BTi-6431S薄板在高温下的组织、性能及断裂行为研究

The research of microstructure,mechanical properties and fracture behavior of BTi-6431S sheet at high temperature

本文采用OM、SEM和高温拉伸实验的方法研究了BTi-6431S钛合金薄板在高温下的组织、性能和断裂行为。试样拉伸后的宏观形貌表明:温度为750℃时,试样呈现45℃剪切断裂;800℃以上时,试样均在缩颈处断裂;850℃和900℃时,拉伸过程中出现了超塑性。显微组织观察发现:750℃时,夹头处和标距内靠近夹头处的显微组织都是条状组织,断口附近的显微组织却出现了等轴组织;800℃时,不但断口附近出现了等轴组织,标距内靠近夹头处也出现了等轴组织;850℃时,夹头处出现了条状和等轴组织,而标距内靠近夹头处和断口附近的显微组织都是等轴组织。通过高温拉伸实验可知:随着温度的升高,强度逐渐降低,伸长率逐渐升高;高温下,R_m、R_(p0.2)和A与温度T服从关系式:R_m=2165.70-2.42T,R_(p0.2)=5675.83-13.22T+0.0077T^2,R_(p0.2)=5675.83-13.22T+0.0077T^2。通过断口形貌观察可知:750℃时,断裂方式为准解理断裂;900℃时,断裂方式为韧窝断裂。

The microstructure,mechanical properties and fracture behavior of BTi-6431S titanium alloy sheet at high temperature are studied by O-M,SEM and high temperature tensile tests in the present paper.The results show that the macroscopic morphology of the specimen is shear fracture in 45°direction at 750℃,and it is broken at the necking point when the temperature is above 800℃,and the superplasticity is observed during the tensile test at 850℃and 900℃.At750℃,the microstructure of the collet and the gauge near the collet are lath structures,the equiaxed structures are observed near the fracture;the microstructure of the gauge near the collet and near the fracture are both equiaxed structures at 800℃;the equiaxed microstructures are seen in the collet,the gauge near the collet as well as near the fracture.The tensile test reveals that the strengths gradually are decreased with increasing temperatures,but the elongations are increased.The relationship of R_m,R_(p0.2)and A between the temperature T are as follows:R_m=2165.70-2.42T,R_(p0.2)=5675.83-13.22T+0.0077T^2,R_(p0.2)=5675.83-13.22T+0.0077T^2.The fracture morphology suggests that the fracture mode is quasi cleavage at 750℃,but the dimple fracture is seen at 900℃.