Effect of Y₂O₃ content on microstructure, mechanical properties, and corrosion resistance of WC-Co hard alloys prepared by powder metallurgy

Abstract

The content of additive Y has a significant impact on the microstructure and mechanical properties of sintered cemented carbides prepared via powder metallurgy. However, the effects of Y content on the properties of cemented carbides remain poorly understood. This study investigates the effect of the content of Y₂O₃, introduced via a spray phase transformation process, on the microstructure, mechanical properties, and corrosion resistance of the WC-Co cemented carbide, to advance knowledge in this field. An ultrafine Co-based composite powder containing Y₂O₃ was synthesised using WC, (CH₃COO)₂Co·4 H₂O, and Y(C₂H₃O₂)₃·4 H₂O. The powder was prepared via spray conversion, calcination, oxidation, and low-temperature reduction. The WC-8Co-Y₂O₃ cemented carbide was fabricated through high-energy ball milling and spark plasma sintering to ensure the uniform distribution of the Co bonding phase. The spray transformation process produced irregular amorphous precursor powders containing Co and Y. After calcination, the powders exhibited a reduction in particle size and underwent agglomeration. The ball milling of the WC-8Co-Y₂O₃ composite powder with added WC further reduced the particle size and intensified agglomeration. An increase in the Y₂O₃ content resulted in grain refinement and an increase in the number of WC/Co grain boundaries, thereby improving the corrosion resistance of the alloy. The mechanical properties of the alloys exhibited a trend in which the density, Vickers hardness, and fracture toughness initially increased and then decreased with increasing Y₂O₃ content. At 1.5 wt% Y₂O₃, these properties reached their maximum values, achieving a relative density of 98.94 %, a Vickers hardness of 2034 HV30, and a fracture toughness of 8.39 MPa·m^1/2. The alloy also exhibited optimal corrosion resistance, with E_corr and i_corr values of −252 mV and 6.464 μA/cm², respectively. The presence of Y₂O₃ promoted the formation of an ultrafine Co phase, which mitigated dislocation motion, thereby enhancing the mechanical performance of the cemented carbide. These findings contribute to a comprehensive understanding of the contribution of Y to the properties of cemented carbides.