Journal Published Online: 12 November 2021
Volume 10, Issue 1

Al-Cr Diffusion Coatings Processed on a Cast and a Heat-Treated Ni-Base Alloy



Diffusion coatings are used to protect components against oxidation and corrosion in high-temperature applications. The processing route and parameters determine the coating characteristics for each substrate. When more than one element is deposited, the number of processing variables increases, as single-step or two-step deposition can be used. With a two-step procedure, the element deposited first affects subsequent diffusion. Under these conditions, a better understanding of the phenomena involved is required, as the substrate plays an important role. To this end, a systematic assessment of chromium and aluminum diffusion coatings processed by out-of-pack cementation on a nickel alloy was carried out. The precipitation-hardened alloy was supplied as-cast and in a heat-treated condition. Three processing routes were used: a single-step procedure and two two-step procedures (AC, aluminizing+chromizing, and CA, chromizing+aluminizing). Characterization of the as-processed coatings showed that the nonuniform structure of the as-cast nickel alloy allowed preferential diffusion paths to form, reducing coating thickness and minimizing differences caused by the processing route. Synthesis of nickel aluminide (NiAl) occurs on coatings processed with the CA route, as aluminum diffuses in a nickel matrix that is richer in chromium, favoring the synthesis of the aluminide. Regardless of the processing route used, exposure to 1,100°C results in parabolic growth of the coating. At 1,100°C, partitioning of aluminum occurs between the upper surface of the coating and the nickel alloy, forming a diffusion barrier.

Author Information

Dalpasquale, Alana S.
Post-Graduation on Materials Science and Engineering, Universidade Federal do Paraná, Centro Politécnico, Curitiba, PR, Brazil
D’Oliveira, Ana Sofia C. M.
Department of Mechanical Engineering, Universidade Federal do Paraná, Centro Politécnico, Curitiba, PR, Brazil
Pages: 18
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Stock #: MPC20210059
ISSN: 2379-1365
DOI: 10.1520/MPC20210059