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通过对不同缺口半径的K418材料平板试样进行静拉伸实验宏观结果分析、组织观察及断口观察分析,研究了K418材料的缺口敏感性及断裂机制。结果表明:由于缺口根部的应力集中,试样的裂纹首先起裂在缺口根部,然后沿着缺陷处进一步扩展直至断裂。材料的抗拉强度随着材料缺口半径的增加及应力集中系数的降低而降低。缺口敏感性在缺口根部半径尺寸位于0.13~0.25 mm之间有一个临界值,当缺口半径尺寸等于或大于这一值时试样存在缺口敏感性,即缺口敏感性指标NSR值小于1;当缺口半径尺寸小于这一临界值时试样不存在缺口敏感度,即NSR接近1。K418材料的原始铸态晶粒尺寸粗大;枝晶偏析、缩松是其主要的缺陷组织。另外该材料的断裂即不是一般的典型脆性断裂,也不是典型的韧性断裂。它是韧脆混合的断裂,韧性断裂的特征表现为有一定的韧窝及撕裂棱。而脆性的特征表现为光滑明亮的解理小平面,同时在小平面内也出现二次微裂纹。同时在这种韧脆混合的断裂形态中也可以看到存在很多柱状树枝晶,疏松及枝晶偏析,这与材料在凝固时的条件有很大的关系。
The K418 material plate specimens with different notched radii were subjected to static tensile test, microstructure observation and fracture analysis. The notch sensitivity and fracture mechanism of K418 material were studied. The results show that due to the stress concentration at the root of the notch, the crack of the specimen first cracked at the notch root and then further extended along the defect until fracture. Tensile strength of the material decreases as the material gap radius increases and the stress concentration factor decreases. The notch sensitivity has a critical value between 0.13 and 0.25 mm at the notch root radius. When the notch radius is equal to or greater than this value, the notch sensitivity exists, that is, the notch sensitivity index NSR is less than 1. When the notch When the radius is less than this critical value, there is no notch sensitivity, that is, the NSR is close to one. K418 material, the original as-cast grain size coarse; dendritic segregation, shrinkage is the main defect organization. In addition, the fracture of the material is not a typical typical brittle fracture nor a typical ductile fracture. It is a ductile-brittle fracture characterized by ductile and torn edges. The brittleness is characterized by a smooth and bright cleavage facet and secondary microcracks in the facet. At the same time, there are many columnar dendrites, loose and dendrite segregation in this kind of ductile-brittle fracture morphology, which has a great relationship with the material’s solidification conditions.