯＰ５０．０８００２６ Ｄｅｖｅｌｏｐｍｅｎｔ ｏｆ Ｆｒｅｅｆｏｒｍ Ｄｅｓｉｇｎ ａｎｄ Ｍａｎｕｆａｃｔｕｒｉｎｇ Ｂａｓｅｄｏｎ Ｓｅｌｅｃｔｉｖｅ Ｌａｓｅｒ Ｍｅｌｔｉｎｇ Ｓｏｎｇ Ｃｈａｎｇｈｕｉ １，２ Ｙａｎｇ Ｙｏｎｇｑｉａｎｇ１， ２ Ｙｅ Ｚｉｈｅｎｇ１ Ｗａｎｇ Ｄｉ １１ Ｓｃｈｏｏｌ ｏｆ Ｍｅｃｈａｎｉｃａｌ ａｎｄ Ａｕｔｏｍｏｔｉｖｅ Ｅｎｇｉｎｅｅｒｉｎｇ，Ｓｏｕｔｈ Ｃｈｉｎａ Ｕｎｉｖｅｒｓｉｔｙ ｏｆ Ｔｅｃｈｎｏｌｏｇｙ，Ｇｕａｎｇｈｚｏｕ，Ｇｕａｎｇｄｏｎｇ５ １０６４０，Ｃｈｉｎａ２ Ｇｕａｎｇｚｈｏｕ Ｒｅｓｅａｒｃｈ Ｉｎｓｔｉｔｕｔｅ ｏｆ Ｎｏｎ－Ｆｅｒｒｏｕｓ Ｍｅｔａｌｓ Ｇｕａｎｇｚｈｏｕ，Ｇｕａｎｇｄｏｎｇ５１０６４１，烄烆烌烎ＣｈｉｎａＡｂｓｔｒａｃｔ Ａｓ ｔｈｅ ｃｏｍｐｌｅｘｉｔｙ ｏｆ ｔｈｅ ｍｅｃｈａｎｉｃａｌ ｓｙｓｔｅｍ ｉｓ ｉｎｃｒｅａｓｉｎｇ，ｄｅｓｉｇｎｅｒｓ ｎｅｅｄ ｔｏ ｇｉｖｅ ｃｏｍｐｒｅｈｅｎｓｉｖｅｃｏｎｓｉｄｅｒａｔｉｏｎ ｔｏ ｔｈｅ ｎｏｖｅｌｔｙ，ｅｘｃｅｌｌｅｎｔ ｐｅｒｆｏｒｍａｎｃｅ ａｎｄ ｍａｎｕｆａｃｔｕｒｉｎｇ ｆｅａｓｉｂｉｌｉｔｙ ｏｆ ｔｈｅ ｓｔｒｕｃｔｕｒｅ ｉｎ ｔｈｅ ｄｅｓｉｇｎ ｏｆ ｔｈｅｔｈｅｏｒｅｔｉｃａｌ ｍｏｄｅｌ ｏｆ ｍｏｄｅｒｎ ｍｅｃｈａｎｉｓｍ．Ｈｏｗｅｖｅｒ，ｔｈｅ ｔｒａｄｉｔｉｏｎａｌ ｍａｎｕｆａｃｔｕｒｉｎｇ ｍｅｔｈｏｄｓ ｉｍｐｏｓｅ ｇｒｅａｔ ｒｅｓｔｒｉｃｔｉｏｎｏｎ ｔｈｅ ｄｅｓｉｇｎ．Ｓｅｌｅｃｔｉｖｅ ｌａｓｅｒ ｍｅｌｔｉｎｇ（ＳＬＭ）ｉｓ ｏｎｅ ｏｆ ｔｈｅ ｔｅｃｈｎｏｌｏｇｉｅｓ ｔｈａｔ ｈａｖｅ ｍｏｓｔ ｄｅｖｅｌｏｐｍｅｎｔ ｐ ｏｔｅｎｔｉａｌ，ｗｈｉｃｈｃａｎ ａｃｈｉｅｖｅ ｄｉｒｅｃｔ ｍａｎｕｆａｃｔｕｒｉｎｇ ｏｆ ｍｅｔａｌ ｆｕｎｃｔｉｏｎａｌ ｐａｒｔｓ ｆｒｏｍ ａｎｙ ｃｏｍｐｌｅｘ ｃｏｍｐｕｔｅｒ－ａｉｄｅｄ ｄｅｓｉｇｎ（ＣＡＤ）ｔｈｅｏｒｅｔｉｃａｌ ｍｏｄｅｌｓ ｉｎ ｔｈｅｏｒｙ．Ｂａｓｅｄ ｏｎ ｔｈｅ ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ ｏｆ ｔｈｅ ｆｒｅｅｆｏｒｍ ｍａｎｕｆａｃｔｕｒｉｎｇ ｏｆ ＳＬＭ，ｃｏｍｂｉｎｉｎｇ ｗｉｔｈ ｔｈｅｒｅｌａｔｅｄ ｒｅｓｅａｒｃｈ ｏｆ Ｓｏｕｔｈ Ｃｈｉｎａ Ｕｎｉｖｅｒｓｉｔｙ ｏｆ Ｔｅｃｈｎｏｌｏｇｙ，ｗｅ ｓｔｕｄｙ ｔｈｅ ｆｒｅｅｆｏｒｍ ｄｅｓｉｇｎ ａｎｄ ｄｉｒｅｃｔ ｍａｎｕｆａｃｔｕｒｉｎｇｐｒｏｃｅｓｓ ｏｆ ｃｏｍｐｌｅｘ ｍｅｔａｌ ｐｉｅｃｅｓ ｗｉｔｈ ｎｏｎ－ａｓｓｅｍｂｌｙ，ｆｕｎｃｔｉｏｎａｌ ｉｎｔｅｇｒａｔｉｏｎ ａｎｄ ｌｉｇｈｔｗｅｉｇ ｈｔ ｃｈａｒａｃｔｅｒｉｓｔｉｃｓ，ｗｈｉｃｈｐｒｏｖｉｄｅｓ ｅｆｆｅｃｔｉｖｅ ｒｅｆｅｒｅｎｃｅ ｆｏｒ ｔｈｅ ｉｎｎｏｖａｔｉｖｅ ｄｅｓｉｇｎ ａｎｄ ｐｅｒｓｏｎａｌｉｚｅｄ ｍａｎｕｆａｃｔｕｒｉｎｇ ｏｆ ｐｒｏｄｕｃｔｓ ｉｎ ｔｈｅ ｆｉｅｌｄｓ ｏｆａｅｒｏｓｐ ａｃｅ，ｍｅｄｉｃａｌ ｔｒｅａｔｍｅｎｔ ａｎｄ ａｕｔｏｍｏｂｉｌｅ．Ｋｅｙ ｗｏｒｄｓ ｏｐｔｉｃａｌ ｆａｂｒｉｃａｔｉｏｎ；ｓｅｌｅｃｔｉｖｅ ｌａｓｅｒ ｍｅｌｔｉｎｇ；ｆｒｅｅｆｏｒｍ ｄｅｓｉｇｎ ａｎｄ ｍａｎｕｆａｃｔｕｒｉｎｇ；ｎｏｎ－ａｓｓｅｍｂｌｙｍｅｃｈａｎｉｓｍ；ｌｉｇｈｔｗｅｉｇ ｈｔ ｓｔｒｕｃｔｕｒｅＯＣＩＳ ｃｏｄｅｓ １ ４０．