Ti-29Nb-13Ta-4.6Zr合金的组织超细化与表面渗氮的耦合作用机理研究

Ti-29Nb-13Ta-4.6Zr（TNTZ）is a new biomaterial with promising prospects for applications. Ultrafine grained TNTZ alloy processed via severe plastic deformation possess enhanced strength and biomedical properties. Nitriding treatment has been widely applied during fabrication of joint prosthesis, to improve their wear resistance. However, when nitriding treatment is performed on ultrafine grained TNTZ, the high temperature of nitriding could cause grain growth, and lead to loss of the favorable properties of ultrafine grained state. In this project, TNTZ alloy with ultrafine grained microstructure will be subject to heat treatment, the evaluation of microstructure and mechanical property will be investigated, to reveal the microstructural evaluation mechanism of ultra-fine grained TNTZ during heat treatment, to find the key parameters enhancing its high temperature stability. Nirtiding treatment will be performed on TNTZ alloys with different grain sizes, a finite element model will be build based on experimental observations and diffusion equations, to investigate the role of non-equilibrium grain boundaries and dislocation density on nitriding process of TNTZ alloy, and seek approaches to promote nitriding process at lower temperatures. Finally, suitable nitriding parameters will be proposed to form hard nitrid layer on TNTZ alloy while preserving its ultra-fine grained structure. The research findings will provide theoretical principles and useful data for developing new biomaterials.

Ti-29Nb-13Ta-4.6Zr（TNTZ）合金是具有良好应用前景的新型生物金属材料。通过剧烈塑性变形方法制备的超细晶TNTZ 合金，具有良好的力学性能和生物性能。渗氮表面处理能够显著提高材料表面耐磨性，已广泛用于人工关节商业化生产。但是，对超细晶TNTZ进行渗氮时，渗氮的高温可能会引起TNTZ组织粗化，导致其丧失超细晶态的优良性能。本项目通过对超细晶TNTZ合金进行热处理、组织和力学性能的表征，研究超细晶TNTZ合金在热处理过程中的组织演变规律，寻求提高超细晶组织高温稳定性的方法；对不同晶粒状态的TNTZ合金进行渗氮实验，结合扩散理论和实验观察建立描述渗氮过程的模拟方法，揭示非平衡晶界和高密度位错对渗氮过程的作用机理，探索降低渗氮温度的途经。结合以上两方面，建立对超细晶TNTZ表面渗氮的工艺参数窗口，使其渗氮后保留超细晶组织。为新型生物金属材料的设计开发提供理论基础和数据积累。

本项目从TNTZ合金制备出发，探索了钽锆、钽锆铌中间合金以及TNTZ合金的制备工艺，并研究了所制得TNTZ合金及其中间合金的微观组织与力学性能，形成了成熟的TNTZ合金制备工艺，可用于制备组织均匀、力学性能优异的大块体TNTZ合金。研究中发现，TNTZ合金及其中间合金在动态加载中，还存在普遍的氧化放热现象。因此该类合金除具备生物应用潜力外，还具备良好的军事应用的前景。通过HPT变形，对TNTZ合金进行了晶粒细化，HPT变型过程中试样表面与截面上都存在细化不均匀现象，随着HPT圈数的增加，材料组织与性能更加均匀，达到10转时，组织与硬度分布达到较均匀的饱和状态。材料的硬度由约300Hv提高到了近500Hv。建立了超细晶基体与粗晶基体对涂层支撑作用的理论模型，同时通过有限元仿真研究了在划痕试验过程中基体与涂层的变形行为，都验证了超细晶基体对表面涂层的良好支撑作用。最后，结合SPD处理与涂层技术，提出了新型关节置换用材料的设计思路。