Resolidification behavior of single-crystal superalloys

Investigation of the final stages of solidification and eutectic phase formation in Re and Ru containing nickel-base superalloys

“…(4) The nucleation and growth of the eutectic island appear to be epitaxially on the primary solidified g dendrite, since no evidence of any misorientation and grain boundaries could be found. In the same vein, it seems reasonable to expect the resolidification of partially molten eutectic islands in the same crystallographic orientation, which has also been experimentally verified by Hegde et al [15]. The upper limit for the homogenisation heat treatment process is thus not necessarily defined by the incipient melting point of the eutectic island, but by the solidus temperature of the primary g dendrite.…”

“…This is generally done by a heat treatment process below the incipient melting point of the coarse eutectic islands. However, there is also a possibility of an improved and more economic heat treatment cycle, by heating above the incipient melting point [13][14][15]. The localized liquid interdendritic region would enable liquid diffusion, which is several orders of magnitude higher than solid state diffusion.…”

An Analysis of Solidification Path in the Ni-Base Superalloy, CMSX10K

“…This requires a detailed characterisation of the interdendritic constituent. While dissolution of the non-equilibrium phases and subsequent homogenization can be achieved by heating to below the incipient melting point and purely relying on solid-state diffusion, a more innovative approach that can appreciably decrease the solutioning time is by heating above the incipient melting point to produce localized melting within the inter-dendritic region [3,4]. By subsequent holding at this temperature, the resultant melted region is "healed" and liquid disappears with growth of the primary solid and is similar in principle to the phenomenon of constitutional liquation [5].…”

Clear path to the directional solidification of Ni-based superalloy CMSX-10: A peritectic reaction

“…It has been commonly accepted that the secondary solidification, leading to the formation of the /' network and coarse ' precipitates in the interdendritic regions, followed the eutectic reaction L →  + ' [4,8,10]. However, a number of authors suggested early that solidification in the interdendritic region could be the result of the peritectic reaction L +  → ' [2,6] and more recent research suggested it faintly though no concrete evidence could be advanced [3,7,8].…”

“…Therefore, a heat treatment process is necessary after casting in order to dissolve the ' precipitates, homogenize the composition across the dendrites and subsequently reform homogeneously fine ' precipitates. It is thus of great interest to reduce the cost of such heat treatment process, at high temperature and for significantly long time [1,[3][4][5]. As a consequence, better understanding of the solidification path is required and in particular the solidification of the interdendritic region, long referred to as "eutectic islands", where these coarse ' precipitates are formed.…”