激光冲击强化对太阳能热发电用渗铝钢显微组织和高温拉伸性能的影响
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摘要
目的研究激光冲击强化前后,渗铝321不锈钢的显微组织变化和高温拉伸行为。方法采用固体粉末包埋渗铝法对321奥氏体不锈钢板材拉伸试样进行渗铝处理,制成渗铝钢,再对渗铝钢中间8 mm?25 mm标距段进行双面激光冲击强化处理,激光波长为1064 nm,单脉冲能量为7 J,脉宽为20 ns,冲击次数为1次和3次,圆光斑直径为2.6～3 mm,搭接率50%,黑胶布为保护层,水为约束层,并评价激光冲击前后渗铝钢表面完整性。对渗铝钢在620下进行高温拉伸试验,获得真应力-真应变曲线、屈服强度、抗拉强度以及断后延伸率,并在扫描电镜下观察拉伸断口微观形貌。结果渗铝钢的表面粗糙度和显微硬度随着激光功率密度和冲击次数的增加而提高。激光冲击强化后的渗铝钢表现出更高的屈服强度、抗拉强度和断后延伸率,其中,以6.59 GW/cm2激光密度三次冲击的渗铝钢的高温拉伸性能最佳。激光冲击强化后的渗铝钢高温拉伸断口表现出韧性断裂特征。结论激光冲击强化后,渗铝钢表面发生明显塑性变形,形成了起伏较大的凹坑和凸台,改变了材料粗糙度。表面晶粒细化、位错运动加剧以及位错增殖使得材料表面硬度和激光冲击硬化影响层深度提高;另外,引入的高幅残余压应力的释放能够抵消外加拉应力,延缓表面裂纹的形核和扩展。激光冲击强化显著改善了渗铝钢力学性能。
The work aims to investigate the effects of laser shock peening on the microstructure and high temperature tensile properties of aluminized 321 stainless steel. The aluminizing was carried out to tensile sample of 321 austenitic stainless steel by packed cementation to prepare the aluminized steel. Then the double-side gauge area(8 mm'25 mm) of aluminized steel was performed by laser shock process with different parameters: pulse wave length of 1064 nm, pulse energy of 7 J, pulse width of 20 ns, circular spot diameter of 2.6～3 mm and overlapping ratio of 50%. Black tape was used as the protective layer and water was used as the restraint layer. The surface integrity of aluminized steel was evaluated and then high temperature tensile test was carried out to aluminized steel at 620 ℃ to obtain the true stress-true strain curve, the yield strength, ultimate strength and elongation. The fracture morphology was observed by scanning electron microscopy. The surface roughness and micro-hardness of aluminized steel increased with the increasing of laser power density and impact times. Aluminized steel processed by laser shock exhibited higher yield strength, tensile strength and elongation. The aluminized steel with laser energy density of 6.59 GW/cm2 and three-times of impact showed the best tensile performance. The high-temperature tensile fracture of aluminized steel strengthened by laser impact exhibited the ductile fracture characteristics. Obvious plastic deformation occurs at the surface of aluminized steel after laser shock, resulting in larger pit and boss and changing the material roughness. Refinement of surface grains, intensive dislocation and increase of dislocation improve the surface hardness and the depth of hardening impact layer by laser shock. In addition, the release of introduced high amplitude residual compressive stress can offset the external tension and delay the formation and extension of surface crack. Therefore, laser shock strengthening improves the mechanical properties of aluminized steel.