３３９０；３５０．３８５０；２３０．４０００ 收稿日期：２０１３－０３－０８；收到修改稿日期：２０１３－０４－０１；网络出版日期：２０１３－０７－ １１基金项目：国家自然科学基金（５１２７５１７９ ）作者简介：宋长辉（１９８６—） ，男，博士研究生，主要从事激光加工与激光快速成型等方面的研究。Ｅ－ｍａｉｌ：ｓｏｎｇ＿ｃｈａｎｇ ｈｕｉ＠１６３．ｃｏｍ导师简介：杨永强（１９６１—） ，男，博士，教授，博士生导师，主要从事激光材料加工、快速成型制造等方面的研究。Ｅ－ｍａｉｌ：ｍｅｙｑｙａｎｇ ＠ｓｃｕｔ．ｅｄｕ．ｃｎ（通信联系人）１ 引 言 随着机械系统复杂性的不断增加，在现代结构理论模型的设计中，设计者需要统筹考虑结构新颖性、性能优良性和制造可行性。其中制造可行性强调在设计阶段就要充分考虑制造中的问题，其基本思想是从产品设计参数中提取与制造过程相关的信息进行分析，以改善设计。传统制造对于产品的形状与结构设计约 ０８００２６－ １
第9卷第21期 2009年11月1671 1819(2009)21 6532 04 科学技术与工程 ScienceTechnologyandEngineering 2009 Sci Tech Engng 9 No 21 Nov.2009 Vol 通信技术 半导体激光器驱动电路设计 何成林 (中国空空导弹研究院,洛阳471009) 摘要半导体激光驱动电路是激光引信的重要组成部分。根据半导体激光器特点,指出设计驱动电路时应当注意的问题,并设计了一款低功耗、小体积的驱动电路。通过仿真和试验证明该电路能够满足设计需求,对类似电路设计有很好的借鉴作用。 关键词激光引信半导体激光器窄脉冲中图法分类号 TN242; 文献标志码 A 激光引信大部分采用主动探测式引信,主要由发射系统和接收系统组成。发射系统产生一定频率和能量的激光向弹轴周围辐射红外激光能量,而接收系统接收处理探测目标漫反射返回的激光信号,而后通过信号处理系统,最终给出满足最佳引爆输出信号。由此可见,激光引信的探测识别性能很大程度上取决于激光发射系统的总体性能,即发射激光脉冲质量。而光脉冲质量取决于激光器脉冲驱动电路的质量。因此,半导体激光器驱动电路设计是激光引信探测中十分重要的关键技术。 图1 驱动电路模型 放电,从而达到驱动激光器的目的。 由于激光引信为达到一定的探测性能,通常会要求激光脉冲脉宽窄,上升沿快,一般都是十几纳秒甚至几纳秒的时间。因此在选择开关器件时要求器件开关速度快。同时,由于激光器阈值电流、工作电流大 [1] 1 脉冲半导体激光器驱动电路模型分析 激光器驱动电路一般由时序产生电路、激励脉冲产生电路、开关器件和充电元件几个部分组成,如图1。 图1中,时序产生电路生成驱动所需时序信号,一般为周期信号。脉冲产生电路以时序信号为输入条件。根据其上升或下降沿生成能够打开开关器件的正激励脉冲或负激励脉冲。开关器件大体有三种选择:双极型高频大功率晶体管、晶体闸流管电路和场效应管。当激励脉冲到来时,开关器件导通,
上海磐川光电科技有限公司 激光发射接收系统 （激光发射接受） 设计原理
