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摘要: 以碳熱預還原和氫氣深還原兩步制備的納米鎢粉作為燒結原料，即先通過碳黑還原脫除三氧化鎢中的大部分氧，再以氫還原脫除殘留的氧。該方法制備的鎢粉顆粒呈球形形貌，平均晶粒度可達90 nm。同時，向鎢粉中摻雜質量分數為1%和2%的氧化鋁，探究了氧化鋁對鎢粉燒結行為的影響。通過燒結樣品的斷口形貌和晶粒的平均尺寸分析發現，氧化鋁對燒結后期的晶粒長大有明顯的抑制作用，相同的燒結溫度下晶粒的尺寸隨著氧化鋁含量的上升而減小。在1600 ℃時，純鎢粉燒結坯的晶粒平均尺寸為2.75 μm，但添加質量分數為1%和2%氧化鋁的燒結樣品晶粒平均尺寸約為1.5 μm，這是由于氧化鋁能有效地抑制燒結后期的鎢粉晶粒長大。純鎢粉和摻雜氧化鋁鎢粉的燒結坯的硬度隨溫度升高具有不同的趨勢。摻雜鎢粉燒結坯的硬度隨著溫度的升高而升高，且其最大值高于800 HV。但是，純鎢粉燒結坯的硬度隨燒結溫度增加而先增加后降低，在1400 ℃時取得最大值（473.6 HV），這是由純鎢粉燒結坯的晶粒在高溫下急劇長大所導致。在燒結溫度為1600 ℃時，純鎢粉、摻雜質量分數1%和2%的氧化鋁摻雜的鎢粉的燒結坯的相對密度依次為98.52%、95.43%和93.5%。Abstract: A two-step reduction method was used to synthesize nano tungsten powder via carbothermic pre-reduction of tungsten oxide, followed by a deep hydrogen reduction. In this process, carbon black first reduced most of the oxygen in tungsten trioxide, while the residual oxygen was removed by hydrogen reduction. The tungsten powder prepared by the two-step reduction method had a spherical shape with an average grain size of 90 nm. Simultaneously, tungsten powders doped with 1% and 2% alumina (mass fraction) were similarly prepared to study the effect of alumina on its sintering behavior. Analysis of fracture morphologies and average grain size of sintered samples showed that alumina significantly inhibited grain growth at the final sintering stage and grain size decreased at the same sintering temperature with an increase in the alumina content. At 1600 ℃, the average grain size of sintered sample of pure tungsten was approximately 2.75 μm, but it was about 1.5 μm for the sintered samples doped with 1% and 2% alumina. This finding could be based on the fact that tungsten grain growth in the final stage of sintering can be effectively inhibited by alumina particles. The sintered pure tungsten powder and alumina doped tungsten powders had different hardness variation levels with temperature increase. The hardness of the sintered sample doped with alumina has always increased with temperature increases, reaching a maximum value above 800 HV. As for the sintered sample of pure tungsten, the hardness first increased and then decreased with temperature increase, reached its maximum value of 473.6 HV at 1400 °C that was caused by the rapid growth of grain size of tungsten at higher temperatures. At a sintering temperature of 1600 ℃, the relative density of the pure tungsten powder was 98.52%, while that of the tungsten powder doped with 1% and 2% alumina were 95.43% and 93.5%, respectively.
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Key words:
- sintering /
- carbothermic reduction /
- tungsten nano powder /
- alumina /
- hardness /
- relative density
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圖 1 原料的微觀形貌圖。（a）WO3；（b）炭黑
Figure 1. Micrograph of raw materials: (a) WO3; (b) carbon black
圖 2 碳熱還原后前體的X射線衍射圖
Figure 2. X-ray diffraction patterns of products after carbothermic reduction
圖 3 氫氣還原后的粉體的X射線衍射圖。（a）W-0.01；（b）W-0.02；（c）NW
Figure 3. X-ray diffraction patterns of products after hydrogen reduction: (a) W-0.01; (b) W-0.02; (c) NW
圖 4 三種鎢粉的相對密度與燒結溫度的關系圖
Figure 4. Variation of relative density of the three kinds of compacts as the function of sintering temperature
圖 5 三種鎢粉在不同溫度下的斷口形貌。（a）1200 ℃；（b）1300 ℃；（c）1400 ℃；（d）1500 ℃；（e）1600 ℃
Figure 5. Fracture morphologies of the three kinds of W bulk materials at different sintering temperatures: (a) 1200 ℃; (b) 1300 ℃; (c) 1400 ℃; (d) 1500 ℃; (e) 1600 ℃
圖 6 三種燒結坯的晶粒尺寸與溫度的關系
Figure 6. Grain size vs sintering temperature in the three kinds of sintered compacts
圖 7 三種鎢粉的硬度與燒結溫度的關系
Figure 7. Change in microhardness with sintering temperature of the three kinds of sintered compacts
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