Transformations of the Microstructure and Phase Compositions of Titanium Alloys during Ultrasonic Impact Treatment Part III: Combination with Electrospark Alloying Applied to Additively Manufactured Ti-6Al-4V Titanium Alloy

Abstract

Scanning electron microscopy, 3D optical surface profilometry, as well as X-ray diffraction and electron backscatter diffraction analysis were implemented for studying the effects of both ultrasonic impact treatment (UIT) and ultrasonic impact electrospark treatment (UIET) procedures on the microstructure, phase composition, as well as the mechanical and tribological properties of Ti-6Al-4V samples fabricated by wire-feed electron beam additive manufacturing. It was shown that he UIET procedure with the WC-6%Co striker enabled to deposit the ~10 µm thick coating, which consists of fine grains of both tungsten and titanium-tungsten carbides, as well as titanium oxide. For the UIET process, the effect of shielding gas on the studied parameters was demonstrated. It was found that the UIET procedure in argon resulted in the formation of a dense, continuous and thick (~20 µm) coating. After the UIET procedures in air and argon, the microhardness levels were 26 and 16 GPa, respectively. After tribological tests, wear track surfaces were examined on the as-built sample, as well as the ones subjected to the UIT and UIET procedures. It was shown that the coating formed during UIET in air had twice the wear resistance compared to the coating formed in argon. The evidence showed that the multiple impact of a WC-Co striker with simultaneous electrical discharges was an effective way to improve wear resistance of the Ti-6Al-4V sample.

Keywords

• titanium alloy
• wire-feed electron beam additive manufacturing
• phase transformation
• microstructure
• ultrasonic impact electrospark treatment
• wear