30C ORROSION—JANUARY 2005Submitted for publication July 2003; in revised form, April 2004. ‡ Corresponding author. E-mail: dxhe@. * Institute of Metal Research of Chinese Academy of Sciences, 72Wenhua Road, Shenyang, People’s Republic of China, 110015. Present address: Max Planck Institute for Metals Research, Heisenbergstraße 3, D-70569 Stuttgart, Germany.** Institute of Metal Research of Chinese Academy of Sciences, 72Wenhua Road, Shenyang, People’s Republic of China, 110015. (1)UNS numbers are listed in Metals and Alloys in the Unifi ed Num-bering System , published by the Society of Automotive Engineers (SAE International) and cosponsored by ASTM International.Erosion-Corrosion of Stainless Steelsin Aqueous Slurries—A Quantitative Estimation of Synergistic EffectsD.D. He,‡,* X.X. Jiang,** S.Z. Li,** and H.R. Guan**ABSTRACTThe synergism between erosion and corrosion of stainless steels (SS) in 3.5 wt% sodium chloride (NaCl) + 0.5 N sulfuric acid (H 2SO 4) + 30 wt% aluminum oxide (Al 2O 3) dual-phase fl u-id has been studied by means of a rotating cylinder electrode apparatus. The erosion/erosion-corrosion behavior of several SS, 1Cr13 (ferritic), Type 316L (austenitic [UNS S31603]), 0Cr14Ni5Mo (martensitic), and CD-4MCu (α+γ duplex), were investigated further to illustrate the synergistic mechanism. The experimental results showed that CD-4MCu had a higher erosion-corrosion resistance because of its excellent deforma-tion strengthening capability. By measuring and calculating each component of the synergistic interaction, it could be con-cluded that the removal of material mainly came from the me-chanical damage in the condition of this study. Based on the classifi cation of erosion-corrosion regimes with respect to the ratio of erosion to corrosion rate, the synergistic mechanism of erosion-corrosion of SS in the condition of this study should be an erosion-dominated corrosion process.KEY WORDS: e rosion-corrosion, dual-phase fl uid, stainless steel, synergistic interactionINTRODUCTIONThe synergistic effect of erosion and corrosion on me-tallic degradation,1-8 as well as on metallic or cermetcoatings used in an erosion-corrosion environment,9-10 has been receiving increasing attention in recent years because of the widespread occurrence of such problems in various materials processing industries. In these conditions, with the appearance of botherosion and corrosion, materials selection could be a major problem and, in many cases, was only carried out on the basis of empirical experience. The wastage rates of the material can be signifi cantly higher than the combined effects of erosion and corrosion acting separately. The phenomena of synergistic effect of ero-sion and corrosion in aqueous environments (liquid-solid dual phases or liquid-solid-gas multi-phases) are more common than that at high temperature(gas-solid dual phases). Although some investigations focused on the erosion-corrosion processes and dis-cussed the possible mechanism of damage, the syner-gistic mechanism of erosion and corrosion in aqueous environments is not well understood.Slurry erosion-corrosion usually occurs in tur-bulent fl ow conditions. Commonly used apparatus in studies of erosion-corrosion are the pipe loop, the impinging jet, the slurry pot, and the rotating cylinder electrode.5-6 Usually, the materials used for the blades or turbulent parts are carbon steels, cast steels, and stainless steels (SS). The SS selected in this investiga-tion are 1Cr13 (ferritic), Type 316L (austenitic [UNS S31603](1)), 0Cr14Ni5Mo (martensitic), and CD-4MCu (α+γ duplex). The erosion and erosion-corrosion be-havior of these SS were studied using a rotating cylin-der electrode (RCE) apparatus. Each component of the synergistic interaction, such as weight loss of steels caused by pure erosion or pure steady electrochemical corrosion, and weight loss increment caused by the0010-9312/04/000007/$5.00+$0.50/0© 2005, NACE InternationalC ORROSION—Vol. 61, No. 131synergy of erosion and corrosion, was measured or calculated. The synergistic mechanism of erosion and corrosion was discussed briefl y.EXPERIMENTAL PROCEDURES Experimental MethodsA RCE system, used in this investigation, was based on the experimental setup reported by Zhou,et al.5 Some modifications had been made to increase the area ratio of the reference electrode and working electrode, and the confi guration of three electrodeswas changed slightly.11Polytetrafluoroethylene (PTFE) was used for all electrode components except the out-er cylinder, which was made from nylon. The rotating speed could be changed from 1.02 m/s to 8.75 m/s step by step. An EG&G Princeton 332† system was used for all electrochemical measurements. A satu-rated calomel electrode (SCE) and a piece of platinum wire (1 mm in diameter) were used as the reference electrode and the counter electrode, respectively. The schematic illustration of this apparatus can be found elsewhere.7 The working electrodes were fabricated from cylindrical SS, with compositions and micro-hardness (Hv) values shown in Table 1. The working area of the test specimen was 12.56 cm 2. Microstruc-tural characterization of these materials revealed fer-ritic, austenitic, martensitic, and α+γ duplex phases for 1Cr13, Type 316L, 0Cr14Ni5Mo, and CD-4MCu, respectively. Prior to testing, the specimen surface was polished to 600 grit with silicon carbide (SiC) abrasive paper, degreased with acetone, dried with air, and weighed.The standard corrosion test was carried out in static solution, and the corrosion rate was calculated by electrochemical parameters, e.g., corrosion poten-tial and current. The erosion/erosion-corrosion test was carried out in both benign and aggressive dual-phase slurry, H 2O + 30 wt% aluminum oxide (Al 2O 3) and 3.5 wt% sodium chloride (NaCl) + 30 wt% Al 2O 3 (or 3.5 wt% NaCl + 0.5 N sulfuric acid [H 2SO 4] + 30 wt% Al 2O 3). The reason for introducing H 2SO 4 into the solu-tion was to accelerate the corrosion process and shorten the test time. The slurry was prepared with Analar †-grade chemical regents, distilled water, andcommercial 100-mesh corundum sand (Al 2O 3). The granularity of the corundum particles was laid in the range of 80 mesh to 100 mesh (125 µm to 160 µm) and their properties were described in detail else-where.11 Before each test, the solution was deaerated for more than 6 h by N 2 purging and then introduced into the RCE. Continuous deaeration was maintained during the test by bubbling nitrogen through the solu-tion. All tests were carried out at room temperature (~25°C). Both Al 2O 3 and solution was changed after 63 min at 5.28 m/s and 38 min at 8.75 m/s, which corresponded to a rotation distance of 20 km with respect to a point on the working surface of the sam-ple. Before and after erosion/erosion-corrosion test, the specimen weight was measured using an analyti-cal balance with a sensitivity of 0.1 mg, and the micro-hardness of specimens was measured with a Shimadzu † micro-hardness tester.All erosion or erosion-corrosion testing were re-peated three to fi ve times; three times were chosen if they were quite consistent with each other, or more duplicates