成形压力对SiC/TiB_2复合材料组织与性能的影响

Effect of Forming Pressure on Microstructure and Mechanical Properties of SiC/TiB_2 Composites

基于熔融Si浸渗法制备出较致密的SiC/TiB_2复合材料,并研究了坯体成形压力对SiC/TiB_2复合材料致密度、相组成、显微组织和力学性能的影响。实验结果表明,复合材料由TiB_2、Si C和Si相组成。SiC/TiB_2复合材料的显微组织特征为:TiB_2相和SiC相均匀分布,游离Si填充在TiB_2相和SiC相的空隙处,且形成了连续相。随成形压力的增大,复合材料中游离Si含量降低,TiB_2颗粒尺寸减小,复合材料的力学性能先增加后降低。坯体最佳成形压力为200 MPa,对应SiC/TiB_2复合材料的体积密度、开口气孔率、抗弯强度、断裂韧性和维氏硬度分别为3.63 g/cm^3、0.90%、(354±16)MPa、(6.8±0.2)MPa·m^(1/2)和(21.0±1.1)GPa。

SiC/TiB2 composites were fabricated by infiltration of molten silicon （Si） into porous preforms containing titanium diboride （TiB2） and free carbon （C） at 1550℃ for 30 min. And the influences of forming pressure on the phase compositions, microstructure, density and mechanical properties of SiC/TiB2 composites were investgated. It is found that forming pressures have significant influence on the microstructure and mechanical properties of SiC/TiB2 composites. XRD results show that the composites consist of TiB2, SiC and Si phases. The microstructure analysis show that the TiB2 and SiC phases distribute in the composite uniformly, with free Si fills in the continuous gaps between TiB2 and SiC phases. TiB2 particle size and volume fraction of free Si both decrease with the increase of forming pressures. The mechanical properties of SiC/TiB2 composites are improved initially and then deteriorated with the increase of forming pressures. Under the optimal pressure of 200 MPa, Vikers-hardness, flexural strength and fracture toughness of the obtained SiC/TiB2 composite are （21.0±1.1） GPa, （354±16） MPa and （6.8±0.2） MPa·m1/2, respectively. The open porosity and bulk density of the obtained SiC/TiB2 composite prepared at 200 MPa forming pressure are 0.90% and 3.63 g/cm3.