线能量密度对选区激光熔化制备316L不锈钢缺陷的影响
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摘要
在拥有自主知识产权的TB-100选区激光熔化设备上制备316L不锈钢。通过金相显微镜对比研究了不同工艺参数(激光功率、扫描速度和扫描间距)下,成形件的低倍缺陷,主要为气泡、孔隙、微裂纹和宏观裂纹;借助扫描电子显微镜和能谱仪,研究了缺陷微观形貌特征和成分,分析了各类缺陷形成机理。结果表明,孔隙主要为圆气泡性孔隙、不规则形状工艺性孔隙和氧化物夹杂,气泡主要为氢气泡和氮气泡,而微裂纹主要为贯穿性孔隙以及内应力过大导致的热裂纹,宏观裂纹主要为由于残余应力过大导致的层状裂纹,属于冷裂纹。引入线能量密度(E=P/v)为综合参数,随着线能量密度的增大,孔隙逐渐减少,但是当线能量密度达到400 J/m时,出现裂纹,且大量出现气泡缺陷,随着线能量密度的继续增大,裂纹逐渐增多;当线能量密度达到583 J/m时,主要为裂纹缺陷,气泡减少;当线能量密度达到875 J/m时,裂纹呈条状且尺寸明显增大,裂纹与裂纹之间已相互连接。经分析测试验证,316L不锈钢较优的工艺参数为激光功率190～210 kW,激光扫描速度800～1 000 mm/s,扫描间距0.90～0.11 mm,此区间线能量密度200 J/m左右,无裂纹,基本无气泡,存在少量孔隙,产品致密度达99.7%。
316 L stainless steel parts were manufactured on TB-100 selective laser melting equipment with independent intellectual property rights. The low-magnification defects of forming parts with different process parameters(laser power, scanning speed and scanning distance) were studied by metallographic microscope, mainly air bubbles, pores, microcracks and macrocracks. The formation mechanism of various kinds of defects were analyzed. the microstructure and composition of the defects were studied by means of SEM and EDS. The results show that the pores are mainly circular air pores, irregular process pores and oxide inclusions. The air bubbles are mainly hydrogen bubbles and nitrogen bubbles, while the microcracks are mainly caused by penetrating pores and thermal cracks caused by excessive internal stress, macrocracks are mainly the layer cracks caused by excessive residual stress, which belong to cold crack. Linear energy density(E=P/v) is introduced as a synthetic parameter. As the line energy density increases, the pores decrease gradually. However, when the linear energy density reaches 400 J/m, cracks appear, and a large number of air bubbles defects appear. As the linear energy density continues to increase, the cracks increases gradually. When the linear energy density reaches 583 J/m, the defects were mainly cracks and bubbles decrease. When the linear energy density reaches 875 J/m, the cracks are strip-shaped and the size is significantly increased, and cracks are connected to each other. According to the analysis and test verification, the optimal process parameters of 316 L stainless steel are laser power 190～210 kW, laser speed 800～1 000 mm/s and scanning interval 0.90～0.11 mm, and the linear energy density is about 200 J/m. There are no cracks, basically no bubbles, a small amount of pores, and the product density reaches 99.7%.
