Enhanced hardness and wear resistance of Al-based hybrid MMCs by using of composite metal boride reinforcement particles

Composite metal boride particles were synthesized and then used as the reinforcement material for fabricating Al-based hybrid metal matrix composites (MMCs). Mechanical alloying and pressureless sintering methods were used to produce the Al - 2 wt % Co-Ni-B/Co-Ti-B hybrid composites. Mechanically alloyed powders and sintered composites were characterized in terms of physical, microstructural and mechanical properties. The low crystallite size of Al particles and high density of the composites provided improved microstructures without needle-shaped secondary phases, and increased nanohardness values of Al matrix, and hence resulted in enhanced mechanical properties. The lowest indentation depths (both for matrix and reinforcement phases), the highest hardness (similar to 2 GPa) and the lowest wear volume loss (similar to 0.13 mm(3)) were obtained from the Al-based MMCs reinforced with Co-Ni-B particles containing CoB and Ni2Co0.67B0.33 phases. Studies revealed that the synergetic effect of the binary and ternary boride phases in the composite reinforcements had a positive role on the hardness and wear resistance of hybrid composites.