钨添加对Si3N4陶瓷力学性能的影响及强韧化机理研究

为了增韧Si₃N₄基陶瓷材料,以钨(W)作为第二相材料,Y₂O₃-Al₂O₃作为烧结助剂,采用气压烧结法制备了W/Si₃N₄复合陶瓷材料。研究了W含量对W/Si₃N₄复合陶瓷材料致密性、力学性能以及结构的影响。结果表明:在W含量小于5%(质量分数)时,样品致密度均达97%以上;在W含量为5%(质量分数)时,获得的W/Si₃N₄复合陶瓷材料综合性能最佳,弯曲强度、硬度和断裂韧性分别为(670.28±40.00) MPa、(16.42±0.22) GPa和(8.04±0.16) MPa·m^1/2,相比于未添加金属W的Si₃N₄陶瓷材料分别提高了38.08%、13.08%和44.34%;通过分析W/Si₃N₄复合陶瓷材料样品抛光面和压痕裂纹的微观结构,发现W的引入能促使裂纹在扩展路径上更易发生偏转、分叉等增韧机制,消耗裂纹扩展能量,从而改善Si₃N₄陶瓷的断裂韧性。

Effect and Toughening Mechanism of Tungsten Addition on Mechanical Properties of Si3N4 Ceramics

To toughen Si₃N₄-based ceramic materials, W/Si₃N₄ composite ceramic materials were prepared in this article by the pneumatic sintering method with tungsten (W) as the second phase material and Y₂O₃-Al₂O₃ as sintering additive. Then the effect of W content on the compactness, mechanical properties, and microstructure of W/Si₃N₄ composite ceramic materials was investigated. The results indicate that the densities of samples all reach more than 97% when the W content is less than 5% (mass fraction). The most outstanding overall performance of W/Si₃N₄ composite ceramic materials is obtained when W content is 5% (mass fraction), and the bending strength, hardness, and fracture toughness are (670.28±40.00) MPa, (16.42±0.22) GPa, and (8.04±0.16) MPa·m^1/2, respectively, which are 38.08%, 13.08%, and 44.34% higher than Si₃N₄ ceramic materials without the addition of metal W. By analyzing the microstructure of the polished surface and indentation cracks of W/Si₃N₄ composite ceramic material samples, it is found that the introduction of W can trigger toughening mechanisms such as deflection and bifurcation of cracks in the propagation path, and consume crack expansion energy, thus improving the fracture toughness of Si₃N₄ ceramics.