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

Abstract

A detailed analysis of solidification path has been conducted in a typical 3 rd generation Ni-base superalloy, CMSX10K. Using calorimetry and X-ray spectroscopy the solidification sequence, pertinent phase transformation temperatures, evolution of fraction solid with temperature and the accompanying micro-segregation has been determined. Particular emphasis is directed at the latter stages of solidification when non-equilibrium phases form within the inter-dendritic regions. A detailed characterisation of this constituent is carried out to highlight the severity of microsegregation. Relevance and applications of these results in the design of optimum heat treatment cycles to eliminate the as-cast coring and also guidelines from the view of alloy design and its implications to castability are discussed.

Solidification Characteristics and Segregation Behavior of Nickel-Base Superalloys in Dependence on Different Rhenium and Ruthenium Contents

“…As a consequence, the experimentally obtained quasi-binary phase diagrams from DSC measurements are only valid for the beginning of solidification, but not for the continuing Bridgman solidification process. While the concentration c D of the first solid formed is assumed to be controlled by the liquid diffusion coefficient, as described earlier, for the c ID , the following two other effects have to be considered: (1) An increase in the freezing range with increasing c 0 (Re) provides more time for liquid diffusion, which in turn leads to an increase in Re microsegregation into the dendrite due to its high solubility limit (thus, c ID decreases) and (2) because the remaining Re concentration at the beginning of the eutectic/peritectic solidification [24,25,33] gets distributed within the eutectic pools, the increasing eutectic fraction with increasing Re content generates, in total, a lower c ID . Altogether, a higher c 0 (Re) thus leads to a decrease in c ID along with an increase in c D , which results in a very strong increase in the experimentally measured segregation coefficient k S (Re) = c D /c ID .…”

“…The necessary undercooling for the onset of solidification is expected to be 5 K, according to investigations of comparable superalloys and equal cooling rates. [24,25] The data were used to develop quasi-binary phase diagrams for Re at different constant Ru contents and for Ru at different constant Re contents. Furthermore, the thermophysical properties of all alloys have been simulated by using ThermoCalc software version R with the database TTNi7 (ThermoTech Ltd., Guildford, United Kingdom) and were compared to experimentally derived values.…”

Influence of withdrawal rate on last stage solidification path of a Mo-rich Ni3Al based single crystal superalloy

“…Meanwhile, the volume fraction of IDP obviously increased with increasing withdrawal rate. It is worth noting that the precipitation morphology of experimental alloy are significantly different from that of Ni based SC superalloys, which are typical c/c 0 eutectic microstructure at the interdendritic region [7][8][9][10][11][12]. Fig.…”

“…Nowadays, in order to further improve the high temperature properties of Ni based SC superalloys, refractory elements (such as Re, W, Mo and Ta) are increasingly added in SC superalloys, which causes severe microsegregation and numerous interdendritic precipitation during solidification, leading to the increment of difficulty of solution treatment [4][5][6]. Therefore the solidification path and interdendritic precipitation have been widely studied in CMSX-4 [7], CMSX-10 [7], CMSX-10K [8][9][10], Astra series alloys [11], CM and UM series alloys [12], etc. Furthermore, with regard to the production of turbine blades, their complex shapes easily promoted the formation of grain defects, e.g.…”

Single-Crystal Casting/Directional Solidification

“…The seed will be partially melt-back during the thermal soaking period of the mold prior casting and can generate copious nucleation of stray grains with random orientations distributed uniformly around the perimeter of the seed at the melt-back interface (33,61,74). In this case, the role of the grain selector is mainly to control the remelting and to eliminate the growth of the formed stray grains especially in the zone between the semisolid seed and the molten alloy (61,64,71,72,75,76). …”