纳米级超细晶粒硬质合金烧结收缩动力学曲线特征的研究

CHARACTERISTICS OF THE SINTERING SHRINKAGE DYNAMIC CURVES OF CEMENTED CARBIDE ALLOYS WITH NANO-METER CRYSTALLINE

利用高温膨胀仪在氢气气氛下首次测定和研究了WC (Ni·Fe) 8%、WC VC (Ni·Fe) 8%纳米级超细晶粒 (WC平均晶粒 2 0 0～ 30 0nm)硬质合金与常规细颗粒 (WC平均晶粒≤ 1 5μm)硬质合金压坯在烧结过程中的膨胀收缩动力学曲线特征、起始收缩温度、剧烈收缩温度随温度变化的收缩速率与WC粉的总碳含量、WC粉的平均粒径以及压坯密度的关系。结果发现 ,超细晶粒硬质合金 (WC粉总碳 6 0 1% )在烧结过程中物理膨胀现象较弱 ,开始收缩温度与剧烈收缩温度均较低 ,分别为 80 0℃ ,1150℃ ,最大收缩速率高达 10 50× 10 -6mm ℃ ,常规细晶粒合金的物理膨胀严重 ,在 62 0～ 130 0℃范围内相对膨胀 1 7% ,开始收缩温度与剧烈收缩温度分别为 132 0℃和 1390℃ ,最大收缩速率为 60 0× 10 -6mm ℃ ,远低于纳米级超细晶粒合金。WC粉总碳含量增加 ,合金的开始收缩温度及剧烈收缩温度均明显降低。压坯密度提高 ,合金的最终收缩率降低。在压坯密度一定的情况下 ,随着烧结温度提高 ,合金收缩率增加。

Utilizing high temperature dilatometer,at the atmosphere of H 2,we have determined and analyzed the characteristics of the expansive and shrinking dynamic curves of the compacts produced from nano meter crystallined hard alloy powders(average grain diameter of WC:200～300nm)and the conventional ultrafine powders(average grain diameter of WC:≤1 5μm)in the system of WC (Ni·Fe)8% and WC VC (Ni·Fe)8%.The starting shrinking temperature,drastically shrinking temperature,and the relationship between the shrinking rate,total carbon content of the powder,the average grain diameter of WC and the density of the corresponding compact were also investigated.The experimental results indicated that the sintering physical expansion was less significant in the ultrafine grained hard metals in nanometer order.And the initial and drastic shrinking temperatures of the alloys with nanometer grains were 800℃ and 1150℃ respectively,relatively lower.Their maximum shrinking rate was up to 1050×10 -6 mm/℃.In contrast,the sintering physical expansion was significant in the conventional grained hard metals with the relative expansion of 1.7% in the temperature range of 620～1300℃.And the initial and drastic shrinking temperatures of the conventional alloys were 1320℃ and 1390℃,respectively.Their maximum shrinking rate was 600×10 -6 mm/℃,much lower than that of the nanometer grained alloys.When the total amount of carbon content of WC powders increased,both the initial and the drastic shrinking temperatures for nanometer grained alloys decreased significantly,and the final shrinkage of the alloys decreased accordingly.However,their compact density increased.When the compact density was kept constant,the sintering shrinkage of the nanometer grained alloys increased with the increasing of the sintering temperature.