原位观察不同冷却速率下GH3625合金的凝固过程

In-situ Observation of Solidification Process of GH3625 Superalloy at Different Cooling Rates

利用带有红外加热炉的共聚焦激光扫描显微镜(CLSM)对GH3625高温合金在不同冷却速率(30℃/min、100℃/min和200℃/min)下的凝固过程进行了动态原位观察,通过差示扫描量热分析仪(DSC)、扫描电镜(SEM)和能谱仪(EDS)研究了凝固后的组织形态及相的析出规律。结果表明,GH3625合金的液相线温度在1 356.5℃,在凝固过程中自由表面液相分数随温度和时间的变化关系满足Avrami方程;凝固过程中主要相的析出顺序依次为γ基体相、碳化物和Laves相;在GH3625合金凝固过程中,随着冷却速率的增大,枝晶细化,枝晶间距减小,成分偏析减轻,Laves相分布更加弥散,且以析出共晶Laves相为主;凝固末期大量的Nb元素富集在枝晶间和晶界,这是形成Laves相的主要原因。

The solidification process of the GH3625 superalloy was in-situ observed at different cooling rates(30℃/min,100℃/min and 200℃/min)by means of confocal laser scanning microscope combined with an infrared image furnace.Differential scanning calorimeter(DSC),scanning electron microscope(SEM)and energy dispersive spectrometer(EDS)were adopted to observe the solidified microstructure and the regularity of precipitated phases.The results showed that the liquidus temperature of GH3625 superalloy was 1 356.5℃,and the relationship between the variation of solid phase content at the free surface and temperature as well as time was in accordance with Avrami equation.With the decrease of temperature,the precipitation sequence of phases wereγmatrix phase,carbides and Laves phase.In the solidification process of GH625 superalloy,with the increasing cooling rate,the dendritic structure refined,the dendrite arm spacing decreased,component segregation reduced,the Laves phase distribution was more dispersed,and mainly precipitated eutectic Laves phase.A large number of Nb segregation occurred in the final period of solidification at the interdendritic and grain boundaries,and this mainly contributes to the formation of Laves phase.