Laser Powder Bed Fusion of Defect-Free NiTi Shape Memory Alloy Parts with Superior Tensile Superelasticity
Laser Powder Bed Fusion of Defect-Free NiTi Shape Memory Alloy Parts with Superior Tensile Superelasticity
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DOI：
10.1016/j.actamat.2022.117781
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发表时间：
2022-02
期刊：
影响因子：
9.4
通讯作者：
L. Xue;K. Atli;C. Zhang;N. Hite;A. Srivastava;A. Leff;A. Wilson;D. Sharar;A. Elwany;R. Arróyave;I. Karaman
中科院分区：
文献类型：
--
作者：
L. Xue;K. Atli;C. Zhang;N. Hite;A. Srivastava;A. Leff;A. Wilson;D. Sharar;A. Elwany;R. Arróyave;I. Karaman
激光粉床熔化是一种很有前途的附加制造技术，可用于制造复杂几何形状的NiTi形状记忆合金零件，而传统的加工方法很难制造这些零件。这项技术对于镍钛形状记忆合金的生物医学应用特别有吸引力，例如支架、植入物以及牙科和外科设备，其中主要是利用超弹性效应。然而，很少有报道称，由于持续的气孔形成或印刷过程中氧化产生的脆性，或两者兼而有之，添加制造的NiTi零件在印刷时的拉伸条件下，在没有制造后热处理的情况下表现出超弹性。在这项研究中，NiTi零件是用激光粉末床熔合制造的，在印刷条件下一直表现出高达6%的室温拉伸超弹性，几乎是文献报道的最大值的两倍。这是通过使用优化的工艺参数消除气孔和裂纹，小心地从富镍镍钛粉末原料中蒸发镍，以及控制印刷室的氧气含量来实现的。晶体织构分析表明，印刷后的NiTi零件具有较强的超弹性择优织构，当复杂形状的零件受到联合载荷时，这一因素需要仔细考虑。透射电子显微镜研究表明，在印制零件中存在纳米氧化物颗粒和富镍析出物，它们通过抑制马氏体相变的非弹性调节机制，在改善超弹性中发挥作用。
Laser powder bed fusion is a promising additive manufacturing technique for the fabrication of NiTi shape memory alloy parts with complex geometries that are otherwise difficult to fabricate through traditional processing methods. The technique is particularly attractive for the biomedical applications of NiTi shape memory alloys, such as stents, implants, and dental and surgical devices, where primarily the superelastic effect is exploited. However, few additively manufactured NiTi parts have been reported to exhibit superelasticity under tension in the as-printed condition, without a post-fabrication heat treatment, due to either persistent porosity formation or brittleness from oxidation during printing, or both. In this study, NiTi parts were fabricated using laser powder bed fusion and consistently exhibited room temperature tensile superelasticity up to 6% in the as-printed condition, almost twice the maximum reported value in the literature. This was achieved by eliminating porosity and cracks through the use of optimized processing parameters, carefully tailoring the evaporation of Ni from a Ni-rich NiTi powder feedstock, and controlling the printing chamber oxygen content. Crystallographic texture analysis demonstrated that the as-printed NiTi parts had a strong preferential texture for superelasticity, a factor that needs to be carefully considered when complex shaped parts are to be subjected to combined loadings. Transmission electron microscopy investigations revealed the presence of nano-sized oxide particles and Ni-rich precipitates in the as-printed parts, which play a role in the improved superelasticity by suppressing inelastic accommodation mechanisms for martensitic transformation.