The work aims to investigate the effects of laser shock peening on the microstructure and high temperature tensile properties of aluminized 321 stainless steel. The aluminizing was carried out to tensile sample of 321 austenitic stainless steel by packed cementation to prepare the aluminized steel. Then the double-side gauge area(8 mm'25 mm) of aluminized steel was performed by laser shock process with different parameters: pulse wave length of 1064 nm, pulse energy of 7 J, pulse width of 20 ns, circular spot diameter of 2.6～3 mm and overlapping ratio of 50%. Black tape was used as the protective layer and water was used as the restraint layer. The surface integrity of aluminized steel was evaluated and then high temperature tensile test was carried out to aluminized steel at 620 ℃ to obtain the true stress-true strain curve, the yield strength, ultimate strength and elongation. The fracture morphology was observed by scanning electron microscopy. The surface roughness and micro-hardness of aluminized steel increased with the increasing of laser power density and impact times. Aluminized steel processed by laser shock exhibited higher yield strength, tensile strength and elongation. The aluminized steel with laser energy density of 6.59 GW/cm2 and three-times of impact showed the best tensile performance. The high-temperature tensile fracture of aluminized steel strengthened by laser impact exhibited the ductile fracture characteristics. Obvious plastic deformation occurs at the surface of aluminized steel after laser shock, resulting in larger pit and boss and changing the material roughness. Refinement of surface grains, intensive dislocation and increase of dislocation improve the surface hardness and the depth of hardening impact layer by laser shock. In addition, the release of introduced high amplitude residual compressive stress can offset the external tension and delay the formation and extension of surface crack. Therefore, laser shock strengthening improves the mechanical properties of aluminized steel.
引文
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[2]KURAVI S,TRAHAN J,GOSWAMI D Y,et al.Thermal energy storage technologies and systems for concentrating solar power plants[J].Progress in energy&combustion science,2013,39(4):285-319.
[3]XU B,LI P,CHAN C.Application of phase change materials for thermal energy storage in concentrated solar thermal power pants:A review to recent developments[J].Applied energy,2015,160:286-307.
[4]WANG Z,WANG H,LI X,et al.Aluminum and silicon basedphase change materials for high capacity thermal energy storage[J].Applied thermal engineering,2015,89:204-208.
[5]TIAMIYU A A,ESKANDARI M,NEZAKAT M,et al.Acomparative study of the compressive behaviour of AISI321 austenitic stainless steel under quasistatic and dynamic shock loading[J].Materials&design,2016,112:309-319.
[6]MOLLARD M,RANNOU B,BOUCHAUD B,et al.Comparative degradation of nickel aluminized by slurry and by pack cementation under isothermal conditions[J].Corrosion science,2013,66(1):118-124.
[7]SINGH K,FERNANDES A,PAUL B,et al.Preparation and investigation of aluminized coating and subsequent heat treatment on 9Cr-1Mo grade 91 steel[J].Fusion engineering&design,2014,89(11):2534-2544.
[8]张冀翔,徐修炎,宋健斐,等.钢的渗铝工艺技术及性能研究进展[J].表面技术,2018,47(2):218-224.ZHANG Ji-xiang,XU Xiu-yan,SONG Jian-fei,et al.Research progress of steel aluminizing technology and performance[J].Surface technology,2018,47(2):218-224.
[9]MENDIBIDE C,STEYER P,FONTAINE J,et al.Improvement of the tribological behaviour of PVDnanostratified TiN/CrN coatings-An explanation[J].Surface&coatings technology,2006,201(7):4119-4124.
[10]张超,花银群,帅文文,等.激光冲击对WC-Co硬质合金微观结构和残余应力的影响[J].表面技术,2018,47(4):230-235.ZHANG Chao,HUA Yin-qun,SHUAI Wen-wen,et al.Effect of laser shot peening on microstructure and residual stress of WC-Co cemented carbide[J].Surface technology,2018,47(4):230-235.
[11]吴健,周建忠,孟宪凯.激光冲击强化对W6Mo5Cr4V2高速钢材料表面性能的影响[J].表面技术,2017,46(6):232-237.WU Jian,ZHOU Jian-zhong,MENG Xian-kai.Effects of laser shock processing on surface properties of W6Mo5Cr4V2 high-speed steel[J].Surface technology,2017,46(6):232-237.
