材料科学基础英文版课件_(11)

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材料科学基础11章扩散

三.扩散系数（cm2/s，m2/s） 1.无序扩散Dr：质点作布朗运动、不存在化学位梯度时的扩散。特点：a.移动方向是无序的，无外场推动；b.由热起伏使原子获得迁移活化能引起；c.不产生定向扩散流，每次跃迁与前次无关。 1 2 Dr / 6 f r 2 6 f为跃迁频率，f=AoNvexp[-Gm/RT]，A比例常数，o振动频率1013次/秒，Nv(空位)缺陷浓度，Gm跃迁(扩散)活化能。r 为每次跃迁距离，r=kao，ao晶格参数，Dr=1/6k2ao2f ，令γ=A/6 k2 ，γ结构因子 Dr=ao2oNvexp[-Gm/RT] 用扩散系数描述质点扩散： D↑→扩散↑； T↑、Nv↑、 Gm↓→D↑→扩散↑。
二、菲克定律与扩散动力学方程
1855年德国物理学家 A· 菲克（Adolf Fick）在研究大量扩散现象的基础上，首先对这种质点扩散过程作出定量描述，得出著名的菲克定律，建立了浓度场下物质扩散的动力学方程。
1.费克第一定律：稳定扩散的原子扩散通量与浓度梯度成正比。一维方向： Jx=-Dc/x c c c J D C D(i j k ) 三维方向： x y z
§11-2 扩散的推动力
一、扩散的一般推动力
根据广泛适用的热力学理论，可以认为扩散过程与其他物理化学过程一样，其发生的根本驱动力应该是化学位梯度。一切影响扩散的外场（电场、磁场、应力场等）都可统一于化学位梯度之中，且仅当化学位梯度为零，系统扩散方可达到平衡。下面以化学位梯度概念建立扩散系数的热力学关系（能斯特-爱因斯坦公式）。
2. 晶界的内吸附
晶界能量比晶粒内部高，如果溶质原子位于晶界上，可降低体系总能量，它们就会扩散而富集在晶界上。
3 .固溶体中发生某些元素的偏聚

2材料科学基础英文版课件_(9)

Impact Fracture Testing (9)
Factors affecting the DBTT
• Strengthening: solid-solution strengthening, precipitation strengthening, and strain hardening (yield strength increase) DBTT increase – hardening embrittlementຫໍສະໝຸດ TICT1 T2 T3
T4
Temperature
Effects of impurity segregation and strengthening on the DBTT
Also read the paper:
S.-H. Song, J. Wu, L.-Q. Weng, and Z.-X. Yuan, “Fractographic changes caused by phosphorus grain boundary segregation for a low alloy structural steel”, Materials Science and Engineering A 497 (2008) 524-527.
• Grain boundary segregation of impurities: segregation of impurities such as P, S, Sn and Sb Grain boundary cohesion decrease DBTT increase – non-hardening embrittlement
Carbon content Strength DBTT and upper shelf energy

材料科学基础英文版课件

Classification of grain boundary segregation
• Equilibrium segregation
– Thermodynamic process – Driving force: solute-boundary binding energy (the
difference in energy caused by a solute atom between staying in the grain interior and on the grain boundary
– One dislocation just has one b
– For metals, b normally points in a close-packed crystal direction and its magnitude is the interatomic spacing because the slip direction is normally in the close-packed direction
• To reduce the surface energy, the materials tend to minimize the total surface area
Grain Boundaries
In polycrystalline materials, a grain boundary is the boundary between two adjacent grains which have different orientations
Linear Defect – Dislocations
Features: one dimensional

材料科学基础英文版

Stress Concentration
Measured fracture strengths for most brittle materials – much lower than their theoretically calculated values on the basis of atomic bonding energies
Sowing many dimples
Typical ductile fracture surface appearance (microscopically) - 1
Ductile Fracture (5)
Typical ductile fracture surface appearance (microscopically) - 2
With naked eyes: ridges which radiate from the origin of the crack
Brittle Fracture (3)
For most brittle materials, crack propagation is along specific crystal planes. The planes are called cleavage planes and the fracture is call cleavage fracture. This type of fracture is Transgranular fracture
Microscopically
Ductile Fracture (2)
Microvoids formation
Initial necking
Coalescence of microvoids to a crack

