Effect of C content on microstructure and mechanical properties of plasma claddingAl_1.5CoCrFeNiNb_0.2C_xhigh-entropy alloys

: Al_1.5CoCrFeNiNb_0.2C_x(x = 0, 0.01, 0.02, 0.05, 0.2, molar ratio) high-entropy alloys with different C contents were prepared by plasma cladding on the surface of low-carbon steel. The effect of C content on the microstructure and mechanical properties of cladding layers was studied by using X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), microhardness tester and wear testing machine. The results indicated that when x = 0 and 0.01, the Al_1.5CoCrFeNiNb_0.2C_x high-entropy alloys were composed of a BCC phase and a small amount of Nb-Laves phase. When x = 0.02-0.2, NbC phase could be synthesized in-situ. The alloys consist of a BCC phase, along with a small amount of NbC and Laves phase. Moreover, the precipitation amount of NbC gradually increased with the increase of C content. With the increase of C content, the NbC content increased gradually. When x = 0 and 0.01, the microstructure of high-entropy alloys was dendritic crystal. The dendrite was BCC phase and the interdendritic was eutectic texture consisted of BCC phase and Nb-Laves phase. When x = 0.02-0.2, in-situ NbC was precipitated on the dendritic matrix. With increasing C content, the content and size of NbC gradually increased, and its morphology was gradually transformed from granular at low C contents (x = 0.02, 0.05) to granular and cross-dendritic at high C content (x = 0.2). TEM showed that the interface between the high-entropy alloy matrix and the NbC reinforcement phase was smooth and clean, without any defects or impurities. As the C content rose from x = 0 to x = 0.2, the hardness increased from 560.1 HV to 762.2 HV, while the weight loss rate decreased from 24.69 mg/min to 4.70 mg/min.