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April 2014 - present
January 2014 - March 2014
March 2008 - June 2012
Publications
Publications (125)
To overcome the Hydrogen embrittlement (HE) susceptibility of the standard Alloy 725 (Mod A), two alloys with minor alloying modifications with B (Mod B) and B+Cu (Mod C) were produced. Then, the intergranular cracking susceptibility was investigated on bi-crystal beams by electrochemical in situ micro-cantilever bending test. The atom probe tomogr...
The effect of cementite morphology on the crack initiation and growth path was studied using in situ electrochem-ical micro-cantilever bending (ECCB) technique under hydrogen (H) charging. Two carbon steels with lamellar cementite morphology (pearlitic microstructure) and spherical or broken lamellas cementite morphology (spheroidite microstructure...
In situ electrochemical microcantilever bending tests were conducted in this study to investigate the role of grain boundaries (GBs) in hydrogen embrittlement (HE) of Alloy 725. Specimens were prepared under three different heat treatment conditions and denoted as solution-annealed (SA), aged (AG) and over-aged (OA) samples. For single-crystal beam...
In the current study, the hydrogen-induced embrittlement on advanced high strength steels (AHSSs) is evaluated by in-situ electrochemical microcantilever bending (IECB) tests. Microcantilevers of 1200 M and 1400 M steels were bent while hydrogen charged inside a miniaturized electrochemical cell and then compared to bent-cantilevers in the air. The...
The hydrogen effect on dislocation nucleation in Ni single crystals with (111) surface orientation has been examined with the aid of a specifically designed nanoindentation setup for in situ electrochemical experiments. The effect of the electrochemical potential on the indent load – displacement curve, especially the unstable elastic-plastic trans...
Since hydrogen-plasticity interaction is a key feature in the study of hydrogen embrittlement, a series of nanoindentation tests were carried out to evaluate the possible impact of hydrogen on the dislocation structures formed during cyclic pre-straining of nickel single crystal. Ex-situ nanoindentation and in-situ electrochemical nanoindentation t...
In this study, the effect of precipitates on the surface mechanical properties in the presence of hydrogen (H) is investigated by in situ electrochemical nanoindentation. The nickel superalloy 718 is subjected to three different heat treatments, leading to different sizes of the precipitates: (i) solution annealing (SA) to eliminate all precipitate...
In order to overcome the poor adhesion of zirconia-silica coating electrophoretically deposited on 316 L stainless steel, graphene oxide (GO) was used as an interlayer. The effect of this interlayer on morphological, microstructural, corrosion performance and bioactivity behavior of ZrO2–10 at. % SiO2 coating was studied. The zirconia-silica coatin...
The hydrogen induced damage and crack initiation in transformation induced plasticity (TRIP) steel is considered in the present work by micro tensile testing and subsequent microstructural assessment. Hydrogen characteristics are studied for two material conditions for this purpose, i.e. TRIP 0% and TRIP 15%. To increase, on the one hand, microstru...
Intergranular failure of nickel (Ni) single grain boundaries (GBs) owing to the segregation of sulfur (S), hydrogen (H), and their co-segregation has been investigated by employing micro-cantilever bending tests and density functional theory (DFT) calculations. A pure Ni GB shows completely plastic behavior with no fracture observed in the experime...
The current study is focused on refining effect of amorphous SiO2 on porosity and interlayer formation of sintered ZrO2-SiO2 composite coatings produced on anodic oxidized 316L substrate. The SiO2 improved particle interaction with the substrate surface and increased thickness of the interlayer formed at the coating/substrate interface. For porosit...
The effect of hydrogen on the microdamage evolution of 1200M advanced high-strength steel was evaluated by the combination of experimental and numerical approaches. In the experimental section, the tensile test was performed under different testing conditions, i.e., vacuum, in-situ hydrogen plasma charging (IHPC), ex-situ electrochemical hydrogen c...
Transition metal carbides (MXenes) with formulas Mn+1CnTx (n = 2 and 3) are emerging as a new family of two-dimensional (2D) materials providing great potential in electronic applications and CO2 conversion catalysts. It has been found already that the electronic and electrochemical properties of Ti3C2Tx MXenes can be tuned by replacing the two out...
