Computational design of model Re/Ru bearing Ni-base superalloys

K.V Vamsi,K.S Vinay,R Balamuralikrishnan,S Karthikeyan,D Banerjee,K.N Goswami,S.K Verma,Niranjan Das

doi:10.1051/matecconf/20141417007

Abstract

It is well established that Re and Ru additions to Ni-base superalloys result in improved creep performance and phase stability. However, the role of Re and Ru and their synergetic effects are not well understood, and the first step in understanding these effects is to design alloys with controlled microstructural parameters. A computational approach was undertaken in the present work for designing model alloys with varying levels of Re and Ru. Thermodynamic and first principles calculations were employed complimentarily to design a set of alloys with varying Re and Ru levels, but which were constrained by constant microstructural parameters, i.e., phase fractions and lattice misfit across the alloys. Three ternary/quaternary alloys of type Ni-Al-xRe-yRu were thus designed. These compositions were subsequently cast, homogenized and aged. Experimental results suggest that while the measured volume fraction matches the predicted value in the Ru containing alloy, volume fraction is significantly higher than the designed value in the Re containing alloys. This is possibly due to errors in the thermodynamic database used to predict phase fraction and composition. These errors are also reflected in the mismatch between predicted and measured values of misfit.

Highlights

It is understood that while Re improves creep resistance via solute strengthening and due to lower diffusivity [13], Ru suppressed the formation of Topologically Close Packed (TCP) phases which would otherwise form in Re containing alloys [8,9,10]
The aim of this work was to explore if one can computationally design a series of alloys with varying levels of Re and Ru, but where microstructural parameters such as γ phase fractions and lattice misfit are constant across the alloys
After homogenization the alloy composition is uniform within the dendrite arms as confirmed by Electron Probe MicroAnalysis (EPMA)

Summary

Introduction

It is understood that while Re improves creep resistance via solute strengthening and due to lower diffusivity [13], Ru suppressed the formation of Topologically Close Packed (TCP) phases which would otherwise form in Re containing alloys [8,9,10]. A possible reason for such contrasting conclusions from these studies is that these alloys were designed such that while systematically varying the relative amounts of Re and Ru, no constraints were imposed on microstructure Such a variation in chemistry across the model alloys could result in a variation in phase fractions, precipitate size and lattice misfit between γ and γ across the alloys.

Objectives

Results

Discussion

Conclusion