58Ni39Ti-3Hf alloy system has been proposed as an alternative for superelastic 60NiTi used in load-bearing applications. This research was focused on the development of heat treatment procedures leading to 58Ni39Ti-3Hf parts with maximum possible hardness values. Meanwhile, the relations existing between the heat treatment – microstructure – hardness of 58Ni39Ti-3Hf as compared to baseline 60NiTi were also investigated. These were done by applying the solution and consequent aging treatments on the studied alloy systems at different temperatures and for different times. The microstructure and hardness of the treated samples were, in the next step, analyzed by applying electron probe micro-analyzer (EPMA), energy dispersive X-ray spectrometer (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM) and macro hardness testing techniques. It was understood that applying solution treatments at temperatures above about 1000 °C resulted in the relatively full dissolution of Ni-rich phases such as Ni₃Ti and Ni₃Ti₂, existing in the microstructure of as-received parts, in the NiTi matrix of 60NiTi. On the other hand, for 58Ni39Ti-3Hf, temperatures above about 900 °C appeared to be adequate to solve these Ni-rich phases in the NiTi matrix. Applying aging treatments had either no significant effect on the hardness of solution treated 60NiTi samples (~58 HRC) or reduced their values; after coarsening of Ni₄Ti₃ particles formed in NiTi matrix and their transformation to Ni₃Ti and Ni₃Ti₂ phases. On the other hand, some of the applied aging treatments could increase the hardness values of the solution treated 58Ni39Ti-3Hf alloys (~54 HRC). The maximum value of hardness (~59 HRC) for the aged 58Ni39Ti-3Hf parts was obtained for the ones treated at 500 °C for just 0.25 h. This level of obtained hardness is comparable to that of solution treated 60NiTi. A delayed precipitation of Ni₃Ti and/or Ni₃Ti₂ phases was noted in aged 58Ni39Ti-3Hf alloy system as compared to 60NiTi.

58Ni39Ti-3Hf 合金系统已被提议作为用于承载应用的超弹性 60NiTi 的替代品。这项研究的重点是开发热处理程序，使 58Ni39Ti-3Hf 零件具有最大可能的硬度值。同时，还研究了 58Ni39Ti-3Hf 与基线 60NiTi 的热处理 - 显微组织 - 硬度之间存在的关系。这些是通过在不同温度和不同时间对所研究的合金系统应用溶液和随后的时效处理来完成的。下一步通过电子探针显微分析仪（EPMA）、能量色散X射线光谱仪（EDS）、X射线衍射仪（XRD）对处理后样品的显微组织和硬度进行分析，透射电子显微镜 (TEM) 和宏观硬度测试技术。据了解，在高于约 1000 °C 的温度下进行固溶处理会导致富镍相（如 Ni）的相对完全溶解。₃ Ti 和Ni ₃ Ti ₂存在于原件的显微组织中，存在于60NiTi 的NiTi 基体中。另一方面，对于 58Ni39Ti-3Hf，约 900 °C 以上的温度似乎足以解决 NiTi 基体中的这些富镍相。应用时效处理对固溶处理的 60NiTi 样品 (~58 HRC) 的硬度没有显着影响或降低了它们的值；在 NiTi 基体中形成的 Ni ₄ Ti ₃颗粒粗化后转变为 Ni ₃ Ti 和 Ni ₃ Ti ₂阶段。另一方面，一些应用的时效处理可以增加固溶处理的 58Ni39Ti-3Hf 合金（~54 HRC）的硬度值。对于在 500 °C 下处理仅 0.25 小时的零件，时效 58Ni39Ti-3Hf 零件的硬度最大值 (~59 HRC) 获得。所获得的硬度水平与固溶处理的 60NiTi 的硬度水平相当。与 60NiTi 相比，在时效 58Ni39Ti-3Hf 合金系统中注意到Ni ₃ Ti 和/或 Ni ₃ Ti ₂相的延迟析出。