氧化预处理对超细晶硬质合金材料性能的影响

Effect of Oxidation Pretreatment on Properties of Ultrafine Grain Cemented Carbide Material

采用超细WC粉末(d≤500 nm)制备的超细晶硬质合金,因WC和Co粉粒度极细,比表面积大,坯体压制成形后,等待烧结过程中容易受到环境氧的影响,使坯体表面与芯部氧含量不同而形成氧梯度,影响硬质合金材料性能。采用创新开发的氧化预处理工艺,结合自主研发设计的预处理设备,对WC-9%Co超细晶硬质合金坯体进行烧结前氧化预处理,再进行后续的低压烧结。对比分析了未经预处理与经过氧化预处理的坯体各部分氧含量,以及烧结后合金各部分磁饱和(σs)、抗弯强度(TRS)、洛氏硬度(HRA)、断裂韧性(KIC)、矫顽磁力(Hc)等材料性能。结果表明:经过氧化预处理后,坯体中总的氧含量增加,氧含量分布更均匀;烧结后,合金的磁饱和显著降低且分布更均匀,同时抗弯强度和硬度等性能得到有效改善,而致密度、孔隙度未发生变化。

Due to the extremely fine grain size and large specific surface area of WC and Co powder, ultrafine grain cemented carbides prepared by ultrafine WC powder(d≤500 nm) is easy to be affected by the ambient oxygen while waiting for sintering after the press molding of the blank, resulting in the different oxygen content of the surface and core of the blank to form an oxygen gradient, which affects the properties of the cemented carbide material.A novel oxidation pretreatment technology, combined with the self-developed pretreatment device, was used to perform the oxidation pretreatment before the sintering of WC-9%Co ultrafine grain cemented carbide blank and then the subsequent low-pressure sintering was performed on the pretreated blank.The oxygen content of each part of the blank before and after oxidation pretreatment, and the magnetic saturation(σs),flexural strength(TRS),Rockwell hardness(HRA),fracture toughness(KIC) and coercivity(Hc) of each part of the sintered cemented carbide were compared and analyzed.The results show that the total oxygen content in the blank increases and the oxygen content is more uniformly distributed after oxidation pretreatment.After sintering, the magnetic saturation of the cemented carbide is significantly reduced and its distribution is more uniform.At the same time, properties including flexural strength and hardness are effectively improved, while the density and porosity remain unchanged.