Experimental Investigation and Thermodynamic Modeling of the Co-Rich Region in the Co-Al-Ni-W Quaternary System

The stabilities of the gamma-(Co), gamma'-Co-3(Al,W), mu-Co7W6, beta-CoAl and alpha-(W) phases in the Co-Al-W and Ni-Al-W ternary systems were investigated at 900, 1000, 1100 and 1300 degrees C. Electron probe microanalysis was used to determine compositions of the phases. Scanning electron microscopy was used to determine area fractions of the phases present after heat treatments. Thermodynamic modeling of the Co-Al-Ni-W quaternary system, using Pandat (TM) software, was incorporated to determine relevant thermodynamic parameters for phases in the Co-rich region of the system. Phases were modeled using the substitutional solution model and compound energy formalism. Excellent agreement was found between experiments and thermodynamic modeling. This new thermodynamic database enables predictions of stable gamma-gamma' compositions for a new class of high temperature, high strength Co-base superalloys.