|Abstract: ||耐火金屬膠結熔融碳化物，是指碳化物與耐火金屬藉熔融方法，將兩者膠結在一起而得之複材，所以稱為Refractory Metal-Cemented Fused Carbides；有別於傳統主要以鈷或鎳為金屬膠結物，藉液相燒結而成的燒結碳化物(Cemented Carbides)。因此，本研究，著重在選擇適當的碳與氮化物硬化相(TiC, ZrC, NbC, VC, TaC, WC, HfC, TiN, ZrN)與耐火金屬膠結相(Mo, W, Nb)，試驗各種可能的組合，目標為得到熔點超過攝氏2500度，與硬度超過1700 HV的瓷金複材，並使用熔融方式，將硬化相與膠結相兩者，進行結合，克服傳統燒結製程上，緻密度低以及成本高的問題，製造出具備高硬度、高熔點和高韌性的複材。與以往燒結瓷金複材比較，高熔點與100 %緻密度，是其中兩個最重要的訴求點。|
Refractory metal-cemented fused carbides are fused multi-carbides cemented with multi-refractory metals. These fused composites, which are different from the conventional Co- or Ni-cemented sintered carbides, are made of high-melting-point components making their solidus temperatures be high enough for applications at elevated temperature. This study emphasizes to select a proper combination of carbide and nitride hard phase from TiC, ZrC, NbC, VC, TaC, WC, HfC, TiN, and ZrN, and refractory metal binding phase from Mo, W, and Nb, and, as a goal, to obtain cermet composites with solidus temperature of above 2500oC and hardness above HV 1700. Since in this study the components are fused by arc-melting, it can overcome the shortcoming of the sintered products such as densification and cost problems to have products with high hardness and high toughness. It is the high solidus temperature and the 100 % densification that are stressed in this study.
This study proposes to use arc melting in vacuum, a process of higher than 3500oC, to melt less- and multi-component equal- and non-equal-molar composites. Although the cast structure being the coarser dendrite-interdendrite is contrary to the submicron size in sintering process, the melting supplies a rapid and convenient process, and obtains 100 % density product that has good hardness and good toughness. The merits are as good as conventional sintering has, or even better. At present the composites are made of W-based or Nb-based with less or larger number of carbides. Among them, the W-based has excellent room-temperature and elevated temperature hardness. However, in order to diversifying research, a series of Mo-based composites is selected in this study.
Although the Mo-cemented less-number carbides have lower room and elevated temperature hardness than that of the W-cemented counterparts, the multi-carbide Mo-cemented composites are with the same level of hardness, but with better toughness, as compared to their W-cemented counterparts.
Recently, cermet composite applications, such as parts for oil exploitation facility and parts for logging, have been emphasized on improved anti-wear and tool life to cost down their commercial run. Accordingly, in this study the pin-on-belt abrasion test that is under a 3-kgf load has been performed and showing a high resistance of wear of higher than 30 m/mm3. Thermal conductivity and electrical resistivity for less- and multi-component composites, respectively, are comparable. It is expected that in the near future by means of multi-carbide addition with precise content adjustment the Mo-cemented fused multi-carbides will have a much better performance in their mechanical properties.