Microstructural characterizations and mechanical properties of NbB₂ and VB particulate-reinforced eutectic Al-12.6 wt% Si composites via powder metallurgy method

Mechanical alloying of elemental Al, Si, NbB₂ and VB powder mixtures constituting the matrix alloy composition of Al-12.6 wt% Si and particulate-reinforced compositions of Al-12.6 wt% Si-x NbB₂ and Al-12.6 wt% Si-x VB (x = 1, 2 and 5 wt%) were carried out for 2, 4 and 8 h in a high-energy ball mill. Mechanically alloyed (MA'd) powders were subjected to cold pressing (450 MPa), cold isostatic pressing (400 MPa) and pressureless sintering (570 °C/2 h) processes. Powder particle morphologies changed from flaky to equiaxed shape after the optimum MA duration of 4 h. 1 wt% NbB₂ and 1 wt% VB particulate-reinforced Al-12.6 wt% Si based composites exhibited better mechanical properties than the Al-12.6 wt% Si matrix alloy and Al-12.6 wt% Si-x NbB₂ and Al-12.6 wt% Si-x VB (x = 2 and 5 wt%) composite samples. In particular, Al-12.6 wt% Si-1 wt% NbB₂ had the highest yield strength (378 MPa), compressive strength (491 MPa) and hardness (1.86 GPa) values. Investigations on the wear behaviors of the composites revealed that significant amount of wear loss occurred as a result of debris formation due to pull-outs of reinforcing boride (NbB₂ and VB) and oxidized Al (Al₂O₃) particles.