The Investigation Of Interfacial Property In Particulate Reinforced Metal Matrix Composite Using Nanoindentation

The interfacial property of particulate reinforced metal matrix composites(MMCs) acting as the connecting bridge between particulate and matrix has a great impact on the mechanical performance of the composites. In the study, we used the SiCp reinforced aluminum alloy under different aging treatments to investigate the evolution of the micro-mechanical property in the vicinity of SiCp/Al interface with the help of nanoindentation. The correlation between the punched zone sizes, indicated by the nanoindentation test and the mechanical performance of the composites were demonstrated after a careful analysis of the interfacial microstructure.Designing a reasonable set of nanoindentations tests is critical in this study. After serious consideration and experiments, the indentation depth is chosen to be 120 nm and the spacing between neighboring indents was chosen to be 1 μm. Indenters were made from the SiCp particles across the smoothing interface to the Al matrix to characterize the hardness distribution near the interface. It has been demonstrated that the punched zone size is consistent with the geometrically necessary dislocations(GNDs) zone size.The composites fabricated by stir casting method using SiCp and 7A04 alloy were treated under different aging treatment, resulting in the as-extruded, underaged, peak-aged and overaged samples. According to the nanoindentation results in different samples, the matrix in the peak-aged composite has the highest strength and the matrix in the as-extruded composite has the lowest strength. The punched zone sizes in peak-aged and overaged samples are smaller than that in as-extruded and underaged ones, where the former is only about 2 μm while the later is up to 6 μm.Besides, the GNDs size is decreasing as the aging time is increasing. In the aging process, the precipitates are likely to nucleate near matrix dislocations and the growth of the precipitates lead to the rearrangement of the dislocations and the movement of subgrain boundaries, leading to the decrease in dislocation density. Moreover, with increasing aging time, the matrix grain size were shown toincrease from the as-extruded sample to the underaged sample, then decrease for the peak-aged sample, and finally increase again for the over-aged sample, which indicates the presence of recrystallization which not only gave rise to the grain size evolution but also altered the dislocation distribution close to the interface.The tensile test results demonstrate that the strain failure shows a monotonous decrease with increasing aging time, which is caused by the appearance of different types of precipitates and the load transfer capacity of the SiCp/Al interface. Meanwhile, the strength of the composite relies more on the strength of the matrix, instead of the nature of the interface.In summary, the micro mechanical property characterized by nanoindentation can be used to evaluate the mechanical performace of the particulate reinforced metal matrix composites. It may also provide experimental evidences for the simulation and optimization of composites.