(北京科技大學 材料科學與工程學院，北京 100083)
摘 要: 通過不同冷卻速度下的凝固重熔試驗，結(jié)合SEM微觀分析及電子探針成分分析，研究GH4169合金凝固過程微觀偏析的演化規(guī)律，分析凝固前沿液相區(qū)的密度變化規(guī)律，并提出基于相對Rayleigh數(shù)的凝固前沿糊狀區(qū)的穩(wěn)定性判據(jù)。結(jié)果表明：冷卻速度低于0.05 ℃/s時，液相中的Nb含量隨出爐溫度的下降很快升高到一個較高值，在較低溫度出爐冷卻時，Nb含量迅速升高到14%以上，可達合金名義成分中Nb元素含量的3倍；提高冷卻速度至0.1 ℃/s，高溫出爐時，Nb含量升高很慢，當出爐溫度低于1 310 ℃時， Nb含量迅速升高到10%以上；進一步提高冷卻速度，殘余液相中Nb元素含量變化不大，與合金的名義成分接近。當冷卻速度較高時(大于0.1 ℃/s)，GH4169合金凝固過程凝固前沿糊狀區(qū)的穩(wěn)定性較好，相對Rayleigh數(shù)較低；而當冷卻速度較低時，即低于0.02℃/s時，凝固前沿糊狀區(qū)穩(wěn)定性判據(jù)Rv值比較高，而且在1 330 ℃附近出爐冷卻時，存在一個峰值區(qū)，最大峰值接近7.5×10-13。說明當凝固過程冷卻速度較低時，元素的微觀偏析使得GH4169合金凝固前沿糊狀區(qū)的穩(wěn)定性降低，可能導致微觀偏析向宏觀偏析轉(zhuǎn)變。
關(guān)鍵字: GH4169合金；冷卻速度；微觀偏析；糊狀區(qū)穩(wěn)定性
（School of Materials Science and Engineering, University of Science and Technology Beijing, Beijing 100083, China）
Abstract:The microsegregation behaviors of GH4169 alloy during its solidification process were investigated by remelting tests, SEM and EMPA analysis. Furthermore, the density variation for the solidification front of this alloy was analyzed and a stability criterion based on relative Rayleigh number model was put forward. The results show that, when the cooling rate is lower than 0.05 ℃/s, Nb content in the residual liquid phase increases with decreasing the pouring temperature, it can reach 14%, three times of the designed Nb content for this alloy. When the cooling rate increases to 0.1 ℃/s and the pouring temperature is lower than 1 310 ℃, Nb content in the residual liquid phase reaches 10% promptly, while when the pouring temperature is higher than 1 310 ℃, Nb content in the residual liquid phase varies slowly. With the increase of cooling rate during the solidification process, Nb content in the residual liquid phase can decrease to the designed value gradually. At the same time, a heavier microsegregation of Nb element may occur at lower cooling rate in the mush zone for GH4169 during its solidifying process, resulting in the bigger relative Rayleigh number and the worse stability of mush zone, which may increase the probability of freckle formation.
Key words: GH4169 alloy; cooling rate; microsegregation; mush zone stability
