Advanced Surface Modification of Titanium Alloys Using Ultrasonic Pulsed Waterjet Peening

Abstract

The primary objective of this study is to investigate the application of a relatively new surface modification technique, known as ultrasonic pulsed waterjet (UPWJ) peening, on titanium alloys. Commercially pure titanium (CP-Ti) and Ti-6Al-4V alloy were selected in wrought and, in the case of Ti-6Al-4V alloy, additively manufactured forms due to their widespread applications in aerospace and biomedical industries. The research was focused on analyzing UPWJ processing parameters, including traverse speed (ranging from 200 to 1000 mm/s) and stand-off distance (ranging from 25.4 to 44.4 mm). An assessment of surface integrity after UPWJ was conducted, engaging alterations in surface roughness, topography, residual stress, and hardness. The findings revealed that there exists an optimal operational window that minimizes surface roughness and erosion, while maximizing the imparted compressive residual stress and scratch hardness. In this context, utilizing higher traverse speeds (i.e., 800-1000 mm/s) and a stand-off distance (i.e., 44.4 mm) proved to be beneficial. Comprehensive characterization of surface microstructure, utilizing several characterization techniques such as SEM, CSLM, XRD, and EDS, provided valuable insight into the waterjet mechanism in developing plastic deformation, material removal, and the evolved damage. In summary, UPWJ peening demonstrated significant potential as an effective surface strengthening treatment. This research lays the foundation for advancements in surface modification techniques for titanium alloys, with promising implications in aerospace and biomedical applications. Further optimization of peening parameters is imperative to enhance fatigue strength and wear resistance following UPWJ peening.