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Effect of Isothermal Treatment on Ni3Al Coatings Deposited by Air Plasma Spraying System

Mehmood K., Rafiq M. A., Durrani Y. A., Khan A. N.

Archives of Metallurgy and Materials

2018

Vol. 63, iss. 1

277--283

Ni3Al coatings were obtained on AISI 321 steel samples by air plasma spraying system. The behavior of heat treatment on intermetallic coatings were evaluated after exposure at various temperatures i.e. 500ºC to 800ºC. The stay time in this regard was varied from 10 to 100 hours. The coatings were then characterized by X-Ray diffraction analysis, optical and scanning electron microscopy, eddy current measurements and stress analysis. It was observed that the formation of NiO increases drastically with time and temperature. The hardness of the coating increases with the formation of NiO. It was noted that the residual stresses can be correlated with the formation of NiO. Further, the development of residual stresses can be monitored by a non-destructive technique i.e. eddy current method.

Properties of Thermal Spraying Ni-Al Alloy Coatings

Starosta R.

Advances in Materials Science

2009

Vol. 9, nr 1(19)

30-40

The article presents the results of testing of Ni-Al alloy coatings with different chemical and phase composition, which might replace currently used electrolytic chromium coatings. Crust chromium coatings are suitable for reconditioning of machine parts because of their very good maintenance properties. However, due to toxicity of electrolytic chromium bath, their application tends to be restricted. Thermal flame and plasma spraying technologies were chosen for nickel aluminium coating application. Obtained coatings were distinguished by significant porosity of structure and surface roughness. The thickness of coatings ranged from 440 to 683 ěm. Microhardness of coatings was not related to applied metal plating technology but to chemical and phase composition. The more aluminium content in coating the harder the coatings were. The hardness of coatings which resulted from NiAl phase was ca 250 HV 0.04. Flame spray coatings are distinguished by nearly 10 times higher corrosion current density compared comparatively with plasma spray coatings. The value of corrosion potential is influenced by structure and chemical composition of coatings. The more aluminium content caused the lower Ecorr.