低铝改性的富氧双相粉末冶金钛合金组织和塑性调控

双相粉末冶金钛合金以其优异的综合性能受到了广泛的关注。但由于难以避免的增氧，烧结钛合金在超过一定的氧含量阈值后塑性显著下降，如TC4合金阈值仅为0.32 wt.%，这也成为制约其应用的主要障碍。最近的研究显示，降低合金中的铝含量能降低有害组织的析出倾向，提升该阈值。本项目鉴于针对微观组织和力学性能的研究尚不透彻等问题，拟以制备高塑性的低铝富氧双相粉末钛合金为出发点，深入研究合金微观组织特征和相变规律，建立合金成分、微观组织与力学性能之间的联系，实现合金的微观组织和力学性能调控。结合热力学计算和热处理揭示新型钛合金的相变规律和温度点；分析不同类型组织和第二相的形成条件，确定各种组织特征的调控方法；研究组织特征对位错移动、变形和断裂机制的影响，形成组织特征和热处理设计的理论依据。本项目的研究对解决粉末钛合金的低塑性难题具有较强的实际意义，且对丰富其烧结和热处理理论有着较重要的学术价值。

Bi-phase powder metallurgy (P/M) titanium alloys have attracted great attentions due to their excellent combination properties. However, associated with inevitable oxygen pick-up, the sintered alloys suffer from significant decrease in ductility when the oxygen content above a threshold, for TC4 alloy this threshold is only 0.32 wt.%. This problem has become the major limitation for the utility of bi-phase titanium alloys. Recent studies have indicated that a low aluminum content is able to prohibit the formation tendency of harmful structure and improve the threshold of oxygen content. Based on the drawbacks such as that researches on the new alloys’ microstructure and mechanical properties are not systematical, this project aims at preparing new types of bi-phase P/M titanium alloys with high ductility using high oxygen and low aluminum content, systematically investigates the alloys’ microstructural characteristics and phase change rule, builds the relationship among the composition, microstructure and mechanical properties, and achieves the modification of microstructure and mechanical properties. The phase change process and phase change temperatures of the new alloys are determined by the thermodynamics calculation and heat treatment experiments. The forming condition of different types of microstructures and secondary phases are analyzed, the controlling method of microstructure characteristics is proposed. The influence of the microstructural characteristics on the dislocation movement, deformation and fracture mechanisms are studied, theoretical basis for the design of microstructural characteristics and heat treatment are suggested. The investigation of present project can not only solve the low-ductility industrial problem of P/M titanium alloys, but also fulfill the theory of alloys’ sintering and heat treatment processes.