将电磁场引入到Inconel 625合金的凝固过程中,研究电磁力对合金凝固组织和力学性能的影响. 结果表明,电磁场可显著细化合金晶粒, 但当施加不合理的电流强度和频率时,电磁场会加速凝固前沿的熔体对流, 导致凝固末端产生更严重的枝晶偏析,形成更多的共晶组织. 微观表征结果表明, 电磁场作用下Nb和Mo元素偏析比的增大,是共晶组织含量增多的根本原因.晶粒细化和共晶组织增多共同影响了合金的室温拉伸性能,使合金屈服强度提高、拉伸塑性下降.合理控制电流强度及频率大小可有效控制共晶组织分数.当施加电磁场的电流强度为100 A, 频率为8 Hz时, 合金中共晶组织含量最少,合金在不损失塑性的前提下屈服强度提高30%以上.

Inconel 625 is a Ni—Cr—Mo—Nb alloy which was developed primarily for high turbine applications. The elemental addition of Nb increases the solidification temperature range, which exhibits a strong propensity to form interdendritic segregation. The enrichment of elements Nb and Mo at the terminal stage of solidification leads to the formation of brittle eutectic structure, i.e., γ+Laves phases, which becomes potential crack origin during the subsequent hot processing and application. The present work has demonstrated that, the introduction of electromagnetic field (EMF) to the solidification process of Inconel 625 alloy has the obvious effect on grain refinement. The EMF can also effectively influence the segregation ratio of Nb and Mo. However, the inappropriate application of electric current intensity and frequency will lead to more severe segregation of elements Nb and Mo, which causes the increment of eutectic structure volume fraction. Further analysis illustrates that both of the grain refinement and eutectic volume fraction control the tensile property at room temperature, increasing the yield strength and decreasing the tensile plasticity for Inconel 625 alloy. It has been proven that a proper selection of input current intensity (100 A) and frequency (8 Hz) can effectively dominate the segregation behavior during solidification process under EMF with more than 30% increase of yield strength and a minute loss of plasticity.