Improvement of the Oxidation Resistance of the Single-Crystal Ni-Based TMS-82+ Superalloy by Ni–Al Coatings with/without the Diffusion Barrier

Abstract

Oxidation behavior of the uncoated base, Ni-Al coated and Re-Cr-Ni plus Ni-Al coated single-crystal (SC) Ni-based TMS-82? superalloy is studied under cyclic air at 900°C for 200 h to assess the oxidation resistance. Regardless of the coating processing, Ni-Al coating is effective in improving the oxidation resistance due to the formation of a continuous a-Al 2 O 3 layer in the scale. For the uncoated base superalloy, the mass-gain curves are fitted by a subparabolic relationship, and complex oxide products including predominately NiO, some 123Oxid Met (2010) 74:287-303 DOI 10.1007 the cyclic exposure environment. The amount of detrimental c 0 -phase and topologically close-packed (TCP) phases in the interdiffusion zone in the coated superalloy with the diffusion barrier is greatly reduced compared with that without the diffusion barrier due to the distinct barrier effect limiting diffusion of elements between the bond-coat and the substrate.

The Improvement of Oxidation Resistance of a Re-Based Diffusion Barrier/Ni–Al Coating on the Single-Crystal Ni-Based TMS-82+ Superalloy

“…As reported by some of present authors [3,[5][6][7], a thick Al 2 Ni 3 layer formed on the surface of the SC Ni-based superalloy after the Ni-Al coating. Applying the Re-Cr-Ni plus Ni-Al coating process, a diffusion barrier layer of the r-phase ReCr-Ni and a Ni 2 Al 3 layer were obtained.…”

“…The high Al activity pack cementation was carried out in a vacuum of 10 -3 Pa at 800°C for 20 min by burying the Ni-plated specimens into a mixture of Al metal powder (15 wt%), NH 4 Cl (5 wt%) as an activator, and Al 2 O 3 powder as an anti-sintering agent. The compositions of the coating were determined to be (71-98) at.% Ni and *40at.%Ni-60at.%Al from the substrate, namely, the coating consisted of an internal Ni-rich layer and an external Ni 2 Al 3 layer [6].…”

“…The constituents of the coating were in the order of Re-Cr-Ni diffusion barrier layer, Ni-Cr-Al layer and Ni 2 Al 3 layer from the substrate. The corresponding compositions of above layer were *41at.%Re-21at.%Cr-17at.%Ni, 75at.%Ni-11at.%Cr-9at.%Al, and 42at.%Ni-58at.%Al, respectively [6]. The details of the forming process of the Re-Cr-Ni phase are described elsewhere [3,[5][6][7].…”

“…The corresponding compositions of above layer were *41at.%Re-21at.%Cr-17at.%Ni, 75at.%Ni-11at.%Cr-9at.%Al, and 42at.%Ni-58at.%Al, respectively [6]. The details of the forming process of the Re-Cr-Ni phase are described elsewhere [3,[5][6][7]. Apart from the Ni-Al coated specimens, the uncoated base superalloy was used to compare the oxidation behavior.…”

“…In previous papers by some present authors [5,6], a new Re-modified Ni-aluminide coating has been adopted, in which a Re-Cr-Ni (r-phase) layer acts as a diffusion barrier to suppress the outer-diffusion of Ni from the substrate. The oxidation behavior of the coated TMS-82?…”