Copper coating on austenitic stainless steel using microwave hybrid heating

Coating of copper on austenitic stainless steel (SS-316) is useful where high thermal conductivity as well as high electrical conductivity along with high strength is desirable. Common applications of these coatings include aerospace systems such as space stations and satellites. Usually, chemical vapour deposition (CVD) and physical vapour deposition (PVD) techniques are employed for developing such coatings. In the present work, copper coatings with an average thickness of 230 micrometers were successfully developed on SS-316 substrates using microwave hybrid heating (MHH) technique. The MHH technique was employed in order to enhance the coupling efficiency of the target material (metallic copper powder) with the incident microwaves at room temperature. Copper powders of average grain size 5 micrometers were melted and deposited on the steel substrates by controlled exposure of microwave radiation of 900 W at 2.54 GHz frequency in a multi-mode applicator. Coatings were analysed through energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), and measurement of microhardness. The developed coatings were reasonably uniform, dense, and homogenous, although the presence of micropores was detected. Coatings were formed by necking, followed by agglomeration, and fusing of melted copper particles during microwave irradiation. Microstructure of the developed coatings consists of 3-D chain like arrays of the fused particles. The presence of oxides of copper in the deposits has been confirmed. The coatings so developed had a mean hardness of 270 +/- 30 HV.