论文标题
微结构和相变的镍形状存储器合金通过定向能量沉积与原位热处理制造
Microstructure and phase transformation of nickel-titanium shape memory alloy fabricated by directed energy deposition with in-situ heat treatment
论文作者
论文摘要
由于其灵活地创造出具有最小的缺陷的复杂结构，因此添加剂制造已被大量应用于制造各种镍 - titanium（NITI）形状合金的结构。但是，微结构异质性和次级形成是两个主要问题，这些问题阻碍了NITI合金的进一步应用。尽管通常采用后加热处理来改善或操纵NITI合金特性，但它无法意识到NITI合金的热和/或机械性能的空间控制。为了克服均匀后加热治疗的局限性，本研究提出了一种原位热处理策略，该策略被整合到NITI合金的定向能量沉积中。提出的方法将有可能导致新的制造能力，以实现与位置有关的性能或财产操纵。研究了原位热处理对印刷NITI结构的热和机械性能的影响。通过3D有限元模拟和实验表征，根据热循环，微结构演化和机械性能进行了研究。采用了低功率激光束，仅将原位热处理定位到当前印刷层，促进了反向观直体反应和瞬时高溶液处理。在样品上提出的原位热处理导致差量扫描量热法曲线中更明显的相变峰，TI2NI相的体积减小约50％〜70％，而微匹配减少了35 hv。
Additive manufacturing has been vastly applied to fabricate various structures of nickel-titanium (NiTi) shape memory alloys due to its flexibility to create complex structures with minimal defects. However, the microstructure heterogeneity and secondary phase formation are two main problems that impede the further application of NiTi alloys. Although post-heat treatment is usually adopted to improve or manipulate NiTi alloy properties, it cannot realize the spatial control of thermal and/or mechanical properties of NiTi alloys. To overcome the limitations of uniform post-heat treatment, this study proposes an in-situ heat treatment strategy that is integrated into the directed energy deposition of NiTi alloys. The proposed method will potentially lead to new manufacturing capabilities to achieve location-dependent performance or property manipulation. The influences of in-situ heat treatment on the thermal and mechanical properties of printed NiTi structures were investigated. The investigations were carried out in terms of thermal cycling, microstructure evolution, and mechanical properties by 3D finite element simulations and experimental characterizations. A low-power laser beam was adopted to localize the in-situ heat treatment only to the current printed layer, facilitating a reverse peritectic reaction and a transient high solution treatment successively. The proposed in-situ heat treatment on the specimen results in a more obvious phase transformation peak in the differential scanning calorimetry curves, about 50%~70% volume reduction for the Ti2Ni phase, and approximately 35 HV reduction on microhardness.
