Ti_2AlC-TiB_2对TiAl基复合材料组织及力学性能的影响

Effects of Ti_2AlC-TiB_2 on the microstructure and mechanical properties of TiAl matrix composites

以Ti、Al和B4C为原料,采用真空电弧熔炼的方法制备了含Ti_2AlC-TiB_2增强相的TiAl基复合材料;分析了添加不同含量的Ti_2AlC-TiB_2对复合材料的物相组成、组织结构及力学性能的影响,并探讨了微观组织结构的形成机制。结果表明:Ti_2AlC-TiB_2/TiAl复合材料主要由TiAl、Ti3Al、TiB_2和Ti_2AlC等物相组成,TiB_2和Ti_2AlC分布在层片状的TiAl+Ti3Al基体中;随着原料中B4C含量的增多,复合材料组织中Ti_2AlC-TiB_2含量增多,且TiAl基体的晶粒被明显细化,TiB_2和Ti_2AlC分布于基体晶界或晶内。Ti_2AlC主要为层片状和板条状,尺寸5~15μm,而TiB_2颗粒形态与其含量有关,当Ti_2AlC-TiB_2含量小于20wt%时,TiB_2颗粒呈针棒状,尺寸为0.5~5μm,当Ti_2AlC-TiB_2含量增加到30wt%时,TiB_2颗粒主要呈块状,尺寸为5~20μm。Ti_2AlC由TiC与Ti-Al熔体发生包晶反应生成,Ti_2AlC和TiB_2的形成提高了Ti_2AlC-TiB_2/TiAl复合材料的硬度、塑性和抗压强度。当4Ti+Al+B4C的加入量为10wt%时,复合材料的变形量比纯TiAl提高14%,而抗压强度达到最高值1 591 MPa。Ti_2AlC和TiB_2通过裂纹偏转、颗粒钉扎、拔出等机制对Ti_2AlC-TiB_2/TiAl复合材料起到增强增塑的作用。

Ti2 AlC-TiB2 reinforced TiAl matrix composites were synthesized by vacuum arc melting using Ti, Al and B4 C powders as the raw materials. The effects of Ti2 AlC-TiB2 contents on the phases, microstructures and me- chanical properties of Ti2 AlC-TiB2/TiAl composites were analyzed. The results show that Ti2 AlC-Tit-/TiAl com- posites are mainly composed of TiAl, Ti3Al, TiB2 and Ti2 AlC phases, among which TiAl and Ti3 Al present a kind of lamellar structure and constitute the matrix. With the increasing of B4 C contents in the raw materials, the amount of synthesized Ti2 AlC and TiBz particles increases, and TiAl grains are refined greatly. In addition, TiBz and Ti2 AlC particles distribute along the grain boundaries or in the grains. And Ti2AlC particles are in lamellar or lath-like shapes with an average particle size of about 5--15 t-m. The morphology of the TiB2is related toits content. When the contents of Ti2 AlC-TiB2 ceramic phase are less than 20wt-, TiB2 particles are in a needle-rod shapes with a size of 0.5--5 9m. With the content increases to 30wt%, TiB2 particles grow into blocky faceted particles from 5-20 μm. The Ti2 AlC is considered to be synthesized from a peritectic reaction between TiC and Ti-Al melt. The av- erage hardness, ductility and the compressive strength of Ti2 AlC-TiB2/TiAl composites increase obviously, with the formation and increase of Ti2AlC-TiB2. The mechanical properties of composites with 10wt% ceramic phases show the highest compression strength of 1591 MPa, and its fracture strain is 14% higher than that of pure TiAl alloy. The reinforcing mechanisms of the Ti2 AlC and TiB2 include crack deflection, pinning and pull-out, which is benefit for the strengthening and ductility of Ti2 AlC-TiB2/TiAl composites.