Influence of Rhenium and Cooling Rate on the Solidification of Ni Base Superalloys, Inconel 718

摘要

Influence of 2-6 percent Re additions has been investigated on the solidification phenomenon of a Ni base superalloy, In718. The solidification of each alloy proceeds in the order of primary gamma, eutectic (gamma+NbC) and eutectic (gamma+Ni_2Nb). Higher additions of Re increase the volume fraction of primary gamma and enlarge the secondary dendrite arm spacing. The influence of cooling rates at 1, 10 and 100 K/min has also been studied on the solidification process of the alloy containing 3.5 percent Re. With increasing cooling rate, the crystallization start temperatures of primary gamma and eutectic phases decrease and the volume fraction of NbC and Ni_2Nb increase. EPMA analysis revealed that the distribution of alloy elements in microstructure also changed depending on cooling rate. The redistribution of alloy elements during solidification was evaluated by Clyne-Kurz and Ohnaka theories.