Microstructure and mechanical properties of B₄C/6061Al laminar composites fabricated by power metallurgy

This study aims to investigate the effects of compositional gradient on microstructure and mechanical properties of a B₄C/6061Al laminar composite fabricated using a powder metallurgy method - spark plasma sintering followed by extrusion and hot rolling. Results show that B₄C particles were distributed fairly uniformly in the fabricated composites. Interfaces among different layers in the composites were bonded well and no porosity were observed in transition regions among different layers. The grains around B₄C particles are smaller than those away from the B₄C particles. Stress concentration is found to occur easily at the tip of the B₄C particle, which facilitates the development of recrystallization nuclei. Compared with those of an extruded B₄C/6061Al laminar composite, yield strength and ultimate tensile strength of the rolled B₄C/6061Al laminar composite are obviously enhanced but its elongation to fracture is weakened. Two yielding points were observed in the rolled three-layer B₄C/6061Al laminar composite due to the existence of B₄C content gradient in the composite. Strengthening mechanisms in the fabricated laminar composites include grain refinement, dislocation strengthening, load transfer effect, and Orowan strengthening.