闵志先沈军熊义龙王伟杜玉俊刘林傅恒志
金属学报
doi:10.3724/SP.J.1037.2011.00015
采用液态金属冷却(LMC)定向凝固结合液淬法, 在温度梯度(G)为250 K/cm, 凝固速率(V)为2-400 μm/s的条件下系统研究了镍基高温合金DZ125的固/液界面形态、胞/枝晶间距及MC碳化物形态. 随着V的增大, 界面形态经历了浅胞状→深胞状→粗枝晶→细枝晶的转变. 一次胞晶间距随着V的增大而增大, 当V=5 μm/s时, 固/液界面达到胞-枝转变点, 且一次枝晶间距达到最大值. 当V≧10 μm/s时, 一次枝晶间距和二次枝晶间距随着V的增大而减小. MC碳化物生长形态随着V的增大由胞-枝转变点的八面体依次向骨架状、汉字体状、细小枝晶转变. 分析表明, 一次枝晶间距与Trivedi模型和Ma模型吻合较好, 同时, 低速下(V≦50 μm/s)一次枝晶间距与Hunt-Lu模型吻合得很好, 但高速时发生了明显的偏差. 通过非线性拟合得到一次枝晶间距和二次枝晶间距与V分别满足λ1=314.6V-0.24±0.02和λ2=97.76V-0.33±0.01. MC碳化物在凝固中后期由液相析出, 其形态主要受到固/液界面形态和V的影响.
关键词:
镍基高温合金
,
directional solidification
,
microstructure
,
dendritic spacing
G.W. Chang
,
G.C. Jin
,
S.Y.Chen
,
X.D. Yue
金属学报(英文版)
According to the nature of the periodic bending deformation of solid-liquid interface in the solidification process of continuous casting slab，The nucleation and extension of crack was analyzed by the variation of temperature gradient and dendritic spacing in the front edge of solid-liquid interface. The results indicate that the bending deformation of interface makes temperature field change in the front edge of solid-liquid interface; the occurrence of temperature gradient along drawing direction provides the condition for the growth of secondary dendrites; The crack source formed during the middle and final stage of solidification may extend to the surface of casting slab and become internal crack. The theoretical analysis is basically agreement with the experimental results.
关键词:
continuous casting
,
null
,
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