激光发射接收系统（激光发射接受器） 1.产品概述： 激光发射接收系统器或称激光发射接收器由两部分组成，一是激光发射模块，二是激光接收模块。（如图所示）激光发射器结果特定频率的调制，发射出一条准直极细的激光光束，通过特定波长的激光光电传感器接收到光信号，通过光电转换电路将光信号转换成电信号输出。 2. 产品特点性能参数： ?激光准直度高，方向性好； ?光束细规则，精确度高； ?接收灵敏度高，响应速度快； ?信号输出接口灵活。接收到的信号可与通讯标准的信号/工业标准电压匹配； ?功耗低；电源要求低，低压直流即可； ?使用寿命长； ?可控距离长； ?体积小，安装方便灵活； 性能参数：Optical and Electrical Characteristics 参数符号数值单位 激光功率（Optical power）P5-100mW 光束发散度 Divergence RMS)<1mrad 电源电压 Power Voltage U5/12DCV 工作电流 Op. Current I<40/<100mA 有效距离eff.distance L0-1/1-1000m 调制频率modulate f范围内可选MHz 响应灵敏度R50 us 工作温度Temperature To-10~50 oC 3．设计原理
3.1 连续型激光器发射接收模块结构框图: 3.2 激光器发射接收模块详细电路图解： 3.2.1 激光发射部分：（激光器驱动发射） 该电路激光编码调制采用集成芯片硬件实现，8地址4数据编码。1-8是地址，10-13数据脚。调整Rosc决定振荡频率；14管脚TE是发射使能端，低电平发射有效。 激光发射驱动电路（在激光器中），是APC（自动功率控制）电路驱动，保证激光二极管光功率输出稳定。 3.2.2 激光接收部分：（激光接收、放大检波及解调解码输出）
3 基金项目:国家科技型中小企业创新基金(项目编号:05C26214201059) 收稿日期:2007212214 第28卷第3期 应 用 激 光 Vol.28,No.32008年6月 A P PL I ED LAS ER J une 2008 选区激光熔化成形温度场模拟与工艺优化 3 章文献, 史玉升, 李佳桂, 伍志刚 (华中科技大学材料成形与模具技术国家重点实验室,湖北武汉430074) 提要 在金属粉末的选择性激光熔化成形过程中,需要解决球化、翘曲、变形等难题。对于一定的金属粉末,通过优化成形工艺参数可以克服以上难题。为此,利用ANSYS 有限元法对成形过程的熔池及温度场模拟,建立有限元模型,分析得出成形过程熔池的深度和宽度,预测并优化成形过程的工艺参数。通过实验验证,应用有限元法优化后的成形工艺参数能够成形出复杂金属零件。 关键词 选择性激光熔化; 有限元模型; 熔池; 温度场 Simulation of T emperature Field for Optimization of Processing P arameters of Selective Laser Melting Metal Powders Zhang Wenxian , Shi Yusheng , Li Jiagui , Wu Zhigang (S tate Key L aboratory of M aterial Processing and Die and Moul d Technology ,H uaz hong Universit y of Science and Technology ,W uhan ,H ubei 430074,China ) Abstract The phenomena such as balling effect ,warp ,and distortion may occur in the process of selective laser melting (SL M )metal powders.These difficulties can be solved by optimizing the processing parameters during the