DEVELOPMENT OF A LOW-DENSITY RHENIUM-FREE SINGLE CRYSTAL NICKEL-BASED SUPERALLOY BY APPLICATION OF NUMERICAL MULTI-CRITERIA OPTIMIZATION USING THERMODYNAMIC CALCULATIONS

摘要

A computational alloy design method based on numerical multi-criteria global optimization is presented (termed MultOPT). Its application is demonstrated by the design of a novel rhenium-free low-density superalloy called ERBO/15. This alloy has been produced and tested on a lab-scale and results on high temperature creep strength and microstructure are presented. Despite its low density of 8.4 g/cm~3 and despite the fact that it contains no Re, the creep strength of ERBO/15 is comparable to that of the rhenium-containing alloy CMSX-4. With our MultOPT approach, in order to identify promising compositions, large compositional spaces can be scanned and the full complexity of superalloys can be taken into consideration. It is ensured that from a mathematical point of view the best possible alloy for the given requirements is found. The alloy properties are predicted by thermodynamic CALPHAD-calculations and by an empirical model for creep strength in the high-temperature, low-stress regime: The creep strength is maximized by maximizing the weighted amount of solid solution strengthening elements in the matrix and maintaining an optimum morphology and fraction of the γ'-phase. The optimization algorithm uses Kriging surrogate models for higher performance. Additionally in order to prepare the future usage of more complex alloy property models in the optimization, an existing TCP-phase precipitation model is validated experimentally within the paper.