Cracking in a hot deformed SiCP/A6061 composite investigated using synchrotron microtomography

We present the first investigation of cracking by hot compression of any metal matrix composite in zones deforming under tri-axial state of stress using synchrotron microtomography (SRμCT). The task required to reduce the unfavourable manifestations of phase contrast in the reconstructed slices is simplified by developing a Fourier domain based filter for processing of reconstructed slices. As a result for the first time an accurate characterisation of the state of 3-D damage developed by compression at 500 °C and 1 s−1 to strains of ~1 is achieved in the bulge region of a hot worked SiCP/A6061 composite. The composition of the damage is found to predominately consist of acicular shaped large to very large pores and “coalesced” micro-cracks. The quantification of the Fourier domain filtered dataset and the analysis of the spatial proximity of the different types of damage provided the mechanism of cracking in metal matrix composites near regions of tri-axial stress at high compressive strains. The propensity for cracking in bulge region of SiCP/A6061 composite is attributed to the development and growth of acicularly shaped pores facilitated by repeated particle fragmentation. It results in a damage architecture that promotes the coalescence of the closely spaced pores and micro-cracks. This mechanism rationalises the high efficiency of power dissipation observed in hot working of SiCP/A6061composite in the absence of microstructural restoration processes.