process for a special metal powders.To optimize the parameters ,the temperature field and molten pool dimensions during the SL M process are modeled and simulated with ANSYS finite element method.The analysis results are given and optimum processing parameters are verified by forming complex structure lattice iron parts with the SL M technology.K ey w ords Selective laser melting ; finite element model ; molten pool ; temperature field 选择性激光熔化(selective laser melting ,SL M )快速成形技术可以直接成形出高精度、综合机械性能好的金属零件。该技术基于离散-堆积成形原理,根据零件CAD 模型直接成形三维实体,成形过程中扫描选区内的金属粉末在激光辐照下完全熔化而获得近100%致密的金属零件[1]。目前,国外应用SL M 快速成形技术可直接制造模具、工具、生物移植物等,它们涉及机械制造、航空航天、生物医学等领域,具有很好的应用前景。 对于特定粉末材料的选择性激光熔化快速成形过程,其成形参数直接影响成形过程的顺利进行及成形零件的致密度、表面质量、成形精度等性能。因此,在成形工艺研究过程中要对成形工艺参数进行优化。然而,目前SLM 快速成形技术的成形工艺参数的优化主要在实验及经验的基础上进行总结,缺少系统科 学的优化理论来指导,不利于SLM 快速成形技术的机理及工艺研究。为此开展了有限元模拟SLM 快速成形过程的相关研究,目前主要有以下人员从事这方面的研究。Childs T.H.C 等人对无基板情况下的粉末单扫描成形截面形状以及面扫描成形层质量进行有限元模拟[2-5]。Shiomi M.等人应用有限元法模拟分析了无基板情况下的粉末面扫描成形层的二维温度场与残余应力[6]。Osakada K 等人也对无基板情况下的粉末面扫描时单层固化成形的应力分布应用有限元模拟进行分析,并提出解决单层固化成形时缺陷的方法[7,8]。因为以上研究主要是针对无基板情况下激光熔化过程中的单线扫描和单面扫描的粉床温度场和应力场的有限元模拟,其主要目的是向无基板下的选择性激光熔化快速成形技术方向发展。然而对于在基板上粉末的选择性激光成形过程的熔池及 — 581—
激光选区熔化（SLM）作为具有发展前景的金属零件3D打印技术，其成型材料多为单一组分金属粉末，包括奥氏体不锈钢、镍基合金、钛基合金、钴-铬合金和贵重金属等。通过激光束快速熔化金属粉末并获得连续的熔道，可以直接获得几乎任意形状、具有完全冶金结合、高精度的近乎致密金属零件。因此，其应用范围已经扩展到航空航天、汽车、微电子、医疗、珠宝首饰等行业。 SLM技术主要优势有：更好的表面质量、更好的性能、更宽泛的材料选择；主要待解决的问题：打印粉末成本高、成型速度慢、打印件受设备成型仓尺寸限制、需要添加支撑、需要后处理。 国内外对SLM技术研究热情较高。国外对SLM工艺进行开展研究的国家主要集中在德国、英国、日本、法国等。其中，德国是从事SLM技术研究最早与最深入的国家。第一台SLM系统是1999年由德国Fockele和Schwarze（F&S）与德国弗朗霍夫研究所一起研发的基于不锈钢粉末SLM成型设备。目前国外已有多家SLM设备制造商，例如德国EOS 公司、SLMSolutions公司、ConceptLaser公司和英国Renishaw公司等。华南理工大学于2003年开发出国内的第一套选区激光熔化设备DiMetal-240。发展至今，国内选区激光熔化设备主要研发及生产商有南京中科煜宸、湖南华曙高科、西安铂利特、无锡飞而康、北京隆源等。
