粉末冶金γ-TiAl基合金放电等离子烧结机理研究

Owning the advantages of both metal and ceramics, γ-TiAl based alloys are considered as the most competitive and developing materials used in the field of aerospace. With combination of plasma activated sintering, hot pressing and resistance heating, spark plasma sintering (SPS) technique has been successfully applied to the fabrication of powder metallurgy γ-TiAl based alloys, and sintered bodies with high densities as well as fine grains have already been gained. However, the densification course of γ-TiAl based alloys during SPS as well as its sintered mechanisms is still unknown up to now. In this project, TiAl-Nb alloy system is going to be selected as the object of study. The phase transformation regularity during SPS of TiAl-Nb based alloys with different initial powder states will be investigated. The sintered densification mechanisms of TiAl-Nb based alloys under the condition of multi-field coupling will be discussed. The effect of the boron powder additions with weak conductivity to the formation and growth of sintered necks during SPS of TiAl-Nb based alloys as well as its mechanisms will be explored. Coordination control of intrinsic characteristic of raw powder, SPS condition, microstructure and typical service performance is being expected to realize. The research results would not only provide the important academic value and theoretical significance in enriching the theory of spark plasma sintering, but also have the practical meaning to break through the performance bottlenecks of γ-TiAl based alloys so as to promote its engineering application process.

γ-TiAl基合金兼具金属和陶瓷的优点，是一种最具竞争力和发展前景的航空航天用新型材料。放电等离子烧结技术融等离子活化烧结、热压、电阻加热于一体，已成功应用于γ-TiAl基合金的粉末冶金制备并获得了高致密度和细晶的烧结体，然而目前有关γ-TiAl基合金放电等离子烧结的致密化过程及其机理尚不明确。本项目拟以TiAl-Nb合金体系为对象，旨在研究不同粉末状态的TiAl-Nb基合金在放电等离子烧结过程中的相转变规律，探讨多场耦合作用下TiAl-Nb基合金的放电等离子烧结致密化机理，获得弱导电B粉末颗粒的添加对TiAl-Nb基合金放电等离子烧结颈形成与长大的影响及其作用机制，以期实现粉末原料本征特征、烧结制度、微观组织及典型性能的协同性控制。本项目的开展不仅对丰富放电等离子烧结理论具有重要的学术价值和理论意义，而且对实现γ-TiAl基合金性能瓶颈的突破、推动其工程化应用的进程具有显著的现实意义。

γ-TiAl基合金是一类最具发展潜力的新型轻质耐高温结构材料。放电等离子烧结(SPS)技术作为一种先进且高效的粉末烧结技术，已成功应用于γ-TiAl合金的制备。然而由于SPS过程中复杂的多场耦合作用，目前关于γ-TiAl合金SPS致密化过程及其机理尚未得到完全阐释，从而导致对于SPS烧结体的微观组织结构控制还缺乏理论的指导。本项目以Ti-45Al-7Nb-0.3W合金成分为研究对象，表征了不同粒度气雾化粉末和不同制度球磨粉末的相组成及微观缺陷，系统研究了不同状态粉末在SPS过程中的相及组织演变规律，探讨了多场耦合作用下合金SPS烧结致密化机理，阐明了B添加对致密化过程及微观组织演化的影响及其作用机制，并提出了基于该合金典型服役性能的微观结构协同性控制方法。.气雾化粉末由大量α2相、少量γ相和微量β相组成；提高烧结温度、减小粉末粒度均可提高其SPS烧结体致密度，其典型组织呈现混合结构，γ晶尺寸不均匀性与变形不均匀性有关。球磨处理、增加球磨时间或转速，粉末中α2相衍射峰宽化，粒径减小；其烧结体致密度不断提高，γ晶和α2晶更为均匀并细化，γ晶尺寸不均匀性与其不均匀形核及α2晶不均匀分布有关。适量B(TiB2)添加可提高SPS致密化速率，细化组织并提高其均匀性。合金粉末SPS致密化符合Olevsky烧结模型，其机制主要包括蠕变变形烧结机制、直流脉冲电流导致的粉末颗粒熔化及压力的作用下熔化表面与凸起或凸起之间的接触致密化机制、扩散机制；低温下以扩散和应力的贡献为主，高温下以蠕变变形的作用为主。高的致密度、细小的晶粒尺寸、低的α2/γ片层晶团含量、均匀的相分布以及适量的B(TiB2)添加均有助于合金粉末SPS烧结体抗拉强度的提高。故建议以球磨粉为原料并添加适量B(TiB2)成分，选择适宜的球磨和SPS工艺参数以提高烧结体的致密度，并控制其晶粒尺寸、O含量、相成分、含量及分布，以期获得力学性能的进一步提高。.上述成果不仅对丰富SPS及其它相关学科理论具有重要的学术价值，而且对实现γ-TiAl基合金性能瓶颈的突破、推动其工程化应用进程具有显著的现实意义。