Effect of Solidification Rate on the Microstructure of a Ni-Base Superalloy

Abstract

The effect of solidification rate on the solidified structure, solute segregation and microstructures such as carbide, gamma'gamma eutectic, gamma' phase and dendrite arm spacing was experimentally investigated employing a method of partially directional solidification and subsequent quick quenching. Three types of the solidified structure were identified: cellular, cellular-dendritic and developed dendrite-type, and the width of a mushy zone was narrowed when solidification rate increased from 2.5 mu m/s to 125 mu m/s. The carbide morphologies were affected by both solidified structure and solidification rate, it formed into bar-type in the cellular structure, and Chinese script-type in the dendrite structure. The increase of solidification rate caused a lot of gamma'/gamma eutectic and the change of gamma' phase from cubic into cubic-round. The dendrite arm spacing decreased and the segregation of Cr, Al, Co, Mo, Ti was alleviated with increasing solidification rate.