Phase transformations and mechanical properties of a Ti36Nb5Zr alloy subjected to thermomechanical treatments

Various solid state phase transformations exist in metastable β-type Ti alloys, which can be employed to optimize the mechanical properties. In this paper, synchrotron X-ray diffraction (SXRD) experiments were carried out to study the phase transformations of a Ti36Nb5Zr alloy subjected to different thermomechanical treatments. Furthermore, the correlation between the phase constitutions and the mechanical properties was discussed. The α″ texture formed, and high-density defects were introduced after cold rolling of the solution treated specimen, leading to the decrease in Young’s modulus and the increase in strength. The cold-rolled specimens were then annealed at temperatures from 423 to 773 K for 30 min. Both the Young’s modulus and strength increased with annealing temperatures increasing up to 673 K, which resulted from the precipitation of the ω and/or α phases. With further increase in annealing temperatures to 773 K, the β → α precipitation replaced the β → ωiso phase transformation, and the density of defects decreased, leading to the decrease in both the Young’s modulus and strength. These results provide theoretical basis for the design biomedical Ti alloys with both low Young’s modulus and high strength. 亚稳β钛合金中存在多种可以用来优化材料力学性能的固态相变。本文利用同步辐射X射线衍射 (SXRD) 实验 研究了Ti36Nb5Zr合金在热机械处理过程中的相变行为, 并讨论了相组成与力学行为的相关性。固溶态合金经冷轧处理后引入高密度缺陷并形成α″织构, 这导致杨氏模量下降和强度上升。冷轧态合金随后在423 到773 K退火30 min。当退火温度升至673 K时, 杨氏模量和强度都升高, 这可以归因于ω相和α相的析出。当退火温度进一步升高至773 K时, β→α析出相变取代β→ωiso相变, 并且位错密度下降, 导致杨氏模量和强度同时下降。本文的结果为新型低模量高强度生物医用钛合金的设计提供了理论基础。