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为弄清合金致密化行为,研究了钨粉平均粒度为1μm与5μm的两种98W—1Ni—1Fe和压坯试样在加热和液相烧结期间的松装密度和显微结构的变化情况。研究表明,平均粒度为1μm的细小钨粉压坯试样,加热到固相阶段约1200℃就开始快速致密,当加热到1460℃的液相烧结温度时,压坯密度可达95％;平均粒度为5μm的钨粉压坯是在固相阶段约1400℃才开始快速致密,当加热到液相烧结温度时,压坯密度达87％。这就是说,在液相出现前就已形成颗粒骨架。在等温液相烧结时,晶粒明显长大,液相流向开孔及闭孔处并从较小截面的孔隙区域开始先后充填这些孔隙。然后,晶粒向孔隙部位出现的液相聚集区长大。因此,先析液相依次充填孔隙可认为是该类合金在液相烧结时起主导作用的致密化过程。这一结论已为早期用模拟球状孔隙进行的研究所证实,并和理论计算相一致。
In order to understand the densification behavior of the alloys, the bulk density and microstructure of two 98W-1Ni-1Fe and compact samples with average particle size of 1μm and 5μm of tungsten powder during heating and liquid phase sintering were studied. The results show that the compact tungsten powder compact sample with an average particle size of 1μm starts to compact rapidly when heated to about 1200 ℃ in the solid phase. When heated to the liquidus sintering temperature of 1460 ℃, the compact density can reach 95% Tungsten powder compacts with a particle size of 5 μm started rapid compacting at about 1400 ° C in the solid phase and reached a compact density of 87% when heated to the liquid phase sintering temperature. This means that the particle skeleton has been formed before the liquid phase occurs. During isothermal liquid phase sintering, the grains grow significantly, the liquid phase flows toward the open and closed cells, and these pores are filled one after the other from the smaller cross-section. Then, the grains grow up in the liquid-phase aggregation zone appearing at the pore site. Therefore, the first analysis of the liquid phase followed by filling the pores can be considered as such alloys play a dominant role in the liquid phase sintering densification process. This conclusion has been confirmed by earlier studies using simulated spherical pores and is consistent with theoretical calculations.