Mechanical properties and microstructure of large IN713LC nickel superalloy castings

¹ UJP PRAHA a.s., Nad Kamínkou 1345, 156100 Praha 5 – Zbraslav, Czech Republic
² Czech Technical University in Prague, Faculty of Mechanical Engineering, Department of Materials Engineering, Karlovo náměstí 13, 12000 Praha 2, Czech Republic
³ První brněnská strojírna Velká Bíteš a.s., Precision Casting Division, Vlkovská 245, 59512 Velká Bíteš, Czech Republic

^a Corresponding author: zyka@ujp.cz

Abstract

When approving large castings for use, mechanical values are measured by room temperature tensile test on test bodies made from the centres of the castings. These test bodies often exhibit lower values than required, in particular ultimate tensile strength and elongation. The presence of fragile niobium carbides in the structure of the alloy was identified as the main cause of this situation, which originated as a result of the slow speed cooling. Because of large grain size compared to gauge length diameter, crystal orientation of individual grains also plays an important role. Interdendritic carbides are oriented parallel with dendrites thus parallel with < 100 > directions in Ni superalloy crystal lattice. Grain oriented with < 100 > axis parallel to tensile direction has platelet carbides oriented perpendicular to the tensile axis. In that position carbides crack easily at low grain deformation. Longitudinal metallographic cuts of selected tested specimen gauge lengths were prepared and grain orientation of individual grains was investigated by EBSD, Specimens, where grain oriented with < 100 > axis parallel to tensile direction were found, performed poor elongation values 3%, compared to 7% where no such oriented grains were found.