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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.
The direction of solidification of Ti-47Al-2Cr-2Nb alloy was investigated by means of directional solidification at different temperatures of 1580 and 1650 ℃ .Microstructure analysis showed that the primary phase of the alloy was β phase, and then the peritectic The reaction forms α phase, and α phase depends on β phase nucleation when β → α transformation. Only one α variant with specific orientation is formed among the 12 α variants. The average temperature gradient of the two phases is increased by 40 K / cm (160K / cm), the morphology of solidified interface was changed from columnar dendrites to cellular dendrites.On the premise of excluding the influence of the cutting plane, the evolution of the orientation of y-lamellar layer was analyzed.The results show that at 1mm / min When the temperature gradient is 40K / cm (heating temperature is 1580 ℃), the columnar crystals with the growth direction of about 74 ° gradually eliminate the other grains with the growth direction of about 45 °. When the temperature gradient is raised to 160K / cm (heating temperature is 1650 ℃), the columnar grains with the growth direction of about 74 ° phased out the growth of other grains with a grain growth of about 90 ° dominant growth.Crystal orientation calculations show that under the experimental conditions β branch The crystal tends to preferentially grow along the <110> _β direction, increasing the temperature gradient The preferred growth direction of β dendrite along the <110> _β direction was enhanced, and other oriented dendrites such as <001> _β were eliminated more quickly.