原位自生TiB_2颗粒增强2024-T4铝基复合材料的损伤断裂行为

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。

Damage and fracture behavior of 2024-T4 aluminum alloy reinforced by TiB2 particles

The microscopic damage and fracture mechanism of an aluminum matrix composite, TiB2 particle reinforced 2024-T4 alloy synthesized through a mixed salt reaction, was investigated via in situ tension test monitored by scanning electron microscopy (SEM). The material fracture behavior can be separated into three stages, i.e. the nucleation, accumulation and coalescence of micro-cracks. The primary micro-cracks firstly initiate in by-product particles, micron-sized TiB2 particles and TiB2 particle clusters. With the increasing load, more micro-cracks appear in the region of TiB2 particle segregation band. Finally, the macro-cracks are formed as the consequence of the coalescence of micro-cracks through the Al matrix of particle sparse region in between, leading to the instant fracture of the material. Based on the analysis of the unit cell finite element model, the effect of particle segregation action on the initiation of micro-cracks in the Al matrix within particle segregation band was studied. The numerical results showed that the particle segregation enhances the maximum equivalent plastic strain and stress triaxiality in the Al matrix, which will facilitate the growth and coalescence of micro voids and results in the nucleation of premature micro-cracks, just as those observed in the tests.