Synergistic mechanisms of fly ash reinforcement on the mechanical characteristics, deformation behaviour, grain refinement, and grain boundary in friction stir processed copper matrix composites

: Fly ash is an attractive reinforcement for copper and its alloys. It is a by-product produced from the combustion of coal in thermal power plant. This solid waste produced massively across the globe is considered as a serious threat to the environment. Researchers across the globes are looking for its utilization. Copper matrix composites reinforced with fly ash instead of costly hard ceramics are one of those applications. However, it is technically challenging to incorporate fly ash in copper matrix uniformly and homogeneously via liquid-based processing techniques due to large density gradient. In the present study, efforts are being put to fabricate fly ash reinforced copper matrix composites by friction stir processing (FSP) and analyze its performance for microstructure and mechanical properties. Microstructural features were depicted by optical microscopy, scanning electron microscope and electron backscattered diffraction across cross-section. Hardness was observed across cross-section of the processed plate for plotting hardness profile. Tensile test was conducted on base and processed plate for strength. The composite exhibited uniform and homogeneous sputtering of fly ash particles in the copper matrix without agglomeration of particles irrespective of the position in stir zone which may be attributed to the solid state nature of the process. No disturbance in terms of voids or irregularities was detected at the interface which shows excellent integrity at the interface. Substantial grain refinement for the copper matrix along with fracture of the reinforced fly ash was observed. It was also observed that the hardness and tensile strength of the composite improved but ductility decreased. The mechanism responsible for hardness and strength improvement may be attributed to grain refinement and uniform dispersion of fly ash particles. Reduced ductility may be due to the presence of fly ash particles which brought brittleness to the composite.