Pb-Bi包晶合金定向凝固微观组织演化

对Pb-(26,28,30,34)Bi(质量分数,%,下同)包晶合金进行平界面生长的低速定向凝固到枝晶状生长的高速定向凝固实验,研究了Pb-Bi包晶合金的微观组织形成及其演化。实验结果表明,在温度梯度G=30K/mm条件下,当凝固速度V=0.25μm/s时,初生α相和包晶β相均以平界面生长,凝固组织的演化过程为:单相初生α相→两相竞争组织→β单相。V=0.5μm/s时,定向凝固组织的演化过程为:单相初生α相→胞状α相+胞间包晶β相→α+β两相竞争组织→β单相。在G=20K/mm条件下,当凝固速度V=1μm/s时,初生α相以胞状领先生长,包晶β相则在胞状α间形核生长,并包裹住α胞。当凝固速度增加至V≥2μm/s时,初生α相由胞状转变为枝晶状,包晶β相则在枝晶间包围α枝晶。

Microstructure Evolution of the Directionally Solidified Pb-Bi Peritectic Alloys

The directional solidification of Pb-(26, 28, 30, 34)wt.%Bi peritectic alloys with growth velocities (V) ranging from low for planar growth to high for dendritic growth were carried out. And the microstructure formation and evolution were investigated. The results indicate that the primary α phase and peritectic β phase all grew with planar interface as the temperature gradient G was 30 K/mm and V was 0.25 μm/s, and the microstructure evolution was presented as: single primary α phase → competitive microstructure → single β phase. As the growth velocity increases to 0.5 μm/s, the microstructure evolution was experienced to single primary α phase → cellular α + inter-cellular β → competitive microstructure →single β phase. As the G was 30 K/mm and V was 1 μm/s, the α phase grew as cells, and the β phase grew around the α cells. When the V increased to higher than 2 μm/s, the α phase grew as dendrites, and the β phase grew in the inter-dendritic region.