Investigation of tribological properties of heat-treated ZrNbTiVAl high entropy alloy in dry sliding conditions

Abstract

This study explored the relationship between tribological performance and microstructural changes induced by heat treatment in a newly developed ZrNbTiVAl high-entropy alloy (HEA). The alloy was evaluated in its as-cast state and after heat treatments at 950 °C for 15, 20, and 25 h, with dry sliding experiments conducted against an alumina ball counterface. Advanced analytical techniques, including 3D optical profilometry, nanohardness testing, field emission scanning electron microscopy (FESEM), energy-dispersive spectroscopy (EDS), and Micro-Raman spectroscopy, were employed for comprehensive surface analysis and to investigate oxide layer formation on the worn surfaces.

The study reveals a nuanced relationship between heat treatment duration, oxide layer formation, and frictional behavior in the ZrNbTiVAl high-entropy alloy (HEA). Increasing the heat treatment duration at 950 °C results in higher hardness (H) and a reduction in the modulus of elasticity (E) of the ZrNbTiVAl high-entropy alloy (HEA). Notably, wear rate and friction were lower in the as-cast and 15 h heat-treated conditions, despite their lower H/E and H³/E² values compared to the 20 h and 25 h heat-treated states. Additionally, the wear mechanisms shift significantly, from mild adhesive/oxidative wear in the as-cast and 15 h conditions to severe adhesive/oxidative wear in the 20 h and 25 h conditions. This improved performance in the as-cast and 15 h conditions is attributed to the enrichment of Ti and V—elements recognized for their solid lubrication properties—and a reduced presence of Al-Zr intermetallics, which helps to minimize the formation of hard wear debris during dry sliding. These findings underscore the importance of optimizing heat treatment parameters to achieve superior tribological performance.