Effect of Soft Phase Size on Compressive Properties of Inverse Nacre Nanocomposites

The inverse nacre composites composed of Al₂O₃/Al nanocomposite (hard phase) and pure Al (soft phase) are prepared by one-step ball milling and vacuum hot pressing. Influence of the soft phase size ranging from ten microns to sub-microns on the compressive properties of the resulting composites is studied, and their failure mechanism is analyzed. The results show that with the decrease of soft phase size, the compressive strength increases gradually accompanying with high failure strain, in particular when the soft phase size is reduced from micro-scale to submicro-scale, the compressive strength reaches 494 MPa, increasing by 60% by comparison with that of the composite with micro-scale soft phase. For the composites with micron-scale soft phase, the cracks originate from the interface between the soft and the hard phases and propagate along the interface-hard phase-soft phase, finally the macro crack at an angel of 45 degrees to the compressive axis is formed. The soft phase blocks the propagation of the secondary cracks. When the soft phase is reduced to submicron level, the cracks are initiated near the deformation band and propagate along the deformation band-hard phase, then gradually develop into microcracks having angles about 45 degrees or -45 degrees with the compressive axis and spreading throughout the composite. This means that when the soft phase size reduces from micro to submicro scale, the toughness mechanism changes from the blocking of the soft phase on the crack propagation to the multiplication and even distribution of the microcracks. The research results provide important reference value for the preparation of high strength and toughness aluminum matrix composites.