Experimental Investigation and Thermodynamic Calculation of the Al-Cr-Pd Ternary System

Abstract

The aluminide coating can extend the service life of the superalloy. The addition of Cr and Pd improves the oxidation and thermal corrosion resistance of the aluminide coating as well as avoiding the formation of brittle precipitates. However, the phase relations of the Al-Cr-Pd ternary system above 1100 ℃ and the thermodynamic description were lacking to guide the compositional design of the Cr and Pd co-modified aluminide coating. Herein, the isothermal section of the Al-Cr-Pd ternary system at 1150 ℃ was experimentally determined through scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy and X-ray diffraction. In addition, a thermodynamic description of the ternary system was established by the application of CALPHAD (CALculation of PHAse Diagrams) technique based on the experimental results of the isothermal section at 930, 970, 990, 1020 and 1150 ℃. The solidification paths of typical alloys determined in the previous literature were also fitted. A set of self–consistent thermodynamic parameters for the Al-Cr-Pd ternary system was obtained with a reasonable agreement between the experimental and calculated results. The results provide a basis for the compositional design of aluminide coatings and enrich the Al-based database.

Keywords: Al-Cr-Pd ternary system, Phase equilibria, thermodynamic modeling, aluminide coating, liquidus projection