Effect of shot peening on the cavitation erosion of manganese aluminium bronze alloy: Microstructural and morphological insights

The effect of shot peening on the cavitation erosion behaviour of as-cast manganese aluminium bronze (MAB) alloy was evaluated under two upstream pressures (150 bar, 200 bar) and cavitation attack angles (30°, 90°). X-ray diffraction (XRD) analysis confirmed grain refinement after shot peening, with crystallite size decreasing from 32.79 nm to 22.56 nm, and optical image analysis showed a reduction in average grain size from ∼ 16.92 µm to ∼ 8.63 µm. Hardness mapping indicated a 250-μm-thick work-hardened layer, elevating near-surface hardness to 290 HV, which improved cavitation erosion resistance of shot-peened samples by 18 %–22 % at 150 bar in comparison to unpeened samples. Shot peening also altered surface morphology, introducing overlapping impact craters, ridges, and increased roughness, which may have influenced cavitation bubble collapse dynamics and stress distribution. At 200 bar, the intense cavitation may have penetrated the hardened layer; resulting in surface fatigue, microcrack development, and increased erosion; undermining the beneficial impact of shot peening on cavitation erosion. Erosion mechanisms varied with cavitation angle: at 90°, direct bubble collapse caused deep pitting, while at 30°, oblique impact resulted in shear-driven material removal. The most severe erosion was observed at 90° for both pressures, with damage increasing at higher pressure. These findings highlight the role of grain refinement, surface morphology, and work hardening in cavitation resistance. Future studies should analyse residual stress and explore wider pressure-angle variations to optimise shot peening for erosion mitigation.