The impact of microstructural refinement on the tribological behavior of niobium processed by Indirect Extrusion Angular Pressing

This research, for the first time, conducted a comprehensive study into the effect of a modern Severe Plastic Deformation technique, "Indirect Extrusion Angular Pressing (IEAP)", on the microstructural refinement of niobium and the subsequent impact on the tribological properties. The samples were processed for 4, 9, and 12 passes of IEAP and then exposed to Pin-on-disk wear test in dry sliding conditions. The results showed that the grain refinement occurred in niobium from an average grain size of 13 mu m to 0.5 mu m, along with an increase in hardness from the initial value of 79 HV to 180 HV after 12 passes. Results of wear tests revealed that IEAP processing reduced the wear width, volume loss, and specific wear rate by 14%, 38%, and 38%, respectively, and thereby enhancing the wear resistance of the material. Evaluation of the morphology of wear tracks demonstrated less spalling and less fatigue propagated cracks as well as finer detachment of wear debris on the surface of the processed samples, which led to producing a mild wear regime. The outcomes suggested that IEAP processing resulted in higher resistance in niobium against abrasion and against the development of fatigue propagated cracks which were respectively associated with higher hardness and larger fractions of high-angle grain boundaries (HAGBs).