The effect of microstructure evolution on the wear behavior of tantalum processed by Indirect Extrusion Angular Pressing

Abstract

This article studies the evolution of microstructure and the wear resistance in tantalum processed by a newly developed Severe Plastic Deformation (SPD) technique called Indirect Extrusion Angular Pressing (IEAP). The microstructure and tribological behavior of nanostructured tantalum processed by IEAP were analyzed in this work. The samples were extruded for two, five, and twelve passes of IEAP and then exposed to ball-on-disk wear testing in dry sliding conditions. It was shown that after twelve IEAP passes, an extensive grain refinement down to 500 nm was achieved, hardness increased, and a high dislocation density formed in the material.

The wear resistance of the material improved successively after each pass of IEAP, and the wear rate decreased, although the friction coefficient did not change. Evaluation of the morphology of the wear tracks showed that the dominant wear mechanisms were comprised of galling, adhesive wear, pitting and microplowing. Refinement of the microstructure by IEAP led to a reduction in adhesive wear and pitting while a slight increase in oxidation appeared. Comparison of the results of wear testing between tantalum against steel balls and tantalum against alumina balls showed that the presence of alumina generated a larger portion of adhesive wear, making the wear mechanism more complicated while the tantalum-steel pair presented milder wear.