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利用扫描电子显微镜结合原位拉伸试验研究了颗粒体积分数为4.167%的原位自生TiB_2颗粒增强2024-T4铝基复合材料(TiB_2/2024-T4)的损伤断裂机理。TiB_2/2024-T4在拉伸下的损伤断裂行为依次有微裂纹萌生、微裂纹累积和微裂纹贯通3个典型过程。结果表明,TiB_2/2024-T4中初始微裂纹率先在副产物颗粒、微米级的TiB_2颗粒以及TiB_2颗粒团聚体中萌生。随着加载的进行,更多的微裂纹出现在TiB_2颗粒偏聚带中,最终微裂纹通过颗粒稀疏区域铝合金基体的韧性断裂而贯通,形成宏观裂纹。通过分析单胞有限元模型,研究了颗粒偏聚对偏聚带中的基体微裂纹萌生的影响机理。数值结果表明:相比于颗粒稀疏区域的基体,颗粒偏聚带中的基体最大等效塑性应变和应力三轴度均有提高,诱使微裂纹会因为偏聚带中基体微孔洞长大和聚合进程的加剧而提前萌生,这与原位拉伸试验中的现象是一致的。
The fracture mechanism of 2024-T4 aluminum matrix composites (TiB 2/2024-T4) reinforced by in-situ TiB 2 particles with a volume fraction of 4.167% was investigated by scanning electron microscopy and in-situ tensile test. Tensile fracture behavior of TiB_2 / 2024-T4 under tensile stress followed by three typical processes of micro-crack initiation, micro-crack accumulation and micro-crack penetration. The results show that the initial microcracking rate in TiB 2/2024-T4 first occurs in the by-product particles, micron-sized TiB 2 particles and TiB 2 particle aggregates. With the loading, more micro-cracks appear in the TiB 2 particle segregation zone, and finally the micro-cracks penetrate through the ductile fracture of the aluminum alloy matrix in the sparse region of the particles to form a macro-crack. Through the analysis of the unit cell finite element model, the effect of particle segregation on the initiation of matrix micro-cracks in the segregation zone was studied. Numerical results show that the maximum equivalent plastic strain and stress triaxiality of the matrix in the particle segregation zone increase compared with that of the matrix with sparse particles. The induced microcracks will increase due to the growth of matrix micropores in the segregation zone and The progress of polymerization proceeded prematurely, which was consistent with the phenomenon in situ tensile test.