Abstract
Super high temperature fused carbide-refractory metal composites in this study are arc-melted carbides and refractory metals (RMs) together and are solidified to form the so-called “refractory metal fused carbides” (RMFCs). Compared with the conventional liquid phase sintered carbides that possess lower melting point such as in the component Co or Ni, bulk RMFCs have the properties of high solidus temperature, high hardness, and high toughness. This study adopts refractory metals, such as Mo, W, Ta, and Re, and transition metal interstitial carbides, such as TiC, ZrC, HfC, VC, NbC, TaC, and WC to form RMFCs of one to two RMs and one to four carbides with different proportions and to investigate ambient- and elevated-temperature hardness, toughness, wear resistance, corrosion resistance, and electrical resistivity. By the assistant analyses of SEM, XRD, and EPMA, RMFCs are hoped to have excellent properties in elevated temperature hardness, toughness, wear resistance, and corrosion resistance. Microstructure of RMFCs is a typical melted and solidified dendrite-interdendrite structure. Their ambient hardness and toughness fall in between 800 HV to 2100 HV and 2.7 MPa m1/2 to 15.2 MPa m1/2, respectively. In order to understand the effect of the individual presence of various carbides on RMFCs, this study firstly uses Mo as a binder. It is observed that Mo-TiC, Mo-ZrC, and Mo-HfC have appearance of MC; Mo-VC and Mo-WC appearance of M2C; and Mo-NbC and Mo-TaC appearance of both MC and M2C. Another important conclusion is that there is a good combination of hardness and toughness in duplex MC-M2C-containing Mo-NbC and Mo-TaC. When both Re and W are used as binders, there is an intermetallic Re3W that results in rapid increase in hardness and obviously decrease in toughness of the composites. When both Ta and W are binders, twin morphology appears in microstructure till the content of W being higher. The pin-on-belt abrasion test of 6 kg loading with Al2O3 belt shows that with nearly the same hardness and toughness W-cardide composites have two times of abrasion resistance higher than that of Mo-cardide composites. Thus both W and Mo are used to supply more strength and hardness of RMFCs. The study in the cases of Re- and Ta-containing composite systems is in the same way as in the case of Mo-bearing system. In dry and heavy turning test the composites in this study is much better than commercial WC-Co. This result significantly appears the superior property in turning at high temperatures. The corrosion resistance of the composites in 3.5 wt% NaCl sea water like aqueous solution is also superior to that of commercial WC-Co. Hardness at 1100oC in RMFCs falls in between 680 HV and 1200 HV; it is better than that of conventional hardmetals. Note that the relative density of bulk RMFCs is 100%. RMFCs have better elevated temperature mechanical properties than the conventional sintered hardmetals. This makes it suitable for applications in cement and metal industries for hardfacing rolls, high temperature parts in reactors, and refractory materials of rockets and turbine engines. Note that the degrees of freedom in designing RMFCs for different applications are also large.