Ti_(3)SiC_(2)陶瓷材料的制备及抗烧蚀行为

Preparation and ablation behavior of Ti_(3)SiC_(2) ceramics

以固溶少量Al的Ti_(3)SiC_(2)粉体为原料,采用热压烧结工艺制备出致密度大于99%的Ti_(3)SiC_(2)陶瓷块体材料,其硬度、抗弯强度和断裂韧度分别为775HV,520.46 MPa和7.62 MPa·m^(1/2)。对Ti_(3)SiC_(2)块体在无冷却条件下进行抗氧乙炔焰烧蚀实验,结果表明:烧蚀10 s内Ti_(3)SiC_(2)陶瓷保持表面平整,烧蚀25 s内样品未出现宏观裂纹。SEM和XRD观察分析表明,Ti_(3)SiC_(2)陶瓷在高温乙炔焰和氧气的高热流冲击作用下,表面发生分解和氧化,Si和C被氧化为Si-O化物和C-O化物气体逸出,Ti元素被氧化成高温稳定的TiO_(2)金红石相覆盖在表面;氧化层呈3层结构分布,最外层为结构疏松的TiO_(2),次表层则为TiO_(2)和Al_(2)TiO_(5)组成的致密复合层,内氧化层为致密Al_(2)O_(3)富集层,Al_(2)O_(3)来源于固溶在原料Ti_(3)SiC_(2)中Al元素的氧化,并在高温下与TiO_(2)反应生成了Al_(2)TiO_(5)。具有高黏度和高熔点的Al_(2)O_(3)富集层可以有效阻碍O^(2)和热流向基体的扩散,从而降低基体的氧化速率,提高Ti_(3)SiC_(2)材料的抗烧蚀性能。

Ti_(3)SiC_(2) ceramic bulk with a relative density greater than 99%was prepared by hot pressing sintering(HP)using Ti_(3)SiC_(2) powder as raw material,and the hardness,flexural strength and fracture toughness of HP Ti_(3)SiC_(2) bulk were 775HV,520.46 MPa and 7.62 MPa·m^(1/2),respectively.To evaluate its oxidation-resistance and thermal shock resistance,ultra-high temperature ablation tests were conducted under oxyacetylene flame without cooling.The results show that the Ti_(3)SiC_(2) ceramics remain flat within 10 s of the ablation,no macrocracks within 25 s.SEM and XRD analysis reveal that Ti_(3)SiC_(2) samples are decomposed and oxidized during the ultra-high temperature ablation,elements Si and C are oxidized into gaseous Si-O and C-O compounds,TiO_(2)(rutile)with a loose structure remains on the surface of the sample.To analyze the internal oxide layer,a dense layer composed of rutile TiO_(2) and Al_(2)TiO_(5) is observed,under which an Al_(2)O_(3) particle-enriched layer is found covering the substrate.The dense internal oxide layer can effectively prevent O^(2) from diffusing inward,thereby reducing the oxidation rate of Ti_(3)SiC_(2).The high melting point and high viscosity Al_(2)O_(3) particle layer can absorb a large amount of heat and then reduce the transfer of heat flow to the Ti_(3)SiC_(2) substrate,thus improving the anti-ablation of the Ti_(3)SiC_(2) material.