鉬膠結熔融碳化物研究

Mo-Cemented Fused Carbides

林伯澔(Po-Hau Lin)

指導教授 ： 陳瑞凱 ； 吳振名

國立清華大學/工學院/材料科學工程學系/碩士(2014年)

摘要

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。
本研究提出了，使用以超過攝氏3500度的真空電弧熔煉，製造多元與少元、等莫爾與非等莫爾「熔煉瓷金」。雖然得到了由較粗大之「樹枝晶」與「樹枝間晶」組成的複合結構，與燒結製程所追求的次微米尺度結構恰好相反；但整體製程，快速、方便，且得出緻密度100 %，以及擁有不錯之硬度、韌性之熔融複材，這些優點，皆足以與傳統燒結複材媲美，甚或大大超越。
目前研究的熔融瓷金複材，由鎢或鉬膠結相，搭配碳化物所組成。其中「鎢膠結熔融碳化物」，擁有良好的常溫與高溫硬度表現，也就是說，在高溫時，強度不會下降太多；為了達到熔融碳化物研究的多元化的目的，「鉬膠結熔融碳化物」被選為本研究的主題。雖然少元鉬膠結瓷金和少元鎢膠結瓷金相比，室溫及高溫硬度，表現較差，但是經由強化相多元添加後，其硬度表現可有相同水準，並且韌性表現甚至更佳，也就是，複材不易有脆裂的情況。除了高硬度、高韌性之外，近年來，瓷金複材的相關應用，如石油鑽油設備，或伐木工具等的工件，以改善磨耗，增進使用壽命，降低營運成本的研究，已陸續地出現。因此，本材料也進行了磨耗測試的量測，並初步發現，擁有3公斤荷重之Pin-on-Belt磨耗，超過30 m/mm3的良好表現。多元複材與少元複材的導熱與導電性質相當。期望在未來，可以透過多元碳化物更縝密的調配變量，進一步提升瓷金各種機械性質的表現。

關鍵字

鉬 ； 碳化物 ； 高溫硬度 ； 擦損磨耗 ； 真空電弧熔煉

並列摘要

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.

參考文獻

[1] H.O. Pierson, Handbook of Refractory Carbides and Nitrides, 1st ed., William Andrew Publishing, Westwood, NJ, 1 (1996).

[4] W. Stevenson, Metals Handbook, 9th ed., ASM, Ohio, 773 (1985).

[5] Fabrication, Microstructures, Properties and Applications of W/(TiC, ZrC) Composites, http://wmrif.bam.de/wp-content/wmrif_uploads/Presentation-Prof.-Y.-Zhou1.pdf.

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[7] G. Zhu, Y. Liu and J. Ye, Early High-Temperature Oxidation Behavior of Ti(C,N)-Based Cermets with Multi-Component AlCoCrFenNi High-Entropy Alloy Binder, International Journal of Refractory Metals and Hard Materials, 44, 35-41 (2014).