Abstract: he NASAIR100 single crystal solidified with the planar,cellular,coarse dendritic and fine dendritic solid liquid interfaces are obtained using‘ seed’ technique in the LMC directional solidification device with higher temperatures and higher thermal gradients made by ourselves.The microstructure and mechanical properties are studied under as cast and 1280℃,1300℃and1320℃×4h A. C. heat treated conditions.The resultS show that the microsegregation getS more and more severe andthe temperature at which the as-cast γ′and γ/γ′ eutectic can be throughly soluted becomes higher and higher as the solid liquid interface shape is turned from the planar into the cellular, then the coarse dendritic and finally the fine dendritic, Compared to the low thennal gradients in industrial production condition,the high thermal gradient can considerably improve the casting quality,and thus enhanee the high tempcrature mechanical properties of the single crystals.A high withdrawal rate and a soluting temperature as high as possible can further improve the mechanical properties.

Key words: nickel alloys, solidification, microstructures, mechanical property