HVOF sprayed Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings: Microstructure, microhardness and oxidation behaviour

• Published in: Journal of alloys and compounds Vol. 736; pp. 236 - 245
• Main Authors: Reddy, Nagaraja C., Kumar, B.S. Ajay, Reddappa, H.N., Ramesh, M.R., Koppad, Praveennath G., Kord, S.
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 05.03.2018; Elsevier BV
• Subjects: Electron microscopy; Flame spraying; Hardness; High temperature; High velocity oxy-fuel process; High velocity oxyfuel spraying; Lamellar structure; Martensitic stainless steels; Microhardness; Microstructure; Nickel oxides; Oxidation; Oxidation rate; Protective coatings; Scale (corrosion); Stainless steel; Substrates; Titanium alloys; Titanium base alloys; X-ray diffraction; X-ray diffraction; Oxidation; High velocity oxy-fuel process; Hardness; Electron microscopy
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2017.11.131

This paper reports the development of Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings on AISI 420 stainless steel (MDN-420) and titanium alloy ASTM B265 (Ti-15) by HVOF technique. Microstructure, microhardness and high temperature oxidation behaviour of coatings were investigated. Microstructure of coatings was dense and displayed layers depicting lamellar structure. The microhardness of coatings was significantly higher than that of substrate owing to higher density and cohesive strength between individual splats of coating materials. Cyclic oxidation studies conducted on Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings showed oxide scale was composed of various oxides like NiO, NiCr2O4 and Cr2O3 phases. The formation of compact and protective NiO phase in case of Ni3Ti coatings; NiO and Cr2O3 phases in Ni3Ti+(Cr3C2+20NiCr) coatings stabilised the weight gain exhibited slow oxidation rate at higher temperatures. •Development of Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings on turbine material based substrates by HVOF technique.•Dense coating with minimal porosity of about ∼2% obtained in both the coatings.•Cyclic oxidation test conducted on two coatings at a temperature of 650 °C for about 50 cycles.•Oxidation test revealed formation of oxide scale composed of NiO and Cr2O3 phases.