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

Abstract

Processing, microstructure and tribomechanical performance of spark plasma sintering (SPS) processed α−SiAlON bonded tungsten carbide (WC) have been reported. SPS at 1750 °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 α−SiAlON having both equiaxed (higher concentration) and elongated (lower concentration) grain morphology. Sharp and clean WC/α−SiAlON interface regions were noticed without any interfacial reaction product. As evidenced from elemental mapping under HAADF-STEM, the α−SiAlON grain boundary region was found to be rich in yttrium and oxygen, whereas, presence of characteristics elements were identified in α−SiAlON and WC grains. Addition of α−SiAlON in WC matrix resulted in progressive improvement in tribomechanical performance of the composites compared to pure WC. The 40 wt% α−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% α−SiAlON/WC composite was found to be around 425 MPa. Unlubricated wear tests also indicated significantly higher damage of hard and tough β−Si3N4 ball when sliding against the composites compared to pure WC. Formation of progressively thicker and adherent tribolayer containing broken particles of WC and α−SiAlON having sharp edges was possibly the primary reason that caused severe abrasive wear of the counterbody. Results indicated the efficacy of SPS processed α−SiAlON bonded WC composites having improved tribomechanical performance over conventional monolithic WC.