Optimization of mechanical properties of cemented carbide: influence of grain size, cobalt content, and grain growth inhibitors

• Main Authors: Jiunn-Cherng Su, 舒圳晟
• Other Authors: Yee-Wen Yen
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/72987828195677809766

碩士 === 國立臺灣科技大學 === 材料科學與工程系 === 105 === Tungsten carbide particles are difficult to joint to each other if there are no intermedia in between. Researchers have found that cobalt’s liquid phase has ability to reinforce the microstructure of tungsten carbide. Thereby, the most widely used tungsten carbide rods usually contain 10wt% of cobalt. This composition has characteristic of high wear-resistance, high impact strength, and high tolerance of chipping because the amount of cobalt provides sufficient toughness and tungsten carbide grains maintain the hardness. Tungsten carbide plays an important role in terms of industrial development. However, commonly used solid tool blanks with 10wt% cobalt is not suitable for all kinds of tasks, since end user’s working environment is becoming more and more difficult with rising industrial requirements, especially in the aerospace industry. Therefore, researchers tend to satisfy the working condition by means of promoting mechanical properties which are governed obviously by grains size of tungsten carbide and the proportion of cobalt. Generally, tungsten carbide’s toughness and hardness are inversely proportional to each other if we merely alter those two parameters mentioned above. According to articles, carbon content indeed influences mechanical properties a lot due to percentages of carburization and wetting angle during sintering process. Therefore, carbon balance control is a crucial factor all over the processes. Wear resistance would greatly reduce if carbon content is over the limit, while insufficiency in carbon content will lead to brittleness and shorten tool’s life time. Tungsten carbide products are often used in the environment with high risks. If the quality is not stable, it is impossible to ensure the security to user and even harmful for the machines where the products being installed in. Through the cooperation of National Taiwan University of Science and Technology(NTUST) and CB-CERATIZIT group(CBCT), experiments have been conducted mainly on the influences of mechanical properties and microstructure of tungsten carbide after doping with varied amount of cubic carbide, such as chromium carbide and vanadium carbide. In order to achieve further improvements, other researchers have started to dope different kinds of carbides, such as titanium carbide, chromium carbide, tantalum carbide, vanadium carbide, etc. Taking the advantage of chemical interaction between those carbides and tungsten carbide or cobalt, people have been trying to enhance mechanical properties of tungsten carbide and pushing the boundary in various applications.