**Abstract**

In this study, the influence of ultrasonic nanocrystal surface modification (UNSM), which was applied as a post-additive manufacturing (AM), in terms of surface, tensile and tribological properties of Ti-6Al-4V alloy by selective laser melting (SLM) was investigated. Ti-6Al-4V alloy was subjected to UNSM at room and high temperatures (RT and HT). It was found that the UNSM enhanced the strength and reduced the roughness of the as-SLM sample, where both increased with increasing UNSM temperature. The UNSM bore influence on tribological properties, where the friction coefficient of the as-SLM sample reduced by about 25.8% and 305% and the wear resistance enhanced by about 41% and 246% at RT and HT, respectively. These are essentially attributed to the enhanced strength, smoothed surface and expelled pores from the surface. Based on SEM images, the damage caused by abrasive wear was the most observed in the wear track of the as-SLM sample than was caused by the highest wear rate. The UNSM temperaturedependent wear mechanisms were comprehensively investigated and elaborated based on the obtained experimental data and observed microstructural images. Indeed, a further investigation is required to improve the characteristics of as-SLM Ti-6Al-4V alloy to the wrought level due to the replacement possibility.

**Keywords:** roughness, strength, tribology, additive manufacturing, ultrasonic nanocrystal surface modification
