Study on the mechanisms of formation of aluminized diffusion coatings on a Ni-base superalloy using different pack aluminization procedures

Abstract

The mechanisms of formation and microstructure of pack aluminized diffusion coatings depend on a wide range of parameters. These impact coatings differently depending on the processing mode selected (out-of-pack or in-pack) and are still the subject of debate. The need to systematize data on the influence of processing mode on the mechanisms of the formation of aluminized coatings was the motivation for this study, which reviews the influence of processing mode based on an analysis of experimental data for aluminized coatings processed in-pack and out-of-pack on a Ni alloy with Al at unit activity at 800 °C [low temperature with high Al activity (LTHA)] and 1100 °C [high temperature with high Al activity (HTHA)]. The results show that processing mode determined the amount of Al deposited at the surface and that the formation of a larger halide-depleted zone during out-of-pack diffusion accounted for the reduced deposition of Al. Processing temperature and Al concentration at the surface of the alloy determined the mobility of the elements in the coating and, consequently, the coating thickness and dominant diffusion mechanisms. Aluminization with the specimen immersed in the pack resulted in a preferential inward diffusion of Al for both processing temperatures. In contrast, coatings processed by out-of-pack diffusion showed a dependence on processing temperature. When a HTHA process was used, the coatings were thinner and formed in a two-stage diffusion process, while a LTHA process failed to form aluminide diffusion coatings.

TEM and Synchrotron X-ray Study of the Evolution of Phases Formed During Bonding of IN718/Al/IN718 Couples by TLPB

“…The concentration of the main elements, i.e. 70Al-18Ni-6Cr-6Fe, suggests that Al3Ni2 phase has formed in the bonding zone at this temperature [18,42], in good agreement with the XRD analysis (Fig. 6).…”

“…These observations verify that the shifts observed in the green set are the result of changes in the phase and not due to experimental errors. experiments on diffusion coating research [42]. The lattice parameters measured in this work are larger than those reported for binary AlNi couples.…”

Microstructure of Aluminide Coatings Modified by Pt, Pd, Zr and Hf Formed in Low-Activity CVD Process

“…Aluminizing is the primary process for production of oxidation resistant coatings for nickel superalloys [1,2]. Aluminide coatings are formed using pack cementation [3], out of pack [4] and chemical vapor deposition (CVD) [5] methods. Out of the pack, and its similar methods, vapor phase aluminizing were most common used in aerospace industry [6].…”

The Influence of Pd on the Structure and Oxidation Performance of β-NiAl Diffusion Coatings

“…Across the diffusion zone where precipitates formed with alloying elements from the substrate Pd content reduces to a residual content over a region of 30 μm and 50 μm on coatings processed on the 8.0 μm and 9.6 μm Pd layer, respectively. A thin interdiffusion zone (IDZ) and the presence of carbides in the intermetallic layer (Figure 1) can be observed in all the coatings, reflecting the preferential inward diffusion of Al 19,25 .…”