二阶段热压烧结工艺对WC-MgO复合材料组织和力学性能的影响

摘要

二阶段烧结是一种通过控制烧结温度变化以实现烧结样品致密化过程中抑制晶粒长大的烧结方法.以高能球磨法制备的纳米WC-MgO复合粉末为原料,并采用二阶段热压烧结法制备WC-MgO复合材料.研究二阶段热压烧结对烧结块体的致密度、晶粒大小和力学性能的影响,优化二阶段烧结中第一阶段温度小第二阶段温度t2及保温时间θ等工艺参数,采用XRD和SEM对复合材料的组织形貌进行表征.结果表明:当t1为1 750℃,t2为1 550℃时能使WC-MgO复合材料的致密度达到99％(理论密度),基体WC晶粒大小为2.59 μm,WC-MgO复合材料的维氏硬度提高到(18.4±0.5) GPa,WC-MgO复合材料的断裂韧性提升至(12.95-0.5) MPa·m1/2,WC-MgO复合材料的抗弯强度提高至(1 283.7±126.6) MPa.%Two-step hot-pressing sintering (TSS) was applied to consolidate nanocomposite tungsten carbide-magnesia powders which were synthesized by high-energy planetary ball milling. A detailed investigation was carried out into the influence of TSS on the microstructure and mechanical properties of the WC-MgO bulk composites. Besides, the technique parameters of two-step hot-pressing sintering method, such as the initial highest sintering temperature (t1), second-step isothermal sintering temperature (t2) and holding time (θ) were studied in detail. The results show that, the sintering temperature plays an important role in densification and grain growth of WC-MgO composite. The optimum TSS regime consisted of heating at 1 750 ℃ (1st step) and 1 550 ℃ (2nd step), resulting in the formation of nearly full dense microstructure (99%, theory density) with suppressed grain growth (2.59 μm). As a result, the hardness, fracture toughness and flexural strength are improved to (18.4±0.5) GPa, (12.95±0.5) MPa-m1/2 and (1283.7±126.6) MPa, respectively.