工学]材料科学基础英文版

• Atomic level: Arrangement of atoms in materials. • Nanostructure: the structure of material at a length-scale
of 100nm. • Microstructure: the structure of material at a length-scale
• Short-range atomic arrangements: the atoms of ions show a particular order only over relatively short distances.
7
2. Atomic Structure
• Atomic structure influences how atoms are bonded together.
13
• The complete set of quantum numbers for each of the 11 electrons in sodium.
3s1 electron 11 n=3, l=0, ml=0, ms=+1/2 or -1/2
{electron 10 n=2, l=1, ml=+1, ms= -1/2 electron 9 n=2, l=1, ml=+1, ms=+1/2
• Orbital (Azimuthal) quantum number l: describe the energy levels in each quantum shell. l=0,1,2,…,n-1. Magnetic quantum number ml: describes the number of energy levels for each orbital quantum number. –l, … +l

材料科学与工程专业英语课件

• These alloy additions are chosen carefully because they invariably bring with them sharply increased material costs. They are justified only by essential improvements in properties such as higher strength or improved corrosion resistance
1.1.1 Iron and Steel
The iron ore which we find on earth is not pure. It contains some impurities that must be removed by smelting. The process of smelting consists of heating the ore in a blast furnace with coke and limestone, and reducing it to metal. Blasts of hot air enter the furnace from the bottom and provide the oxygen that is necessary for the reduction of the ore.
1.1.1 Iron and Steel
• We can melt this down again in another furnace-a cupola-with more coke and limestone, and tap it out into a ladle or directly into molds. This is cast iron. Cast iron does not have the strength of steel. It is brittle and may fracture under tension.

材料科学基础双语课件

control the material properties (for example by altering the
grain structure, or the presence of defects in the atom
packing) or to fabricate the material into the desired shape.
extra material, joining parts (e.g., by soldering or welding),
forming (forging, rolling, bending, etc.), or compacting particles which are then fused together (sintering, used for
gases (and most engineering materials are used in solid
form).
1.1 What is Materials Science and Engineering?
It may seem abstract and remote from real engineering to
The Science and Engineering of Materials
Aim
English atmosphere: speaking, reading, writing and lisห้องสมุดไป่ตู้ening; Specialty vocabulary; Specialty knowledge;
form. As this mixture solidifies, different structures form as a function of temperature. The phase diagrams that provide

材料科学基础英文版课件（ＰＤＦ）

Law • Steady State: the concentration profile doesn't
change with time.
Steady State:
J x(left)
J x(right) J x(left) = J x(right)
x
Concentration, C, in the box doesn’t change w/time.
Non Steady State Diffusion
• Concentration profile,
dx
C(x), changes with time. J (left)
J (right)
• To conserve matter:
J (right)
− J (left)
=
dC −
dx
dt
dJ = − dC
ΔJ y
=
− ∂J y ∂y
dxdydzδt
ΔJ z
= − ∂J z ∂z
dxdydzδt
对整个元体积：
−
⎜⎜⎝⎛
∂J x ∂x
+
∂J y ∂y
+
∂J z ∂z
⎟⎟⎠⎞dxdydzδt
若 δt 时间内粒子浓度变化δc ，则在dxdydz
元体积中粒子变化为
δcdxdydz
∴ ∂c ∂t
=
−⎜⎜⎝⎛
∂J x ∂x
Fick’s Second Law
δt 时间内沿x方向扩散
元体积dxdydz
流入的粒子数： J x dydzδt
流出的粒子数：
(J x
+
∂J x ∂x
dx)dydzδt

【大学】材料科学基础(中英版)

Materials in first industrial revolution (1881-1935). Materials in second industrial revolution (1935-1980). Materials today – too,ooo,ooo… many (1980- ）.
第21页
Materials science and engineering
The relationship between materials science and materials engineering
Materials science Why it has…
Materials engineering How to make…
Time: Location: Activities:
Present new study material Announce reading and homework Take quizzes
第4页
授课信息
授课人：时间：地点：主要活动：
教授新课布置作业课堂测验
第5页
Recitations
第1Байду номын сангаас页
What is material?
Classifications of materials
Based on the chemical composition: Metals, Non-metal inorganic materials (ceramic mateials) Polymers, Composites
Materials, energy and information are the three pillars of current human civilization.

