Structural changes in high velocity oxy-fuel sprayed Cr3C2/NiCr 75/25 coatings after annealing treatments

The structural properties of Cr3C2/NiCr 75/25 coatings, prepared with the high velocity oxy-fuel (HVOF) spraying method, have been studied at room temperature by XRD techniques. The dependence of the phase composition and of the amorphous-crystalline transformations on the thermal history of the specimens have been investigated by varying the annealing temperature of the samples in the range 300-1073 K, with different annealing schedules. In parallel, a microstructural examination with SEM and EDS has been made on the starting powders and on the cross section of the coatings before and after annealing treatments. The HVOF coating evaluated in this study does not present carbides with relatively poor content of carbon as Cr7C3and Cr23C6. In all specimens Cr3C2and M3C2(M=Cr,Ni) carbides and small amount of Cr2O3were found. The results, in terms of XRD spectra, are compared with those obtained for the Cr3C2/NiCr 75/25 starting powders.