Microstructure and annealing behavior of Cr-coatings deposited by double glow plasma on AISI 5140 steel

Cr-coatings processed for different times were synthesized on the surface of AISI 5140 steel by double glow plasma surface alloying (DGPSA). The microstructures, microchemistry and phases of the coating were characterized by backscattering electron imaging (BSEI), energy dispersive spectrometry (EDS), and X-ray diffraction (XRD). The results show that the Cr-coating prepared by DGPSA consists of three layers: a deposited-layer, a diffusion-layer and an affected-layer. With increasing DGPSA processing time, the relative thickness, microstructure and phase composition of the three layers vary greatly. The deposited-layer is mainly composed of pure-Cr, the diffusion-layer consists of Cr-Fe solid solution (Cr-Fe SS) and/or Cr-Fe intermetallic compound (Cr-Fe IMs), while the affected-layer is composed of high-Cr pearlite. After depositing Cr by DGPSA, the corrosion potential is improved and the corrosion current is reduced. Subsequent annealing not only promotes the precipitation of the multiple carbides particles within the pure-Cr coating, but also promotes the transformation of Cr-Fe IMs into Cr-Fe SS. However, these changes have little effect on the hardness and corrosion resistance of the coatings. Keywords: Double glow plasma surface alloying, Chromizing, Hardness, Corrosion resistance, Annealing