掺杂氧化铝对纳米钨粉烧结过程的影响

以碳热预还原和氢气深还原两步制备的纳米钨粉作为烧结原料，即先通过碳黑还原脱除三氧化钨中的大部分氧，再以氢还原脱除残留的氧。该方法制备的钨粉颗粒呈球形形貌，平均晶粒度可达90 nm。同时，向钨粉中掺杂质量分数为1%和2%的氧化铝，探究了氧化铝对钨粉烧结行为的影响。通过烧结样品的断口形貌和晶粒的平均尺寸分析发现，氧化铝对烧结后期的晶粒长大有明显的抑制作用，相同的烧结温度下晶粒的尺寸随着氧化铝含量的上升而减小。在1600 ℃时，纯钨粉烧结坯的晶粒平均尺寸为2.75 μm，但添加质量分数为1%和2%氧化铝的烧结样品晶粒平均尺寸约为1.5 μm，这是由于氧化铝能有效地抑制烧结后期的钨粉晶粒长大。纯钨粉和掺杂氧化铝钨粉的烧结坯的硬度随温度升高具有不同的趋势。掺杂钨粉烧结坯的硬度随着温度的升高而升高，且其最大值高于800 HV。但是，纯钨粉烧结坯的硬度随烧结温度增加而先增加后降低，在1400 ℃时取得最大值（473.6 HV），这是由纯钨粉烧结坯的晶粒在高温下急剧长大所导致。在烧结温度为1600 ℃时，纯钨粉、掺杂质量分数1%和2%的氧化铝掺杂的钨粉的烧结坯的相对密度依次为98.52%、95.43%和93.5%。 

Effect of Al2O3 addition on the sintering behavior of nano tungsten powder

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.