Aluminium composite coatings produced by plasma transferred arc surfacing technique

Abstract

Plasma transferred arc surfacing (PTA) is a hardfacing technique by which a coating is deposited on to a substrate by the injection of metal powder and/or ceramic particles into a weld pool. Establishment of a plasma column initiates this weld pool formation. Few studies have been published on the use of PTA in the surface modification of low density substrates such as aluminium or titanium alloys. In the present work, the deposition of metal matrix composite (MMC) coatings on to aluminium 5083 alloy substrates has been achieved. The experimental process involved the codeposition of an aluminium-nickel (Al₂ wt-%Ni) powder containing various ceramics (Al₂O₃, SiC, and TiC) with discontinuous particulate morphology. Composite coatings of varying reinforcement volume fractions V_f (0–40%) and particulate sizes (70–140 μm) have been fabricated. The first part of the research involved optimisation of the PTA parameters. The second part concentrated on characterising the features of the coatings. Two main aspects were assessed in this endeavour, namely bulk coating properties and microstructural features. Parameters such as dilution content, hardness, surface roughness, and coating adhesion were classified as bulk properties. Microstructural features were represented by porosity, aluminium cell size, matrix structure, and attributes associated with the reinforcement phase, such as V_f, particle length, and aspect ratio. For the optimum values of PTA parameters used, ceramic particle attributes, such as thermal properties, wettability, and V_f directly influenced the coating structure. With this information afabrication strategy has been presentedfor the production of coatings which may offer superior tribological properties.