Microstructure and thermophysical properties of NiTiZr phase change alloys for downhole tool heat storage

To overcome the limitations of solid-liquid phase change materials, such as liquid leakage, unstable shape, and serious corrosion at elevated temperatures, the design of a solid-solid phase change material using Ni-Ti-Zr as a metal element was utilized for its high thermal conductivity and stability to provide new thermal storage solutions for downhole tools. The influence of Zr content on the thermophysical properties and microstructure of the material was also investigated. The results showed that the designed solid-solid phase change material could reach 4129.93 × 10⁶ J²K⁻¹s⁻¹m⁻⁴ quality factor, which was much higher than most of the phase change materials. This was attributed to the increase in Zr content, where Zr atoms took the place of Ti atoms, creating vacancy defect and leading to the distortion of the alloy lattice where the Ti₂Ni phase gradually became the (Ti, Zr)₂Ni phase, the rise in density and enthalpy of the phase transition, and the increase in the temperature of the phase transition. When the Zr content was 12%, the phase transition temperature of the alloy matched the downhole working temperature, demonstrating excellent thermal cycling stability, and is expected to be a heat storage material for downhole tools.