Influence of rhenium and cooling rate on the solidification of Ni base superalloys, inconel 718

Abstract

Influence of 2-6% 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 γ, eutectic (γ+NbC) and eutectic (γ+Ni2Nb). Higher additions of Re increase the volume fraction of primary γ and enlarge the secondary dendrite arm spacing. The influence of cooling rates at 1, 10 and 100K/min has also been studied on the solidification process of the alloy containing 3.5% Re. With increasing cooling rate, the crystallization start temperatures of primary γ and eutectic phases decrease and the volume fraction of NbC and Ni2Nb 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. © 2005 The Japan Institute of Metals.