Characterization of the friction behavior of wrought and hot isostatic pressed laser powder bed fusion Ti6Al4V alloys

Abstract

This paper presents determination of the friction coefficients and an analysis of the frictional behavior of wrought and hot isostatic pressed Laser Powder Bed Fusion (LPBF) Ti6Al4V alloys against uncoated cemented carbide (WC-Co) under conditions that simulate those encountered in metal cutting. For this purpose, a series of pin-on-bar tribological tests were performed in an open tribometer configuration at a high average contact pressure (∼1.5 GPa) and different sliding speeds (9.58–38.3 m/min) under dry conditions. The tests permitted to determine sliding speed dependent apparent friction coefficients (μ_app) between WC-Co pins and wrought/LPBF Ti6Al4V bars. A 3D model of the tribological test was developed for the purpose of obtaining the adhesive friction coefficients (μ_adh) through the post-processing of the test data of μ_app. The tribological behavior was evaluated in terms of the friction coefficient, the build-up material (adhesion) to the pin, surface topography, and subsurface microstructure. The test results showed that wrought and LPBF Ti6Al4V alloys have a different tribological behavior. The μ_app exhibited a range of values for the wrought Ti6Al4V alloy spanning from 0.458 to 0.327, while the LPBF Ti6Al4V alloy demonstrated a slightly different range, from 0.499 to 0.251, depending on the sliding speed. At high sliding speeds, the wrought material exhibited higher adhesion volumes on the pins, as well as higher friction coefficients and a greater deformation zone thickness in comparison to the LPBF Ti6Al4V alloy. The μ_adh values obtained for both the wrought and LPBF Ti6Al4V alloys can be employed in the modelling and simulation of metal cutting operations.