Nickel-Titanium (NiTi) alloys have the unique shape memory effect and pseudoelasticity, good damping capacity, good corrosion resistance, and excellent biomechanical compatibility. These properties make NiTi alloys attractive in industries like automobile, aerospace, medical device, etc. However, it’s difficult to fabricate and machine NiTi alloys due to their rapid work-hardening property and pseudoelasticity. Traditional manufacturing methods, such as casting and powder metallurgy, show disadvantages of high cost, time-consuming, and limitations in fabrication of parts with complex geometry. In order to reduce or solve these problems, laser additive manufacturing (LAM) methods have been applied for the fabrication of NiTi alloys. Among the LAM methods, laser directed energy deposition (DED) in-situ synthesis of NiTi alloys from the premixed Ni and Ti powders shows its unique advantages of cost-effectiveness and flexibility in altering NiTi alloys’ phase transformation and mechanical properties. However, heterogeneous microstructures and the formation of secondary phases are two crucial issues that impede the application of laser DED to in-situ synthesis NiTi alloys. Ultrasonic vibration has pronounced effects on liquid materials solidification processes, which could be utilized in homogenizing the microstructure and reducing the secondary phase of laser DED in-situ synthesized NiTi alloys. This paper, for the first time, reports in-situ synthesis of NiTi alloys by laser DED with ultrasonic vibration assistance. The effects of ultrasonic vibration on microstructure properties (microstructure homogeneity, internal defects, elemental composition, grain size, and phase constituents) and mechanical properties (pseudoelasticity, microhardness, and Young’s modulus) have been investigated.

镍钛（NiTi）合金具有独特的形状记忆效果和拟弹性，良好的阻尼能力，良好的耐腐蚀性以及出色的生物力学相容性。这些特性使NiTi合金在汽车，航空航天，医疗设备等行业中具有吸引力。但是，由于NiTi合金具有快速加工硬化性和拟弹性，因此难以制造和加工。传统的制造方法（例如铸造和粉末冶金）显示出高成本，费时的缺点，并且在制造具有复杂几何形状的零件时存在局限性。为了减少或解决这些问题，已经将激光增材制造（LAM）方法用于制造NiTi合金。在LAM方法中，由预混合的Ni和Ti粉末原位合成NiTi合金的激光定向能量沉积（DED）表现出其独特的成本效益和灵活性，可改变NiTi合金的相变和机械性能。但是，异质的微观结构和第二相的形成是阻碍激光DED在原位合成NiTi合金中应用的两个关键问题。超声波振动对液态材料的凝固过程具有显着影响，可用于均匀化微观结构并减少激光DED原位合成NiTi合金的第二相。本文首次报道了在超声振动辅助下通过激光DED原位合成NiTi合金的方法。