were introduced to get a comparable and reliable results. In the meantime, an assumption was made that porously attached corrosive product could be completely removed by the erosion process; there-fore, the sample surface was cleaned after erosion-corrosion testing in the same way as that used before testing, prior to the weight measurement.Experimental ResultsErosion Behavior — The erosion behavior of four SS was tested in a Al 2O 3 + H 2O dual-phase slurry (benign environment) at two particle velocities of 5.28 m/s and 8.75 m/s. The erosion rates of SS are illustrated in Figure 1. The Type 316L SS had the highest weight loss at both velocities, which was ap-proximately twice the value for the others. At a lower velocity, there is no major difference in the weight loss among 1Cr13, 0Cr14Ni5Mo, and CD-4MCu. But at a higher velocity, the duplex phase steel showed good resistance. In ascending order, the sequence of weight loss was CD-4MCu, 1Cr13, 0Cr14Ni5Mo, and Type 316L SS. In the benign environment, the erosion resistance of SS would depend principally on the me-chanical properties of the materials, especially their hardness here, when they were exposed to the benign environment.† Trade name.TABLE 1Chemical Composition and Micro-Hardness of SS (wt%)CCrNiMo Cu SiMnNFeHvFerritic SS 1Cr130.1 13.5 0.2 — — 0.4 0.1 — Bal. 530Austenitic Type 316L SS 0.03 17.2 13.1 2.1 — 0.8 1.0 — Bal. 200 Martensite SS 0.00 12.8 5.7 1.7 0.2 0.3 0.5 — Bal. 410 0Cr14Ni5MoDuplex SS CD-4MCu 0.06 25.7 5.4 2.0 3.0 1.5 0.7 Trace Bal. α-235γ-280Composition (wt%)32C ORROSION—JANUARY 20053. At lower velocities, the performance of Type 316L SS here was completely different from that in 3.5% NaCl + 30% Al 2O 3. Its erosion-corrosion resistance was much better than 1Cr13 and 0Cr14Ni5Mo steel, and its weight loss approached that of CD-4MCu. The erosion-corrosion resistance of CD-4MCu is the best among all steels at this speed. Correspondingly, at higher velocities, both Type 316L SS and CD-4MCu steels had higher weight loss in the erosion-corrosion process than those at lower velocities. But CD-4MCu still sustained better performance under this condi-tion, especially after a long exposure time, for exam-ple, after 104 min (three cycles).SYNERGISTIC EFFECT AND ITS MECHANISMAnalysis of Experimental ResultsIn all the dual-phase slurries, H 2O + 30% Al 2O 3, 3.5% NaCl + 30% Al 2O 3, and 0.5 N H 2SO 4 + 3.5% NaCl + 30% Al 2O 3, the erosion or erosion-corrosion behavior of four SS could be summarized briefl y. The 1Cr13 and 0Cr14Ni5Mo steels had similar performance in all erosion/corrosion tests. Their weight losses increased with the increase in corrosion of the aggressive media and the velocity of impacting particles.The hardness of Type 316L SS is not very high, but its concentration of Ni + Cr is on the top, in com-parison to the other three alloys. It could be expected that Type 316L SS would be vulnerable to mechanical (erosion) damage and be highly resistant to a corrosive environment. This is verifi ed by the experimental re-sults. At a higher velocity of 8.75 m/s, Type 316L SS had the last place in the ascending sequence of ero-sion (-corrosion) resistance of those four alloys in H 2O+ Al 2O 3, but had the first place in the strong corrosive media of H 2SO 4 + NaCl + Al 2O 3. That means that the stronger the corrosion of the media, the better perfor-mance that the Type 316L SS had in this investiga-tion when compared with others. At a lower velocity of 5.28 m/s, the Type 316L SS had the highest weight(a)(b)FIGURE 1. Weight loss of steels vs exposure time with