High-Dense Shock Reactive Processing of Molybdenum and Titanium Silicides

冲击反应合成可以分为两类：1）冲击辅助反应和2）冲击诱导反应。在前者中，由于热瞬变和残余热往往压倒在冲击加载过程中的反应机制，冲击反应被迫终止在中间步骤和反应物的液相应该发挥作用的冲击反应机制。在后者中，冲击压力对冲击反应的影响揭示了冲击反应机理，导致非平衡相和奇异物质的形成。从元素粉末混合物开始，每个冲击反应合成变成冲击辅助反应，因此仅对于部分反应，应该需要超过20 GPa的高压来提高冲击反应性。另一方面，从机械合金化预处理的粉末开始，这些MA前驱体可以完全反应成金属间化合物，具有或不具有非平衡相材料。本文分别采用块体机械合金化和改进的铣削式机械合金化方法来改变预混合程度，研究预混合对冲击诱导反应的影响。以Ni-Al、Ti-Al、Mo-Si、Ti-Si和Nb-Si系为靶材料，验证了在p < 15 GPa下，由预处理粉末进行冲击反应合成可得到致密的完全反应的金属间化合物。实验中，采用预处理粉末的单轴压缩压坯作为试样，进行了不同冲击压力下的冲击恢复试验。通过与热点燃、机械诱导SHS和元素粉末混合物的冲击反应合成的比较，认为冲击诱导反应的反应机理是冲击化学在难熔金属铝化物和硅化物制备中的重要进展。

Shock reactive synthesis can be classified into two categories : 1) Shock Assisted Reaction and 2) Shock Induced Reaction. In the former, since thermal transients and residual heating often overwhelm the reaction mechanism during shock loading, the shock reactions are forced to be terminated at the intermediate steps and the liquid phase of reactants should play a role in the shock reaction mechanism. In the latter, effect of shock pressure on the shock reactive reactions reveals the shock reaction mechanism, resulting in the formation of non-equilibrium phase and exotic materials. Starting from the element powder mixture, every shock reactive synthesis becomes a shock assisted reaction, so that high pressure beyond 20 GPa should be needed to improve the shock reactivity only for partial reaction. On the other hand, starting from the pretreated powders by mechanical alloying, those MA precursors can be fully reacted into intermetallic compound with or without non-equilibrium phase materials. In the present paper, both the bulk mechanical alloying and the modified milling-type mechanical alloying were employed to vary the premixing level in the pretreatment process for investigation of the pretratment effects on the shock induced reactions. Ni-Al, Ti-Al, Mo-Si, Ti-Si and Nb-Si systems were used for target material for experimental demonstration to verify that the shock reasctive synthesis from pretreated powders should yield dense fully-reacted intermetallic compounds for p < 15 GPa. In the experiments, the uniaxilly compressed compacts of pretreated powders were employed as a sample of shock recovery tests for various shock prssure. With comparison to thermally-ignited and mechanically-induced SHS and shock reactive synthesis from elemental powder mixture, reaction mechanism of shock induced reactions was considered to make advancement in shock chemistry for processing of refractory metal aluminides and silicides.