两种Ni-Cr-Co基高温合金的凝固偏析及其对Rayleigh数的影响

利用SEM和EDAX研究了2种Ni-Cr-Co基高温合金GH742和GH738凝固过程中组织、液相成分变化,用图像分析软件测定了各温度下的液相分数,并计算了2种合金凝固过程中液相密度差和相对Rayleigh数变化。结果表明,GH742凝固过程中主要是Cr、Co和Nb的偏析,GH738合金凝固过程中主要是Cr、Co和Ti的偏析;GH742和GH738合金凝固过程中都存在着液相密度反转,后者密度差的绝对值较大;GH738合金相对Rayleigh数绝对值的最大值是GH742的3.5倍,凝固时更易形成黑斑。

Variation of Liquid Composition and its Effects on Relative Rayleigh Number during Solidification of Two Kinds of Ni-Cr-Co based Superalloys

Solidification microstructure and liquid composition were analyzed by SEM and EDAX during solidification of Ni-Or-Co based superalloys GH742 and GH738. The liquid fraction under different temperatures was calculated by image analyzing software. The liquid density difference and relative Rayleigh number were also calculated. It is found that the main segregating alloy elements during solidification of GH742 are Or, Co and Nb, and that of GH738 are Or, Co and Ti. There is liquid density inversion during solidification of both alloys and the absolute value of liquid density difference of GH738 is larger than that of GH742. The maximum absolute value of relative Rayleigh number of GH738 is 3.5 times of that of GH742 and the former is more prone to freckling.