Al Coating Desposited On The Nickel-base Alloy GH30 By Double Glow Plasma Surface Alloying Technique And Research For High Temperature Oxidation Properties

As a typical high-temperature alloy, Nickel-based alloys have been widely used in the manufacture of aircraft engines and various types of gas turbine hot-section components which require good high strength and good oxidation resistance at elevated temperature. However, the oxidation resistance at elevated temperature of nickel-based alloys is insufficient. So that an effective surface strengthening on nickel- based alloys is required commonly. Among numerous kinds of coatings applied on nickel-based alloys diffusion aluminized coating has excellent high temperature oxidation resistance and enough adhesion strength. Currently, diffusion aluminized coating has become the mainstream of advanced coatings for anti-oxidation at high-temperature.In this paper, an aluminizing coating was prepared on the surface of the nickel-base alloy GH30 by double glow plasma surface alloying method. A set of orthogonal programmed experiments was carried out. The roles of major parameters on the coatings were studied. The results showed that the influence of source cathode voltage on the diffusion layer thickness was maximal during depositing while the influence of cathodes spacing was minimal. A maximal thickness of the aluminum diffusion layer was obtained when following conditions were taken: source cathode voltage 950V, work piece voltage 500V, pressure 45Pa, and cathodes spacing17mm. SEM observation showed that the coating was dense and homogeneous. EDS analysis indicated that the thickness of the deposited layer was about 15μm. Beneath the deposited layer, there was a diffusing layer of 10μm, with the content of Al decreased in gradient. XRD revealed that the diffusion layer consisted of Al₄CrNi₁₅, Al3Ni, AlNi3 and Al₃Ni₅. Scratch test identified that the diffusion layer with a good toughness had a superior combination with the substrate. Finally, an oxidation experiment of 1000℃, 300h was conducted. The oxidation kinetics curve of aluminized sample accorded with the parabolic law. The oxidation weight gain of GH30 with aluminized layer was obviously less than that of GH30 without any surface modified. XRD analysis indicated that oxides mainly consisted ofα-Al₂O₃,θ-Al₂O₃ and NiAl₂O₄. The formation of a continuous and dense Al₂O₃ oxide during the high-temperature oxidation process was the critical reason why materials had a good high-temperature oxidation resistance. The high temperature oxidation resistance of aluminum diffused samples was significantly improved compared with bare GH30 specimens.