Microstructure and formation mechanism of the Si-Cr dual-alloyed coating prepared by pack-cementation

• Published in: Surface & coatings technology Vol. 399; p. 126142
• Main Authors: Zeng, Jing, Hu, Jianjun, Yang, Xian, Xu, Hongbing, Li, Hui, Guo, Ning, Dong, Qingshan
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 15.10.2020; Elsevier BV
• Subjects: Alloying; Backscattering; Cementation; Chromium; Chromizing; Coatings; Diffusion effects; Electron imaging; Ferrosilicon; Growth mechanism; Interdiffusion; Iron silicide; Kirkendall effect; Microhardness; Microstructure; Morphology; Pack-cementation; Raw materials; Si-Cr coating; Silicon; Substrates; Wear resistance; Kirkendall effect; Si-Cr coating; Wear resistance; Pack-cementation; Growth mechanism
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2020.126142

In this study, two types of SiCr coatings (named as SiCr-1 and SiCr-2) were fabricated on AISI 5140 steels by pack-cementation via different Si feedstocks, aiming to strengthen the steel surface and avoid the carbon-poor layer caused by chromizing. Phases, microstructure, and composition were characterized by X-ray diffraction technique (XRD), secondary electron imaging (SEI) and backscattering electron imaging (BSEI), and energy dispersive spectroscopy (EDS), respectively. The results show that both the coatings mainly consist of α-Fe (with Si and Cr in concentration), Fe3Si, CrFe8Si, and CrC. However, there are some apparent differences between the two coatings including the morphology, element content, microhardness, and wear resistance, which is owing to the difference in the coating growth mechanism. The coating growth of SiCr-1 sample using Si powders as Si feedstock is controlled by the interdiffusion mechanism of the substrate and coating elements, while the coating growth of SiCr-2 sample using ferrosilicon powders as Si feedstock is mainly dominated by the reaction deposition mechanism. For both samples, the presence of micropores in the coatings is observed and their formation is mostly due to the non-equilibrium diffusion induced Kirkendall effect. A new gradient growth mode of micropores based on the Kirkendall effect was proposed. •SiCr coatings were prepared by pack-cementation with different Si feedstocks.•Feedstock composition significantly affects the morphology and structure of the coating.•Using Si powder as feedstock shows slow coating growth controlled by interdiffusion mechanism when.•Using ferrosilicon powder as the feedstock presents rapid coating growth controlled by reaction deposition mechanism.•SiCr coating using ferrosilicon powders as feedstock has more large micropores.