Spark plasma sintering processed α-SiAlON bonded tungsten carbide: Densification, microstructure and tribomechanical properties

Processing, microstructure and tribomechanical performance of spark plasma sintering (SPS) processed alpha-SiAlON bonded tungsten carbide (WC) have been reported. SPS at 1750 degrees C under 40 MPa for 25 min resulted in almost theoretically dense composites. Microstructure analysis using scanning and transmission electron microscopy revealed formation of principally micron sized, equiaxed WC grains surrounded by sub-micron to micron sized alpha-SiAlON having both equiaxed (higher concentration) and elongated (lower concentration) grain morphology. Sharp and clean WC/alpha-SiAlON interface regions were noticed without any interfacial reaction product. As evidenced from elemental mapping under HAADF-STEM, the alpha-SiAlON grain boundary region was found to be rich in yttrium and oxygen, whereas, presence of characteristics elements were identified in alpha-SiAlON and WC grains. Addition of alpha-SiAlON in WC matrix resulted in progressive improvement in tribomechanical performance of the composites compared to pure WC. The 40 wt% alpha-SiAlON bonded WC matrix composite offered almost 30-33% higher Vickers hardness and toughness than those obtained for pure WC. Three point flexural strength of the 40 wt% alpha-SiAlON/WC composite was found to be around 425 MPa. Unlubricated wear tests also indicated significantly higher damage of hard and tough beta-Si3N4 ball when sliding against the composites compared to pure WC. Formation of progressively thicker and adherent tribolayer containing broken particles of WC and alpha-SiAlON having sharp edges was possibly the primary reason that caused severe abrasive wear of the counterbody. Results indicated the efficacy of SPS processed alpha-SiAlON bonded WC composites having improved tribomechanical performance over conventional monolithic WC.