CoCrNiSi_(0.3)中熵合金动态剪切性能及其织构演化研究

Study on the Dynamic Shear Properties and Texture Evolution of CoCrNiSi_(0.3) Medium-Entropy Alloy

利用分离式霍普金森压杆对CoCrNiSi_(0.3)中熵合金进行动态加载,研究不同应变率下的压缩性能,发现其对应变率较为敏感,且有明显的应变率强化效应。准静态压缩下(应变率10-4s-1),应变率敏感度m为0.13,而动态压缩下(应变率5 150 s^(-1))m为0.25.通过帽型剪切实验,研究了该合金的剪切性能,结果表明准静态剪切屈服强度为330 MPa,动态剪切的屈服强度为630 MPa.随预留剪切区域宽度的增加,峰值应力有所下降,但剪切失效应变明显增加,当预留剪切区域宽度为50μm时,剪切应变高达12.8.通过剪切“冻结”实验,研究了剪切变形的增大对材料内部的晶粒微观结构和织构演化特征的影响。结果表明,晶粒内的几何必要位错密度随变形加剧而增加,变形织构向A、P类型织构演化,同时Cu型织构逐渐减少。在绝热剪切带形成前,功热转换计算的温升缺乏准确性,佐证了绝热剪切带的形成并不是由热软化引起的。

The dynamic loading of CoCrNiSi_(0.3)medium-entropy alloys was performed by using Split Hopkinson Pressure Bar. The compression properties at different strain rates were investigated, and found to be sensitive to strain rates and have obvious strain rate strengthening effect. Under quasi-static compression(strain rate 10-4s-1), the strain rate sensitivity m is 0.13, while under dynamic compression(strain rate 5 150 s^(-1)) m 0.25. The shear properties of the alloy were studied through hat shaped shear test. The results show that the quasi-static shear yield strength is 330 MPa and the dynamic shear yield strength is 630 MPa. With the increase of the width of the reserved shear region, the peak stress decreases, but the shear failure strain increases obviously. When the width of the reserved shear region is 50 μm, the shear strain is as high as 12.8. Through the shear “freezing” experiment, the effect of increasing shear deformation on the grain microstructure and texture evolution of the material was studied. The results show that the geometric dislocation density in the grain increases with the increase of deformation, and the deformation texture evolves to A and P type texture, while the Cu type texture decreases gradually. Before the formation of adiabatic shear band, the temperature rise calculated by power-heat conversion lacks accuracy, which proves that the formation of adiabatic shear band is not caused by thermal softening.