Mechanical and electrochemical behavior of Fe3Al-xCr intermetallics

Different concentrations of Cr were added to the binary intermetallics, in order to enhance the ductility and pitting resistance of alloys. The results of nanoindentation in air show the influence of Cr on various mechanical properties like Young’s modulus, Gibbs free energy needed for homogeneous dislocation nucleation, and hardness. The increase of the Young’s modulus and Gibbs free energy after addition of Cr is due to the enhancement of the strength of interatomic bonds. Moreover, Cr decreases the flow stress and eases the cross slipping of dislocations. Furthermore, the results of nanoindentation under cathodic and anodic charging show the impact of hydrogen on the reduction of Young’s moduli of alloys; whereas measurements of the pop-in load indicate a drastic decrease after cathodic charging in samples with low Cr content. This is thought to be due to the decrease of the dislocation line energy based on the defect acting agents concept. Based on our results, the mechanism of dislocation shielding should be considered for analyzing the fracture characteristics of in aqueous solutions, and in atmospheres containing hydrogen. Finally, the effect of Cr on electrochemical properties of passive layer, and susceptibility of alloys to pitting and crevice corrosion in solutions with different concentrations of ions, was studied using various methods like cyclic polarization, cyclic voltammetry, impedance spectroscopy and the Mott-Schottky.Um die Duktilität und den Widerstand gegen Lochkorrosion zu verbessern, wurde in einer intermetallischen - Legierung die Konzentrationen an Cr variiert. Durch Nanoindentations-Messungen an Luft konnte gezeigt werden, dass Cr die mechanischen Eigenschaften wie z.B. den E-Modul, die Gibbs-Energie für homogene Versetzungsbildung und die Härte beeinflusst. Der Anstieg des E-Moduls und der Gibbs-Energie durch die Zugabe von Cr kann auf die Verstärkung der interatomaren zurückgeführt werden. Außerdem verringert Cr die Fließspannung und erleichtert das Quergleiten von Versetzungen. Die Ergebnisse der Nanoindentation mit kathodischer und anodischer Beladung zeigten, dass Wasserstoff den E-Moduls der Legierung verringert; Bei geringem Cr-Gehalt kam es hingegen zu einem drastischen Abfall der „pop-in load“ bei kathodischer Beladung, was durch die Verringerung der Versetzungslinienenergie aufgrund des „defect acting agents“ Konzepts erklärt werden kann. Unsere Ergebnisse zeigen, dass der shielding-Effekt der Versetzungen für die Analyse des Bruchverhaltens von Legierungen in wässrigen Lösungen und wasserstoffhaltigen Umgebungen berücksichtigt werden sollte. Des Weiteren wurde die Wirkung von Cr auf passive Oxidschichten, elektrochemische Eigenschaften und die Neigung zu Loch- und Spaltkorrosion in Lösungen mit verschiedenen Ionen Konzentrationen mit Hilfe verschiedener Methoden u.a. Polarisation, zyklische Voltammetrie, Impedanz Spektroskopie und Mott-Schottky untersucht

The Impact of Hydrogen on Mechanical Properties; A New In Situ Nanoindentation Testing Method

We have designed a new method for electrochemical hydrogen charging which allows us to charge very thin coarse-grained specimens from the bottom and perform nanomechanical testing on the top. As the average grain diameter is larger than the thickness of the sample, this setup allows us to efficiently evaluate the mechanical properties of multiple single crystals with similar electrochemical conditions. Another important advantage is that the top surface is not affected by corrosion by the electrolyte. The nanoindentation results show that hydrogen reduces the activation energy for homogenous dislocation nucleation by approximately 15–20% in a (001) grain. The elastic modulus also was observed to be reduced by the same amount. The hardness increased by approximately 4%, as determined by load-displacement curves and residual imprint analysis

A Review on the Properties of Iron Aluminide Intermetallics

Iron aluminides have been among the most studied intermetallics since the 1930s, when their excellent oxidation resistance was first noticed. Their low cost of production, low density, high strength-to-weight ratios, good wear resistance, ease of fabrication and resistance to high temperature oxidation and sulfurization make them very attractive as a substitute for routine stainless steel in industrial applications. Furthermore, iron aluminides allow for the conservation of less accessible and expensive elements such as nickel and molybdenum. These advantages have led to the consideration of many applications, such as brake disks for windmills and trucks, filtration systems in refineries and fossil power plants, transfer rolls for hot-rolled steel strips, and ethylene crackers and air deflectors for burning high-sulfur coal. A wide application for iron aluminides in industry strictly depends on the fundamental understanding of the influence of (i) alloy composition; (ii) microstructure; and (iii) number (type) of defects on the thermo-mechanical properties. Additionally, environmental degradation of the alloys, consisting of hydrogen embrittlement, anodic or cathodic dissolution, localized corrosion and oxidation resistance, in different environments should be well known. Recently, some progress in the development of new micro- and nano-mechanical testing methods in addition to the fabrication techniques of micro- and nano-scaled samples has enabled scientists to resolve more clearly the effects of alloying elements, environmental items and crystal structure on the deformation behavior of alloys. In this paper, we will review the extensive work which has been done during the last decades to address each of the points mentioned above

