Nb-16Si-10Ti-10Mo-5Hf原位复合材料拉伸性能及其变形机制

采用机械合金化和放电等离子烧结方法制备了Nb-16Si-10Ti-10Mo-5Hf原位复合材料。采用不同温度下的拉伸试验评价了其力学性能,结合其不同温度下的断口形貌研究了其变形机制。结果表明,复合材料的微观组织由Nbss(铌固溶体)、金属间化合物Nb_5Si_3和少量的Nb_3Si相组成,晶粒呈等轴状。室温和1200℃抗拉强度分别为413和496 MPa。从室温到1200℃拉伸断裂方式为Nb5Si3相解理脆性断裂,1200℃拉伸延伸率仅为1.2%;然而,在1300℃拉伸试验中,其拉伸延伸率为27%,这归因于Nbss延性的增加和界面/晶界强度的降低;在1400℃和更高的温度,材料具有极大的塑性或超塑性,塑性变形机制由晶内滑移转变为晶界滑移。晶界滑移在三叉晶界处产生的应力集中通过软化的Nbss协调而释放,从而避免了早期断裂。

Tensile properties and deformation mechanism of the Nb-16Si-10Ti-10Mo-5Hf in situ composite

An ultra-fine Nb-Silicide in situ composite whose nominal composition is Nb-16Si-10Ti-10Mo-5Hf was fabricated by mechanical alloying followed by spark plasma sintering. The microstructure consists of an Nb solid solution, Nb₅Si₃ and a small amount of Nb₃Si with all three phases being in the sub-micro range. This in-situ composite exhibits good balance of strength between ambient temperature and high temperature; the ultimate tensile strength is 413 and 496 MPa at room temperature and 1200oC, respectively. The tensile fracture behavior is dominated by cleavage of the Nb₅Si₃ phase at 1200oC and lower temperatures. However, the fracture behavior is governed by ductile rupture of Nbss at 1300oC and higher temperature, which would be ascribed to both the increased ductility of Nbss and the decreased interface strength. At 1400oC and higher temperature, the material exhibits extensive plasticity or superplasticity; the dominant deformation mechanism is grain boundary at 1400oC and higher temperature.