Abstract

Abstract A precipitation study was carried out during the isothermal aging at 850 °C for Fe-10at.%Ni-15at.%Al, Fe-10at.%Ni-15at.%Al-2.5at.%Cu and Fe-10at.%Ni-15at.%Al-5at.%Cu alloys. The experimental, Calphad, and Kinetic/Precipitation calculated results indicated that the Cu-addition to the ternary alloy promoted a higher volume fraction of β´precipitates, which caused a better aging response for the Cu-containing alloys. The coarsening resistance was the highest for the 2.5 at. % Cu-containing alloy, compared to the ternary alloy because of its lower interfacial free energy, 0.009 Jm-2, between the precipitate and the matrix. The Cu alloying element was located mainly in the β´ precipitate according to its expected thermodynamic behavior, and it caused an atomic relation of Ni to Al close to that of NiAl intermetallic compound for the β´phase. A content of 5 at. % Cu in the ternary alloy promoted higher interfacial energy, 0.04 Jm-2, and thus the fastest coarsening process.

Highlights

  • The development of heat-resistant alloys is a critical issue to satisfy the current requirements of industrial equipment used in the power generation and petrochemical industries[1]

  • The size, distribution, morphology, and coherence play a significant role to keep their creep strength during service operation at high temperatures[1,2,3,4]

  • Transmission Electron Microscope (TEM) specimens were prepared by a two-jet electropolishing method with an electrolyte composed of 40 vol % nitric acid in methanol at -60 °C and 20 V (d.c.), and subsequently observed by TEM at 200 kV

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Summary

Introduction

The development of heat-resistant alloys is a critical issue to satisfy the current requirements of industrial equipment used in the power generation and petrochemical industries[1]. Most of these alloys based their mechanical strength and creep properties on the precipitation of different phases in a soft matrix. These precipitates include, for instance, M23C6, M7C3, MC carbides, η phase, Ni3Al γ, and NiAl βphase used in both ferrous and nonferrous alloys[1,2]. The coherent precipitation of βphase in a α ferrite matrix phase is responsible for the creep strength after aging treatment during the service operation. Additional advantages of Fe-Ni-Al alloys are their lower density and cost than that of Ni-based superalloys[5,6]

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