采用放电等离子烧结(SPS)和超高压力通电烧结(RSUHP)2种快速烧结新方法,对纳米钨粉的致密化行为进行研究.结果表明,采用SPS工艺于1600℃下烧结可获得烧结颗粒结合良好,致密度达97.8%的试样,但晶粒粗化明显;而采用RSUHP方法获得的试样,烧结过程中晶粒几乎不长大,但致密度较低,颗粒间结合较差.将2种方法结合,充分利用SPS的清洁效应和RSUHP的晶粒细化效果,先用SPS在1400℃下预烧结,再由RSUHP二次烧结完成最终致密化,获得平均晶粒尺寸小于400 nm,相对密度大于99%的超细晶粒的钨块体材料.烧结过程无需添加任何晶粒长大抑制剂.
Pure tungsten with ultra-fine grains has been fabricated by two novel sintering methods, namely spark plasma sintering (SPS) and resistance sintering under ultra high pressure (RSUHP). The sample fabricated by SPS at 1600 ℃ has a high density of 97.8% and tightly bound grains. However, during the SPS process the W grains obviously grew. On the contrary, the sample fabricated by RSUHP has a low density and weakly bound fine grains. The disadvantages in both the techniques can be avoided via combining the two methods by fabricating green compacts using SPS at 1400 ℃ followed by consolidating that by RSUHP. By employing the combined method, the product with a relative density of more than 99% and an average grain size less than 400 nm can be obtained. The consolidating mechanism has been explored and the process has been optimized. In addition, any rare earth metal element additives to prevent grains from growing are not needed during the sintering process.
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