Abstract
The study is an investigation on high-temperature fused composites (HTFCs) formed by metal borides and metal carbides cemented with refractory metal binders (RMBs) according to agenda as follows:1. The optimal combination ratio of cemented phase (species and doses) in boride-based HTFCs.2. The optimal RMB in boride-based HTFCs.3. Composites of 1-component boride and 1-component carbide cemented with Mo.Conventional cemented carbides (CCs) were first patented by Schroter in 1923. The patent claimed on cementing carbides, such as, WC, TiC and TaC with Co, Ni and Fe in liquid phase sinter (LPS) to produce composites equipped with high hardness of carbides and high toughness of metal binders. Nevertheless, due to the lack of densification in the LPS process, the mechanical properties and utility of the cemented carbides resulted are lower than the expectation. In order to create CCs with high density, high hardness, high toughness and high melting point (mp), this study employs refractory metals to substitute the low mp metal binders, as well as a vacuum melting process for manufacturing.From the perspectives of high strength, high mp and cost effectiveness, the study chooses TiB2 and ZrB2 as the base for borides. In addition, interstitial carbides of high strength and high mp, such as, TiC, ZrC, HfC, VC, NbC, TaC and WC, are employed as carbide candidates. Through various combinations of species and doses, two series of composites are resulted for the study, and they are: “boride only” and “boride and carbide both”. These composites are analyzed on their hardness, toughness, microstructure, abrasion resistance and hardness at elevated temperatures.HTFCs of this study show typical solidified dendritic and interdendritic structures. Precipitates of phases are determined by the combined enthalpy of relevant phases. The range of hardness is observed between 900 and 2100 HV, while the fracture toughness (KIC) varies from 5 to 13 MPa m1/2. In the pin-on-belt abrasion resistance test against Al2O3 belt, a high value of 84.8 m/mm3 under 6 kgf load is obtained, which is lower than 135.7 m/mm3 of commercial WC-Co sample using the same test. The abrasion resistance of composites is proportional to their hardness, and it relates to phase wettability in the microstructure as well. At 1100 °C, composites of the study impart hardness from 800 to 1400 HV. Furthermore, the composites exhibit two advantages over the commercial WC-Co:1. Hardness decline with temperature elevation is smaller than that of commercial carbide, and2. Hardness at elevated temperatures is higher than that of commercial counterpart.The 1100 °C-hardness of composites in this study renders them a suitable tool material for heavy-duty applications.