Microstructure and High Temperature Strengthen of Pure Cr and Cr-Cr_2B Eutectic Alloy

以30 mm/h和800 mm/h的速度单向浇注铬-13.5mol%B共晶铸锭，组织观察表明，铬-铬_2B共晶复合材料为单向共晶组织。铬相宽度约为3μm，Cr2B相宽度约为1μm。在温度为1000℃~1400℃、应变速率为5×10~(-5)~1×10~(-3)~1×10~(-3)~(-3)~(-1)的条件下进行了压缩试验，评价了屈服应力随温度和应变速率的变化规律。试验结果表明，在1200℃下的高温强度约为400 Mpa，接近镍基高温合金的应力水平。应变速率的应力指数约为15，这一高指数与层状复合材料的应力指数相吻合。从屈服应力对温度的依赖关系出发，求出其活化能约为1000kJ/mol。从高温形变的透射电子显微镜观察到，铬相中出现了回复结构，即位错网络，并在Cr2B相中发现了许多典型的微观孪晶。由此可见，Cr-Cr2B共晶复合材料的高温强度对Cr2B相的孪生机制有影响

Cr-13.5mol%B eutectic ingots were unidirectionally casted with rates 30 mm/h and 800 mm/h. From a structure observation, it was cleared that Cr-Cr_2B eutectic composite had a unidirectional eutectic structure. Width of Cr and Cr_2B phase are about 3 μm and 1 μm, respectively. And then, it was found that there was unique crystal orientation relation between Cr and Cr_2B phase.Compression test was conducted in temperature range form 1000 ℃ to 1400 ℃ and strain rate from 5 x 10^<-5> s^<-1> to 1 x 10^<-3> s^<-1>, and temperature and strain rate dependences of yield stress were evaluated. From these tests, high temperature strength at 1200 ℃ was about 400 MPa and this stress level was close to the stress of Ni base super alloys. And, a stress exponent of strain rate was about 15. This high exponent was agreed with the exponent of lamellar composites. From temperature dependence of yield stress, an activation energy was evaluated and was about 1000 kJ/mol. This energy was extremely larger than the energy of self-diffusion.From the TEM observation deformed at high temperature, recovery structure, that is dislocation network, was revealed in Cr phase and many typical micro twins in Cr_2B phase.From these findings, it was concluded that the high temperature strength of Cr-Cr_2B eutectic composite affected to the twining mechanism of Cr_2B phase