Structure and preferred orientation of primary phases of Ni-Al-Co-based alloy alloyed by Rhenium after annealing and creep exposure

Elena Nikonenko,Nina Koneva,Natalya Popova,Alisa Nikonenko,N.O Kopanitsa,A.A Klopotov,T.Y Ovsyannikova,V.S Plevkov,L.A Teplyakova,P.A Radchenko

doi:10.1051/matecconf/201814303003

Elena Nikonenko, Nina Koneva + Show 8 more

Open Access

https://doi.org/10.1051/matecconf/201814303003

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Abstract

The present paper investigates phase composition and fine structure of Ni-Al-Co-based alloy alloyed by Rhenium (Re) (~3 at.%), as well as studies preferred orientation of the given alloy primary phases by means of scanning electron microscopy and X-ray diffraction analysis. The original state was given as the alloy which underwent a complete cycle of heat treatment: stepwise homogenization, cooling, annealing, and cooling at 100°C/min back to room temperature. The alloy was further subject to annealing at 1000°C for 105 h and 968 h. It was also exposed to creep experiments at the same temperature for 105 h (loading 320 MPa), and for 968 h (220 MPa). γ- and γ′-phases were established to be the primary phases in both states of face-centered cubic crystal lattice. γ′-phase (phase with ordered atom arrangement having L12 superstructure) was the primary phase in all states of the alloy. Investigations showed that Re being able not to dissolve in the primary phases served as a phase-forming element. Phase composition and phase morphology were studied. The influence of high-temperature annealing and creep on superalloy structure and morphology of γ′-phase were defined. The influence of creep on the structure was proven to be different from the annealing effect. First, creep generated larger dissipation of orientations than annealing. Second, anisotropy of γ′-phase cuboids could be observed at meso-level. Cuboids partially joined together. Third, spheroidized cuboids could be often met after creep.

Highlights

Development and application of metallic materials to a large extend define advance in modern engineering due to their required operation properties
Superalloys based on ( + )-phases can serve as an example, where -phase is a disordered face-centered cubic solid solution, while -phase is an ordered phase with L12 superstructure [1,2,3]. -phase is the primary phase in these modern superalloys
X-ray diffraction analysis (XRD) on thin foils using EM-125 transmission electron microscope with 125 kV accelerating voltage was used as the main research method

Summary

Introduction

Development and application of metallic materials to a large extend define advance in modern engineering due to their required operation properties. The requirement levels applied to these materials constantly grow along with the new objectives engineers are facing while new equipment development, and its operation under extreme conditions in particular – high speeds, high temperatures, etc. -phase is the primary phase in these modern superalloys. This is the reason why -phase is largely responsible for the formation of superalloy properties. Superalloys are often produced based on the Ni – Al alloy [1], alloyed by various refractory elements [1, 3, 4]. Introduction of large amount of different alloying elements as well as annealing and creep of superalloy can change its texture [5].

Materials and methods

Phase composition and -phase state

Preferred orientation of - and -phases

Conclusion