温度梯度对定向凝固TiAl基合金片层取向的影响

来源期刊：金属学报2010年第10期

论文作者：肖志霞 郑立静 杨莉莉 闫洁 张虎

文章页码：1223 - 1229

关键词：TiAl基合金； 定向凝固； 片层取向； 择优生长

Key words：TiAl-based alloy； directional solidification； lamellar orientation； preferred growth

摘    要：利用定向凝固方法研究了在1580和1650℃加热温度下Ti-47Al-2Cr-2Nb合金不同片层取向的晶粒竞争生长规律.显微组织分析表明,合金初生相为β相,随后发生包晶反应形成α相,并在β→α转变时α相依附已有β相形核,12种α变体中仅形成了一种特定取向的α变体,两相区平均温度梯度由40K/cm增大至160K/cm,从而使凝固界面形态由柱状树枝晶转变为胞状树枝晶.在排除切割面影响的前提下,对γ片层取向的演变过程进行了分析.结果表明,在1mm/min的抽拉速度下,温度梯度为40K/cm(加热温度为1580℃)时,与生长方向呈74°左右的柱状晶逐渐淘汰其他与生长方向约呈45°的晶粒;提高温度梯度至160K/cm(加热温度为1650℃)时,与生长方向呈74°左右的柱状晶逐步淘汰其他与生长方向约呈90°的晶粒而生长占优.晶体取向计算表明,在本实验条件下β枝晶倾向于沿〈110〉_β方向择优生长,提高温度梯度使β枝晶沿〈110〉_β方向择优生长趋势增强,〈001〉_β等其他取向枝晶被更快淘汰.

Abstract: Directional solidification experiments under heating temperatures of 1580℃ and 1650℃ were performed on Ti-47Al-2Cr-2Nb alloy in order to obtain the evolution of lamellar grains.Prom microstructural analysis in the mushy zone of directional solidified ingots,β phase was firstly solidified, then α phase was formed through peritectic reaction;α phase depended on the pre-existed β phase on which it nucleated,and only one of the 12 α orientation variants was selected during solid state β→α transformations.As the average temperature gradient of the mushy zone was increased from 40 K/cm to 160 K/cm,the solidification interface morphologies were changed from columnar dendrite to celluar dendrite.Eliminating the influence of cutting plane to the γ-lamella orientation,it was shown that the columnar lamellar grains with an angle of approximately 74° to growth direction gradually overgrew the ones with the angle of nearly 45° to the growth direction at the withdrawal rate of 1 mm/min and temperature gradient of 40 K/cm.Increasing temperature gradient to 160 K/cm,the grains with the angle of about 74° progressively rejected other with the angle of nearly 90° to the growth direction.Calculation of the β dendrite preferred growth orientation indicated that β dendrites tend to grow along the <110>_β orientation at the present solidification experiments.Increasing temperature gradient,the preferred growth tendency of β dendrite became more drastically,other orientations,such as the <001>_β directional orientation,could rapidly be replaced.