SiC_(f)/TiAl复合材料界面反应及热稳定性

Interfacial Reaction and Thermal Stability of the SiC_(f)/TiAl Composites

采用真空吸铸法制备了SiC_(f)/TiAl复合材料,利用SEM和TEM对制备态复合材料界面反应层进行元素扩散分析和产物确定。结果表明,制备态复合材料的界面反应产物主要由靠近碳层的等轴细晶TiC和靠近钛合金涂层的等轴粗晶TiC组成。对复合材料进行800℃热暴露实验,结果显示,界面反应层随热暴露时间的延长而增长,且在长大过程中出现了分层现象。根据热暴露后反应层厚度随时间的变化规律,绘制出800℃界面反应的动力学曲线,并推测出界面生长速率。热暴露200 h后的界面反应产物共有4层,从纤维一侧到基体一侧分别是细晶TiC层、粗晶TiC层、(Ti,Zr)_(5)Si_(4)层和Ti_(3)Sn+Ti_(2)AlC层。分别对制备态和热暴露态的SiC_(f)/TiAl复合材料界面反应产物的形成机理进行了分析,得出热暴露过程中界面分层出现的主要原因是Ti_(2)AlC新相的生成消耗了部分TiC相。

SiC-fiber-reinforcedγ-TiAl composite materials are promising for high-temperature structural applications owing to their excellent mechanical properties.However,the interfacial reaction of the composites during subsequent high-temperature processing and service is unstable as elements continue to diffuse around the interfacial reaction layer at high temperatures,and more interfacial reaction products are generated.When excessive brittle reaction products are generated,they have detrimental effects on the mechanical properties of the composites.Therefore,to better design and control the interfacial reaction,it is particularly important to study the formation and growth of the complex interfacial products of the composites.In this study,the formation mechanism of interfacial reaction products and ther-mal stability of SiC_(f)/TiAl composites were investigated by thermal exposure for different time.First,the SiC_(f)/TiAl composites were prepared by suction casting.Next,the specimens were examined by SEM and TEM to investigate the element diffusion and composition of the interfacial reaction products of the asprepared composites.The interfacial reaction products in the as-prepared composites were mainly composed of a fine equiaxed TiC layer near a carbon layer and a coarse equiaxed TiC layer near a titanium alloy coating.Then,the thermal exposure was conducted at 800℃ to investigate the growth of the interfacial reaction products and thermal stability of the interfacial reaction layer.The results show that the thickness of the interfacial reaction layer increased with heat exposure time.Meanwhile,interfacial stratification was observed during the growth of the interface reaction layer.Further,the growth kinetics curve of the reaction layer was drew according to the thickness of the reaction layer with time,and the interfacial reaction growth rate was determined.According to the morphology and TEM analysis results,the interfacial reaction layer was divided into four layers after 200 h thermal exposure,unlike in the as-prepared state.From the fiber side to matrix side,fine-grained TiC,coarse-grained TiC,(Ti,Zr)_(5)Si_(4),and Ti_(3)Sn+Ti_(2)AlC layers,respectively,were observed.Finally,the formation mechanism of the interfacial reaction products and element diffusion ofSiC_(f)/TiAl composites under different conditions were studied,the interfacial stratification occurred during thermal exposure because some TiC participated during the formation of Ti_(2)AlC.