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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and sample into a quartz tube, which was subsequently sealed under vacuum. The tube was then subjected to a temperature of 980 °C and 1100 °C for a period of 4, 9 and 16 hours. Figure 3 illustrates the formation of a homogeneous single-phased layer with a coating thickness of 50 µm following 16 hours of sample treatment at 1100 °C. Additionally, the concentration profile exhibits a high chromium content in the layer, ranging from 50 to 60 at. %, indicative of a solid solution of chromium and iron in the coating.

Table 1. Parameters of the Pack cementation of Cr.

Cr pack cementation

Source of coating elements

10 wt pct Cr

Activator Inert filler

2 wt pct MnCl 2 88 wt pct Al 2 O 3

Heat treatment

1050 C, 5h, 5K/min

Atmosphere

6 L/h Ar + 5 Vol pct H 2

The mass gain versus time of samples shows that after a transition time of about 1 hour, the oxidation reactions obey a parabolic law in all cases (Fig. 3). The mass gain of chromized alloy is demonstrably greater than that of uncoated or aluminium alloy. The authors concluded that chromium is not an effective reservoir material due to the high proportion of chromium, which may induce a rapid growth of the oxide layer (Kofstad, 1988). Furthermore, the deposit exhibited poor oxidation resistance due to the large amounts of chromium present, resulting in a high-strain level in the Cr2O3 layer. In conclusion, it is of paramount importance to exercise meticulous control over the quantity of chromium employed during coating by means of the pack cementation method.

Fig. 3. (a) Cross-section of the chromization coating after 16h of treatment at 1100°C; (b) Concentration profile of the chromization coating (Ledoux et al., 2011).

In (Yener, 2019), the author investigated the efficacy of low-temperature chromium aluminide coatings on a FeCrNi-based superalloy and Inconel 718, which were applied using the pack cementation method. Even at low temperatures, the Al-Cr coatings exhibited minimal cracking, holes, or other defects. Additionally, the coating demonstrated uniformity on the surface. The application of such coatings also enhanced the mechanical properties of the superalloys.

3. Overlay Cr-based coatings

In contrast to the aforementioned diffusion coatings, no elements of the substrate are incorporated in the overlay coatings. These coatings offer the possibility of applying compositions that are entirely distinct from those of the base materials. Furthermore, their properties can be optimized in order to fulfil the requisite requirements. Overlay coatings are predominantly based on a general MCrAlY composition, typically comprising more than four elements (M = Co or Ni) (Barwinska et al., 2023; Kamal and Sharma, 2016; Rani et al., 2017; Yuan et al., 2015) (Barwinska et al., 2023; Kamal and Sharma, 2016; Rani et al., 2017; Yuan et al., 2015). The Al content is typically lower than that observed in diffusion coatings (Nicholls et al., 2002). Overlay coatings exhibit enhanced