Microstructural and mechanical characterization of thermal sprayed nickel–alumina composite coatings

• Published in: Surface & coatings technology Vol. 216; pp. 78 - 92
• Main Authors: Grewal, H.S., Singh, H., Agrawal, Anupam
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.02.2013; Elsevier
• Subjects: Alumina; Applied sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Hydroturbine; Materials science; Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology; Metals. Metallurgy; Nickel; Nonmetallic coatings; Physics; Production techniques; Surface treatment; Surface treatments; Thermal spray coating; Thermal spray coating; Nickel; Alumina; Hydroturbine; Composite materials; Composite coating; Spray coatings; Hot spraying; Mechanical properties; Surface treatments; Microstructure; Non metal coating
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2012.11.029

In the current work, Ni–Al2O3 based composite coatings were fabricated using High Velocity Flame Spray (HVFS) system. The effect of alumina content on the microstructure and various mechanical properties viz. microhardness, fracture toughness, density, residual stress and scratch resistance was studied. Microstructure of the coating was characterized with the help of Scanning Electron Microscope (SEM) equipped with Energy Dispersive Spectroscopy (EDS), Optical Microscope (OM) and X-ray Diffraction (XRD). It was observed that microstructural properties such as splat size, porosity, un-melted particles and surface roughness are highly affected by the alumina content in the coatings. Microhardness improved with the rise in alumina fraction and a maximum of 1151HV could be achieved with 60wt.% alumina blending. Cracking and spallation were found to be the mechanisms responsible for damage of coatings during scratch testing. A model has been proposed to explain the variation in surface roughness and porosity of the Ni–Al2O3 coatings based on coating build-up mechanism. ► Ni–Al2O3 composite coatings were successfully deposited using thermal spray technique. ► Content of Al2O3 in coating significantly effects the coating's microstructure ► Mechanical properties of coatings were also affected by the presence of Al2O3. ► Effect of Al2O3 content on porosity and roughness has been explained through proposed model.