Through-thickness particle distribution, microstructure evolution and tribological performance of B4C/BN-AA6061 composite via friction stir processing

In this study, we investigated the interactions between BN and B₄C particles in particle reinforced Al matrix composites (PRAMCs) during friction stir processing (FSP), focusing on particle distribution, microstructure evolution, hardness, and wear resistance. PRAMCs were fabricated with BN accounting for 0 wt%, 10 wt%, 20 wt%, 30 wt% and 100 wt% of the reinforcement particles. Optical microscopy (OM) and scanning electron microscopy (SEM) revealed that particle distribution varied through thickness, becoming more inhomogeneous with increasing BN mass ratio. The most uniform distribution was noted 3 mm beneath the surface, particularly in the BN-30%-3 mm sample. This sample also showed improved homogeneity in B₄C distribution, as confirmed by the box-counting (BC) method. The refined grain structure due to particle stimulated nucleation (PSN) and Zener pinning contributed to an average hardness of 96.67 HV in the BN-30%-3 mm sample, significantly enhancing wear resistance. The wear rate in this sample was reduced by 97.2 % compared to the FSP-3 mm sample, likely due to finer grains, higher hardness, and increased reinforcement, which collectively reduced adhesion and fatigue wear.