Ti-1.5Al-4.5Fe-6.8Mo合金在氢气相变烧结（HSPT）过程中的致密化及相变机理研究

Powder metallurgy (PM) technology is considered as a method which can effectively reduce the fabricating cost of Ti products. However, the performance/cost ratio of PM Ti products is yet difficult to be accepted widely up to date. Hydrogen sintering and phase transformation process (HSPT）is a new process which has been reported to fabricate high-performance α-Ti (pure Ti) and (α+β)-Ti (Ti-6Al-4V) alloy with a relatively low cost. This project is proposed to carry out a research on fabricating β-Ti alloy (Ti-1.5Al-4.5Fe-6.8Mo) by HSPT. The main research contents are including the follows: Studying the densification mechanism of the β-Ti alloy during hydrogen sintering by comparing sintering behavior of the alloy in hydrogen and vacuum as well as investigating effects of the parameters such as H2 content, sintering temperature, dwelling time, heating rate on sintering behavior of the alloy; Studying the phase transformation mechanism of the alloy by investigating the effects of H2 content, sintering temperature, dwelling time, heating/cooling rate on element distributions, phases, phase transformations, microstructures and properties; Improving HSPT and developing a process to fabricate β-Ti alloy with high performance/cost ratio. It would enhance the comprehension of densification mechanism and phase transformation mechanism of β-Ti alloy during HSPT and extend the application range which is suitable to adopt HSPT through carrying out the project. Hence, the project has important scientific meanings and wide application prospects.

粉末冶金(PM)技术能够有效降低钛制品生产成本。但目前PM钛制品的性价比还难以被广泛接受。新报道的氢气相变烧结工艺(HSPT)能够制备出低成本高性能的α-Ti(纯钛)及(α+β)-Ti(Ti-6Al-4V)合金。本项目拟开展HSPT制备β-Ti合金(Ti-1.5Al-4.5Fe-6.8Mo)的研究。主要包括：通过对比β-Ti合金在氢气和真空中的烧结行为，并考察H2含量、烧结温度、烧结时间、升温速率等因素对烧结行为的影响，研究β-Ti合金在HSPT中的致密化机理；考察HSPT四个阶段H2含量、保温温度、保温时间、升降温速率等因素对合金元素分布状态、物相、相变过程、显微形貌及性能的影响，研究相变机理；改进HSPT工艺，开发一种制备高性价比β-Ti合金的工艺。项目实施将提高对HSPT过程中β-Ti合金致密化机理和相变机理的认识，并拓展HSPT适用范围，具有重要的学术意义和广泛的应用前景。

钛及钛合金具有密度低、比强度高、耐腐蚀等特点，在航空航天、航海、化工、汽车、体育休闲、医疗等领域都具有非常重要的应用价值和广阔的应用前景。然而，高成本极大地限制了其实际应用。寻求高性能、低成本制备技术一直是钛基材料的研究重点。氢致相变烧结（HSPT）工艺已经被成功用于制备高致密度细晶CP-Ti及Ti-6Al-4V。本项目将HSPT应用于制备Ti-1.5Al-4.5Fe-6.8Mo这一代表性的β-Ti合金。主要研究了TiH2粉和Ti/TiH2混合粉末的模压和冷等静压成型特性，通过参数优化，确定模压压强为500MPa、添加2%的液体石蜡和0.3%的硬脂酸可以使TiH2粉获得最好的成型效果；当Ti/TiH2混合粉末中TiH2粉添加比例为10～50 wt%时，采用模压可以获得较高质量的压坯；对比研究了真空烧结和HSPT制备Ti-1.5Al-4.5Fe-6.8Mo、Ti-xFe（x=1、5、10、15）的物相、形貌和性能差异；系统研究了Ti-xFe在HSPT各阶段的物相和微观组织演变规律，分析了HSPT烧结机理；优化了HSPT工艺参数，发现对于Ti-xFe合金，当升温速率为3 ℃/min时，合金密度最高，当升温速率为1 ℃/min时，合金显微硬度最高。本研究揭示了在纯钛粉中添加30～50 wt%的TiH2粉，既可发挥纯Ti粉末成型性好的优势，又可发挥TiH2粉末易破碎、烧结活性高的优势，可以在保持压坯良好光洁度和完整性的前提下获得更高的压坯密度，从而通过较低烧结温度获得较高致密度的Ti合金。该研究提供了一种TiH2粉的使用新方法，有望发展成为一种制备高性能低成本粉末冶金钛合金的新工艺。本研究证明对于β型钛合金，采用HSPT工艺同样可以起到细化晶粒的效果。但是在H元素参与下，HSPT高温阶段β相的晶界迁移速度较快，非常容易将气体包裹进晶粒内部中，导致致密度不如真空烧结合金。这为后续研究提供了参考。