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

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

Severe Plastic Deformation of Metals by Using High Pressure Torsion Extrusion. Metallide s\ufcvaplastne deformeerimine k\uf5rgsurve-v\ue4\ue4ndeekstrusiooni meetodil

Doctoral thesis 61/2019 Doktorit\uf6\uf6 61/201

Synthesis and characterization of mechanical properties of boron–carbon-based superhard composites

In this work, we investigated a modern combined processing technique for the synthesis of lightweight superhard composites based on boron–carbon. We used traditional B4C with precipitates of free graphite and Al powder as initial materials. In the frst stage, the composites were fabricated by the self-propagating high-temperature synthesis (SHS) with the subsequent hot pressing of the compound. Further, by the disintegration and attrition milling, the ultrafne-grained powder was obtained. We used HCl and HNO3 acids for the chemical leaching of the powder to remove various impure compounds. At the last stage, a solid composite was obtained by the spark plasma sintering (SPS) method under nitrogen pressure. The main feature of this approach is to implement diferent synthesis techniques and chemical leaching to eliminate soft phases and to obtain superhard compounds from low-cost materials. The phases were studied by X-ray difraction and scanning electron microscopy with energy-dispersive spectroscopy. The composites compacted by the SPS method contained superhard compounds such as B13C2, B11.7C3.3, and c-BN. The fabricated composite has an ultrafne-grained microstructure. Using a Berkovich indenter, the following nanohardness results were achieved: B13C2~ 43 GPa, c-BN~ 65 GPa (all in Vickers scale) along with a modulus of elasticity ranging between~400 GPa and~450 GPa

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 μm to 0.5 μm, 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)