The mechanisms behind the tribological behavior of titanium alloys processed by laser powder bed fusion sliding against steel.

The sliding behavior of two titanium alloys processed by laser powder bed fusion, with and without heat treatment, was investigated alongside two as-received conventionally-processed versions of these alloys. These samples presented a wide range of microstructures often encountered in Ti alloys. Oxidative, abrasive and adhesive wear always occurred when sliding against steel. However, wear rates were similar regardless of the friction and hardness if material removal mainly occurred through abrasion and/or adhesion. Martensitic phases decomposed during sliding while nano-crystalline grains enhanced oxidative wear which reduced friction. With a stable nanocrystalline microstructure that confers ultrahigh hardness, wear rate and friction can be substantially reduced by promoting oxidative over abrasive or adhesive wear. • Dry sliding of two conventionally- and LPBF-processed Ti alloys was investigated. • A nano-crystalline microstructure enhances oxide formation which reduces friction. • α′ or α″ is unstable in the presence of frictional heat and oxygen diffusion. • A stable ultrahard nanocrystalline microstructure can reduce both wear and friction. • This microstructure promotes oxidative wear and minimizes adhesion/abrasion. [ABSTRACT FROM AUTHOR]