Abstract
AlCrCoNiFeCTax (x = 0, 0.5 and 1.0) high-entropy alloys coatings were synthesized on 45# steel by laser cladding. The microstructural evolution of the coatings with the change in x was analyzed in detail. The effect of Ta content on the wear behaviors of the coatings at different circumstances (in air and 3.5 wt.% NaCl solution) was especially highlighted. The microstructure presented the following change: equiaxed BCC (Body Centered Cubic) grains + fine MC (carbide, M = Al, Cr, Co and Ni) particles (x = 0) → equiaxed BCC grains + coarse TaC blocks + fine TaC particles (x = 0.5) → flower-like BCC grains + coarse TaC blocks + eutecticum (BCC + TaC) (x = 1.0). The average microhardness of the coatings demonstrated an upward tendency with increasing x due to the combination of the stronger solid solution and dispersion strengthening from the significant difference in atomic radius between Ta and Fe and the formation of TaC with an extremely high hardness. The wear rates of the coatings were gradually reduced both in air and in NaCl solution along with the increase in Ta content, which were lower than those of the substrate. The wear rates of the coatings with x = 0.5 and 1.0 in NaCl solution were slightly reduced by about 17% and 12% when compared with those in air. However, the values of the substrate and the coating without Ta in NaCl solution were sharply enhanced by 191% and 123% when compared with those in air. This indicated that the introduction of Ta contributed to the improvement in wear resistance both in air and in NaCl solution.
Highlights
Steel is extensively applied in industrial components such as shaft parts, gear wheels and screws on account of its good machinability, excellent comprehensive mechanical properties and high performance-to-cost ratio [1,2]
AlCrCoNiTax was selected as the cladding material to laser clad highentropy alloy coatings of AlCrCoNiFeCTax on 45# steel, and the effect of Ta on the microstructure and mechanical properties was investigated comprehensively
The serious lattice distortion resulting from the Ta introduction will play a positive role in solid solution strengthening, which will contribute to the improvement in hardness and wear resistance
Summary
Steel is extensively applied in industrial components such as shaft parts, gear wheels and screws on account of its good machinability, excellent comprehensive mechanical properties and high performance-to-cost ratio [1,2]. Considerable research has been carried out to improve the wear resistance of steels by laser cladding high-entropy alloy coatings on them. The coating, composed of FCC (Face Centered Cubic), BCC and Laves phase, had high hardness (741 HV), which was far higher than that of the substrate (240 HV) It demonstrated low weight loss per unit area (0.36 g·mm2 ) in dry friction, which was only 27% of that of 45# steel. The introduction of Ta, with a larger atomic radius of 1.48 Å than that of Fe, into the high-entropy alloy system prepared on steels contributes to the improvement in Coatings 2021, 11, 358 hardness due to the strong solid solution strengthening. AlCrCoNiTax was selected as the cladding material to laser clad highentropy alloy coatings of AlCrCoNiFeCTax on 45# steel, and the effect of Ta on the microstructure and mechanical properties (especially wear behaviors in air and NaCl solution) was investigated comprehensively. The suitable content of Ta was confirmed, with which the coating demonstrated excellent wear resistance both in air and in NaCl solution
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