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

Abstract

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.