Nanopowder derived Al/h-BN composites with high strength and ductility

Abstract

Al/h-BN composites with high tensile and compressive strength at room and elevated temperatures, as well as enhanced ductility, were obtained by a combination of ball milling (BM) and spark plasma sintering (SPS) using Al and hexagonal BN nanopowders (0, 1, 2, 3, 4, 5, and 10 wt% of h-BN). The use of two types of nanopowders is intended to ensure uniform distribution of the reinforcing phase and improve Al-BN chemical interaction at the manufacturing stages by increasing the surface-to-volume ratio. Due to Al with h-BN interaction, the Al/h-BN composites were simultaneously strengthened by three types of nanoparticles: Al2O3, AlN(O) and h-BN, predominantly located along the Al grain boundaries. Compared to BM+SPS aluminum, the tensile strength of Al-2 wt%BN composite increased by 82% (25 °C), 64% (300 °C), and 65% (500 °C), and the compressive strength by 107–119% (25–500 °C) while maintaining high elongation to failure in tension (13.6%, 11.6% and 10.8%) and compression (12.6%, 13.1% and 8.1%) at 25 °C, 300 °C, and 500 °C, respectively. In terms of combination of tensile and compressive strength at room and elevated temperatures, the Al/h-BN materials are superior to many other Al-based composites. The high strength and relative elongation to fracture of the Al/h-BN composites can be explained by the formation of a heterogeneous microstructure consisting of pure Al grains surrounded by a metal-matrix composite material with fine metal grains and reinforcing ceramic nanoinclusions. The obtained results significantly expand the scope of Al/h-BN materials, since their strength at 500 °C is higher than that of pure Al at room temperature.