Two challenges facing high temperature shape memory alloys (HTSMAs) involve extending the actuation fatigue life and maximizing the actuator response. Thus, the focus of this study was to determine alternative processing parameters to form the optimal microstructure for actuation applications involving NiTiHf HTSMA wires. In this study, the effect of rapid thermal annealing (RTA) on the thermo-mechanical properties of Ni-lean Ni_49.8Ti_40.2Hf₁₀ and Ni-rich Ni_50.3Ti_29.7Hf₂₀ HTSMA wires was investigated. Both alloys were produced from a large-scale ingot, homogenized, then extruded, and subsequently cold-drawn to wire. In the final pass, the wires were rapid thermal annealed in an Ar environment for short times at various temperatures. The samples were characterized using differential scanning calorimetry, scanning electron microscopy equipped with energy dispersive spectroscopy, transmission electron microscopy, and thermo-mechanical testing. RTA was shown to be a time efficient technique to control grain size and oxidation of small diameter Ni-lean and Ni-rich NiTiHf HTSMA wires. The resulting grain size proved to be critical to controlling the actuation fatigue life and actuation strain response; however, an inverse relationship was found between fatigue life and actuation strain, i.e., longer fatigue life also meant lower actuation strain.

高温形状记忆合金 (HTSMA) 面临的两个挑战涉及延长致动疲劳寿命和最大化致动器响应。因此，本研究的重点是确定替代工艺参数，以形成适用于涉及 NiTiHf HTSMA 线材的致动应用的最佳微观结构。_{在本研究中，快速热退火 (RTA) 对贫镍 Ni 49.8} Ti _40.2 Hf ₁₀和富镍 Ni _50.3 Ti _29.7 Hf ₂₀热机械性能的影响研究了 HTSMA 线材。两种合金均由大型铸锭制成，均质化，然后挤压，随后冷拉成线材。在最后一道工序中，导线在 Ar 环境中在不同温度下短时间快速热退火。使用差示扫描量热法、配备能量色散光谱的扫描电子显微镜、透射电子显微镜和热机械测试对样品进行表征。RTA 被证明是一种控制晶粒尺寸和小直径贫镍和富镍 NiTiHf HTSMA 线材氧化的时间高效技术。由此产生的晶粒尺寸被证明对控制驱动疲劳寿命和驱动应变响应至关重要；然而，在疲劳寿命和驱动应变之间发现了反比关系，即