抽拉速率对Co-Al-W高温合金定向凝固生长取向的影响

Effects of Withdrawing Rate on the Growth Orientation of Directionally Solidified Co-Al-W Superalloys

对Co-9Al-9W-0.1B合金在不同抽拉速率下进行定向凝固,观察其凝固显微组织,并利用电子背散射衍射检测其晶粒生长取向。当抽拉速率为20mm/h和60mm/h时,合金凝固界面前沿分别为平面状和胞状,晶粒生长取向均接近〈101〉方向。随着抽拉速率增大,合金凝固界面前沿转变为枝晶状;当抽拉速率为180mm/h时,晶粒生长取向为〈013〉方向;当抽拉速率为360mm/h时,晶粒生长取向偏离〈101〉方向约30°。Co-9Al-9W合金在抽拉速率180mm/h的定向凝固中,经过一段竞争生长后择优取向为〈001〉。由于缺少硼化物强化晶界,Co-9Al-9W合金蠕变强度相比同速率下定向凝固的Co-9Al-9W-0.1B合金较差。经过抽拉速率为180mm/h的定向凝固后Co-9Al-9W-0.1B合金具有柱状晶组织,其蠕变强度高于具有等轴晶组织的Co-9Al-9W-0.1B合金。

Co-9 Al-9 W-0.1 Balloy was directionally solidified at different withdrawing rate,and its solidified microstructure was observed and the grain growth orientation was investigated by electron backscatter diffraction.With the withdrawing rate of 20 mm/h and 60 mm/h,the solid-liquid interface fronts are plane and cellular,respectively,and the growth orientation is both close to the〈101〉direction.With withdrawing rate increasing,the solid-liquid interface front changes into dendrites.When the withdrawing rate is 180 mm/h,the growth orientation is〈013〉direction.With the withdrawing rate of 360 mm/h,the grain growth orientation deviated from 〈101〉by about 30°.Co-9 Al-9 Walloy has a preferred orientation of〈001〉after a period of competition growth during directional solidification at 180 mm/h withdrawing rate.Borides can strengthen grain boundaries and the absence of borides results in the poorer creep strength of Co-9 Al-9 W alloy,compared with Co-9 Al-9 W-0.1 Balloy directionally solidified at the same withdrawing rate.Co-9 Al-9 W-0.1 B alloy directionally solidified at 180 mm/h withdrawing rate has columnar grains and higher creep strength than Co-9 Al-9 W-0.1 Balloy with equiaxed grains.