| Summary: | 碩士 === 國立臺灣大學 === 材料科學與工程學研究所 === 87 === The sintering temperature of molybdenum is usually greater than 1700℃. Although it has been postulated that lower sintering temperature can be achieved through the activated sintering technique by adding a small quantity of nickel, palladium or cobalt, the brittleness of such sintered molybdenum has prevent it from being accepted by the industry. The purpose of this study was to find out the cause of the brittleness of activated sintered molybdenum.
In the experiment, pure molybdenum powders were compacted and then sintered at 1750℃ in vacuum in order to evaluate the effect of sintering time and atmosphere on the post-sintered properties. After selecting the adequate parameters, molybdenum compacts with different contents of nickel powder additives were sintered at 1300℃ (activated sintering) and 1370℃ (liquid phase sintering), respectively, in order to understand the mechanism of enhanced sintering and to find out the causes of brittleness.
The results showed that, for vacuum sintering, 5-hour sintering gave fine grain size but with poor ductility compared to those with 10-hour sintering. The phenomenon was caused by different oxygen contents in the sintered compacts, which decreased as the sintering time increased.
For activated sintering and liquid phase sintering, it was found that a layer MoNi existed in the grain boundaries of sintered compacts. This intermetallic compound is hard and brittle and leads to the brittle behavior of the sintered compact.
It was also found that when 33.3% of Ni was replaced by Cu, Mo-1%Ni-0.5%Cu for example, the relative sintered density increased from 95.3% to 99% for activated sintering.
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