Casting Fe-Al-based intermetallics alloyed with Li and Ag
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rbajal-De la Torre Facultad de Ingeniería Mecánica, Universidad Michoacana de San Nicolás de Hidalgo, C.P. 58000, Morelia, México
J.C. Romo-Castañeda Facultad de Química, Universidad Nacional Autónoma de México, C.P. 04510 Ciudad de México, D.F., México
A. Bedolla-Jacuinde Instituto de Investigación en Metalurgia y Materiales, Universidad Michoacana de San Nicolás de Hidalgo, C.P. 58000, Morelia, México
H.A. González-Rojas Department of Mechanical Engineering (EUETIB), DEFAM Group, Universitat Politécnica de Catalunya, 08034 Barcelona, Spain
M.A. Espinosa-Medinaa) Facultad de Ingeniería Mecánica, Universidad Michoacana de San Nicolás de Hidalgo, C.P. 58000, Morelia, México (Received 9 February 2016; accepted 15 June 2016)
The effect on the mechanical properties at room temperature of Li and Ag additions to the Fe–Al (40 at.%)-based alloy produced by conventional casting were evaluated in this work. Alloying elements were added into a previously molted Fe–(40 at.%) aluminum-based alloy, stirred, and then cast into sand molds to directly produce tensile specimens. To determine the mechanical properties, tensile tests and hardness measurements were performed. The additions of both Ag and Li showed an increase in ductility and tensile strength of the intermetallic alloys. In addition, hardness was substantially increased with the Li addition. Lithium additions promoted a solid solution hardening, whereas 3 at.% of Ag additions promoted ductility due to a microstructural modification and to the formation of a soft Ag3Al phase. Characterization by both optical and electronic microscopy, energy dispersive spectroscopy microanalysis, and x-ray diffraction supported the mechanical characterization.
I. INTRODUCTION
In the past, the Fe–Al-based intermetallic alloys had been studied with interest due to their excellent corrosion resistance and their potential application as structured materials at elevated temperatures in hostile environments in the energy conversion industries as: geothermal or fossil fuels and nuclear fuels to generate electrical power systems.1–7 However, the use of those alloys as structural components had been limited due to their brittle fracture behavior and low ductility properties at room temperatures resulting from environmental embrittlement, weak grain boundaries, vacancy hardening, and embrittlement.7 Environmental embrittlement involves moisture in air, which is the major cause of low tensile ductility. Such environmental embrittlement is the consequence
Contributing Editor: Jürgen Eckert a) Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2016.249
of a chemical reaction involving the reaction of Al with oxygen from moisture, releasing hydrogen atoms that could be absorbed.8 However, there are other factors that can modify mechanical behavior at room temperature, such as grain size, improving ductility as the grain size is reduced.9 The quantity of Al in the FeAl alloy systems also has an important effect on both the mechanical properties10 and corrosi
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