Two-dimensional (2D) transition metal carbides, corbonitrides, and nitrides (named as MXenes) have become of the fastest growing family of 2D materials in terms of compositions and their applications in different areas. One of the least explored properties of MXenes is their mechanical properties. While the basic elastic properties of MXenes have b...
The effect of hydrogen on the mechanical properties of X70 pipeline steel was investigated by a combination of macro- and microscale approaches. Various tensile tests under vacuum, in-situ H-plasma charging (IHPC), and ex-situ electrochemical H-charging (EEHC) conditions were conducted to elucidate the hydrogen effect in the macroscale approach. Al...
The present paper discussed the impact of hydrogen on the mechanical response of cyclically strained nickel single crystal oriented for multi-slips at different length scales. At macroscale, hydrogen seems to induce competition between softening and hardening of the metal as a function of the plastic strain amplitude. Then, by separating internal s...
ZrO2-10 mol.% SiO2 composite coatings has been produced on 316L stainless steel, surface treated using mechanical polishing, electropolishing and anodic oxidizing procedures. For this purpose, the composite particles were prepared using sol-gel processing method, electrophoretically deposited on pre-treated substrate and then sintered at 1100 °C. T...
We have used the density functional theory within the plane-wave framework to understand the reconstruction of most stable (110) chalcopyrite surfaces. Reconstructions of the polar surfaces are proposed, and three different possible nonpolar terminations for the (110) surface, namely, I, II, and III, are investigated. A detailed discussion on stabi...
Precipitation-hardened nickel-based superalloys are some of the best candidates for subsea oil and gas industries due to their excellent mechanical properties and good corrosion resistance. However, these high-strength alloys are susceptible to hydrogen embrittlement-a phenomenon with a detrimental effect on in-service metals leading to unexpected...
The effect of hydrogen on the nanomechanical properties of CoCrFeMnNi high-entropy alloy was investigated by in-situ electrochemical nanoindentation testing. The changes in surface morphology, elastic modulus, pop-in load, and hardness during hydrogen ingress and egress processes were systematically evaluated. The results show that hydrogen chargin...
It is well known that ferrous materials can be damaged by absorption of hydrogen. If a sufficient quantity of hydrogen penetrates into the material, static fracture and the material's fatigue performances can be affected negatively, in particular causing an increase in the material crack growth rates. The latter is often referred as Hydrogen Affect...
We show for the first time that a critical amount of dissolved hydrogen can induce a phase transformation from γ-austenite to ε-martensite in an interstitial metastable high-entropy alloy. This is demonstrated by in-situ hydrogen charging in combination with nanoindentation and scanning probe microscopy, plus further electron channeling contrast im...
The susceptibility of age-hardened nickel-based 718 superalloy to hydrogen embrittlement was studied by the controlled electrochemical charging combined with slow strain-rate tensile tests (SSRT) and advanced characterization techniques. We proposed some novel ideas of explaining hydrogen embrittlement mechanisms of the studied material in regard t...
Hydrogen effect on an interstitial CoCrFeMnNi high-entropy alloy was investigated by micro-cantilever bending tests with pre-notched {111} plane as a case study. Results showed sharp mode I cracks on (001) plane bisecting two {111} planes in hydrogen-charged cantilevers, which was explained by hydrogen-assisted defects formation and hydrogen pins d...
The hydrogen embrittlement phenomenon of iron aluminides (Fe3Al and FeAl) at microscale was investigated by microcantilevers bending tests with a (1 0 0)[0 0 1] crack system. The cantilevers were loaded in-situ in an environmental scanning electron microscope under two conditions: one with water vapor to promote hydrogen uptake and the other one wi...
Chalcopyrite (CuFeS2) is an antiferromagnetic semiconductor with promising magnetic and electrical properties, although these properties are not yet completely understood. The structural, magnetic, and electronic properties of bulk CuFeS2 were studied via first-principles plane-wave pseudopotential calculations based on density functional theory (D...