航空航天零部件打印： 图1.涡轮增压器压缩机叶轮图2.叶轮图3.燃烧室机匣航空工业应用的3D打印主要集中在钛合金，铝锂合金，超高强度钢，高温合金等材料方面，这些材料基本都是强度高，化学性质稳定，不易成型加工，传统加工工艺成本高昂的类型，并且存在部分如下图所示的结构复杂的薄壁结构件。 汽车零部件打印： 近些年来，新能源汽车行业受到大力扶持与发展，其中零件的轻量化设计是减少能量损耗，提高汽车续航能力的一个重要因素。然而一些内部复杂的薄壁件采用传统制造工艺研发周期较长、加工难度较高。因此，3D打印技术逐渐走入研发人员的视野。图4为某汽车厂家打印的一个薄壁内流道结构件，该件使用过程中内壁需要承受一定的水压，因此，需要零件成型后致密性好。而SLM 3D打印零件通过工艺参数的优化，其致密度可以达到99%。 牙齿的打印： 市场现有的3D打印设备和生物相容性材料能够满足牙科产品的制造需求，例如SLM 技术打印的烤瓷牙金属冠的钴铬合金。目前，在牙科领域，3D打印不仅可以制造最终产品，还可以打印定制化的间接产品，例如牙科模型。这些产品往往对力学性能没有太高的要求，但确是最终产品制造和牙齿修复过程中的有力工具。这些直接亦或是间接应用产品需求将长期推动3D打印技术在牙科行业的增长与发展。
脉冲式激光测距系统设计 摘要本文通过对高精度脉冲式激光测距系统的研究，并在参照课题技术指标的基础上，旨在提供一种高精度脉冲式激光测距系统的解决方案，并对脉冲式激光测距仪系统设计中所涉及的脉冲读取与放大电路、时刻鉴别、时间间隔测量等关键技术进行了深入的研究和探讨。 本论文详细讨论了一种可实现高速激光测距的接收电路和计时电路。实验系统采用APD作为光电传感器，将激光脉冲信号转变为微弱电流脉冲，经过两级放大后，信号变为幅度较大的电压脉冲，经过时点鉴别电路分别确定计时起点和终点后，由计时电路来精确测量两个时间点之间的时间间隔。 关键词:脉冲激光测距，时刻鉴别，TDC-GP2，传递延时，APD
Pulse laser rangefinder system design Abstract：A high-precision pulse laser rangefinder solution is proposed in this paper through the research of high-precision pulsed laser rangefinder system on the basis of referring to the subject technical indexes. Besides, some key technology involved in pulse laser range finder system design such as pulse reading, amplifying circuit, timing discrimination, time-interval measurement, etc, have been researched and discussed in depth. A type of receiver circuit and