[12]曹子文,杨清,高宇.激光冲击强化TC17钛合金室温和高温拉伸性能研究[J].表面技术,2018,47(3):85-90.CAO Zi-wen,YANG Qing,GAO Yu.Tensile properties at room and high temperature of TC17 titanium alloy treated by laser shock peening[J].Surface technology,2018,47(3):85-90.
[13]ZHANG L,LU J Z,ZHANG Y K,et al.Effects of laser shock processing on morphologies and mechanical properties of ANSI 304 stainless steel weldments subjected to cavitation erosion[J].Materials,2017,10(3):292.
[14]LUO S H,HE W F,ZHOU L C,et al.Aluminizing mechanism on a nickel-based alloy with surface nanostructure produced by laser shock peening and its effect on fatigue strength[J].Surface&coatings technology,2018,342:29-36.
[15]任旭东,张田,姜大伟,等.激光冲击与渗铝复合处理对12Cr Mo V组织性能的影响[J].红外与激光工程,2011,40(2):241-244.REN Xu-dong,ZHANG Tian,JIANG Da-wei,et al.Effects of laser shock processing and aluminizing on microstructure and properties of 12CrMoV alloy[J].Infrared and laser engineering,2011,40(2):241-244.
[16]周磊,李应红,汪诚,等.激光冲击强化渗铝法提高K417合金疲劳性能[J].稀有金属材料与工程,2011,40(6):1093-1096.ZHOU Lei,LI Ying-hong,WANG Cheng,et al.Vibration fatigue performance improvement of K417 alloy by laser shock processing and aluminizing[J].Rare metal materials and engineering,2011,40(6):1093-1096.
[17]FABBRO R,PEYRE P,BERTHE L,et al.Physics and applications of laser-shock processing[J].Journal of laser applications,1998,10(6):155-164.
[18]汪诚,赖志林,何卫锋,等.激光冲击次数对1Cr11Ni2W2MoV不锈钢高周疲劳性能的影响[J].中国激光,2014(1):46-51.WANG Cheng,LAI Zhi-lin,HE Wei-feng,et al.Effect of multi-impact on high cycle fatigue properties of1Cr11Ni2W2MoV stainless steel subject to laser shock processing[J].Chinese of lasers,2014(1):46-51.
[19]林吉忠,刘淑华.金属材料的断裂与疲劳[M].北京:中国铁道出版社,1989.LIN Ji-zhong,LIU Shu-hua.Fracture and fatigue of metallic materials[M].Beijing:China Railway Publishing House,1989.
[20]孙永庆,梁剑雄,杨志勇,等.热处理工艺对AM355不锈钢力学性能的影响及机理[J].钢铁,2014,49(9):77-80.SUN Yong-qing,LIANG Jian-xiong,YANG Zhi-yong,et al.Effect and mechanism of heat treatment on mechanical property of AM355 steel[J].Chinese journal of iron and steel,2014,49(9):77-80.
[21]YOSHIMI K,HANADA S.The strength properties of iron aluminides[J].JOM,1997,49(8):46-49.
[22]STOLOFF N S.Iron auminides:Present status and future prospects[J].Materials science&engineering A,1998,258(1-2):1-14.
[23]ESHELBY J D,FRANK F C,NABARRO F,et al.The equilibrium of linear arrays of dislocations[J].The London,Edinburgh,and Dublin philosophical magazine and journal of science,1951,42:351-64.
[24]ZHONG Jin-shan.Influence of laser shock processing on tensile properties and tribological behaviors of AISI304stainless steel[J].Chinese journal of lasers,2013,40(5):0503002.
[25]钟金杉,鲁金忠,罗开玉,等.激光冲击对AISI304不锈钢拉伸性能和摩擦磨损性能的影响[J].中国激光,2013,40(5):62-68.ZHONG Jin-shan,LU Jin-zhong,LUO Kai-yu,et al.Influence of laser shock processing on tensile properties and tribological behavior of AlSI304 stainless steel[J].Chinese of lasers,2013,40(5):62-68.