CMSX-10 단결정 초내열합금에서 일방향 응고 공정변수에 따른 응고조직 변화도

Directional solidification experiments were carried out on a single crystal Ni base superalloy CMSX-10 over a wide range of growth velocity and temperature gradient conditions. Under the imposed temperature gradients, the primary dendrite arm spacings decreased proportionally with the growth velocity. Microstructural characteristics at the solid/liquid interface were found to depend strongly on the growth velocities and temperature gradients. Based on the experimental observations, a growth velocity versus temperature gradient map was selected for planar to cellular and cellular to dendritic transitions during solidification. As a result, the microstructure selection map for the alloy was established by comparing it to theoretical models. Good agreement was obtained from the results for planarcellular and cellular-dendritic transitions. The columnar-equiaxed transition, however, was calculated using Hunt`s model for castings. The results are discussed in terms of the combined effects of constitutional undercooling and nucleation undercooling ahead of the growing dendrite tips.