摘要
NiTi shape memory alloy(SMA)with nominal composition of Ni 50.8 at%and Ti 49.2 at%was additively manufactured(AM)by selective laser melting(SLM)and laser directed energy deposition(DED)for a comparison study,with emphasis on its phase composition,microstructure,mechanical property and deformation mechanism.The results show that the yield strength and ductility obtained by SLM are 100 MPa and 8%,respectively,which are remarkably different from DED result with 700 MPa and 2%.The load path of SLM sample presents shape memory effect,corresponding to martensite phase detected by XRD;while the load path of DED presents pseudo-elasticity with austenite phase.In SLM sample,fine grain and hole provide a uniform deformation during tensile test,resulting in a better elongation.Furthermore,the nonequilibrium solidification was studied by a temperature field simulation to understand the difference of the two 3D printing methods.Both temperature gradient G and growth rate R determine the microstructure and phase in the SLM sample and DED sample,which leads to similar grain morphologies because of similar G/R.While higher G×R of SLM leads to a finer grain size in SLM sample,providing enough driving force for martensite transition and subsequently changing texture compared to DED sample.
利用激光增材制造技术成形了Ni50.8Ti49.2形状记忆合金,对比分析选区激光熔化(SLM)成形试样与激光定向能量沉积(DED)成形试样的物相分布、微观结构、力学性能与变形机理。结果表明SLM试样具有100 MPa的屈服强度和8%的伸长率,而DED试样的屈服强度高达700 MPa但仅有2%的伸长率。SLM试样的变形行为主要体现为形状记忆效应,DED试样的变形行为体现为伪弹性。XRD结果表明SLM基体为马氏体态而DED试样为奥氏体态。分析发现非平衡凝固和激光定向凝固过程导致激光增材试样存在明显的熔池行为,但由于SLM工艺的扫描速度明显高于DED工艺的,其存在更高的温度梯度和生长速度,形成了更小的晶粒尺寸分布和更强的织构强度,且形成的气孔缺陷较为均匀,使得材料的均匀变形更易发生,具有较高的伸长率。Ni元素的挥发以及更强的晶界界面能使得SLM试样具有足够的驱动力发生马氏体相变,改变了SLM试样的强织构方向和变形方式。
作者
ZHENG Dan
LI Rui-di
YUAN Tie-chui
XIONG Yi
SONG Bo
WANG Jia-xing
SU Ya-dong
郑聃;李瑞迪;袁铁锤;熊熠;宋波;汪嘉兴;苏亚东(State Key Laboratory of Powder Metallurgy,Central South University,Changsha 410083,China;State Key Laboratory of Materials Processing and Die&Mould Technology,Huazhong University of Science and Technology,Wuhan 430074,China;Shenyang Aircraft Design and Research Institute,Shenyang 110035,China)
基金
Project(2020JJ2046)supported by the Science Fund for Hunan Distinguished Young Scholars,China
Project(S2020GXKJGG0416)supported by the Special Project for Hunan Innovative Province Construction,China
Project(2018RS3007)supported by the Huxiang Young Talents,China
Project(GuikeAB19050002)supported by the Science Project of Guangxi,China。