timing circuit which can be applied in high-speed laser range- finder is discussed in this paper. After two-level amplification we got a voltage pulse that had a enough amplitude to be applied，the timing point was discriminated by the constant-fraction timing discriminator circuit. Key words: Pulsed Laser Rangefinder,Timing Discrimination,TDC-GP2,Propagation delay,APD
《激光无线传声器》 专业班级：12级电信三班 姓名：李佳姗汪德玮张晨晨 学号：080212110 080212115 080212108 指导教师：王陈宁 设计时间: 2014年12月1日 物理与电气工程学院 2014 年12 月8 日
摘要正文 主要内容利用激光发射接收器件制作一个无线传声电路，包括一台激光发射机和一台激光接收机可以将声音通过激光发射和接收。 激光传感器已经在现代化的生产实践中发挥着它的巨大作用,人们一方面通过提高与改善传感器的技术性能;一方面通过寻找新原理、新材料、新工艺及新功能来改善传感器性能,制造出更多的传感器。而激光传感器作为其中的一部分也必将得到更大的发展。随着探测设备和其他部分的技术的提高,激光传感器能够拥有更多的性能和更好的灵敏度。 关键字：三极管，LM386，激光二极管，光敏三极管，TDA2030
1.课程设计任务书 (1) 2.摘要正文 (2) 3.概述 (4) 3.1 激光无线传声器设计任务和要求 (4) 3.2 系统组成框图及原理图 (4) 3.3 发射电路图和接收电路图介绍 (5) 4.三极管工作原理及其放大原理 (6) 4.1三极管的结构图和实物图 (6) 4.2三极管的工作原理 (6) 4.3三极管的放大原理 (7) 4.4三极管和二极管的比较 (7) 5.音频功率放大器LM386和TDA2030 (7) 5.1 LM386简介 (7) 5.2 LM386特性 (8) 5.3 LM386的引脚图 (8) 5.4 TDA2030简介 (9) 小结 (11) 参考文献 (11)
3.1激光无线传声器设计任务和要求 设计任务：利用激光二极管和光敏三极管设计制造出可以实现两米以上的激光无线传声系统，声音失真不能太大，声音不能太小。 设计要求：基于二极管激光器设计声音发射电路，基于光电三极管实现激光传声接收电路，接收电路负载阻抗8欧姆，功率大于0.5W。 3.2 系统组成框图及原理图 激光传感器已经在现代化的生产实践中发挥着它的巨大作用,人们一方面通过提高与改善传感器的技术性能;一方面通过寻找新原理、新材料、新工艺及新功能来改善传感器性能,制造出更多的传感器。而激光传感器作为其中的一部分也必将得到更大的发展。随着探测设备和其他部分的技术的提高,激光传感器能够拥有更多的性能和更好的灵敏度。 本课题采用的是以三极管8050和音频功率放大器LM386和TDA2020为核心开发激光传声的系统。系统硬件电路原理框图及结构图如下图1 图1（a）激光发射电路原理图 图1（b）激光接收电路原理图
