一种镍基单晶高温合金的高温度梯度定向凝固组织及枝晶偏析

来源期刊：金属学报2010年第1期

论文作者：刘刚 刘林 赵新宝 张卫国 金涛 张军 傅恒志

文章页码：77 - 83

关键词：镍基单晶高温合金； 高温度梯度； 枝晶偏析； 微观组织

Key words：Ni-based single crystal superalloy； high thermal gradient； microsegregation； microstructure

摘    要：采用双区加热和液态金属冷却法(LMC)相结合,对一种含4%Re(质量分数)的镍基单晶高温合金进行了高温度梯度定向凝固。结果表明:与传统的"高速凝固法(HRS)"(温度梯度G=20-40 K/cm,抽拉速率V=50-100μm/s,一次枝晶间距λ₁=200-400μm)相比,该技术可以显著提高凝固界面前沿的温度梯度(G=238 K/cm)和抽拉速率(V=500μm/s)。随着抽拉速率的提高,凝固界面形态呈现出平面、胞状、粗大枝晶和细枝晶形态,一次枝晶间距不断减小,通过固态相变析出的γ′强化相也被显著细化,当G=238 K/cm,V=500μm/s时,λ₁和枝晶干γ′相平均尺寸分别减小到61.3和0.04μm。电子探针测定表明,随着抽拉速率的提高,枝晶偏析呈现先增大后减小的趋势。这是高温度梯度条件下,固相反扩散作用强烈影响元素在枝晶中分布的结果。

Abstract: In order to understand the effect of high thermal gradient on the microsegregation of refractory elements in Ni-based superalloys,a Ni-based single crystal superalloy containing 4% Re(mass fraction) was prepared by dual heating zone melting and liquid-metal cooling(LMC) directional solidification technique.Comparing with the traditional high rate solidification(HRS) method with thermal gradient G=20-40 K/cm,withdrawal rate V=50-100μm/s and primary dendritic arm spacing λ₁=200-400μm,this technique can significantly increase the thermal gradient(up to 238 K/cm) and withdrawal rates(up to 500μm/s).Planar-like and cellular-like solid-liquid interfaces,coarse dendrite and fine dendrite were sequentially obtained with increasing withdrawal rates.Under the condition of G=238 K/cm and V=500μm/s,the primary dendritic arm spacingλ₁ and the mean size of γ’ precipitates(in dendrite core) obviously decreased to 61.3 and 0.04μm,respectively.In addition,the microsegregation increased initially and then decreased with increasing withdrawal rate,especially for the microsegregations of W and Re.EPMA line scan indicated that solid-back diffusion has an obvious influence on the microsegregation for the fine dendrite structure under high thermal gradient directional solidification.