选区激光熔化成形316L表面质量及工艺试验研究
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摘要
目的提高选区激光熔化成形316L不锈钢的成形表面质量,达到高质高效成形效果。方法采用380W功率的激光进行SLM成形,对比160μm大层厚和1000 mm/s以上高速率两种工艺组合,对表面及截面缺陷形成机理进行试验研究,检测其表面形貌、致密度、微观组织、力学性能等,探索316L高质高效打印成形的工艺方法。结果选区激光熔化成形316L不锈钢主要有球化、搭接、熔池间未熔合的表面缺陷,截面具有气孔、球化、熔池间未熔合的缺陷。曝光时间对于大层厚成形截面质量影响最大,增加曝光时间会提高成形致密度;而较小的曝光时间和点距以及线间距更有利于高速率成形。在1000 mm/s高速率试验条件下,即曝光时间、点距、线间距分别为30μs、30μm、90μm时,试件致密度达到99.99%。结论高速率成形的截面质量通过工艺优化组合可达到高致密度,且通过表面重熔工艺改善表面效果明显,整体性能最优。大层厚参数打印成形虽可达到高致密度,但在表面质量方面与高速率成形参数存在较大差距。综合比较,高速率成形在保证较好表面质量的前提下可以达到高致密度。
The work aims to improve the surface quality of the 316 L stainless steel formed by the selective laser melting(SLM), so as to achieve the high-quality and high-efficiency forming effects. SLM forming was performed with a laser power of380 W. The formation mechanism of defects on surface and cross section of 316 L stainless steel was tested and studied based on high layer thickness of 160 μm and high scanning speed over 1000 mm/s to determine the surface morphology, density, microstructure, mechanical properties, etc. and explore the process of high-quality and high-efficiency printing and forming of 316 L.The surface defects of SLM forming 316 L stainless steel were mainly spheroidization, lap, and poor fusion between molten pools. The cross-section defects mainly consisted of pores, spheroidization, and poor fusion between molten pools. The exposure time had the greatest influence on the quality of the high layer thickness forming section, and increasing the exposure time improved the forming density; while the smaller exposure time, point distance and hatch space were more favorable for high scanning speed forming. Under the high scanning speed experimental conditions of 1000 mm/s, namely that the exposure time,point distance and hatch space were 30 μs, 30 μm, and 90 μm, respectively, the density of the test piece reached 99.99%. The quality of cross section formed by high rate can achieve high density through process optimization combination, and the surface re-melting process improves the surface effect obviously. Therefore, the overall performance is optimal. High layer thickness parameter printing can achieve high density, but has large difference from the high rate forming parameters in surface quality.After comprehensive comparison, high rate forming can achieve the high density under the premise of ensuring better surface quality.
The work aims to improve the surface quality of the 316 L stainless steel formed by the selective laser melting(SLM), so as to achieve the high-quality and high-efficiency forming effects. SLM forming was performed with a laser power of380 W. The formation mechanism of defects on surface and cross section of 316 L stainless steel was tested and studied based on high layer thickness of 160 μm and high scanning speed over 1000 mm/s to determine the surface morphology, density, microstructure, mechanical properties, etc. and explore the process of high-quality and high-efficiency printing and forming of 316 L.The surface defects of SLM forming 316 L stainless steel were mainly spheroidization, lap, and poor fusion between molten pools. The cross-section defects mainly consisted of pores, spheroidization, and poor fusion between molten pools. The exposure time had the greatest influence on the quality of the high layer thickness forming section, and increasing the exposure time improved the forming density; while the smaller exposure time, point distance and hatch space were more favorable for high scanning speed forming. Under the high scanning speed experimental conditions of 1000 mm/s, namely that the exposure time,point distance and hatch space were 30 μs, 30 μm, and 90 μm, respectively, the density of the test piece reached 99.99%. The quality of cross section formed by high rate can achieve high density through process optimization combination, and the surface re-melting process improves the surface effect obviously. Therefore, the overall performance is optimal. High layer thickness parameter printing can achieve high density, but has large difference from the high rate forming parameters in surface quality.After comprehensive comparison, high rate forming can achieve the high density under the premise of ensuring better surface quality.
引文
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[2]SCHWENDNER K I,BANERJEE R,COLLINS P C,et al.Direct laser deposition of alloys from elemental powder blends[J].Scripta materialia,2001,45(10):1123-1129.
[3]蒲以松,王宝奇,张连贵.金属3D打印技术的研究[J].表面技术,2018,47(3):78-84.PU Yi-song,WANG Bao-qi,ZHANG Lian-gui.Metal 3Dprinting technology[J].Surface technology,2018,47(3):78-84.
[4]KOTHARI K,RADHAKRISHNAN R,WERELEY N M.Advances in gamma titanium aluminides and their manufacturing techniques[J].Progress in aerospace sciences,2012,55(5):1-16.
[5]CHIANEH V A,HOSSEINI H R M,NOFAR M.Micro structural features and mechanical properties of Al-Al3Ti composite fabricated by in-situ powder metallurgy route[J].Journal of alloys&compounds,2009,473(1):127-132.