316 L stainless steel parts were manufactured on TB-100 selective laser melting equipment with independent intellectual property rights. The low-magnification defects of forming parts with different process parameters(laser power, scanning speed and scanning distance) were studied by metallographic microscope, mainly air bubbles, pores, microcracks and macrocracks. The formation mechanism of various kinds of defects were analyzed. the microstructure and composition of the defects were studied by means of SEM and EDS. The results show that the pores are mainly circular air pores, irregular process pores and oxide inclusions. The air bubbles are mainly hydrogen bubbles and nitrogen bubbles, while the microcracks are mainly caused by penetrating pores and thermal cracks caused by excessive internal stress, macrocracks are mainly the layer cracks caused by excessive residual stress, which belong to cold crack. Linear energy density(E=P/v) is introduced as a synthetic parameter. As the line energy density increases, the pores decrease gradually. However, when the linear energy density reaches 400 J/m, cracks appear, and a large number of air bubbles defects appear. As the linear energy density continues to increase, the cracks increases gradually. When the linear energy density reaches 583 J/m, the defects were mainly cracks and bubbles decrease. When the linear energy density reaches 875 J/m, the cracks are strip-shaped and the size is significantly increased, and cracks are connected to each other. According to the analysis and test verification, the optimal process parameters of 316 L stainless steel are laser power 190～210 kW, laser speed 800～1 000 mm/s and scanning interval 0.90～0.11 mm, and the linear energy density is about 200 J/m. There are no cracks, basically no bubbles, a small amount of pores, and the product density reaches 99.7%.
引文
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[2] 杨永强,罗子艺,苏旭彬,等.锈钢薄壁零件选区激光熔化制造及影响因素研究[J].中国激光,2011,38(1):60-67.
[3] 王黎.选择性激光熔化成形金属零件性能研究[D].武汉:华中科技大学,2012.
[4] 王沛,黄正华,戚文军,等.基于SLM技术的3D打印工艺参数对316不锈钢组织缺陷的影响[J].机械制造文摘-焊接分册,2016(2):2-7.
[5] 王梦瑶,朱海红,祁婷,等.选区激光熔化成形Al-Si合金及其裂纹形成机制研究[J].激光技术,2016,40(2):219-222.
[6] GEBHARDT A,SCHMIDT F M,HOTTER J S,et al.Additive manufacturing by selective laser melting the realizer desktop machine and its application for the dental industry[J].Physics Procedia,2010,5(2):543-549.
[7] ATZENI E,IULIANO L,MINETOLA P,et al.Proposal of an innovative benchmark for accuracy evaluation of dental crown manufacturing[J].Computers in Biology and Medicine,2012,42(5):548-555.
[8] YADROITSEV I,BERTRAND P,SMUROV I.Parametric analysis of the selective laser melting process[J].Applied Surface Science,2007,253(19):8064-8069.
[9] 王迪.选区激光熔化成型不锈钢零件特性与工艺研究[D].广州:华南理工大学,2011.
[10] 李雅莉.选区激光熔化AlSi10Mg温度场及应力场数值模拟研究[D].南京:南京航空航天大学,2015.
[11] 李瑞迪.金属粉末选择性激光熔化成形的关键基础问题研究[D].武汉:华中科技大学,2010.
[12] 满达虎,王丽芳.奥氏体不锈钢焊接热裂纹的成因及防止对策[J].热加工工艺,2012,41(11):181-184.
[13] 张博,李涤尘,曹毅.基于粉体熔化的选区激光熔化成型方向误差分析[J].激光与光电子学进展,2017(1):184-190.
[14] 王同鹤.选区激光熔化成型件后处理问题研究[D].杭州:浙江工业大学,2017
[15] 程慧.选区激光熔化成形往复扫描工艺研究[D].杭州:浙江工业大学,2016.
[16] ROSENTHAL I,STERN A,FRAGE N.Strain rate sensitivity and fracture mechanism of AlSi10Mg parts produced by selective laser melting[J].Materials Science and Engineering: A,2017(682):509-517.
[17] 张安峰,李涤尘,梁少端,等.高性能金属零件激光增材制造技术研究进展[J].航空制造技术, 2016,517(22):16-22.
[18] 刘洋,杨永强,王迪,等.激光选区熔化成型免组装机构的问隙特征研究[J].中国激光,2014,41(11):88-95.
[19] 杨启云.选区激光熔化成形用 Inconel 625 合金粉末及制品的性能研究[D].北京:机械科学研究总院,2016.
[20] 钱德宇.选区激光熔化成形多孔铝合金的工艺及组织性能研究[D].马鞍山:安徽工业大学,2016.