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层厚比对TiC–WC/TiC–TiN层状陶瓷微观组织及力学性能的影响

Effect of layer thickness ratio on microstructure and mechanical properties of TiC–WC/TiC–TiN laminated ceramics

  • 摘要: 以TiC为基体材料,WC和TiN分别为TiC–WC(TW)层和TiC–TiN(TT)层的添加相,采用干压成形法和真空热压烧结技术制备了五种不同层厚比(TW/TT分别为2:1、1:1、1:2、1:3和1:4)的TiC–WC/TiC–TiN层状陶瓷,研究了层厚比对层状陶瓷内部残余应力、微观结构以及力学性能的影响。结果表明,TW层中存在的残余压应力随着TT层厚的增加逐渐增大,TT层中存在的残余拉应力逐渐减小,但两者差值相对稳定。随着TT层厚的增大,TW层的硬度和层状陶瓷的相对密度均缓慢增加,TW层的断裂韧性和层状陶瓷的抗弯强度先增大后减小;而TT层的硬度则随着TT层厚的增加略有减小,断裂韧性却在一直降低。当层厚比为1:3时,层状陶瓷的微观形貌缺陷较少,晶粒大小均匀,结合紧密,获得了最佳的力学性能,其相对密度为(96.47±0.02)%,抗弯强度为(946.01±19.1) MPa;此时,TW层硬度和断裂韧性分别为(16.68±0.17) GPa和(10.19±0.22) MPa·m1/2,TT层的硬度和断裂韧性分别为(15.73±0.15) GPa和(7.78±0.26) MPa·m1/2。同时,TT层的平均晶粒尺寸明显小于TW层,裂纹在穿越层交界处时出现裂纹偏转和裂纹桥连,断裂方式为穿晶断裂和沿晶断裂。

     

    Abstract: The TiC–WC/TiC–TiN laminated ceramics with the layer thickness ratios as 2:1, 1:1, 1:2, 1:3 and 1:4, respectively, were prepared by dry pressing and vacuum hot pressing sintering with TiC as the base materials and WC and TiN as the additive phases of the TiC–WC (TW) layer and TiC–TiN (TT) layer, respectively. The effects of layer thickness ratio on the residual stress, microstructure, and mechanical properties were investigated. The results show that the residual compressive stress existing in the TW layer gradually increases with the increase of TT layer thickness, and the residual tensile stress existing in the TT layer gradually decreases, but the difference between the two is relatively stable. With the increase of the TT layer thickness, both the hardness of the TW layer and the relative density of the laminated ceramics increase slowly, while the fracture toughness of the TW layer and the flexural strength of the laminated ceramics increase first and then decrease. The hardness of the TT layer slightly decreases with the increase of the TT layer thickness, while the fracture toughness keeps decreasing. When the layer thickness ratio is 1:3, the microstructure defects of the laminated ceramics are fewer, the grain size is uniform, the combination is tight, and the best mechanical properties are obtained as the relative density of (96.47±0.02)% and the flexural strength of (946.01±19.1) MPa. At this time, the hardness and fracture toughness of the TW layer are (16.68±0.17) GPa and (10.19±0.22) MPa·m1/2, respectively, and the hardness and fracture toughness of the TT layer are (15.73±0.15) GPa and (7.78±0.26) MPa·m1/2, respectively. Meanwhile, it is observed that the average grain size of the TT layer is significantly smaller than that of the TW layer. Crack deflection and crack bridging occur when the cracks cross the junctions of the layers, and the fracture modes are transgranular fracture and intergranular fracture.

     

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