Microstructures and Wear Resistance of Boron-Chromium Duplex-Alloyed Coatings Prepared by a Two-Step Pack Cementation Process

In this study, a two-step pack cementation process (preboronizing and then chromizing) was employed to prepare the B-Cr duplex-alloyed coating on the steel. After the first step of preboronizing (PB sample), box-type furnace chromizing (BC-1 sample) and induction heating chromizing (BC-2 sample) were carried out, respectively. The phases and microstructure of the coatings were characterized by X-ray diffraction (XRD), backscattering electron imaging (BSEI), and energy dispersive spectroscopy (EDS). The results reveal that the heating mode of the second step of chromizing has a significant effect on the phase composition and microstructure of the B-Cr coating. The efficiency of induction heating is higher than that of the box furnace heating, resulting in a thicker, denser, flatter surface, and B-Cr coating with fully reacted B and Cr elements. The wear and corrosion resistance of the steel is found to be significantly improved by the formation of effective B-Cr coating. The formation mechanisms and properties of the two duplex-alloyed coatings are investigated and discussed.