Abstract
The application of high-entropy alloys (HEA) in surface technology has great potential due to the high corrosion and wear resistance. A further improvement can be achieved by applying thermochemical treatments. Powder-pack boriding enables the formation of a protective precipitation layer. This process has already been applied for cast HEAs causing the formation of a diffusion-enriched surface layer and a distinct increase in wear resistance. In the current investigations, the alloy CrFeCoNi with a single-phase face-centred cubic (fcc) structure is considered. An efficient application can be achieved by limiting the material usage of HEAs to the surface. Therefore, the high-velocity-oxygen-fuel (HVOF) thermal spray process is applied. Boriding was conducted with an adapted powder-pack routine. Furthermore, borided bulk HEAs were considered as a reference. The influence of the production route and boriding treatment on the microstructure, phase formation, and properties was investigated in detail. For the coating and the cast HEA, a precipitation layer is formed. Hence, the hardness and wear resistance are significantly increased. The current study proves the suitability of the investigated process combination.
Highlights
High-entropy alloys (HEA) are a new group of multiprincipal alloys comprised of at least four alloying elements
The process combination shows of depositing thermal oxide spraying and subsequent precipitation areas of the metallic material, grooves in wear direction occur due to abrasive wear
Feedstock of the single-phase fcc HEA CrFeCoNi was produced of the casting in borided state shows no distinct changes
Summary
High-entropy alloys (HEA) are a new group of multiprincipal alloys comprised of at least four alloying elements. Thermochemical treatments are conducted to improve surface properties e.g., hardness, sliding characteristics, and wear resistance These processes are state of the art for cast iron- and nickel-base alloys. Limited investigations have been conducted for HEAs. Previous investigations by Lindner et al proved the suitability of a gasnitrocarburisation process for the treatment of the alloys Cr(Mn)FeCoNi. An increase of hardness and wear resistance could be achieved by the formation of an expanded austenitic phase, whereas the corrosion resistance was not significantly impaired [5]. Boriding of the fcc phase HEAs Cr(Mn)FeCoNi has been investigated by Lindner et al, proving the formation of a precipitation layer and a significant increase of hardness and wear resistance. The current feasibility study investigates the process combination of HVOF thermal spraying the fcc HEA CrFeCoNi and thermochemical treatment by powder-pack boriding. The influence on the wear resistance under various conditions is considered
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