EBSD STUDIES OF GRAIN EVOLUTION AND GRAIN SELECTION BEHAVIOR DURING THE PREPARATION OF Ni–BASED SINGLE CRYSTAL SUPERALLOY DD3

Abstract

Ni-based single-crystal superalloy DD3 was prepared by using the modified Bridgman apparatus with spiral grain selector. Grain structure evolution and grain selection in spiral selector have been investigated. Electron back scattered diffraction (EBSD) technique was used to characterize the grain texture evolution. The main function of starter block is to optimize the grain orientations. At the height of 36.1 mm from the copper chill plate, the misorientations of nearly 90% grains are less than 10 ◦ , and few grains' orientations deviate from solidification direction more than 12 ◦ . Finally, only one grain is allowed to grow into the cast by grain selcting with one pitch in spiral part. Moreover, due to the geometric constraint of spiral selector, the grains near the outer wall are gradually overgrown by the grains close to the inner wall of spiral passage. The grain selection in the spiral selector can be mainly attributed to the geometric constraint of narrow passage.