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以Ti-52%Al合金为研究对象,在Bridgman定向凝固炉中进行不同时间的热稳定处理实验及相关的定向凝固实验,研究了定向凝固前糊状区的形成及其微观组织演化、界面形态和溶质分布,并考察了热稳定处理对定向凝固组织的影响.结果表明,试样熔化后形成了由α相晶粒、晶粒间富Al液滴和液相通道组成的糊状区,糊状区前沿为完全液相区.随着热稳定处理时间的增加,糊状区内α晶粒逐渐融合且沿温度梯度方向定向排布,富Al液滴和液相通道逐渐消失,固/液界面变得光滑平整.热稳定处理时间足够长时,糊状区内为单一的α相,溶质Al的成分在生长方向近似沿着α固相线变化.根据溶质守恒计算得出完全液相区内溶质Al含量为52.21%,高于试样原始成分,与实验测量结果相一致.进一步研究热稳定处理对后续定向凝固组织的影响,发现合理的热稳定处理时间(≥30 min)确保了定向凝固启动界面处存在稳定的温度场和浓度场,柱状晶沿生长方向能够平行并列生长,试样具有良好的定向效果.
Taking Ti-52% Al alloy as the research object, the experiments of thermal stabilization at different time in Bridgman directional solidification furnace and the related directional solidification experiments were carried out. The formation of the paste-like zone before the directional solidification, the microstructure evolution and the interface morphology And solute distribution were investigated and the effect of heat treatment on the directionally solidified structure was also investigated.The results showed that the melted sample formed a paste-like area composed of α-phase grains, Al-rich droplets and liquid passage between grains, With the increase of heat treatment time, the α grains in the mushy zone gradually fuse and are aligned along the temperature gradient direction, and the Al-rich droplets and the liquid phase passage disappear gradually. The solid / liquid The interface becomes smooth and smooth.When the heat treatment time is long enough, the mushy zone is a single α phase, and the composition of solute Al changes along the α solidus in the growth direction.According to the conservation of solute, the complete liquid region The content of solute Al was 52.21%, which was higher than that of the original sample, which was in good agreement with the experimental results.Further study was made on the effect of heat-stable treatment on the subsequent directional solidification structure and found that reasonable heat-stable treatment time (≥30 min) solidification The presence of a stabilizing action at the interface temperature and concentration fields, columnar grain growth direction can be parallel to the parallel growth, the sample has a good directional effect.