The high precision offered by small-scale mechanical testing has allowed the relationships
between mechanical behavior and specifi c microstructural features to be determined to an
unprecedented degree. However, of most interest to scientists and engineers is often the
behavior of materials under service conditions in an extreme environment, such a...
CO2 liquid is applied as an Enhanced Oil Recovery (EOR) method in oil reservoirs to increase the displacement efficiency. Because of the high temperature and pressure in the reservoirs, the viscosity of the CO2 decreases leading to poor macroscopic sweep efficiency. We study the effect of morphology of aluminum oxide nanoparticle (Al2O3 NP) on the...
Medium-Mn steel is the newly developed steel acting as a promising candidate of the 3rd-generation advanced high strength steels. In the present study, the effect of hydrogen on the mechanical behavior and martensite transformation process in a duplex medium-Mn steel is investigated by in-situ nanoindentation test. The mechanical response of indivi...
The stabilization of nanoparticles is a main concern to produce an efficient nanofluid. Here, we carry out Molecular Dynamics (MD) modeling to evaluate the stabilization of 2D graphene, oxygen- and hydrogen- functionalized graphene, and Ti2CO2 MXene nano-sheets in carbon dioxide (CO2) liquid at supercritical condition. The rheological properties (i...
In this work, the effect of Zn2+ cations on the calcareous scales during the cathodic protection of mild steel was studied. The Zn2+ cations were introduced into the epoxy and alkyd coatings in the form of zinc chloride. Also, the influence of Zn2+ cations was investigated in the zinc -rich primer coated mild steel. The study was conducted in the e...
The temperature-dependent elasticity of the B19′ NiTi is unknown today. To gain insights into the lattice-level temperature-dependent elasticity of the B19′ crystal, we present results of in-situ neutron diffraction experiments performed on polycrystalline martensitic specimens in the temperature range of 300 down to 50 K. The experimental results...
https://authors.elsevier.com/a/1Z87P4r9SUFF3p
Fatigue crack growth (FCG) test was done on a pre-cracked single-edge notched tensile (SENT) specimen with oligocrystalline ferritic structure. Innovative in-situ hydrogen (H)- charging by plasma inside an environmental scanning electron microscope (ESEM) was adopted to directly observe the H influence on the FCG behavior of this material. Diverse...
The present study evaluates the hydrogen induced damage by in-situ hydrogen plasma charging in dual phase (DP) steel. Cold deformation of 15% is applied on the material to change microstructural defects, such as dislocation density. The susceptibility to hydrogen embrittlement is hence evaluated for two material conditions, i.e. DP 0% and DP 15%. S...
In-situ electrochemical nanoindentation was applied to study the effect of hydrogen on the mechanical properties of Fe-22Mn-0.6C TWIP steel at nanoscale. Distinctive behaviors in three defined grain orientations: (001), (101), and (111) were investigated in a sequence of air, hydrogen ingress, and hydrogen egress processes. The obvious pop-in load...
The effect of hydrogen (H) on the fatigue behavior is of significant importance for metallic structures. In this study, the hydrogen-enhanced fatigue crack growth rate (FCGR) tests on in-situ electrochemically H-charged ferritic Fe-3wt%Si steel with coarse grain size were conducted. Results showed strong difference between the H-charged and the non...
A multi-scale computational methodology based on the density functional theory and molecular dynamics has been used to investigate the rheological properties of super critical CO2 with CuO nano-particle (NP). Density functional theory which treats the electron density as the central variable has been used to explore the adsorption of CO2 molecules...
The sub-surface deformation structure after cryogenic (77 K) brittle fracture in a ferritic steel was characterized by scanning electron microscopy (SEM). Twin-like structures were found in many grains below the fracture surface. Electron backscatter diffraction (EBSD) was used to identify the crystallography of the structures, and the twin relatio...
An electrolyte for electrochemical hydrogen charging of corrosion-susceptible alloys is developed, which preserves the surface integrity at nano-scale by minimizing the surface roughness alternation. To assure the formation and adsorption of the hydrogen from the electrolyte, permeation tests were performed on Fe 3wt.%Si ferritic steel. X-ray photo...
