B和C对铸造TiAl基合金宏观和显微组织的影响

对比研究了B和C含量的变化对铸造TiAl基合金宏观和显微组织的影响。结果表明 ，B或C含量的增加均能细化TiAl基合金的晶粒，但二者的作用特点不同。B含量对宏观组织和晶粒尺寸的影响是渐进的，而C对其影响存在一个临界含量。显微观察表明，微量的B就能使合金析出TiB2，随着合金中B含量的增加，硼化物颗粒呈不同的形貌。对于含C合金，当C含量低于临界含量时，在光学尺度上观察不到碳化物相，而当C含量高于临界含量时，合金中生成大量的Ti2AlC碳化物颗粒。讨论了B和C细化TiAl基合金的机制。

EFFECTS OF B OR C ON THE MACRO-AND MICRO-STRUCTURES OF CAST NEAR GAMMA TiAl ALLOYS

The effects of B and C on the macro- and micro- structures of near gamma TiAl alloys were compared. The results show that fine equiaxed grains are obtained with increasing concentration of B or C, but grain refinement by the two alloying additions exhibits different features. The grain size of the B containing alloy decreases gradually with increasing B content, whereas for alloying with C, the grain size drops suddenly beyond a critical C content. Microscope observations reveal that even trace lavel of B triggers the formation of TiB2-type boride which exhibits different morphologies with increasing B content. In alloys containing C, carbide particles can not be observed under optical microscope beneath the critical level of C, but large amounts of carbide particles are seen once the critical concentration is reached. The carbide is predominantly Ti2AlC as identified by electron diffraction. A brief analysis was made of the grain refining effects by B and C.