Influence of composition on microstructural parameters of single crystal nickel-base superalloys

Fourteen nickel-base superalloy single crystals containing a range of chromium (Cr), cobalt (Co), molybdenum (Mo), and rhenium (Re) levels, and fixed amounts of aluminum (Al) and tantalum (Ta), were examined to determine the effect of bulk composition on basic microstructural parameters, including gamma' solvus, gamma' volume fraction, topologically close-packed (TCP) phases, gamma and gamma' phase chemistries, and gamma-gamma' lattice mismatch. Regression models describing the influence of bulk alloy composition on each of the microstructural parameters were developed and compared to predictions by a commercially-available software tool that used computational thermodynamics Co produced the largest change in gamma' solvus over the wide compositional range explored and Mo produced the biggest effect on the gamma lattice parameter over its range, although Re had a very potent influence on all naicrostructural parameters investigated. Changing the Cr, Co, Mo, and Re contents in the bulk alloy had an impact on their concentrations in they gamma matrix and to a smaller extent in the gamma' phase. The software tool under-predicted gamma' solvus temperatures and gamma' volume fractions, and over-predicted TCP phase volume fractions at 982 degrees C. However, the statistical regression models provided excellent estimations of the microstructural parameters and demonstrated the usefulness of such fummlas. (C) 2012 Elsevier Inc. All rights reserved.