原位反应自发渗透法TiC／AZ91D镁基复合材料及AZ91D镁合金的拉伸变形与断裂行为

利用原位反应自发渗透技术合成了47．5％碳化钛TiC（体积分数，下同）增强AZ91D镁基复合材料，对比研究了该复合材料与铸态镁合金AZ91D基体的室温与高温拉伸变形行为，观察了拉伸断口微观组织形貌，并分析了这两种材料的断裂特征。结果表明，TiC／Mg复合材料具有良好的高温力学性能，在拉伸变形速率为0．001s^-1以及温度为723K，时其拉伸强度可达91．1MPa，而此时相同变形条件下的铸态AZ91D镁合金拉伸断裂强度只有41．1MPa，增幅达120％。而在室温下，镁基复合材料的拉伸断裂强度仅高出基体铸态镁合金23．4％。镁基复合材料的断裂应变较低，高低温时均表现为脆性断裂；而镁合金则由室温下的脆性断裂向高温下的韧性断裂过渡。

Tensile Deformation and Fracture Behavior of AZ91D Magnesium Alloy and TiC/Mg Magnesium Matrix Composites Synthesized by in situ Reactive Infiltration Technique

A newly developed cost-effective processing route, in situ reactive infiltration technique, was utilized to fabricate 47.5vol.%TiC/AZ91D magnesium matrix composites. A comparative study was made on the tensile deformation behavior at room and elevated temperatures for the as synthesized composites and the matrix alloy magnesium AZ91D and their fracture characteristics were also analyzed as well. The results show that the TiC/Mg composites fabricated by in situ reactive infiltration process possess excellent high-temperature mechanical properties. The ultimate tensile strength of the matrix magnesium alloy AZ91D at 723 K and a strain rate of 0.001 s^-1 is 41.1 MPa, while that of TiC/Mg composites at the same deformation conditions increases by 120% and reaches 91.1 MPa. At room temperature, the ultimate tensile strength of the composites increases only by 23.4% as compared with the AZ91D alloy. The SEM observation of the morphologies for the fractured surfaces reveals that the fracture mode differs from one another in that the composites are of brittle characteristic at room and elevated temperatures due to its limited failure strain, whereas the fracture mode of the magnesium alloy has a transition from brittleness at room temperature towards ductileness at elevated temperature.