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由于不同材料的热膨胀系数不同,涂层在冷却过程中可能因为热应力不同而产生裂纹,表面富粘结相的梯度硬质合金基体因粘结相含量高,韧性好,能有效吸收裂纹扩展时的能量,延长涂层刀具的使用寿命。为了研究WC晶粒度对梯度硬质合金的组织及性能的影响,制备了三种WC粒度的硬质合金。采用XRD和SEM对梯度硬质合金的相成分、微观组织进行了分析。实验结果表明,三种WC晶粒度的硬质合金表面均形成了梯度层。随着WC晶粒度的增大,梯度层厚度减小,抗弯强度和断裂韧性增大。三种梯度硬质合金表层显微硬度分布趋势相似。当WC晶粒度较小时,梯度硬质合金无梯度的合金芯部断裂形式均以沿晶断裂方式为主,随着WC晶粒度的增加,穿晶断裂方式增多;梯度表层出现了Co相变形和撕裂形貌,存在蜂窝状的韧性花样。
Due to the different thermal expansion coefficients of different materials, the coating may crack due to different thermal stresses during the cooling process. The gradient cemented carbide matrix with a binder phase on the surface has high content of binding phase and good toughness and can effectively absorb the crack propagation The energy to extend the life of coated tools. In order to study the effect of WC grain size on the microstructure and properties of the gradient cemented carbide, three WC cements were prepared. The phase composition and microstructure of the gradient cemented carbide were analyzed by XRD and SEM. The experimental results show that the graded layer is formed on the surfaces of the three kinds of WC grains. With the increase of WC grain size, the thickness of gradient layer decreases and the flexural strength and fracture toughness increase. The three kinds of gradient cemented carbide surface microhardness distribution trends are similar. When the grain size of WC is small, the fracture morphology of graded cemented carbide without graded alloy is dominated by the intergranular fracture mode. With the increase of WC grain size, the transgranular fracture mode increases. The Co phase Deformation and tear morphology, there are honeycomb toughness patterns.