Effect of dual shot peening pretreatment on the performance of Ti-6Al-4V alloy after active screen plasma nitriding

The effect of dual shot-peening (DSP) pretreatment on the performance of Ti-6Al-4V alloy after active screen plasma nitriding (ASPN) was systematically studied. DSP pretreatment was designed by combining an optimized primary shot peening (conducted under 0.3 MPa for 20 min) with a secondary shot peening conducted at reduced pressures (0.1–0.2 MPa) and shorter durations (2–8 min). The secondary peening step effectively decreased surface roughness while maintaining the severe plastic deformation (SPD) layer introduced by primary peening. The optimized DSP parameters were identified as 0.1 MPa for 5 min with a primary stage at 0.3 MPa for 20 min, which reduced the surface roughness from 2.61 to 1.75 μm without inducing excessive subsurface deformation. ASPN treatment on DSP-modified samples produced a thicker and more compact nitride layer, resulting in significantly enhanced wear and corrosion performance in contrast to samples subjected only to ASPN. The improvements are attributed to the refined surface nanostructure and improved surface integrity generated by DSP pretreatment.