Development of Metal Matrix Composite Castings through Microwave Processing

Abstract

The application of microwave energy is not new in material processing, lots of developments in material processing have been carried out through this technology. This technology has been implemented in sintering, joining and coating/cladding with metal powders. After getting the tremendous advantages in material properties as well as economy, the domain has been extended towards the melting of metal powder and to cast the metal matrix composite castings. None of the material fulfils all its requirements for specific application/purpose. So, to make it perfect for different applications, the two materials are added so that the combined advantages of two materials can be obtained and known as metal matrix composites castings. One of the comm on ex ampl e of MMC ’ s are copper-graphite composites, in which copper provides excellent electrical and thermal conductivity and graphite acts as solid lubricant and have lower coefficient of thermal expansion. These composites are widely used in electrical appliances, generator bushes, bearing materials etc. because of excellent properties of graphite and selflubrication due to graphite content. In this dissertation report, Cu-graphite composite castings have been developed through Microwave Hybrid Heating (MHH) technique. In this dissertation, Copper-graphite MMCs were fabricated by mixing 2 and 5wt. % graphite, into copper powder followed by microwave processing route and compared with the cast of pure copper through same processing route. In the characterization phase, XRD spectra showed the presence of Cu and carbon in the form of graphite. The smaller peaks showed the formation of oxides with the copper but the lesser amount of oxides helped to increase the hardness of composites. The maximum Vickers micro-hardness value of around 85 Hv has been achieved for Cu-5wt% graphite composite castings and it was around 75 Hv for 2wt% graphite composite castings, which is comparatively higher than pure copper. The micrographs of Cu-graphite shows that graphite particles are uniformly distributed into copper matrix. From wear study, it is concluded that the wear resistance of the composite increases with increase in graphite content due to the lubricating properties of graphite and decrease in wear rate with addition of graphite is also calculated.