镍基合金激光超高温度梯度定向凝固

ULTRA HIGH TEMPERATURE GRADIENT DIRECTIONAL SOLIDIFICATION OF Ni BASE SUPERALLOY BY LASER BEAM

采用高能激光束作为定向凝固的热源，研究了镍基合金在超高温度梯度（１．０×１０４Ｋ／ｃｍ）定向凝固下的组织结构特征。在定向凝固组织中得到了平均一次枝晶间距仅为１０．６μｍ的细枝晶和完全无侧向分枝的“超细胞晶”。对合金元素在不同组织中偏析行为的分析表明：传统的定向凝固组织中存在严重的微观偏析，而激光超高温度梯度定向凝固组织中，元素的微观偏析大大改善甚至完全消除。

A novel ultra high temperature gradient directional solidification apparatus for metal slice has been set up, in which a high energy laser beam was used as the heating source. The microstructure of a Ni base superalloy under the condition of ultra high temperature gradient (1.0×10 4K/cm) with a wide range of G/R ratio was comprehensively investigated. Both superfine dendrite with average primary spacing of 10.6μm and a novel 'superfine cellular crystal', which is the extremely fine needle like cell without sidebranches, have been obtained in the laser directionally solidified microstructures. The cause for the formation of the superfine cellular crystal has been analyzed, namely, under the condition of high temperature gradient and high solidification rate, the sidebranch loses its space and time to grow and develop. The result on microsegregation shows that there exists severe microsegregation in coarse dendrite, however, the microsegregation in the laser directionally solidified microstructures is significantly improved,or even completely eliminated.