Processing and characterization for zirconia toughened alumina (ZTA) coatings on Ti6Al4V (Ti64) alloy by directed energy deposition (DED)-based additive manufacturing (AM) is presented here. The objective of the study was to achieve a dense ZTA coating with the intent of providing an alternative to fully ceramic implants for articulating surfaces of total hip arthroplasty (THA). Preliminary work resulted in failed samples due to cracking, porosity, and delamination. After careful parameter optimization, a Ti64+5wt.%ZTA (5ZTA) composition produced a metallurgically sound and coherent coating with minimal porosity. Additionally, bulk structures were also feasible with the optimized coating parameters. Characterization of the 5ZTA composition displayed a 27.0% increase in hardness, 25% reduction in normalized wear rate, an increase in contact resistance during in vitro tribological testing along with a faster surface re-passivation post-tribological testing.
Tribo-corrosion response of additively manufactured high-entropy alloy
Abstract High-entropy alloys (HEAs) with multiple principal elements represent a paradigm shift in structural alloy design and show excellent surface degradation resistance in corrosive environment. Here, the tribo-corrosion response of laser-engineered net-shaped CoCrFeMnNi HEA was evaluated in 3.5 wt% NaCl solution at room temperature. The additively manufactured (AM-ed) CoCrFeMnNi showed five times lower wear rate, regenerative passivation, and nobler corrosion potential during tribo-corrosion test compared to its arc-melted counterpart. A significant anisotropy was seen in the tribo-corrosion response with 45° to the build direction showing better performance compared to tests along the build direction and perpendicular to it. The open circuit potential curves were characterized by a sharp drop to more negative values as wear began, followed by continuous change for the active tribo-corrosion duration and finally a jump to nobler value at the end of the test indicating excellent surface re-passivation for the AM-ed alloy. The superior tribo-corrosion resistance of AM-ed CoCrFeMnNi was attributed to the refined microstructure and highly protective surface passivation layer promoted by the sub-grain cellular structure formed during additive manufacturing. These results highlight the potential of utilizing additive manufacturing of HEAs for use in extreme environments that require a combination of tribo-corrosion resistance, mechanical durability, extended more »
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- npj Materials Degradation
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- National Science Foundation
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