different velocity in H 2O + Al 2O 3.FIGURE 2. Weight loss of steels with different velocities in NaCl + Al 2O 3 slurry.Erosion-Corrosion Behavior — In Cl –-containing dual-phase slurry (3.5% NaCl + 30% Al 2O 3), the aver-age weight loss of materials was also linearly propor-tional to the exposure time. The average weight loss per 63 min (20 km) of CD-4MCu, 1Cr13, 0Cr14Ni5Mo, and Type 316L SS was 0.42, 0.57, 0.69, and1.54 mg/cm 2-h at a lower velocity; the average weight loss per 38 min (20 km working distance) at a higher velocity was2.27, 2.55,3.28, and 3.47 mg/cm 2-h, respectively (Figure 2). Excluding the duplex phase steel, the average weight loss of the other three SS has the same order as their respective hardness.Among the alloys 1Cr13, 0Cr14Ni5Mo, and Type 316L, the ferritic 1Cr13 had the highest micro-hardness and was found to lose the least weight.Another erosion-corrosion test was carried out in a stronger corrosive dual-phase slurry of H 2SO 4 (3.5% NaCl + 0.5 N H 2SO 4 + 30% Al 2O 3) at two velocities. Theweight-loss curves of the SS are illustrated in FigureC ORROSION—Vol. 61, No. 133loss in both benign (H 2O) and mild (3.5% NaCl + H 2O) corrosive media. It was much better in strong corro-sive media (0.5 N H 2SO 4 + 3.5% NaCl) and got close to the performance of duplex-phase steel, where both of them showed high erosion-corrosion resistance. That means that Type 316L SS is resistant to erosion or erosion-corrosion in strong corrosive media and at low velocity, in which case the damage of materials was not mainly caused by mechanical damage.In general, dual-phase CD-4MCu steel had the best performance at high rotation speed, especially at high rotation speed and in strong corrosive media. In 0.5 N H 2SO 4 + 3.5% NaCl + 30% Al 2O 3, there was no signifi cant difference between CD-4MCu steel and Type 316L SS at low velocity, but the former was bet-ter after a long-term exposure at high velocity. The reason for the superior performance under strong corrosive media and low velocities may have been aresult of the better corrosion resistance (due to the(a)(b)FIGURE 3. Weight loss of steels vs exposure time with different velocities in H 2SO 4 + NaCl + Al 2O 3 slurry.FIGURE 4. Sectional micro-hardness of steels.higher nickel and chromium content in these two steels). Moreover, under more severe conditions, CD-4MCu exhibited the best behavior not just because of its high corrosion resistance, but also its highwork-hardening capability (Figure 4). Micro-hardness testing indicated that the dual-phase has very high work-hardening capability, which was demonstrated in other experiments. CD-4MCu exhibited high work-hardening capability only at high external force, in-cluding long-term exposure to particle impacting. This was consistent with its result of steady-state corrosive wear in 69% phosphoric acid (H 3PO 4).12-13Regime Defi nitions and Calculation of SynergyReferring to the investigation methods and prin-ciples of corrosive wear and the characteristics of the erosion-corrosion itself, erosion-corrosion rate and its components were measured and calculated.7-8,12-15 The erosion-corrosion process of four alloys in a strong corrosive environment (0.5 N H 2SO 4 + 3.5% NaCl + 30% Al 2O 3), at both 5.28 m/s and 8.75 m/s, was con-sidered for the calculation. The total weight loss of erosion-corrosion (W), which is the removal of SS in dual-phase slurry caused by erosion-corrosion pro-cesses, should be composed of the following:—pure mechanical damage (no electrochemical corrosion) or pure erosion W e—pure steady electrochemical