[6]KAMATH C,EL-DASHER B,GALLEGOS G F,et al.Density of additively-manufactured,316L SS parts using laser powder-bed fusion at powers up to 400 W[J].International journal of advanced manufacturing technology,2014,74(1-4):65-78.
[7]LAOHAPRAPANON A,JEAMWATTHANACHAI P,WONGCUMCHANG M,et al.Optimal scanning condition of selective laser melting processing with stainless steel 316L powder[J].Advanced materials research,2011,341-342:816-820.
[8]YADROITSEV I,SMUROV I.Selective laser melting technology:from the single laser melted track stability to3D parts of complex shape[J].Physics procedia,2010,5:551-560.
[9]KRUTH J P,WANG X,LAOUI T,et al.Lasers and materials in selective laser sintering[J].Assembly automation,2003,23(4):357-371.
[10]ZIETALA M,DUREJKO T,POLANSKI M,et al.The microstructure,mechanical properties and corrosion resistance of 316L stainless steel fabricated using laser engineered net shaping[J].Materials science&engineering A,2016,677:1-10.
[11]BUTOMO D G,FIRKOVICH I A.The causes of the formation of cracks in the MNA-13-3 copper-base alloy[J].Metal science&heat treatment,1966,8(6):481-484.
[12]MA M,WANG Z,GAO M,et al.Layer thickness dependence of performance in high-power selective laser melting of 1Cr18Ni9Ti stainless steel[J].Journal of materials processing technology,2015,215(1):142-150.
[13]DADBAKHSH S,HAO L.Effect of layer thickness in selective laser melting on microstructure of Al/5?wt.%Fe2O3powder consolidated parts[J].The scientific world journal,2014(6):106-129.
[14]BUCHBINDER D,SCHLEIFENBAUM H,HEIDRICHS,et al.High power selective laser melting(HP SLM)of aluminum parts[J].Physics procedia,2011,12(1):271-278.
[15]VERHAEGHE F,CRAEGHS T,HEULENS J,et al.Apragmatic model for selective laser melting with evaporation[J].Acta materialia,2009,57:6006-6012.
[16]陈洪宇,顾冬冬,顾荣海,等.5CrNi4Mo模具钢选区激光熔化增材制造组织演变及力学性能研究[J].中国激光,2016(2):60-67.CHEN Hong-yu,GU Dong-dong,GU Rong-hai,et al.Microstructure evolution and mechanical properties of5CrNi4Mo die steel parts by selective laser melting additive manufacturing[J].Chinese journal of lasers,2016(2):60-67.
[17]宋长辉,杨永强,王赟达,等.CoCrMo合金激光选区熔化成型工艺及其性能研究[J].中国激光,2014(6):52-59.SONG Chang-hui,YANG Yong-qiang,WANG Yun-da,et al.Research on process and property of CoCrMo alloy directly manufactured by selective laser melting[J].Chinese journal of lasers,2014(6):52-59.
[18]SHI W T,LIU Y D,SHI X Z,et al.Beam diameter dependence of performance in thick-layer and high-power selective laser melting of Ti-6Al-4V[J].Materials,2018,11(7):1237.
[19]LIN X,LI Y M,WANG M,et al.Columnar to equiaxed transition during alloy solidification[J].Science in China,2003,46(5):475-489.
[20]CASATI R,LEMKE J,VEDANI M.Microstructure and fracture behavior of 316L austenitic stainless steel produced by selective laser melting[J].Journal of materials science&technology,2016,32(8):738-744.
[21]李洋,陈长军,王晓南,等.选区激光熔化技术制备316L多孔不锈钢工艺及性能研究[J].应用激光,2015,35(3):319-323.LI Yang,CHEN Chang-jun,WANG Xiao-nan,et al.Study the process and properties of biomedical 316L porous stainless steel prepared by selective laser melting technique[J].Applied laser,2015,35(3):319-323.
[22]GAUMANN M,TRIVEDI R,KURZ W.Nucleation ahead of the advancing interface in directional solidification[J].Materials science&engineering A,1997,226-228(1):763-769.
[23]STAMBOULIS A G,BOCCACCINI A R,HENCH L L.Novel biodegradable polymer/bioactive glass composites for tissue engineering applications[J].Advanced engineering materials,2002,4(3):105-109.
[24]SUN Z,TAN X,SHU B T,et al.Selective laser melting of stainless steel 316L with low porosity and high build rates[J].Materials&design,2016,104:197-204.
[25]SURYAWANSHI J,PRASHANTH K G,RAMAMURTYU.Mechanical behavior of selective laser melted 316Lstainless steel[J].Materials science and engineering:A,2017,696:113-121.
[26]MERTENS A,REGINSTER S,CONTREPOIS Q,et al.Microstructures and mechanical properties of stainless steel AISI 316L processed by selective laser melting[J].Materials science forum,2014,783-786:898-903.
[27]ZHONG Y,RANNAR L E,LIU L,et al.Additive manufacturing of 316L stainless steel by electron beam melting for nuclear fusion applications[J].Journal of nuclear materials,2017,486:234-245.