Evaluation of aluminide diffusion coatings for thermal cyclic oxidation protection of a nickel-base superalloy

Abstract

Active element modified aluminide diffusion coatings on IN738 substrates were produced by a new route using continuously cast, aluminum alloy wires consisting of Al-Y, Al-Ce, Al-La and Al-Si-Y. The cast wires were used as evaporation sources for ion-vapour deposition followed by diffusion heat treatments to form nickel aluminide coatings. In order to examine the oxidation resistance of these coatings at elevated temperatures, thermal cyclic oxidation experiments were carried out in air at 1050 8C. While all coatings were found to provide significant protection, the Al-La modified coatings provided the greatest resistance to cyclic oxidation. On the other hand, with coatings based on Al-Si-Y alloys, while silicon has a strong ability to reduce the outward diffusion of aluminum, the adverse effect of silicon on mechanical properties of the coating, together with the formation of volatile silicon monoxide, led to catastrophic localized oxidation of the protective coatings.

Oxidation Resistance of a Cr0.50Al0.50N Coating Prepared by Magnetron Sputtering on Alloy K38G

“…h-Al 2 O 3 grows very fast and is undesirable for protection [34]. The oxidation of B1-(Cr,Al)N also forms (Cr,Al) 2 [25,[35][36][37]. However, at low oxidation temperatures, a-Al 2 O 3 is not favored and dissolves in the Cr 2 O 3 lattice in small amounts.…”

“…A scanning electron microscope (SEM, LEO Super 35, Germany) equipped with EDS was used to investigate the morphologies of the as-deposited coatings and the oxide scales. Lattice parameters of the oxides and the quantitative phase composition for the as deposited coating and the oxides were calculated from the XRD analysis by the Rietveld method [23], which was accomplished in a DBWS program in the Cerius [2] software (Molecular simulation Inc., USA). The intensity of the XRD profile is represented by…”

“…With increasing operating temperatures of aircraft and marine turbine engines, various high-performance coatings have been developed, such as diffusion coatings [1,2], MCrAlY overlay coatings [3,4], modified diffusion coatings [5][6][7][8][9] and thermal-barrier coatings [10][11][12][13][14]. Overlay coatings were recently developed by Nicholls et al [15][16][17] to protect superalloys from various forms of hightemperature corrosion.…”

Corrosion Resistance of Reactive Element Aluminide Diffusion Coatings on a Nickel‐based Superalloy and an Austenitic Stainless Steel

“…Microstructural observation of the coating after 600 hours of exposure revealed that no sulfidation had occurred, indicating that sulphur penetration through the oxide layer was effectively blocked. It has been suggested that this may be related to the distribution of the reactive element within the oxide layer [19]. Thus, among the reactive elements investigated, the AI-Ce modified coating was found to provide the most effective hot corrosion protection for IN738 exposed to a molten sulphate environment.…”

“…Thus , in comparison with the other modified coatings, the AI-La coating was found to be the most effective for oxidation protection during high temperature thermal cycling. A detailed description of this behaviour has been presented elsewhere [19]. Figure 4 shows the weight variations of IN738 specimens caused by hot corrosion with molten sulphate at 900°C.…”