材料科学基础英文版课件-(13)

Ductility
The ability of a material to be stretched without breaking.
Toughness
The ability of a material to absorb energy before fracturing.
Physical Properties
Some common examples of polymers include plastic, rubber, and fiberglass.
Polymers can be natural or synthetic.
Composites
Composites are materials that consist of two or more materials with different physical and chemical properties.
Nondestructive testing techniques: 超声波检测，射线检测，涡流检测等。
02
Materials Properties
Mechanical Properties
Elasticity
The ability of a material to return to its original shape after being deformed by an external force.
Metals
Metals are materials that are typically ductile, malleable, and conduct electricity well.
They are often used in the manufacturing of various

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Chapter Three
Structures of Metals and Ceramics
Lecturer: Shenhua SONG
• • • • •
ቤተ መጻሕፍቲ ባይዱ
Unit cells Metallic crystal structures Ceramic crystal structures Crystal systems Crystallographic directions and planes
Some common metals: Al, Ni, Au, Cu, and Mn
Metallic crystal structures (4)
Interstices in FCC structures: octahedral interstices and tetrahedral interstices
Metallic crystal structures (2)
1) Face-centered cubic (FCC) crystal structure
a 2R
4R a 2
R
a 2 4
Each unit cell contains 4 atoms
Metallic crystal structures (3)
Metallic crystal structures (7)
3) Hexagonal close-packed (HCP) crystal structure
Each unit cell contains 6 atoms (12(1/6) + 2(1/2) + 3 = 6)
2R = a
R = a/2
Two other features: coordination number (CN) and atomic packing factor (APF) CN: the number of nearest-neighbour atoms – 12 for FCC APF: the fraction of atom-occupied volume in a unit cell
APF = (atom-occupied volume in a unit cell)/(unit cell volume) For FCC crystals: 4 atoms in a unit cell
atom-occupied volume = 4(4/3)(R3) = 4(4/3)(3.14(a2/4)3 = 0.74a3 unit cell volume = a3 APF = atom-occupied volume/unit cell volume = 0.74
Metallic crystal structures (1)
Three major types: 1) Face-centered cubic (FCC) crystal structures
2) Body-centered cubic (BCC) crystal structures 3) Hexagonal close-packed (HCP) crystal structures
Unit cells
Small repeat atom groups in a crystal structure
Representation of a unit cell: (a) hard-sphere model; (b) reduced hard-sphere model; (c) an aggregate of many atoms
Metallic crystal structures (9)
APF = atom-occupied volume/unit cell volume
atom-occupied volume = 6 (4/3)(R3) = 6 (4/3) 3.14 (a/2)3 = 3.14a3
unit cell volume =base height = (6(1/2)a2sin60o) c = 3 a2(3/2) 1.633a = 4.24a3 APF = 3.14/4.24 = 0.74 (ideal packing)
a
4R 3a
Each unit cell contains 2 atoms
CN = 8 APF = 2(4/3)(R3)/a3 =
3a R 4
2(4/3)(3.14 (a3/4)3 /a3 = 0.68
Metallic crystal structures (6)
Interstices in BCC structures: octahedral interstices and tetrahedral interstices
a =4R/3
Roz = (a – 2R)/2 = (4R/3 2R)/2 = 0.155R
Rt = a5/4 - R = (4R/3)5/4 – R
= (5/3 – 1)R = 0.291R
Roxy = (a 2 – 2R)/2 = ((4R/3)
2 - 2R)/2 = 0.633R
CN = 12 c/a = ?
APF = ?
Metallic crystal structures (8)
f
Equilateral triangle
x=a3/3
x=2h/3 h = asin60o = a3/2
a
e
f
a
e
c/2
f
x e
g
a2 = (c/2)2 + (a3/3)2
c/2 g
c/a = (8/3)1/2 = 1.633 (ideal ratio, actually 1.58 ~ 1.89)
Diagonal length: 3a
(1/2,1/2,1/2)
Ro = (a – 2R)/2 = (22R 2R)/2 = 0.414R
(1/4,1/4,1/4)
Rt = 3a/4 – R = (3/4) 22R) – R
= 0.224R
Metallic crystal structures (5) 2) Body-centered cubic (BCC) crystal structure