INTERACTION BETWEEN Ti-47Al-2Cr-2Nb ALLOY AND Y2O3 CERAMIC DURING DIRECTIONAL SOLIDIFICATION

Interaction between Ti-47Al-2Cr-2Nb alloy and inner layer Y2O3 of Y2O3/Al2O3 double-layer ceramic tube has been investigated during directional solidification. The results show that the Y2O3 layer effectively prevents the chemical reactions between TiAl alloy melt and exterior layer Al2O3 with lower chemical stability by blocking their direct contact. The DS alloy ingot contains Y2O3 inclusions which mainly come from the shedding of Y2O3 from ceramic tube inwall by being penetrated and eroded by fluid alloy melt in the initial phase of the directional solidification test. The average volume fraction of the inclusions is only about 0.14% and is insensitive to time. The re-sintering of the Y2O3 ceramic surface layer occurs and a 2-10 mu m dense barrier layer is formed by dint of alloy melt at high temperature. It prevents further pervasion of alloy melt into the Y2O3 ceramic and shedding of imperfectly sintered Y2O3 particles into the alloy melt.