Effect of niobium on the microstructure and wear resistance of iron-based alloy coating produced by plasma cladding

The iron-based alloy coatings have been deposited on plain steel using plasma cladding technique. The effects of niobium element on the microstructure and wear resistance property of the iron-based coatings were investigated using scanning electron microscopy (SEM) with energy dispersive spectrum (EDS), X-ray diffraction (XRD) and ball-on-disc wear tester. Results showed that there were γ-(Fe,Ni) austenite and lots of compounds such as Cr7C3, Mo1.24Ni0.76 and MoSi2 in the iron-based clad coating. And the carbide NbC formed in the Nb-contained clad coating. The SEM micrographs of the cross section of Nb-free coating revealed that the clad coating had a fine dendritic microstructure which was a typical microstructure of rapidly solidified austenite (γ). With the niobium addition, the rate of solidification varied and the equiaxed grain formed in the clad coating. And Nb also made the microstructure become finer. The Nb-free and Nb-contained clad coatings both owned an excellent wear resistance property compared to 0.45% C carbon steel under dry sliding wear tests. And the wear resistance of Nb-contained clad coating was higher than that of the Nb-free clad coating because the high hardness carbide NbC distributed in clad coating and the dispersion strengthening in the iron-based clad coating was obvious, which increased the wear resistance of clad coating under dry sliding wear test.