PSI - Issue 65

V.A. Bryzgalov et al. / Procedia Structural Integrity 65 (2024) 25–31 Bryzgalov V.A., Korznikova E.A./ Structural Integrity Procedia 00 (2024) 000–000

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Fig. 1. The fundamental principles of manufacturing diffusion coatings (Galetz, 2015)

One of the most popular techniques to apply diffusion coatings is pack cementation method. Pack cementation is an in situ chemical vapor deposition (CVD) batch process that has been used for over 75 years (Bianco and Rapp, 1996). Such method has been extensively used to readily form coatings consisting of Al (Aluminizing) (Zandrahimi et al., 2012), Cr (Chromizing) (König et al. (2022)), Si (siliconizing) (Chaia et al. (2020)) and multiple intermetallic compounds (Bateni et al., 2009; Chen et al., 2012; Xiang and Datta, 2003). The traditional pack consists of four components: the substrate or parts to be coated, the masteralloy (i.e a powder of the element or elements to be deposited on the surface of the parts, such as Cr, Al, Si etc.), a halide salt activator or energizer (e.g. NaCl, NaF, NH4Cl, etc.) and a relatively inert filler powder (Al2O3, SiO2 or SiC) (Dossett and Totten (2013); Fähsing et al. (2017); Tong et al. (2010)). The master alloy powder, the halide salt activator, and the inert filler are combined in a homogeneous mixture, which is then applied to the components to be coated within a heat-resistant retort. Schematic representation for pack cementation process is presented in Fig. 2

Fig. 2. Schematic representing pack cementation process (Nourpoor et al., 2022).

This process is particularly effective for coating superalloys with Cr, which involves the diffusion of chromium into the surface of superalloys to enhance their oxidation and corrosion resistance. König et al. (König et al. (2022)) used pack cementation to coat gamma/gamma' ERBOCo-1 (Co/Ni: 1.4), ERBOCo-1X (Co/Ni: 0.7) and derivatives of these with lower W contents. Prior to cementation, the specimens were rinsed in deionized water and then ultrasonically cleaned in acetone. The authors measured the weight of the specimens before and after the coating process using an analytical balance. Parameters of the pack cementation are given in Table 1. All materials were weighed using a balance. The coating element and the inert filler were combined in a turbula mixer for a period of 30 minutes. Ledoux et al. (Ledoux et al. (2011)) employed pack cementation method to develop chromium and aluminum coatings on the surface of austenitic nickel-iron-chromium superalloy to enhance its corrosion resistance to be sufficient for applications as steam methane reformer (SMR). In case of chromium coatings, the pack mixture was composed of a Cr 70 Fe 30 master alloy and CrCl 3 . The chromisation process was conducted by introducing the mixture