Development of new Fe\u2013Al\u2013Nb(\u2013B) alloys for structural applications at high temperatures

Angelika Gedsun,Frank Stein,Martin Palm

doi:10.1557/s43580-021-00045-w

Angelika Gedsun, Frank Stein + Show 1 more

Open Access

https://doi.org/10.1557/s43580-021-00045-w

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Journal: MRS Advances	Publication Date: Mar 31, 2021
Citations: 7	License type: open-access

Affiliation: Max-Planck-Institut für Eisenforschung

Abstract

It is known for Fe–Al–Ta alloys, that a homogeneous distribution of strengthening Laves phase precipitates in the matrix and aligned at the grain boundaries can be obtained when the formation of the stable Laves phase is preceded by the formation of the metastable Heusler phase. Several Fe–Al–Nb alloys with different Al and Nb contents and with or without boron doping are studied to elucidate whether comparable microstructures can be obtained in this system. It was found that the Heusler phase only occurs within a limited composition range. The time-dependent evolution of the microstructure shows that the transformation proceeds faster in Fe–Al–Nb alloys. Microhardness was measured in dependence on the microstructural evolution with increasing annealing time, and compressive yield stress was determined for alloys annealed 700 °C/1000 h to evaluate the influence of microstructure and composition.Graphic

Highlights

Due to their outstanding wear and corrosion resistance, iron aluminides are considered for structural applications at high temperatures [1]
At 700 °C the Fe–Al matrix is B2-ordered for all compositions, but it transforms to D03 during cooling to room temperature [6]
In the boron-doped alloys, no boride precipitates were observed by X-ray diffraction (XRD), scanning electron microscopy (SEM) or EMPA

Summary

Introduction

Due to their outstanding wear and corrosion resistance, iron aluminides are considered for structural applications at high temperatures [1]. E.g. strengthening coherent or incoherent second phases such as borides or Laves phase precipitates, the mechanical properties of iron aluminides can be further enhanced at higher temperatures [2, 3]. In many Fe–Al–X systems the Laves phase forms directly from the melt and solidifies as coarse dendrites [4, 5] In this case, the distribution of the Laves phase cannot be controlled, and rather brittle alloys are obtained [5]. Heat treatments were performed at 700 °C for 1 h, 10 h, 100 h and 1000 h in order to evaluate the microstructural evolution and kinetics of the transformation from metastable L21 Heusler phase to the stable C14 Laves phase. The microhardness was established by Vickers indents with 0.0098 N

Results and discussion

Conclusions

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