Densification and physical properties of SiC-diamond polycrystalline materials produced by pressureless sintering
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摘要: 以AlN−Y2O3−Sc2O3为液相烧结助剂，添加不同质量分数金刚石，经无压烧结制备SiC-金刚石多晶材料。采用扫描电镜观察多晶材料显微结构，利用激光闪射法测量其热扩散系数和热导率。研究了金刚石质量分数（1.0%、2.5%、5.0%）和粒度（0.25 μm、1.00 μm）对SiC陶瓷材料致密化行为和力学性能的影响。结果表明，金刚石质量分数低于5.0%，烧结后的材料相对密度均超过94%；金刚石含量为5.0%的样品相对密度远远低于其他样品。SiC多晶材料的相对密度随金刚石添加量的增加而降低，原料中添加过量的金刚石会降低材料的相对密度。在实验条件下，多晶材料晶粒尺寸没有发生异常长大，硬度为16～18 GPa，断裂韧性为3.8～4.4 MPa·m1/2，抗弯强度为239～540 MPa。材料的热导率和热扩散系数随着温度的升高而降低，气孔是影响复合材料热导率的主要因素。Abstract: SiC-diamond polycrystalline materials doping by diamond with different mass fraction were prepared by pressureless sintering with AlN−Y2O3−Sc2O3 as liquid phase. The microstructure and thermal properties were analyzed by scanning electron microscopy and laser flash method, respectively. The effects of mass fraction (1.0%, 2.5%, 5.0%) and particle size (0.25 μm, 1.00 μm) of diamond on the densification and mechanical properties of the SiC-diamond polycrystalline materials were studied. The results show that, the relative density of the sintered samples is over 94% when the diamond mass fraction is below to 5.0%, while the relative density of the sample with 5.0% diamond is lower than that of other samples. The relative density of SiC polycrystalline materials decreases with the increase of diamond content, and the excessive diamond in raw materials may reduce the densification of samples. Under the experimental conditions, the grain size does not grow abnormally. The hardness, fracture toughness, and bending strength of the samples are in ranges of 16~18 GPa, 3.8~4.4 MPa·m1/2, and 239~540 MPa, respectively. The thermal conductivity and thermal diffusion coefficient of samples decrease with the increase of temperature, and the porosity is the main factor affecting the thermal conductivity of the sintered samples.
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图 1 试样表面显微形貌：（a）S1；（b）S2；（c）S4；（d）S5
Figure 1. SEM of the samples: (a) S1; (b) S2; (c) S4; (d) S5
图 2 试样晶粒粒径分布：（a）S1；（b）S2；（c）S4；（d）S5
Figure 2. Grain diameter distribution of the samples: (a) S1; (b) S2; (c) S4; (d) S5
图 4 试样在不同温度下的热导率
Figure 4. Thermal conductivity of the samples at the different temperatures
图 5 试样在不同温度下的热扩散系数
Figure 5. Thermal diffusion coefficient of the samples at the different temperatures
表 1 实验主要原材料
Table 1. Main raw materials in the experimental
原料 粒径，D50 / μm 纯度 / % 生产厂家 SiC 0.70 98.5 H.C. Starck UF-15 金刚石 0.25 99.9 明源金刚石微粉厂 1.00 AlN 5.00 ≥99.5 阿拉丁试剂有限公司 Y2O3 5.00 ≥99.5 阿拉丁试剂有限公司 Sc2O3 5.00 ≥99.5 阿拉丁试剂有限公司 
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表 2 实验原料配比
Table 2. Components of the experimental materials
试样 质量分数 / % 金刚石粒径 / μm 烧结助剂 SiC 金刚石 S1 8.0 91.0 1.0 0.25 S2 8.0 89.5 2.5 0.25 S3 8.0 87.0 5.0 0.25 S4 8.0 91.0 1.0 1.00 S5 8.0 89.5 2.5 1.00 S6 8.0 87.0 5.0 1.00
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表 3 试样烧结性能
Table 3. Sintering properties of the specimens
试样 体积密度 / (g·cm−3) 相对密度 / % 气孔率 / % S1 3.22 97.9 2.1 S2 3.12 94.6 5.4 S3 2.70 81.7 18.3 S4 3.18 96.6 3.4 S5 3.20 97.1 2.9 S6 2.74 82.9 17.0
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表 4 试样的力学性能
Table 4. Mechanical properties of the specimens
试样 维氏硬度 / GPa 断裂韧性 / (MPa·m1/2) 抗弯强度 / MPa S1 18.12±1.00 4.32±0.67 413±17 S2 17.19±1.03 3.88±0.56 239±10 S4 16.52±1.34 4.46±0.41 542±19 S5 18.09±1.25 4.20±0.69 302±16
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