Effect of NbB₂ addition on the microstructure and mechanical properties of mechanically alloyed Al-12.6Si alloys

This study reports the effect of NbB2 particles on the Al-12.6 wt.% Si matrix powders and composites in regard of physical, microstructural and mechanical properties. In order to obtain hybrid powders, Al-12.6 wt.% Si-2 wt.% NbB2 blends were mechanically alloyed (MA'd) for various durations (1, 4 and 8 h ) in a Spex™ Mixer/Mill using hardened steel vial/balls with a 7/1 ball-to-powder weight ratio. A hydraulic press with a uniaxial pressure of 450 MPa was used for the compaction of the as-blended/MA'd powders. Green compacts were sintered at 570°C for 2 h under Ar gas atmosphere. X-ray diffractometry (XRD) and scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) techniques were utilized for the microstructural characterization of the as-blended/MA'd powders and the sintered composites. Differential scanning calorimetry (DSC) analyses were also conducted on the powder products. Sintered samples were characterized by density and Vickers microhardness measurements and sliding wear tests. With increasing MA time, mechanical improvement in composite properties was observed. Reinforcing particles had positive effect on the mechanical properties of the matrix: Al-12.6 wt.% Si-2 wt.% NbB₂ MA'd for 4 h showed higher microhardness value (158.50±10.02 MPa) and lower wear volume loss (0.161 mm³) than those of Al-12.6 wt.% Si matrix MA'd for 4 h. Al-12.6 wt.% Si matrix MA'd for 4 h showed microhardness value (146.70±8.81 MPa) and wear volume loss (0.194 mm³).