Al_2O_3对B_4C-Al_2O_3-Al显微组织与力学性能的影响

Effect of Al_2O_3 on Microstructure and Mechanical Properties of B_4C-Al_2O_3-Al Composites

在B4C-Al2O3预烧体中真空熔渗铝制备了B4C-Al2O3-Al复合材料,分析了w(Al2O3)对复合材料显微组织和力学性能的影响.结果表明:B4C-Al2O3-Al复合材料主要由B4C,Al2O3,Al,Al3BC和AlB2等相组成;随着w(Al2O3)的增加,复合材料的HRA硬度先增大后减小,材料的抗弯强度和断裂韧性均先减小后增大,当w(Al2O3)为25%时,复合材料具有较好的综合性能,它的气孔率、硬度、抗弯强度和断裂韧性分别为2.06%,84.4HRA,440.36 MPa和6.53 MPa.m1/2;延性铝的加入、裂纹的偏转和分叉、晶粒的细化、增韧相AlB2的生成及热膨胀的不匹配是造成材料断裂韧性提高的主要原因,断裂方式主要为沿晶和穿晶混合的方式,材料断口中存在金属撕裂棱的特征.

B4C-Al2O3-Al composites were prepared by aluminizing the B4C-A1203 preforms in vacuum, and the effect of Al2O3 on the microstructure and mechanical properties of the composites was analyzed. The results showed that B4C-Al2O3-Al composite is mainly composed of B4C, Al2O3, Al, Al3BC and AlB2. With the increasing w （Al2O3）, the hardness increases first then decreases, but the bending strength and fracture toughness decrease first then increase. The porosity, hardness, bending strength and fracture toughness of the composite when w （Al2O3） = 25 % are 2.06%, 84.4 HRA, 440.36 MPa and 6.53 MPa· m1/2, respectively. The toughening improvement of the composites mainly results from the addition of ductile aluminum, crack deflection/bifurcation, grain refinement, formation of toughening phase AlB2 and mismatching of thermal expansion between the matrix B4C and the Al2O3 particles. It was found that the fracture is mainly in intergranular and transgranular forms, and on the fracture surface there are torn edges due to aluminizing.