以平均粒径为150, 75, 48和38 μm的4种Ti粉为原料(依次定义为A, B, C和D粉末), 采用高速压制技术进行成形, 考察粉末粒径对压坯密度、最大压制力和脱模力的影响, 进一步研究粉末的高速压制特性和压坯的烧结性能. 结果表明, 高速压制的压坯密度与粉末粒径和松装密度有关. 冲击能量较小时, 压坯密度主要取决于松装密度, 而冲击能量较高时, 则主要取决于粉末粒径. 在冲击能量≦761 J下成形时, 具有最大松装密度的B粉末所获得的压坯密度最高; 进一步增大冲击能量, 平均粒径最大的A粉末所获得的压坯密度最高. 粉末粒径对压坯密度和最大压制力具有相似的影响, 并且4种粉末的最大压制力和压坯密度之间的关系均符合黄培云压制方程; 但粉末粒径对脱模力无明显影响. 试样的烧结密度随粒径的细化而增加, 同时伴随着不同程度的晶粒长大. 4种压坯经1250 ℃真空烧结后, 最终均获得了近全致密的试样.
The Ti powder forming is more difficult through traditional pressing methods due to inductile and high hardening rate of Ti. Some advanced forming methods, although, are effective for increasing the green density, such as hot--pressing and isothermal--statistic pressing, they are too expensive. In our previous research, it has been demonstrated that compacting high green density of Ti powders would be achieved by high velocity compaction (HVC) which seems to be an attractive candidate that has an excellent balance between performance and cost in forming Ti powders. In this paper, the four Ti powders with average particle size of 150, 75, 48 and 38 μm, namely A, B, C, and D powder, were separately pressed by HVC technology. The influences of particle size on the green density, the maximum impact force and withdraw force in compacting were investigated. The compactability features of the four powders in HVC and the properties of sintered samples were studied. The results show that the green density of compacts obtained by HVC method is related with both particle size and apparent density. At relatively small impact energy, the green density of compacts is mainly determined by the apparent density of powders. While at larger impact energy, it is mainly determined by the particle size. For powders pressed at impact energy lower than 761 J, the highest green density is obtained for compacts made of B powders which has maximum apparent density. With higher impact energy, the highest green density is obtained for compacts made of A powder which has maximum particle size. It is found that the influence of particle size on the maximum impact force is similar to those on the green density, and for the four powders the relationships between the maximum impact force and the green density all comply with Huang Pei-yun equation. Particle size shows no observable influence on withdraw force. The sintered density increases with decreasing particle size of powders, accompanying with grain growth of different degrees. After vacuum sintering at 1250 ℃, nearly fully dense samples can be prepared for the compacts of four powders.
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