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采用选晶法在改进的Bridgman定向凝固炉上进行镍基单晶高温合金DD3定向凝固实验,研究了选晶法制备镍基单晶高温合金过程中晶粒组织演化和螺旋选晶行为,采用电子背散射衍射(EBSD)技术对晶粒的竞争过程进行分析.结果表明,选晶器引晶段的主要作用是优化晶粒取向.获得取向良好的<001>定向凝固组织.在距激冷板36.1 mm处,90%的<001>取向晶粒与轴向偏离小于10°,只有很少的晶粒取向与轴向偏离大于12°.螺旋选晶段的主要作用是确保只有一个晶粒进入型腔,在选晶段沿螺旋方向攀旋一周时就可获得单晶组织.选晶过程中,远离选晶器螺旋通道内侧的晶粒由于受到螺旋通道较强的几何约束,进而被靠近螺旋通道内侧的晶粒所淘汰.螺旋选晶器的狭窄通道对枝晶生长的阻碍作用是实现螺旋选晶的主要原因.
In the modified Bridgman directional solidification furnace, a directional solidification experiment of DD3 on Ni-based single crystal superalloy was carried out. The evolution of microstructure and spiral crystal growth during the preparation of Ni-based single crystal superalloy were studied. The results show that the main function of the seeding section of the crystallizer is to optimize the grain orientation and to obtain the well-oriented <001> directional solidification structure. In the distance from the cold plate At 36.1 mm, 90% of the <001> oriented grains deviate less than 10 ° from the axial direction with only a few grain orientations deviating from the axial direction by more than 12 °. The main effect of the helical grains is to ensure that only one grain enters In the process of selecting crystal, the grains far away from the inside of the spiral channel of the crystal selector due to the strong geometric constraint of the spiral channel are further close to the spiral Channel inside the elimination of the grain.The narrow channel of the spiral selector for dendrite growth impede the main reason for spiral selection.