Enhanced reactive NiAl coatings by microwave assisted SHS

Purpose – The paper aims to focus on microwave (2.45 GHz) assisted SHS (MA-SHS) preparation ofNiAl intermetallic coatings on titanium substrates conducted in single mode applicator in order topromote the formation of a complex Ni-Al-Ti interface. This enhances the NiAl coating adhesion to thesubstrate and presents high hardness, toughness and the capability of stopping the fracturepropagation.Design/methodology/approach – Numerical modelling, coupling electromagnetic and heattransfer, allowed to demonstrate that the interface cooling rate can be controlled immediately afterSHS using microwaves, benefiting from the possibility of conveying energy to the newly formedintermetallic compounds, despite an adverse temperature gradient which would negatively affectconventional heating techniques, based exclusively on heat transfer. Experimental validation of themodelling results confirmed that by altering the synthesis conditions (load geometry, microwavepower, auxiliary microwave absorbers) the thickness of the Ni-Al-Ti layer can be controlled.Findings – The growth of the interface layer can be ascribed to the formation of a liquid phase(ternary eutectic) which progressively consumes NiAl and Ti from the substrate. In case of MA-SHS,the liquid phase presence can be prolonged during cooling, thus explaining the formation of the thickinterface layer.Practical implications – Microwave selective heating can be used to initiate the SHS withoutaffecting the metallic substrate, which is only heated locally by the reaction products, thus preservingits properties.Originality/value – Coupling numerical simulation