corrosion W c—increment/synergy of erosion and corrosion ΔW The increment of the synergistic interaction of erosion and corrosion is composed of two aspects, the increment of corrosion, ΔW c , due to mechanical dam-age, and the increment of erosion, ΔW e , due to electro-chemical corrosion.15 Others, such as the protection or degradation deceleration of material due to electro-chemical corrosion in mechanical damage (e.g., the corrosion products restrain the mechanical damage of materials because of its lubricative effect sometimes) and the increment of local electrochemical corrosion due to the fretting process (e.g., the weight loss comes from crevice corrosion), can be ignored.15-16 So the34C ORROSION—JANUARY 2005total weight loss of materials in the erosion-corrosion process W can be described as Equation (1): W W W W e c =++∆(1)where:∆∆∆W W W e c =+(2)Erosion-corrosion testing was carried out in 30 wt% Al 2O 3 + 3.5 wt% NaCl + 0.5 N H 2SO 4 slurry at two par-ticle velocities, 5.28 m/s and 8.75 m/s. The erosion-corrosion rates of SS at two velocities were obtained. The testing period was four cycles, 4 × 63 min at 5.28 m/s and 4 × 38 min at 8.75 m/s. During the test, the solution, including sand, was replaced for each cycle. The pure erosion rate, W e , was obtained in 30% Al 2O 3 + H 2O. In this case, it was supposed that there was no corrosive media in the slurry of 30% Al 2O 3 + H 2O, and there was no difference after replac-ing H 2O with 3.5% NaCl + 0.5 N H 2SO 4 solution. The pure steady electrochemical corrosion W c was carried out under the standard corrosion test. The corrosionrate due to erosion-corrosion W cʹ was calculated by the corrosion current in Equation (3):′=×W M nFi c (3)where M was the equivalent molecular weight, n was the equivalent electrons in reaction, F was Faraday’s constant and equal to 96,500 coulomb per molar electrons, and i was the corrosion current in the ero-sion-corrosion process. The erosion rate in the ero-sion-corrosion process W e ʹ could be calculated by subtracting the corrosion rate W c ʹ from the total ero-sion-corrosion rate W. From the above defi nitions, two more equations could be obtained: ′=×W W W c c c ∆ (4)′=+W W W e e e ∆(5)And then:W W W c e =′+′(6)From the experimental and calculated results and previous analysis in the literature, it is proposed that the most appropriate regimes in terms of the ratio of the corrosion to erosion rate could be classifi ed:14 110./,erosion dominated ′′≥W W e c(7) 2101./,corrosion-assisted erosion >′′≥W W e c(8)3101./.,erosion-assisted corrosio >′′≥W W e e n (9)401./.,corrosion dominated ′′<W W e c(10)It should be pointed out that the steady electrochemi-cal corrosion was preferably recognized as the purecorrosion in this study, although the erosion-corro-sion in single-phase pure water was used in some of the literature. It was found that there was a large dif-ference between the corrosion rates in these two ex-perimental methods. The corrosion rate in the former conditions were 0.08, 0.03, 0.04, and 0.03 mg/cm 2-h for 1Cr13, Type 316L, 0Cr14Ni5Mo, and CD-4MCu SS, respectively. However, in the latter conditions, the corrosion rates increase to 0.34, 0.22, 0.31, and 0.18 mg/cm 2-h. Both groups of those results were obtained at a fl uid velocity of 8.75 m/s. It can be said that the erosion did infl uence the corrosion pro-cess even in single-phase pure water, and this effect should increase with increasing fl uid velocity.Calculated ResultsLow Velocities of 5.28 m/s — At 5.28 m/s, the measured or calculated results of the erosion-corrosion rate