Microstructure, Microhardness, and Wear Resistance of AlCoCrFeNiTi/Ni60 Coating by Plasma Spraying

In this comparative study, Ni60 was used as a reinforcement and added into an AlCoCrFeNiTi high-entropy alloy (HEA) matrix coating in order to enhance its hardness and wear resistance. An AlCoCrFeNiTi/Ni60 coating was prepared by plasma spraying with mechanically-blended AlCoCrFeNiTi/Ni60 powder. The coating microstructure was observed and analyzed. Bonding strength, microhardness, and wear resistance of the coating were investigated. The results showed that a compact AlCoCrFeNiTi/Ni60 coating with Ni60 splats uniformly distributed in the AlCoCrFeNiTi matrix was deposited. After spraying, matrix body-centered cubic (BCC), face-centered cubic, and ordered BCC phases were detected in the coating. The added large Ni60 particles played an important role in strengthening the coating. Tensile test results showed that bonding strength of this coating was above 60.1 MPa, which is far higher than that of the AlCoCrFeNiTi HEA coating in the previous study. An average microhardness of 676 HV was obtained for the main body of the coating, which is much higher than that of the AlCoCrFeNiTi HEA coating. Solution hardening in γ-Ni and dispersion strengthening of the hard interstitial compounds, such as Cr7C3, CrB, Cr2B, and Cr23C6 increased the hardness of Ni60, and then the AlCoCrFeNiTi/Ni60 coating. During wear testing at 25 °C, adhesive wear and abrasive wear occurred, while, at 500 °C, abrasive wear took place. Volume wear rates of the coating at 25 °C and 500 °C were 0.55 ± 0.06 × 10−4 mm3·N−1·m−1 and 0.66 ± 0.02 × 10−4 mm3·N−1·m−1, respectively. Wear resistance of this coating was better than that of the AlCoCrFeNiTi HEA coating, which can be attributed to addition of the hard Ni60. Therefore, Ni60 is an appropriate reinforcement to further enhance the wear resistance of HEA coating.