The effects of laser assisted ultrasonic nanocrystal surface modification on 3D-printed Ti6Al4V alloy

This study investigates the synergistic effects of laser-assisted ultrasonic nanocrystal surface modification (LA-UNSM) on the surface integrity and microstructural evolution of 3D-printed Ti6Al4V alloy. By integrating localized laser heating (optimal power of 23 W) with ultrasonic peening, LA-UNSM significantly enhances material plasticity during treatment. As a result, compared to conventional UNSM, the process markedly improves surface finish, hardness, and compressive residual stress. Detailed analyses show that LA-UNSM refines the surface microstructure by reducing roughness (from 17.8 µm in as-fabricated samples to approximately 3.2 µm) and increasing hardness (from 359.5 HV to over 487.5 HV). Additionally, LA-UNSM promotes deeper plastic deformation, effectively reducing surface porosity and refining the grain size from an average of 1.1 µm to 0.53 µm. The treatment further modifies the crystallographic texture and slip behavior by favoring pyramidal 〈c+a〉 slip, which enhances strain accommodation and reinforces the compressive residual stress field. These findings demonstrate that LA-UNSM is a transformative, energy-efficient post-processing technique that substantially enhances the performance of additively manufactured Ti6Al4V alloys.