and its components for SS are listed in Table 2, and the calculated ratios of each component to the total weight loss are listed in Table 3. As for the pure erosion in H 2O-Al 2O 3 (noncorrosive environment), there was no big difference among the erosion rates W e of four SS, although that of the CD-4MCu SS was a little bit lower. However, in the corrosive environ-ment, the erosion rate of ferritic 1Cr13 SS W e ʹ was much higher than the rate of the other three steels; the erosion increment due to corrosion ΔW e was sig-nifi cant and increased to 50% of the total erosion-corrosion rate. The increment due to the synergistic effect ΔW was 60% of the total weight loss. The ero-sion increment due to electrochemical corrosion W e ʹ and the synergistic interaction ΔW of Type 316L,0Cr14Ni5Mo, and CD-4MCu SS were not as much as that of 1Cr13. This may result from the difference in the corrosion resistance of those steels. In 3.5 wt% NaCl + 0.5 N H 2SO 4 + 30 wt% Al 2O 3, the corrosion re-sistance of Type 316L and CD-4MCu SS were the best and that of the 1Cr13 was the worst (pure corrosion, W c in the Table 2).Both the pure steady corrosion W c and the cor-rosion component in the erosion-corrosion W cʹ were smaller than the corresponding erosion component W e or W e ʹ. Furthermore, in the erosion-corrosion pro-cess, the ratios W e ʹ/W cʹ of erosion (W e ʹ) to corrosion (W cʹ) were 5.4, 11, 4.8, and 4.8 for 1Cr13, Type 316L, 0Cr14Ni5Mo, and CD-4MCu SS, respectively. Accord-ingly, the removal of materials at 5.28 m/s mainly came from the mechanical damage. Referring to the classifi cation of erosion-corrosion regimes based on the ratio of erosion to corrosion rate, the synergistic mechanism of erosion-corrosion of SS under this con-dition could be attributed to corrosion-assisted ero-sion regime (Regime 2, Equation [8]). For instance, thecorrosion component in erosion-corrosion W cʹ of Type 316L SS was just 8.3% of the total weight loss W.High Velocities of 8.75 m/s — At 8.75 m/s,the measured or calculated results of the erosion-corrosion rate and its components of SS are listed in Table 4, and the calculated ratios of each component to the total weight loss are listed in Table 5 as well. When compared to the results at low velocity, theratio of both pure corrosion and corrosion in erosion-corrosion to the total weight loss of materials was smaller. Both the increment of erosion and the total synergistic increment of Type 316L, 0Cr14Ni5Mo, and CD-4MCu increased with increasing velocity. More-over, the synergistic increments of erosion-corrosion for 1Cr13 and 0Cr14Ni5Mo SS were 50% of the total weight losses, respectively.Similarly, the pure steady corrosion Wcor the cor-rosion component in erosion-corrosion Wcʹ was smaller than the pure erosion and the erosion component in synergistic interaction, respectively. In the erosion-corrosion process, the ratios Weʹ/W cʹ of erosion to cor-rosion were 2.6, 11, 4.6, and 8.1 for 1Cr13, Type 316L, 0Cr14Ni5Mo, and CD-4MCu SS, respectively. Accord-ingly, the removal of materials at 8.75 m/s mainly came from the mechanical damage. Referring to the classifi cation of erosion-corrosion regimes based on the ratio of erosion to corrosion rate, the synergistic mechanism of erosion-corrosion of SS at this condi-tion was similar to that at lower fl uid velocities and it was corrosion-assisted erosion regime. For instance, the corrosion in erosion-corrosion Wcʹ of Type 316L SS was just 8.2% of the total weight loss W.Synergistic Mechanism of Erosion and Corrosion In the erosion-corrosion experiments, Type 316L