长期热循环条件下全片层高Nb-TiAl合金显微组织稳定性

MICROSTRUCTURE STABILITY IN A FULLY LAMELLAR HIGH Nb-TiAl ALLOY AFTER LONG-TERM THERMAL CYCLING

分别在900和1000℃下对全片层Ti-45Al-8.5Nb(W,B,Y)合金进行了长期热循环(500和1000 cyc)实验,通过光学显微镜(OM)、扫描电镜(SEM)及透射电镜(TEM)研究了该合金在不同温度长时热循环条件下的显微组织稳定性.研究表明,合金经全片层热处理工艺后凝固偏析(Al偏析)仍未完全消除,900℃下长期热循环后Al偏析处易产生不连续粗化,合金1000 cyc热循环后仍未发现α_2相的球化;1000℃下合金长期热循环后Al偏析处易析出大块γ晶粒,合金经500 cyc热循环后沿晶界产生了许多细小的等轴γ晶粒,同时α_2相在γ晶粒内球化析出.1000 cyc热循环后晶界、晶内均有大量的等轴γ晶粒析出,且晶粒内部有不同取向的长条状或颗粒状α_2相析出;合金1000℃下长期热循环后,长条状或颗粒状α_2相从γ晶粒内沿晶面{111}_γ析出,α_2相与γ基体保持共格位向关系.

Microstructure stability in the fully lamellar Ti-45Al-8.5Nb（W, B, Y） alloy were investigated by OM, SEM and TEM after long-term thermal cycling （500 and 1000 cyc） at 900 and 1000℃. The results showed that Al-segregation could not be eliminated completely after the heat treatment. After long-term thermal cycling at 900℃, the discontinuous coarsening was inclined to occur in the Al-segregation region in the alloy. And almost no spheroidized precipitates ofα2 were observed even after 1000 thermal cycles. After long-term thermal cycling at 1000℃, the massive γ grains were generated in the Al-segregation region. After 500 thermal cycles, the spherodized α2 precipitates were produced within γ grains which were found at colony boundaries. After 1000 thermal cycles, however, the large equiaxed γ grains containing different orientation of plate-shaped precipitates of theα2 phase were observed within the lamellar structure or at colony boundaries. After long-term thermal cycling at 1000℃, the plate-shaped or particle-shapedα2, which is coherent with the γ matrix, precipitates on the {111}γ plane in the γ grain interior.