Effects of powder characteristics and mixing powders on cold sprayability and corrosion properties of tantalum coatings

Abstract

Tantalum is an expensive ‘exotic’ metal and it is of particular interest in terms of extreme corrosion resistance and bio-compatibility. Previous studies on cold spray of tantalum show that it can be successfully deposited, but limited effort has been performed to investigate and optimize the powder characteristics for improved cold sprayability and corrosion properties. In this study, two spherical (P1: hard, P3: soft) and one angular (P2) tantalum powders were used as the feedstock. Two mixed powders (20 wt% P2 + P1, 20 wt% P3 + P1) were also prepared and were deposited as well as the three single component powders. After cold spray, the coating microstructure (as-polished and etched cross-sections, top surfaces) was characterized via optical and electron microscopy techniques. Several industrial coating metrics, i.e. cold sprayability (porosity, deposition efficiency (DE), cohesion strength) and electrochemical corrosion properties were evaluated. Results show that: i) angular P2 powder, which is preferred for industrial productions due to its lower cost, exhibits the highest DE, corrosion resistance, and high cohesion strength compared to the other two spherical ones (P1, P3); ii) adding either P2 or P3 powders into P1 leads to much improved metrics compared to single component P1.