To study the hydrogen embrittlement (HE) effect, a novel in-situ slow strain rate tensile test together with in-situ hydrogen (H) charging by H-plasma was conducted in an environmental scanning electron microscope (ESEM). The introduction of H-plasma gave a reduction in tensile elongation by about 5% in comparison with a reference test in vacuum. F...
Fatigue crack growth (FCG) behavior of a Fe-3wt.%Si ferritic alloy under different environmental conditions using in-situ electrochemical (cathodic) hydrogen (H) charging has been investigated. Three frequencies have been applied. Results clearly show that the FCG rate increased by a factor spanning from 20 to 1000 times, depending on the loading f...
It is well known that the presence of hydrogen in ferrous materials promotes both static fracture and affect the material fatigue crack growth rates. The latter is often referred to as Hydrogen Enhanced Fatigue Crack Growth Rate (HE-FCGR) which defines the reduction of crack growth resistance of the material under cyclic stresses when hydrogen is p...
The present work addresses the impact of quenched-in thermal vacancies on the mechanical properties of B2 iron aluminides. For this reason different binary Fe-Al alloys with different histories of heat treatment were indented at room temperature. The contributions of mono- and bi-vacancies in addition to triple defects on the elastic, plastic and e...
The susceptibility of Fe–26Al–0.5Cr (at.%) intermetallic alloy to hydrogen assisted cracking was evaluated by micromechanical fracture mechanics specimens. The notched micro-beams were loaded in situ in an environmental scanning electron microscope under two conditions: one with low pressure to avoid any hydrogen effect and the other with water vap...
The susceptibility of the FeAl intermetallic alloy to hydrogen-assisted cracking was investigated by in situ
fracture experiments using notched micrometre-sized specimens using an Environmental Scanning Electron
Microscope (ESEM). The notched beams were loaded under two different environmental conditions: one in
high vacuum (5 × 10−4 Pa) to avoid h...
The ever-growing energy demand requires the exploration and the safe, profitable exploitation of unconventional reserves. The extreme environments of some of these unique prospects challenge the boundaries of traditional engineering alloys as well as our understanding of the underlying degradation mechanisms that could lead to a failure. Despite th...
Hydrogen (H) enhanced cracking was studied in Fe–3wt%Si by means of in situ electrochemical microcantilever bending test. It was clearly shown that the presence of H causes hydrogen embrittlement (HE) by triggering crack initiation and propagation at the notch where stress concentration is existing. Additionally, the effect of carbon content and th...
To evaluate the hydrogen (H)-induced embrittlement in iron aluminium intermetallics, especially the one with stoichiometric composition of 50 at.% Al, a novel in situ micro-cantilever bending test was applied within an environmental scanning electron microscope (ESEM), which provides both a full process monitoring and a clean, in situ H-charging co...
In situ electrochemical nanoindentation has been used to study the effect of hydrogen on the nanomechanical response of Alloy 718. Observations show that hardness increase as a result of hydrogen charging. Also, the hydrogen charging gives a reduced pop-in load and pop-in width. This is related to a reduction in the energy needed for dislocation nu...
The ever-growing energy demand requires the exploration and the safe, profitable exploitation of unconventional reserves. The extreme environments of some of these unique prospects challenge the boundaries of traditional engineering alloys as well as our understanding of the underlying degradation mechanisms that could lead to a failure. Despite th...
Single crystalline microcantilevers of Fe–3wt% Si were bent while electrochemically hydrogen (H) charged in situ inside a miniaturized electrochemical cell and are compared with cantilevers bent in air. Yield point decreases, crack initiation and propagation were observed for the cantilevers bent in the presence of H, while notch blunting occurred...
A novel approach of in-situ micro-cantilever bending tests is introduced, integrating nanoindentation and environmental scanning electron microscopy (ESEM) to elucidate hydrogen embrittlement (HE) in FeAl. Bending tests were performed in vacuum (~ 5 × 10− 4 Pa) and in ESEM with water vapor (180 Pa, 450 Pa) conditions, which introduce H in-situ into...
This work is part of a multi scale computational and experimental approach in which first principle modelling, nanoscale experiments and continuum simulations are combined in order to represent hydrogen induced degradation and cracking. Nanomechanical testing in air and under electrochemical hydrogen charging conditions are carried out on µm sized...
