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

Abstract

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.

Evolution of the Microstructure and Properties of Pre-Boronized Coatings During Pack-Cementation Chromizing

“…It should be noted that the brittle FeB phase may also be formed during preboronizing treatment, which leads the degradation of coating properties [41]. FeB is mainly generated in the outermost layer of the coating [14] and has been ground away before the XRD test in this study. The average thickness of the B-coating is about 70 μm.…”

“…The samples were denoted as BCr-15, BCr-30 and BCr-60, respectively. Readers may refer to [14] for details of the pack-cementation process.…”

“…In our previous study, it has been found that the B-Cr duplex-alloyed coating with excellent properties can be obtained through a two-step pack-cementation process of pre-boronization and subsequent chromization [14]. Moreover, there is no carbon-poor zone in the substrate in the BCr sample [14].…”

“…working in severe environments, which are characterized by high-speed, cyclic heavy-load, and/or corrosiveness [11,13]. For example, the wear resistance of boronized sample (hardness higher than 1600 HV) can be strengthened greatly [14,15], but the corrosion resistance is still poor and is also accompanied by brittleness [14].…”

“…Likewise, previous works have proved that the boron-chromium duplex coating (B-Cr coating) has excellent comprehensive properties, such as high hardness, good wear resistance, and corrosion resistance [24,25]. In addition, the brittleness of boronizing can also be modified by the B-Cr coating treatment [14,25]. Therefore, the B-Cr coating has great application prospects in the field of surface protection of metal materials.…”