Properties of Thermal Spraying Ni-Al Alloy Coatings

Abstract

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 µm. 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 E corr .

Thermal spraying of transition metal aluminides: An overview

“…Starosta et al produced NiAl coatings with the aim to possibly use them to replace currently used electrolytic chromium coatings and compared their microstructure and corrosion behaviour with that sprayed by flame spraying. Also the corrosion potential and current density values were evaluated for different Al concentrations in NieAl coatings tested in 0.01 M H 2 SO 4 electrolite solution at ambient temperature [127]; it is observed that the higher aluminium content causes a decrease of current densities.…”

“…The unique D-gun coatings found in the literature are those already presented in the FeAl section for Senderowski et al, who used NiAl and NiCr as bond coatings for FeAl [88,89]. Flame Spray: NiAl coatings can be regarded as substitutes of electrolytic chromium coatings [127,134]. Flame spray coatings are reported to show about 10 times larger corrosion current density when compared with plasma spray coatings; they concluded that the structure and chemical constitution of coatings greatly influences the value of corrosion potential (E corr ) and, the more aluminium content the lower E corr .…”

“…Cold Spray: due to the brittle intermetallic phases, like FeAl deposits, blends and non-completely alloyed ball-milled NieAl powders are sprayed and further annealed to induce the compound formation [136,137]. Whereas starting from a blend, a heterogeneous structure consisting of different intermetallics depending on the annealing temperature is observed [136], the composition along the coating is more homogeneous when [121] Oxidation in air at 900 C under cyclic conditions [125] Cyclic oxidation studies in air and molten salt (Na 2 SO 4 e60% V 2 O 5 ) heating at 900 C [127] Cyclic studies for 100 h each cycle under a flue gas atmosphere starting from the mechanically alloyed powders [137]. Fig.…”

Formation Mechanism of Nanostructured (Ni, Fe)3Al-Al2O3Nanocomposite and Its Characterization

“…Among these, the alloys based on Ni 3 Al may offer significant advantages because of the attractive combination of the properties. Ni 3 Al is very resistant to heat and corrosion, and finds use in heat-treating furnaces and other applications where its longer lifespan and reduced corrosion give it an advantage over stainless steel [3]. However, commercial use of nickel aluminides is limited due to low ductility and toughness of the aluminides at ambient temperature.…”

“…Some processing problems may intensify these obstacles such as: the exothermic nature of formation of nickel aluminides and high difference in the melting point of Al and Ni. Microstructural modifications are processing routes which can overcome part of mentioned problems [3,4]. One of the effective techniques for preparing nanocomposite powders consisting of more than two phases is mechanochemical synthesis.…”