Experimental investigation of phase equilibria in the Co-rich part of the Co-Al-X (X = W, Mo, Nb, Ni, Ta) ternary systems using diffusion multiples

Insight in phase equilibria is very valuable for the design of Co-based superalloys that have the potential of 50 degrees C higher temperature capability than Ni-based superalloys. The Co-rich part of the Co-Al-X (X = W, Mo, Nb, Ni, Ta) ternary systems is especially important and was thus investigated using two sets of diffusion multiples (Ni-Co-CoAl-Cr-Mo-Nb-Ta-Wand Ni-Co-NiAl-Si-Zr). Isothermal sections of the Co-Al-W and Co-Al-Nb systems at 900 degrees C as well as the Co-Al-Mo, Co-Al-Ni and Co-Al-Ta systems at both 900 degrees C and 800 degrees C were constructed from the results of scanning electron microscopy (SEM) and electron probe microanalysis (EPMA). The data can be used as experimental input to future thermodynamic assessments of the Co-Al-X ternary systems in order to improve the relevant thermodynamic databases for the design and development of Co-based superalloys. (C) 2016 Elsevier B.V. All rights reserved.