Strength and toughness of L1_0-type intermetallic TiAl with duplex structure.

主要采用透射电镜对微结构控制的L1_0-TiAl进行了实验研究。结果如下：l1_0有序TiAl的显微组织随Al含量的变化。在1373 K的温度下，以0.25 at% AI的间隔对47 ~ 52的TiAl化合物进行固溶热处理。通过光学显微镜（OM）检查，其结构接近单相。在973 K时效过程中，透射电子显微镜（TEM）发现基体γ中没有析出物。在1473 K条件下，对% Al为56 ~ 62，% AI为2.0的TiAl化合物进行固溶热处理。其结构为OM单相γ。TEM观察表明，在973 ~ 1173 K.2的时效过程中，TiAl_2析出物较细小。在% C或n浓度下，含0.1 ~ 2.0的L1_0有序TiAl在时效过程中仅在L1_0基体的[001]方向形成细小的针状Ti_3AlC和钙钛矿型Ti_3AlN。针的横截面不是圆形而是方形的。在含碳合金中，形成了具有相似形貌和相同晶体结构的析出相。选择区电子衍射分析表明，析出相具有钙钛矿型晶体结构，具有与（100）TiAl平行的(100)-Ti_3AlC/Ti_3AlN和与[001]-TiAl平行的[001]-Ti_3AlC/Ti_3AlN取向关系。在较高温度下，Ti_3AlC/Ti_3AlN析出相被具有六方晶格结构的Ti_2AlC和Ti_2AlN所取代。室温抗压强度。钙钛矿相的析出可能没有预料到强度的增加。含0.5% % N的合金强度高于含0.5% % C的合金。

Experimental studies were made on microstructure-controlled L1_0-TiAl mainly by means of transmission electron microscopy. Results are as follows.1. Microstructural variations of L1_0-ordered TiAl with Al contents.TiAl compounds ranged from 47 to 52 at% AI at intervals of 0.25 at% AI were solution heat treated at 1373 K. The structure was nearly single-phase gamma by optical microscope(OM)examination. During aging at 973 K, transmission electron mocroscope(TEM)revealed that no precipitates were found in the matrix gamma. TiAl compounds ranged from 56 to 62 at% Al at intervals of 2.0 at% AI were solution heat treated at 1473 K. The structure was the single-phase gamma by OM. TEM observation that TiAl_2 precipitate, which was not so fine, was formed during aging at temperatures in the range of 973 to 1173 K.2. Microstructural variations of stoichiometric L1_0-ordered TiAl containing 0.1 to 2.0 at% C or N.Fine needle-shaped Ti_3AlC and Ti_3AlN of perovskite type were formed only [001] direction of the L1_0 matrix during aging. The cross-section of the needle was not circular but square. In the carbon containing alloys, precipitates with the similar morphology and the same crystal structure was formed. The selected area electron diffraction analyses suggested that the precipitates had a perovskite-type crystal structure and had the orientation relationship(100)-Ti_3AlC/Ti_3AlN parallel to(100)TiAl and[001]-Ti_3AlC/Ti_3AlN parallel to [001]-TiAl. At higher temperatures, Ti_3AlC/Ti_3AlN precipitates were replaced by Ti_2AlC and Ti_2AlN with hexagonal lattice structure.3. Room temperature compression strength.The strength increase might be not so anticipatated by the precipitation of perovskite phase. The alloy containing 0.5 at% N indicated higher strength than that containing 0.5 at% C.