Abstract Thermal stimulus-responsive NiTi-based shape memory alloys, which undergo reversible, diffusion-less martensitic phase transformation, have emerged as important functional materials. Amongst them, Ni-rich NiTiHf high temperature shape memory alloys exhibit martensitic phase transformation temperatures well above 100 °C, making them suitable for high temperature applications. However, during repeated thermal cycles their transformation temperatures show instabilities which limit their practical applications. Here, we perform thermal cycling experiments at fixed as well as variable heating/cooling rates on the Ni50.3Ti29.7Hf20 alloy which is heat-treated at different temperatures. We successfully minimized the variations in phase transformation temperatures to an acceptable range by aging the alloy below 500 °C for 3 h. We further show that this minimization correlates well with high activation energy required for the phase transformation elucidating the physical reason behind this observation. Our results pave the way forward for designing Ni-rich NiTiHf shape memory alloys with a stable functional response.

中文翻译：

---

调整 Ni50.3Ti29.7Hf20 高温形状记忆合金中马氏体相变的热循环稳定性

摘要 热刺激响应型 NiTi 基形状记忆合金具有可逆的、无扩散的马氏体相变，已成为重要的功能材料。其中，富镍 NiTiHf 高温形状记忆合金的马氏体相变温度远高于 100 °C，使其适用于高温应用。然而，在重复的热循环中，它们的转变温度表现出不稳定性，这限制了它们的实际应用。在这里，我们对在不同温度下热处理的 Ni50.3Ti29.7Hf20 合金以固定和可变加热/冷却速率进行热循环实验。通过将合金在 500 °C 以下时效 3 小时，我们成功地将相变温度的变化降至可接受的范围。我们进一步表明，这种最小化与相变所需的高活化能密切相关，阐明了这一观察背后的物理原因。我们的结果为设计具有稳定功能响应的富镍 NiTiHf 形状记忆合金铺平了道路。