Mechanical and electrochemical behavior of Fe3Al-xCr intermetallics

Different concentrations of Cr were added to the binary intermetallics, in order to enhance the ductility and pitting resistance of alloys. The results of nanoindentation in air show the influence of Cr on various mechanical properties like Young’s modulus, Gibbs free energy needed for homogeneous dislocation nucleation, and hardness. The increase of the Young’s modulus and Gibbs free energy after addition of Cr is due to the enhancement of the strength of interatomic bonds. Moreover, Cr decreases the flow stress and eases the cross slipping of dislocations. Furthermore, the results of nanoindentation under cathodic and anodic charging show the impact of hydrogen on the reduction of Young’s moduli of alloys; whereas measurements of the pop-in load indicate a drastic decrease after cathodic charging in samples with low Cr content. This is thought to be due to the decrease of the dislocation line energy based on the defect acting agents concept. Based on our results, the mechanism of dislocation shielding should be considered for analyzing the fracture characteristics of in aqueous solutions, and in atmospheres containing hydrogen. Finally, the effect of Cr on electrochemical properties of passive layer, and susceptibility of alloys to pitting and crevice corrosion in solutions with different concentrations of ions, was studied using various methods like cyclic polarization, cyclic voltammetry, impedance spectroscopy and the Mott-Schottky.Um die Duktilität und den Widerstand gegen Lochkorrosion zu verbessern, wurde in einer intermetallischen - Legierung die Konzentrationen an Cr variiert. Durch Nanoindentations-Messungen an Luft konnte gezeigt werden, dass Cr die mechanischen Eigenschaften wie z.B. den E-Modul, die Gibbs-Energie für homogene Versetzungsbildung und die Härte beeinflusst. Der Anstieg des E-Moduls und der Gibbs-Energie durch die Zugabe von Cr kann auf die Verstärkung der interatomaren zurückgeführt werden. Außerdem verringert Cr die Fließspannung und erleichtert das Quergleiten von Versetzungen. Die Ergebnisse der Nanoindentation mit kathodischer und anodischer Beladung zeigten, dass Wasserstoff den E-Moduls der Legierung verringert; Bei geringem Cr-Gehalt kam es hingegen zu einem drastischen Abfall der „pop-in load“ bei kathodischer Beladung, was durch die Verringerung der Versetzungslinienenergie aufgrund des „defect acting agents“ Konzepts erklärt werden kann. Unsere Ergebnisse zeigen, dass der shielding-Effekt der Versetzungen für die Analyse des Bruchverhaltens von Legierungen in wässrigen Lösungen und wasserstoffhaltigen Umgebungen berücksichtigt werden sollte. Des Weiteren wurde die Wirkung von Cr auf passive Oxidschichten, elektrochemische Eigenschaften und die Neigung zu Loch- und Spaltkorrosion in Lösungen mit verschiedenen Ionen Konzentrationen mit Hilfe verschiedener Methoden u.a. Polarisation, zyklische Voltammetrie, Impedanz Spektroskopie und Mott-Schottky untersucht

Influence of temperature on the deformation behavior of single-and bi-crystal microbending beams

The mechanical behavior of micron-scale structures varies drastically from their macro-scale counterparts. This phenomenon is known as size effect and has been extensively investigated for several decades. The understanding of the influence of temperature on the mechanical properties of components of electronic devices with micron or even sub-micrometer dimensions is essential for a reliable design. Hence micro-compression and micro-tension experiments on pure single-crystalline and polycrystalline face-centered cubic (fcc) metals have been carried out at different temperatures. However, in real microstructures complex stress and strain gradients arise from incompatibilities in elastic and plastic deformation, which are not addressed in tension or compression tests. Therefore, micro bending was used to study the influence of temperature on the “gradient dominated” deformation behavior. Furthermore, compared to micro-compression, micro-bending offers several advantages: one of them is that the deformed region is far away from the contact between tip and sample. This allows the study of the deformation behavior and dislocation pile-up phenomena in single- and bi-crystalline beams at high temperatures, while the temperature gradient between tip and sample may scarcely influence the results. On that account, the present work focusses on bending experiments of Cu single- and bi-crystal micro-beams at different temperatures in order to study the dislocation processes at the beams’ neutral axis and the interaction between the dislocations and the grain boundaries. Therefore, in situ bending experiments of single- and bi-crystal micro-beams with different crystallographic orientations were carried out in a scanning electron microscope (SEM) using a nanoindenter at 300, 400 and 500 K. The micrometer-sized samples were fabricated using a two step ion milling technique: first a narrow fillet was milled with the ion slicing technique using low energy Ar+ ions, and second the focused ion beam (FIB) method was used for final milling. Bending tests enable us to understand the influence of temperature on the size effect, the work hardening, the Bauschinger-effect and its correlation with plastic deformation at micron-scale (see Figure 1) as well as the temperature-dependent interaction between grain boundaries and dislocations

