Slurry erosion behaviour of friction stir processed nickel aluminium bronze

Nickel aluminium bronze (NAB) alloy is widely used in marine and engineering applications due to its excellent mechanical properties and corrosion resistance. In the present study, the influence of friction stir processing (FSP) on the microstructure, mechanical properties, and slurry erosion behaviour of NAB alloy was systematically investigated. The FSPed NAB alloy revealed ultrafine grained recrystallized microstructure with an average grain size of ∼1 μm along with a high fraction of high-angle grain boundaries (∼87%) and a random crystallographic texture. In addition, the coarse κ intermetallic network present in the as-cast base material (BM) was fragmented and uniformly redistributed throughout the Cu-rich matrix after FSP. Owing to these microstructural modifications, the FSPed NAB alloy exhibited enhanced microhardness (∼244 HV) compared to the BM (∼166 HV), together with an excellent combination of tensile strength (∼593 MPa) and elongation (16.5%). Slurry erosion tests under varying impingement angles (30°, 60°, and 90°), impact velocities (10, 15, and 20 m/s), and slurry concentrations (4, 8, and 12 wt.%) revealed that mass loss decreased with increasing impingement angle, whereas increasing impact velocity and slurry concentration led to higher mass loss in both the BM and FSPed samples. Among the investigated parameters, impact velocity was found to be the most dominant factor influencing erosion behaviour, contributing ∼39% and ∼43% to the mass loss of the BM and FSPed NAB alloy, respectively. Furthermore, under all testing conditions, the FSPed NAB alloy consistently exhibited lower mass loss compared to the BM, indicating superior slurry erosion resistance which is primarily attributed to its ultrafine recrystallized grain structure, homogeneous redistribution of κ phases, and enhanced hardness, which collectively suppressed localized material removal during slurry particle impingement.