Effect of Heating Treatment on the Microstructure and Properties of Cr–Mo Duplex-Alloyed Coating Prepared by Double Glow Plasma Surface Alloying

In this study, Cr−Mo duplex-alloyed coating was prepared on carbon steel by double glow plasma surface alloying (DGPSA). The effect of annealing and quenching and tempering (Q&T) treatments on the microstructure and performance of the coating was investigated by X-ray diffraction (XRD), energy dispersive spectrometry (EDS), backscattering electron imaging (BSEI) and electron backscattering diffraction (EBSD) techniques. The results show that a gradient structured coating composed of an Fe−Cr−Mo solid solution (Fe−Cr−Mo SS) layer and an alloyed pearlite layer was obtained on the steel surface. The affected layer was adjacent to the coating. After annealing or Q&T, more carbides precipitated in the Fe−Cr−Mo SS layer and alloyed pearlite layer. Most of the C atoms in the subsurface were dragged into the coating to form carbides in the Fe−Cr−Mo SS and alloyed pearlite layers of the coating, transforming the affected layers into a carbon-poor zone. Annealing and Q&T hardly modified the thickness of the coating, but greatly changed the hardness and corrosion resistance of the coating. The Q&T treated samples had higher hardness and better corrosion resistance than the as-DGPSA treated and the annealed samples