SCS-6 SiC/Ti_2AlNb复合材料的界面反应及机理

Interfacial Reaction and Mechanism of SiC /Ti_2AlNb Composite

运用量子化学计算理论,求出了有关化合物的热化学参数,并根据有关热力学模型,计算了金属间化合物Ti2AlNb中元素的活度,由此计算了SCS-6SiC长纤维增强Ti2AlNb金属间化合物复合材料界面反应的Gibbs函数变值ΔrG,用ΔrG判据推测了界面反应产物并与透射电镜实验结果进行了对比分析。研究表明,由于Ti2AlNb中原子结合力较Ti3Al强,因而SCS-6SiC/Ti2AlNb复合材料的界面反应较SCS-6SiC/Ti3Al轻。反应初期形成晶粒非常细小的TiC,Ti5Si3,晶粒较大的TiC和Ti3Si是由于元素扩散和反应所形成。在对复合材料的热暴露中,这些反应产物均进一步长大,并由于反应Ti3Al+C→Ti3AlC,在Ti2AlNb基体中形成一些三元反应产物Ti3AlC晶粒。

After getting thereto-chemical data of some compounds by using Gaussian 98 software of quantum chemistry and obtaining activities of elements in Ti2AlNb by thermodynamic calculation, the Gibbs function increments, Delta,G, for possible chemical reactions at the interface of SCS-6 SiC/Ti2AlNb composite were calculated. Results predicted by thermodynamic calculation were compared with experimental ones made by transmission electron microscopy. It is shown that the interfacial reaction in SCS-6 SiC/Ti2AlNb is not so severe as in SCS-6 SiC/Ti3Al because of the smaller activity of titanium in Ti2AlNb. At the beginning of the interfacial reaction, there appears a layer of TiC and Ti3Si with fine grains. A layer of TiC and a layer of Ti3Si with large grains were formed due to element diffusion and reaction during composite consolidation. In the SCS-6 SiC/Ti2AlNb composite which was thermally exposed at 800degreesC for 1 000h, these reaction products grew up and a ternary compound of Ti3AlC were formed in the Ti2AlNb matrix according to the reaction of Ti3Al + C-->Ti3AlC.