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Loss of mass due to evaporation during molten metal levitation processing significantly influences the evaluation of density, viscosity and surface tension during thermophysical property measurement. Since there is no direct way to track the evaporation rate during the process, this paper describes a mathematical approach to track mass loss and quantify any changes in alloy composition as a function of time and temperature. The Ni-based super alloy CMSX-4 Plus (SLS) was investigated and a model was developed to predict the dynamic loss of mass with time and track the potential for composition shifts throughout each thermal cycle based on the Langmuir's equation for ideal solution behavior. Results were verified by post-test chemical analysis of key elemental constituents including Al, Cr, Ti, and Co where the error in composition for each element was less than 1% when the activity of aluminum in solution was fixed at zero - effectively eliminating evaporation of aluminum for ground-based electrostatic levitation (ESL) testing in vacuum. This model predicts the mass evaporation for Al and Co within ± 6% errors for CMSX-4 plus samples processed in ESL. Application of this technique to the space tests using the ESA ISS-EML facility shows that by conducting experiments in an inert shielding-gas environment, composition shifts due to differential relative evaporation become negligible and the composition is maintained within the desired limits. By tracking overall mass loss during testing the influence of evaporation on density measurements is discussed. [ABSTRACT FROM AUTHOR]

The solidification path of directionally solidified Ni-based superalloys is an important feature to define the heat treatments necessary after casting. Ni-based superalloy CMSX-10 was solidified at different velocities in a modified Bridgman type furnace allowing rapid quenching of the samples in water. The results of the experiments allowed to clarify the solidification of the interdendritic region, from nucleation of fine γ′ precipitates at the primary γ dendrite surface to the spatial growth and coarsening of the interdendritic colonies' morphology towards the end of solidification. A three-dimensional model is proposed and explains the different morphologies in the interdendritic region according to the observation plane. The study revealed strong evidence of a solidification in the interdendritic region of peritectic nature. Solute rejection into the liquid ahead of the growing phases, diffusion and convection effects lead to the coupled growth of the γ and γ′ phases according to the reactions L → γ and L + γ → γ′ respectively. [ABSTRACT FROM AUTHOR]

Abstract: Quantitative microsegregation analyses were systematically carried out during the solidification of the Ni-base superalloy CMSX-10 to clarify the methodological effect on the quantification of microsegregation and to fully understand the solidification microstructure. Three experimental techniques, namely, mushy zone quenching (MZQ), planar directional solidification followed by quenching (PDSQ), and random sampling (RS), were implemented for the analysis of microsegregation tendency and the magnitude of solute elements by electron probe microanalysis. The microprobe data and the calculation results of the diffusion field ahead of the solid/liquid (S/L) interface of PDSQ samples revealed that the liquid composition at the S/L interface is significantly influenced by quenching. By applying the PDSQ technique, it was also found that the partition coefficients of all solute elements do not change appreciably during the solidification of primary γ. All three techniques could reasonably predict the segregation behavior of most solute elements. Nevertheless, the RS approach has a tendency to overestimate the magnitude of segregation for most solute elements when compared to the MZQ and PDSQ techniques. Moreover, the segregation direction of Cr and Mo predicted by the RS approach was found to be opposite from the results obtained by the MZQ and PDSQ techniques. This conflicting segregation behavior of Cr and Mo was discussed intensively. It was shown that the formation of Cr-rich areas near the γ/γ′ eutectic in various Ni-base superalloys, including the CMSX-10 alloy, could be successfully explained by the results of microprobe analysis performed on a sample quenched during the planar directional solidification of γ/γ′ eutectic. [Copyright &y& Elsevier]

Push–pull fatigue tests were conducted under a sinusoidal stress waveform with a frequency of 1 Hz and a trapezoidal one with a hold time in both tension and compression at 300 MPa-amplitude. Tests were conducted at a temperature of 1273 K using smooth bar specimens of the nickel-base single-crystal superalloy CMSX-10. Small cracks were observed on the surface of the interrupted specimens by means of optical and scanning electron microscopes and their number and length were measured. The fatigue behaviour was characterized as follows: (1) A number of small cracks were initiated at a relatively early stage on the grain boundaries of the surface oxide which were perpendicularly to the tensile stress axis direction. (2) Some of these cracks grew inside and reached the base metal. Their growth brought about final fracture of the specimen. (3) The creep strain during the stress hold period accelerated the growth rate of the small cracks and shortened the fatigue life. [ABSTRACT FROM AUTHOR]