and CD-4MCu exhibited high corrosion resistance in both pure corrosion condition, and erosion and corro-sion acted simultaneously. In particular, the corrosion component in erosion-corrosion of Type 316L SS was approximately 8% at the two velocities. The removal of materials mainly came from the mechanical damage. Interestingly, the weight loss of CD-4MCu was lower at the higher velocity than that at the lower velocityin this study. The erosion-corrosion resistance ofSS at low velocity could be correlated to their micro-hardness. This is consistent with literature data.12 The results obtained in this study showed that erosion and corrosion promoted each other and accel-TABLE 2Erosion-Corrosion Rate of SS at 5.28 m/s (mg/cm2-h) in a Slurry of 3.5 wt% NaCl + 0.5 N H2SO4+ 30 wt% Al2O3Alloys W Wc WeWcʹW eʹΔW cΔW eΔW1Cr13SS 1.54 0.08 0.53 0.24 1.30 0.16 0.77 0.93 Type 316L SS 0.72 0.03 0.57 0.06 0.66 0.03 0.09 0.12 0Cr14Ni5MoSS 0.69 0.04 0.45 0.12 0.57 0.08 0.12 0.20 CD-4MCu 0.52 0.03 0.38 0.09 0.43 0.06 0.05 0.11TABLE 3Ratio of Each Component to the Total Weight Loss (%, 5.28 m/s, 3.5 wt% NaCl + 0.5 N H2SO4+ 30 wt% Al2O3)Alloy Wc /W We/W Wcʹ/W W eʹ/W ΔW c/W ΔW e/W ΔW/W1Cr13SS 5.2 34.4 15.6 84.4 10.3 50.0 60.4 Type 316L SS 4.1 79.1 8.3 91.7 4.1 12.5 16.7 0Cr14Ni5MoSS 5.8 65.2 17.4 82.6 11.6 17.4 29.0 CD-4MCu 5.8 73.1 17.3 82.7 11.5 9.6 21.1TABLE 4Erosion-Corrosion Rate of SS at 8.75 m/s (mg/cm2-h) in a Slurry of 3.5 wt% NaCl + 0.5 N H2SO4+ 30 wt% Al2O3Alloy W Wc WeWcʹW eʹΔW cΔW eΔW1Cr13 SS 3.47 0.08 1.34 0.95 2.52 0.87 1.18 2.05 Type 316L SS 2.55 0.03 1.61 0.21 2.34 0.18 0.73 0.91 0Cr14Ni5Mo SS 3.28 0.04 1.57 0.58 2.70 0.54 1.13 1.67 CD-4MCu 2.27 0.03 0.95 0.25 2.02 0.22 1.07 1.29TABLE 5Ratio of Each Component to the Total Weight Loss (%, 8.75 m/s, 3.5 wt% NaCl + 0.5 N H2SO4+ 30 wt% Al2O3)Alloy Wc /W We/W Wcʹ/W W eʹ/W ΔW c/W ΔW e/W ΔW/W1Cr13SS 2.3 38.6 27.4 72.6 25.1 34.0 59.1 Type 316L SS 1.2 63.1 8.2 91.8 7.0 28.6 35.70Cr14Ni5MoSS 1.2 47.9 17.7 82.3 16.4 34.4 50.9 CD-4MCu 1.3 41.8 11.0 89.0 9.7 47.1 56.8C ORROSION—Vol. 61, No. 13536C ORROSION—JANUARY 2005erated the removal of materials, but it must be men-tioned that the weight loss of Type 316L in 0.5 N H 2SO 4-included slurry was much lower than that in both H 2O and 3.5% NaCl + 30% Al 2O 3 slurry at 5.28 m/s. In this case, the passivation fi lms devel-oped in H 2SO 4-included solution was promoting the erosion resistance of Type 316L SS, although the weight loss increased signifi cantly with the increase of velocity to 8.75 m/s. The corrosion and erosion processes would infl uence each other, and sometimes the synergistic effect might greatly increase the weight loss of materials. Corrosion might promote erosion by dissolving the work-hardened layer on the specimen surface as well as roughening the surface. The erosion might inhibit corrosion by making the fi brous struc-ture on the bottom of craters on which crystal planes of an interior dissolving rate are arranged.12,15A possible explanation 17-18 for the effect of corro-sion on erosion could be, on the one hand, that the adhesion between the corrosion products and sub-strate was not so strong and, consequently, these cor-rosion products were removed easily when impacted by particles and/or fl uid. On the other hand, the corrosion process, even if it is uniform corrosion or localized corrosion such as pitting, would damage the integrity and smoothness of the material surface. The rougher the materials’ surface, the easier the materi-als can be removed by the mechanical process.A possible explanation for the effect of erosion on