Formation mechanisms and mechanical properties of interfacial intermetallic compounds

在Ti-Al二元体系中，形成了三种不同的金属间化合物，即Ti_3Al、TiAl和Al3Ti。这三种金属间化合物具有作为新型轻质高温材料的潜力，因此它们的力学性能得到了广泛的研究。特别是由TiAl和少量Ti_3Al组成的两相材料引起了广泛的关注。当Ti-Al合金具有接近等原子成分时，合金呈现由TiAl和Ti_3Al片层组成的层状结构，Ti_3Al片层通常很薄，夹在相邻的两个TiAl片层之间。因此，TiAl/Ti_3Al片层结构可以作为研究界面化合物对界面力学性能影响的有效载体。Ti_3Al相的强度比TiAl相大得多，TiAl与Ti_3Al之间的较大强度差异导致TiAl/Ti_3Al界面处存在较大的应变积累和不相容。因此，在垂直于界面方向的应力作用下，TiAl/Ti_3Al/TiAl夹层结构是脆性结构。通过在TiAl/Ti_3Al两相合金中加入不同的元素，研究了TiAl/Ti_3Al两相合金的配分行为，以寻找能减小TiAl和Ti_3Al强度差异的元素。发现锡在界面上表现出这样的有利作用。然而，含锡TiAl/Ti_3Al合金的力学性能测试结果并不如预期的那样好。这是因为含锡Ti_3Al相的强度低于二元Ti_3Al相，但仍然是脆性的。对MoSi_2和SiC的界面进行了研究，发现两相的取向匹配关系与以往报道的不同。

In the Ti-Al binary system, three different intermetallic compounds, namely Ti_3Al, TiAl and Al3Ti are formed. These three intermetallic compounds have potential as new light-weight high-temperature materials and thus their mechanical properties have been intensively investigated. In particular two-phase materials composed of TiAl and a small volume fraction of Ti_3Al have been attracting considerable attention. When Ti-Al alloys with nearly equiatomic compositions are cast, the alloys exhibit the lamellar structure composed of TiAl and Ti_3Al lamellae, The lamellae of Ti_3Al is often thin and sandwiched between the two neighboring TiAl lamellae. The TiAl/Ti_3Al lamellar structure can thus be used as a useful vehicle for studying effects of interfacial compound on the mechanical properties of interface. The Ti_3Al phase is much stronger than the TiAl phase and the large difference in strength between TiAl and Ti_3Al results in the large strain accumulations and incompatibilities at the TiAl/Ti_3Al interface. Thus, the TiAl/Ti_3Al/TiAl sandwich structure is brittle when it is stressed along the direction perpendicular to the interface. Various elements were added to TiAl/Ti_3Al two-phase alloys and their partition behavior between the two constituent phases was investigated to find elements which reduce the difference in strength between TiAl and Ti_3Al. Tin is found to exhibit such an beneficial effect on the interface. However, the results of the mechanical testing of Sn-bearing TiAl/Ti_3Al alloys were not as good as expected. This is because the Sn-bearing Ti_3Al phase exhibits a lower stringth than the binary Ti_3Al phase but it is still brittle.Interface between MoSi_2 and SiC was also investigated and the two phases were found to be matched in an orientation relationship which was different from that reported previously.