晶须增强多相钼硅硼合金的力学与抗氧化性能研究

Multi-phases Mo-Si-B alloy is the composite material which consists of a ductile α-Mo solid solution and the high-strengthed Mo3Si and Mo5SiB2 intermetallics. The metal α-Mo phase can increase the toughness of the Mo-Si-B alloy. But high α-Mo contents will reduce the high temperature mechanical and oxidation resistance properties of the alloy markedly. The improved intermetallics contents which are beneficial to increase the high temperature properties, but the low room temperature toughness will leads to its hard to be machine-shaped. Thus, in the premise that Mo-Si-B alloy has well high temperature properties, how to further advance its room temperature toughness has become one of the most urgent problems in the properties control of the alloy. There have been some researches shows that whisker doping has better effect on toughening reinforcement to metal, ceramics and intermetallics. This application attempts to dope nano-scale carbide and oxidation ceramic whiskers in the prepared fine-grained and multi-phases Mo-Si-B alloy in early experiment. The fine-grained Mo-Si-B alloy contains high amounts of grain boundaries and phase interfaces. Therefore, it probably could improve the adhesion property of the multi-phases and increase the alloy’s room temperature toughness, high temperature strength and oxidation resistance, by using the stability of the whiskers at high temperature and the uniform distribution of the whiskers in phases and inter-phases of the Mo-Si-B alloy. This research results will help to comprehend the mechanism of the nano-scale whiskers in multi-phases Mo-Si-B alloy.

多相Mo-Si-B合金是由延性的钼固溶体（α-Mo）和高强的金属间化合物（Mo3Si和Mo5SiB2）组成的复合材料。金属α-Mo相在增韧Mo-Si-B合金的同时，其含量过高将显著降低合金的高温力学和抗氧化性能，而增加对高温性能有利的金属间化合物含量将导致合金的室温韧性不足而难以加工成型。因此，在保证Mo-Si-B合金具有良好高温性能前提下，如何进一步提高其室温韧性已成为该类合金性能调控中亟待解决的问题之一。已有研究结果表明，晶须掺杂对金属、陶瓷和金属间化合物均有较好的增韧补强效果。在前期实验基础上，本申请试图在内含大量晶界和相界面的细晶Mo-Si-B合金制备过程中分别掺杂碳化物和氧化物陶瓷晶须，利用晶须的高温稳定特性及其在各相内、多相间均匀分布来改善界面的结合性能，将有可能同时提高合金的室温韧性、高温强度和抗氧化性能。研究结果有助于理解多相Mo-Si-B合金中纳米尺度晶须的作用机理。

本项目从材料组织结构优化设计出发在内含大量界面的细晶Mo-12Si-8.5B合金制备过程中分别掺杂SiC晶须和TiO2晶须，利用晶须高温稳定性及其在各相内、多相间均匀分布来改善合金的组织并优化其性能。研究结果展示两种晶须掺杂合金均具有多层级的微观组织，其中，碳化物晶须掺杂合金的组织为岛状金属颗粒分布在连续金属间化合物基体上，反应性碳化物显著降低了界面O杂质浓度和SiO2颗粒含量。而非反应性氧化物晶须掺杂合金具有细小金属间化合物均匀分布在连续金属基体的微观组织。两种晶须材料均对合金产生了较好的强韧化效果，反应性碳化物晶须的界面纯化和增强作用主要对合金产生较好的强化效果，而非反应性氧化物晶须具有适宜的晶须/基体界面强度，有利于晶须的脱粘、拔出和断裂以及由此引起的裂纹偏转、桥联和微裂纹等机制发挥，产生优异的韧化效果。两种晶须也提高了合金的超高温抗氧化能力，尤其是SiC晶须将合金抗氧化能力提升至1400℃，而TiO2晶须掺杂的合金能在表面形成由SiO2-B2O3和SiO2/TiO2层组成的双层结构氧化膜，也改善了该合金的抗氧化能力。