Microstructure, phase constitution and mechanical properties of WC-Cr3C2-CoNiLa coatings fabricated by using HVOF spraying core-shell powder

Abstract

To reduce the decarburization of WC, the core-shell WC-16Cr3C2-10Co4Ni-La2O3 (named as WC-Cr3C2-CoNiLa in following) powder was prepared through second agglomeration and spray granulation process and deposited using high velocity oxygen fuel (HVOF) spraying. Microstructure and phase constitutions of the deposited coating were characterized using scanning electronic microscopy (SEM) with energy dispersive spectrometer (EDS) and X-ray diffraction (XRD), respectively. Microhardness, elastic modulus, and fracture toughness of the coating were tested by indentation method. Wear properties of the coating under different applied loads were evaluated by two body dry sliding wear using a pin-on-disc tester. Experimental results showed that the HVOF sprayed WC-Cr3C2-CoNiLa coating was mainly consisted of WC, Cr3C2, Co, Ni phases and a little of Cr2O3 without any WC decarburized phases including W2C, M6C and M12C). Most of WC carbide in the coating presented a round outline with the average particle size of 0.54 ± 0.35 μm and average crystal sizes 401 ± 91.41 Å in different crystal orientation index. The coating presented dense microstructure with the porosity about 1.16 ± 0.39%, and some lamella features with well bonded interfaces of carbide particles/binder phase, inter-splats and coating/substrate. Microhardness, elastic modulus, fracture toughness and wear rate of the coatings were 12.57 ± 0.52 Hv0.3, 153.91 ± 31.66 GPa, 5.31 ± 0.51 MPa⋅m1/2 and 6.67*10−3-11.11*10−3 mg/(Nm) when the applied load increased form 5 N to 15 N, respectively. The abrasive wear of the coating occurred mainly in the form of gouging and plastic deformation as well as peeling off carbide particles.