Development of novel environmental resistant Fe3Al-X intermetallic alloys by means of in situ electrochemical nanoindentation
Final Report Abstract
There are two barriers for the wide usage of the Fe3Al intermetallic at room temperature. One is for hydrogen embrittlement and the other is for localized corrosion of the alloys in the Cl- containing solutions. During this DFG project, we tried to shed more light on the reasons for each of the aforementioned problems; and also evaluate the possibility of overcoming the problems with the addition of different concentrations of chromium to the binary alloys. The nanoindentation technique was used for studying the influence of Cr content on the elastic and plastic properties. The results show that chromium increases the Young’s modulus, maximum shear stress for homogeneous dislocation nucleation and friction stresses in Fe 3Al intermetallics. Additionally, Cr decreases the σ-flow and facilities the cross slipping of dislocations. This project examines the further application of nanoindentation, investigates materials under different environments, and establishes possibilities for obtaining new and unique information about the effect of hydrogen on various mechanical properties. In-situ nanoindentation was performed to detect the sensitivity of Fe3Al intermetallics with different Cr content to hydrogen embrittlement. The decrement of Young’s modulus and dislocation mobility was observed at cathodic potentials. Hydrogen also decreases the pop-in load and Gibbs free energy needs for homogeneous dislocation nucleation especially in samples with low Cr content, a sign of increased sensitivity to HE in Cr free alloys. This occurs because the addition of physically adsorbed hydrogen increases the dislocations core radius. Among all different mechanisms of HE, it was shown that the dislocation shielding mechanism could be used for explaining the low ductility of Fe3Al based intermetallics in a hydrogen containing environment. Finally, with the XPS and electrochemical techniques we studied the incorporation of Cr as a ternary alloying element into the passive film. The resistance of alloys to pitting and crevice corrosion in Cl- containing solutions was enhanced with the addition of Cr. The addition of 5 at. % Cr to the binary Fe 3Al intermetallics does not completely hinder the pitting and crevice corrosion of alloys, while it decreases the average density of pits. The effect of Cr on the polarization resistance was more obvious at high anodic potentials where the strong enrichment of the passive layer with Cr3+ and Cr6+ could make a more protective p-type layer, instead of the n-type layer, such as at lower potentials, or alloys with lower Cr content. Additionally, it was shown that the addition of Cr also increases the effective capacitance and donor density of the passive layers.
Publications
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A Review on the Properties of Iron Aluminide Intermetallics, Crystals
Crystals, M. Zamanzade, A. Barnoush, C. Motz
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Cr effect on hydrogen embrittlement of Fe3Al-based iron aluminide intermetallics: Surface or bulk effect, Acta materialia 69, 210-223
M. Zamanzade, H. Vehoff, A. Barnoush
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Effect of chromium on the electrochemical properties of iron aluminide intermetallics, Corrosion Science 78, 223-232
M. Zamanzade, A. Barnoush
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Mechanical behavior of iron aluminides: A comparison of nanoindentation, compression and bending of micropillars, Materials Science and Engineering: A 652, 370-376
M. Zamanzade, J.R. Velayarce, O.T. Abad, C. Motz, A. Barnoush
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An Overview of the Hydrogen Embrittlement of Iron Aluminides,Procedia Materials Science 3, 2016-2023
M. Zamanzade, A. Barnoush
