基于SENB和IM法的特种陶瓷断裂韧性试验研究

Fracture toughness of fine ceramics based on SENB and IM method

以氮化硅(Si_(3)N_(4))、碳化硅(SiC)、碳化硼(B_(4)C)为研究对象,通过单边切口梁法获得陶瓷缺口尺寸和断裂韧性关系模型,并开展基于模型结果验证压痕法适用性的试验研究。结果表明:单边切口梁法测得的断裂韧性与切口尖端曲率直径存在拟合相关性R>0.95的指数函数关系,在切口尖端直径约20μm时出现拐点,激光熔融切口获得的断裂韧性与基于指数函数计算裂纹条件下的断裂韧性相当。压痕法在满足表面压痕裂纹形貌的前提下,大载荷产生的裂纹受显微组织影响扩展进程不一致及多裂纹交汇形成台阶等,使裂纹内部呈不规则的半月型,计算结果与基准值差异较大。经基准值验证,氮化硅推荐压痕法载荷为49 N,碳化硅为29.4 N,计算公式为Evans,碳化硼推荐载荷为9.8 N,计算公式为ISO,获得的断裂韧性均在基准值±10%误差内。

Taking silicon nitride,silicon carbide and boron carbide as the research objects,the relationships between ceramic notch size and fracture toughness were obtained by the single⁃side notch beam method,which were carried out to verify the applicability of the indentation method.The results show that there is an exponential function relationship with a fitting correlation of R>0.95 between the fracture toughness measured by single⁃sided notch beam method and the curvature diameter of the notch tip,the notch tip diameter significant turning point appears at about 20μm.The fracture toughness obtained by laser melting notch is equivalent to that calculated based on the exponential function under one real crack.As for indentation method with the premise of satisfying the surface indentation crack morphology,the crack propagation process caused by large load is inconsistent due to the influence of microstructure and the formation of intersection of multiple cracks,which cause the irregular half⁃months crack,and the calculation results are also quite different from the reference value.After the verification of the reference value,the recommended indentation load of silicon nitride is 49 N,and that of silicon carbide is 29.4 N,and the calculation formula is Evans,while the recommended load of boron carbide is 9.8 N,and the calculation formula is ISO.The fracture toughness results obtained are within the error range of±10%of the reference value.