Effect of hydrogen on the nucleation and motion of dislocations

Conventional mechanical tests are costly, time consuming, and due to their large scale, not very successful in obtaining mechanistic information. In contrast, the local method like nanoindentation, compression or bending test of micro pillars have comprehensive ranges of possibilities to achieve an essential understanding about the influence of substitutional atoms and/or interstitial atoms (e.g., hydrogen and nitrogen) on the mechanical properties like Young´s modulus, Gibbs free energy for homogeneous dislocation nucleation, dislocation line energy and also friction stress. These methods allow us to measure the mechanical behavior in simulated environments and atmospheres close to the routine industrial applications. Nanoindentation was applied for studying the sensitivity of various materials like nickel, Cu, steels and iron aluminides to hydrogen embrittlement, as it offers sufficiently high resolution in determining load and displacement and works effectively non-destructive. Nevertheless, the method of in-situ nanoindentation suffers from the complexity of the stress field below the nanoindenter. Furthermore, a novel method was developed where miniaturized compression samples are machined using focused ion beam (FIB) milling and loaded in a nanoindenter system equipped with a flat diamond punch. This method is able to probe mechanical properties on the micrometer and sub-micrometer scale under nominally uniaxial loading. Additionally, very small volume of pillar guarantees a fast and homogeneous distribution of hydrogen. More recently the influence of hydrogen on the elastic properties and interaction of dislocations was studied using the in-situ bending test of micro pillars (see Figure 1). The advantage of the bending test is the presence of high tensile stress in the pillar during the test. It is in contrast to other techniques like in-situ nanoindentation or micropillar compression tests with the compressive stress field which works as driving force for the hydrogen diffusion out of the highly stressed region

Investigations on micro-mechanical properties of polycrystalline Ti(C,N) and Zr(C,N) coatings

Micro-mechanical properties of Ti(C,N) and Zr(C,N) coatings deposited by chemical vapor deposition on a WC-Co cemented carbide substrate were examined by micro-compression testing using a nanoindenter equipped with a flat punch. Scanning Electron Microscopy, Focused Ion Beam, Electron Backscattered Diffraction and Finite Element Modeling were combined to analyze the deformation mechanisms of the carbonitride layers at room temperature. The results revealed that Ti(C,N) undergoes a pure intergranular crack propagation and grain decohesion under uniaxial compression; whereas the fracture mode of Zr(C,N) was observed to be inter/transgranular failure with unexpected plastic deformation at room temperature.Peer ReviewedPostprint (author's final draft

Micromechanical investigations of CVD coated WC-Co cemented carbide by micropillar compression

Deformation behavior of an industrial coated cemented carbide (WC-Co substrate coated with CVD multilayer of TiN/Zr(C,N)/Ti(C,N,O)/Al2O3) was investigated by means of micropillar compression method. In addition to the WC-Co substrate pillars, new composite pillar combination consisting of substrate, TiN interlayer and carbonitride hard coating were tested. The study targeted to document and analyze interactions between different phases and components (substrate, interlayer and coating) while subjected to compressive stress. It is found that deformation of the substrate depends mainly on the assemblage and the distribution of WC and Co phases within the pillar. The phase assemblage is subjected to changes after deformation which has an impact on the stiffness. Detailed analysis of plastic deformation within WC coarse grains pointed out that strain energy can be extensively dissipated in this phase by means of single and multiple slip. The composite/hybrid pillar formed by association of the substrate and the coating enhanced the ultimate strength in comparison to their respective individual components, highlighting the effective load-bearing response of coating and substrate acting as a coated system. This assessment was further supported by the excellent interfacial strength attested by the established TiN interlayer between the substrate and the coating

A Review on the Properties of Iron Aluminide Intermetallics

Iron aluminides have been among the most studied intermetallics since the 1930s, when their excellent oxidation resistance was first noticed. Their low cost of production, low density, high strength-to-weight ratios, good wear resistance, ease of fabrication and resistance to high temperature oxidation and sulfurization make them very attractive as a substitute for routine stainless steel in industrial applications. Furthermore, iron aluminides allow for the conservation of less accessible and expensive elements such as nickel and molybdenum. These advantages have led to the consideration of many applications, such as brake disks for windmills and trucks, filtration systems in refineries and fossil power plants, transfer rolls for hot-rolled steel strips, and ethylene crackers and air deflectors for burning high-sulfur coal. A wide application for iron aluminides in industry strictly depends on the fundamental understanding of the influence of (i) alloy composition; (ii) microstructure; and (iii) number (type) of defects on the thermo-mechanical properties. Additionally, environmental degradation of the alloys, consisting of hydrogen embrittlement, anodic or cathodic dissolution, localized corrosion and oxidation resistance, in different environments should be well known. Recently, some progress in the development of new micro- and nano-mechanical testing methods in addition to the fabrication techniques of micro- and nano-scaled samples has enabled scientists to resolve more clearly the effects of alloying elements, environmental items and crystal structure on the deformation behavior of alloys. In this paper, we will review the extensive work which has been done during the last decades to address each of the points mentioned above