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Abstract: The NiCrAlYSi coating with a diffusion barrier (DB) and/or buffer layer (BL) on DSM11 substrates was deposited by continuous arc ion plating (AIP) method. The interfacial strength, oxidation resistance and diffusion-barrier effectiveness were investigated. The tensile adhesion test result showed that the interfacial adhesive strength was stronger than that in the coating system with a diffusion barrier deposited by the conventional two-step AIP. The pre-deposition of the buffer layer into the DB/DSM11 interface could improve the interfacial strength further. The oxidation test results indicated that the multilayer could provide more effective protection for the DSM11 substrate than the single coating system. During thermal exposure, continuous and adhered Al2O3 scales were presented to the coating surface and the interdiffusion of alloying elements between the overlayer and the substrate was suppressed markedly. After thermal exposure or thermal cycle, the diffusion barrier was stable and kept efficient. [Copyright &y& Elsevier]

Abstract: NiCoCrAlYSiB coatings were obtained using an arc ion plating technique on a directionally solidified Ni-base superalloy. Thermal shock resistance of the bare and coated specimens were investigated by cycling between high temperature (900, 1000 and 1050°C) and room temperature (forced water quenching). The experienced attack during thermal shock cycling was studied by gravimetry, XRD, SEM and EDS. The results showed that bare alloys and coated specimens experienced aggravating oxidation under thermal shock cycling conditions. The coated specimens exhibited excellent thermal shock resistance and provided enough protective effect on the superalloys under thermal shock cycling conditions. The accelerated oxidation mechanism and crack formation and propagation in the coatings were also investigated. The accelerated oxidation can be attributed to the accelerating oxide formation and breakdown due to compressive stresses accumulation in the oxides due to oxide growth at high temperature and thermal mismatch during cooling. The formation and propagation of cracks formed in coatings can be attributed to tensile stresses in oxides generated by irreversible cyclic creep accumulation in the metallic coatings and the “wedging” effect of oxide protruded into the coatings. [Copyright &y& Elsevier]

Abstract: NiCoCrAlYSiB coatings were obtained using an arc ion plating technique on a directionally solidified Ni-base superalloy. Thermal shock resistance of the bare and coated superalloys were investigated by cycling between high temperature (900, 1000 and 1050°C) and room temperature (forced water quenching). The microstructure evolution in coatings and the underneath substrates was studied. The results showed that phase transformation from γ′ to γ occurred at the surface of the coated and bare specimens due to the consumption of Al and Ti by oxidation. A directional coarsening of the γ′ precipitates (γ′ rafting) just beneath the γ′-impoverishing zone (or interdiffusion zone) is observed. This kind of rafting is believed to come into being from the compressive stresses by temperature gradients due to high cooling rate during cooldown. The relationship between microstructure evolution and cracks formation and propagation is also discussed. [Copyright &y& Elsevier]