半导体激光器设计 摘要:半导体激光器产生激光的机理,即必须建立特定激光能态间的粒子数反转，并有光学谐振腔。由于半导体材料物质结构的特异性和其中电子运动的特殊性,一方面产生激光的具体过程有许多特殊之处,另一方面所产生的激光光束也有独特的优势,使其在社会各方面广泛应用。从同质结到异质结,从信息型到功率型,激光的优越性也愈发明显,光谱范围宽, 相干性增强,使半导体激光器开启了激光应用发展的新纪元。 关键词:受激辐射;光场;同质结;异质结;大功率半导体激光器 0 前言 半导体激光器是指以半导体材料为工作物质的激光器,又称半导体激光二极管(LD) ,是20世纪60年代发展起来的一种激光器。半导体激光器的工作物质有几十种,例如砷化镓(GaAs) ,硫化镉(CdS)等,激励方式主要有电注入式,光泵式和高能电子束激励式三种。半导体激光器从最初的低温(77K)下运转发展到室温下连续工作;从同质结发展成单异质结,双异质结,量子阱(单,多量子阱)等多种形式。半导体激光器因其波长的扩展,高功率激光阵列的出现以及可兼容的光纤导光和激光能量参数微机控制的出现而迅速发展.半导体激光器的体积小,重量轻,成本低,波长可选择,其应用遍布临床,加工制造,军事,其中尤以大功率半导体激光器方面取得的进展最为突出。 1半导体激光器的工作原理 1.1激光产生原理 半导体激光器是一种相干辐射光源,要使它能产生激光,必须具备三个基本条件: (1)增益条件:建立起激射媒质(有源区)内载流子的反转分布,在半导体中代表电子能量的是由一系列接近于连续的能级所组成的能带,因此在半导体中要实现粒子数反转,必须在两个能带区域之间,处在高能态导带底的电子数比处在低能态价带顶的空穴数大很多,这靠给同质结或异质结加正向偏压,向有源层内注入必要的载流子来实现。将电子从能量较低的价带激发到能量较高的导带中去。当处于粒子数反转状态的大量电子与空穴复合时,便产生受激发射作用。
中北大学
课 程 设 计 说 明 书
学生姓名： 学 专 题 院： 业： 目：
杜俊
学 号： 0805014116
信息与通信工程学院 电子信息科学与技术
超声波的接收电路设计 程耀瑜 李文强 职称: 职称: 教授 讲师
指导教师：
2011
年
1
月
6
日
中北大学
课程设计任务书
2010/2011 学年第 一 学期
学 专
院： 业：
信息与通信工程学院 电子信息科学与技术 杜俊 学 号： 0805014146
学 生 姓 名： 课程设计题目： 起 迄 日 期： 课程设计地点： 指 导 教 师： 系 主 任：
超声波接收电路设计 12 月 26 日～1 月 7 日 中北大学 程耀瑜，李文强 程耀瑜
下达任务书日期:
2010 年 12 月 26 日
课 程 设 计 任 务 书
1．设计目的：
本课程设计主要针对模拟电子技术和数字电子技术课程要求，培养学生在查阅资料 的基础上，进行实用电路设计、计算、仿真、调试等多个环节的综合能力，同时培养学 生用课程中所学的理论独立地解决实际问题的能力。另外还培养学生用专业的、简洁的 文字,清晰的图表来表达自己设计思想的能力。
2．设计内容和要求（包括原始数据、技术参数、条件、设计要求等） ：
（1）了解超声波的特点； （2）掌握超声波接收电路的设计、仿真与调试； （3）掌握方案设计与论证； （4）掌握用相关软件进行电路图设计、仿真，以及对仿真结果的分析、总结；
3．设计工作任务及工作量的要求〔包括课程设计计算说明书(论文)、图纸、 实物样品等〕 ：
（1）提供核心器件的工作原理与应用介绍； （2）提供用 Protel99 设计的电路原理图，也可给出印刷板电路图； （3）提供用 Multisim、MaxPluss、Proteus 等其他软件对电路的仿真结果与分析； （4）提供符合规定要求的课程设计说明书； （5）提供参考文献不少于三篇，且必须是相关的参考文献；