激光扫描速度对Ti-Ni形状记忆合金影响规律研究

Effects of Laser Scanning Speed on Microstructure and Properties of Ti-Ni Shape Memory Alloy

采用激光选区熔化(selective laser melting, SLM)成形技术制备Ti-Ni形状记忆合金,利用OM、SEM、XRD和室温压缩等研究SLM增材制造参数改变对成形合金内部缺陷、熔池形貌、相变行为及力学性能等影响规律。结果表明,在SLM其它打印参数保持不变的情况下,随激光扫描速度增加成形合金内部缺陷形貌由近规则球形转变为不规则形状;逐行扫描熔池形貌宽度减小且连续性下降;随激光扫描速度增加富Ni基Ti-Ni形状记忆合金相组成含量发生改变,B2奥氏体相含量增加,B19’马氏体相含量减少;成形富Ni基Ti-Ni形状记忆合金相变温度随激光扫描速度增加先降低后升高,但升降温相变过程中均为单一相变峰;当扫描速度为900mm/s时成形富Ni基Ti-Ni形状记忆合金相对密度达到98.5%,内部缺陷含量较少且处于缺陷类型转变范围内,同时试样的最大抗压强度为3120MPa,对应压缩应变为41%,具有较好的综合性能,为最佳打印参数。

Selective laser melting(SLM)was used to fabricate Ti-Ni shape memory alloys.The effects of scanning speed on internal defects,molten pool morphologies,phase transformation behavior and mechanical properties of the alloy were studied using OM,SEM,XRD,and room-temperature compression.The results show that with the increase of laser scanning speed,the internal defect morphology changes from a nearly regular spherical shape to an irregular one when other printing parameters of SLM remain unchanged.For instance,the width and continuity of the molten pool morphology decrease with the increase of laser scanning speed.Besides,the increasing laser scanning speed initiates that the phase composition of Ni-rich Ti-Ni shape memory alloy changes,B19’martensite content decreases,and B2 austenite content increases.And the transformation temperature of the formed Ni-rich Ti-Ni shape memory alloy decreases at first and then increases with the increase of laser scanning speed,but there is a single transformation peak during the process of temperature rise and fall.At 900 mm/s of the scanning speed,the relative density of the alloy reaches 98.5%,yielding the minimum internal defects.Simultaneously,the sample has a maximum compressive strength of 3120 MPa and a compressive strain of 41%,which is the best printing parameter to produce exceptional properties.