corrosion could be, on the one hand, that erosion accelerated the corrosion process by damaging the passivation fi lms from the impacting of particles and, consequently, erosion exposed fresh metal to the cor-rosive media. On the other hand, the impact of parti-cles on the materials’ surface might have changed the uniformity of surface stress and electrochemistry due to elastic deformation, for example, leading to the for-mation of active corrosion sites such as impacting pitsFIGURE 5. Polarization curves of Type 316L SS at three fl uid velocities in the dual-phase slurry of 0.5 N H 2SO 4 + 3.5% NaCl + 30 wt% Al 2O 3.and protuberant lips. In the stress-concentrated or low-stress zone, there might be some corrosion cells due to the stress difference from its peripheral zone, which then would accelerate the corrosion process. The representation of this effect on the polarization of materials might be the shortening of the polarization range and the increasing of the polarizing current and polarization maintaining current (Figure 5).CONCLUSIONS❖ In 3.5% NaCl + 30% Al 2O 3 dual-phase slurry, the sequence of the erosion-corrosion resistance for SS could be CD-4MCu>1Cr13>0Cr14Ni5Mo>Type 316L. Their micro-hardness infl uenced the erosion-corrosion behavior.❖ In 3.5% NaCl + 0.5 N H 2SO 4 + 30% Al 2O 3 dual-phase slurry, the CD-4MCu and the Type 316L SS had the best erosion-corrosion resistance at low ve-locities. However, at high velocities the performance of the CD-4MCu improves. The sequence of the erosion-corrosion resistance for SS under this condition could be CD-4MCu>Type 316L>0Cr14Ni5Mo>1Cr13.❖ In solid-liquid dual-phase slurry, the superior ero-sion-corrosion performance of α+γ duplex-phase SS may be attributed to its high corrosion resistance and high work-hardening capability.❖ Under the experimental conditions of this study, the corrosion component was a small amount of the total erosion-corrosion weight loss, and the removal of materials mainly resulted from mechanical damage. The synergistic mechanism of erosion-corrosion of SS in the condition of this study can thus be termed cor-rosion-assisted erosion behavior.REFERENCES1. C.H. Pitt, Y.M. Chang, Corrosion 42 (1986): p. 312. 2. B.W. Madsen, Wear 123 (1988): p. 1273. Y. Oka, M. Uhkubo, Corrosion 46 (1990): p. 687.4. M.M. Stack, S. Zhou, R.C. Newman, Mater. Sci. Technol. 12(1996): p. 261.5. S. Zhou, M.M. Stack, R.C. Newman, Corros. Sci. 38 (1996): p.1,071.6. Y.G. Yan, “Mechanism of Erosion-Corrosion in Liquid-Solid DualPhase Aqueous Environments” (Ph.D. diss., Institute of Corrosion and Protection of Metals of Chinese Academy of Science, 1998). 7. A. Neville, M. Reyes, H. Xu, Tribol. Int. 35 (2002): p. 643-650. 8. R.J.K. Wood, J.A. Wharton, A.J. Speyer, K.S. Tan, Tribol. Int. 35(2002): p. 631-641.9. V.A. de Souza, A. Neville, Wear 255 (2003): p. 146-156. 10. J.M. Perry, A. Neville, V.A. Wilson, T. Hodgkiess, Surf. Coat.Technol. 137 (2001): p. 43-51. 11. D.X. He, X.X. Jiang, S.Z. Li, H.R. Guan, Corrosion 58 (2002): p.276. 12. X.C. Lu, X.X. Jiang, S.Z. Li, T.C. Zhang, J. Chin. Soc. Corros.Prot. 14 (1994): p. 201. 13. T.C. Zhang, X.X. Jiang, S.Z. Li, C.X. Shi, Acta Metall. Sin. 29(1993): p. PB217. 14. M. Bjordal, E. Bardal, T. Rogne, T.G. Eggen, Wear 2 (1995): p. 186. 15. X.X. Jiang, S.Z. Li, Mech. Chem. Eng. 18 (1991): p. 150. 16. R.J.K. Wood, S. Phutton, Wear 140 (1990): p. 150. 17. Y.G. Zheng, Z.M. Yao, Li He, W. Ke, Mater. Sci. Eng. 12 (1994): p.27. 18. Y.G. Zheng, Z.M. Yao, X.Y. Wei, W. Ke, Wear 186-187 (1995): p.556.。
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