While a large bulk of experimental results from cracked specimens of polycrystalline graphite under pure modes of loading, in particular under mode I loading, can be found in the literature, only a very limited number of tests have been carried out on notches. At the best of authors’ knowledge dealing with the specific case of V-notches under mixed...
Mixed mode I/III behavior of Perspex (polymethyl methacrylate (PMMA)) is studied experimentally and theoretically in this research using a new and simple laboratory test configuration. The specimen is a circular disc containing a sharp V-notch along the diameter that is loaded by the conventional three-point bend fixture. The critical values of not...
Various local testing methods, namely, nanoindentation, compression and bending tests of micropillars were used to better understand the influence of ternary Cr atoms on the extrinsic and intrinsic mechanical properties of Fe3Al intermetallics with the D03 super lattice.
Using such local techniques enables us to quantify the influence of Cr on the...
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...
Despite its superior corrosion resistance, super duplex stainless steels (SDSS) are prone to hydrogen embrittlement. In this paper, a novel in situ electrochemical nanoindentation technique is used to investigate the hydrogen effect on the nanomechanical response of the existing phases in SDSS, i.e. ferrite and austenite. A systematic change in ele...
The variation in the pop-in load during electrochemical nanoindentation of Fe 3 wt.% Si alloy at different cathodic polarizations was measured. It is clearly shown that a higher hydrogen chemical potential results in a lower pop-in load, which is an indication of easier dislocation nucleation below the tip. Classic dislocation theory and defactant...
In this study, oxygen argon plasma (OArP) treatment was introduced as a new method for controlling hydrogen uptake in austenitic stainless steels during cathodic protection. It was determined that a 5-min treatment with OArP did not affect the nanomechanical properties of the material or the dislocation nucleation process; but it greatly inhibited...
New technologies often lead to the development of new materials with better mechanical, thermal and chemical behaviors. Recently, transition metals (TM), or aluminide intermetallics, for example TiAl, NiAl, FeAl, and Fe3Al, have attracted considerable interest due to their unique properties such as high melting points, enhanced corrosion resistance...
The objective of this work is to reduce the susceptibility of binary Fe3Al intermetallics to hydrogen embrittlement with the addition of chromium as the ternary element. The Young’s modulus, Gibbs free energy for homogeneous dislocation nucleation (HDN) and velocity of dislocations were evaluated by an in situ nanoindentation method in air and unde...
Hydrogen effects on dislocation nucleation in polycrystalline ferritic Fe–15Cr binary alloy were investigated using in situ electrochemical nanoindentation. Linear elastic finite element calculations taking account of the cubic symmetry of BCC crystals were made to extract the resolved shear stresses on the different slip systems of the indented gr...
Micropillar compression tests were performed on martensite (M) and retained austenite (A) containing constituents formed in high-strength low-alloy steel after simulated thermal weld heat treatment. Due to the complicated fine microstructure of the constituent, the resulted stress–strain curves were further analyzed by considering the post-mortem s...
A highly stable austenite phase in a super duplex stainless steel was subjected to a combination of different gallium ion doses at different acceleration voltages. It was shown that contrary to what is expected, an austenite to ferrite phase transformation occurred within the focused ion beam (FIB) milled regions. Chemical analysis of the FIB mille...
The effect of chromium content on the electrochemical properties of Fe3Al intermetallics is examined. The susceptibility of alloys to pitting and crevice corrosion in solutions with different concentrations of Cl− ions was studied with the aid of cyclic polarization and galvanostatic methods. The form of the pits, and their concentration on differe...
Metal foams are a relatively new class of bionic materials, which offer special material
properties. Open-cell metal foams are cellular structures consisting of a three-dimensional network of stochastically distributed pores and mimic the construction elements of biological load-bearing structures like wood and bones. According to this special stru...
By atomistic simulations, we show that H is mainly absorbed on the surface of the crack tip in Ni and reveal that H switches from decreasing the activation energy for dislocation nucleation at low load to increasing it at high load, owing to H‐reduced activation volume. This counterintuitive finding explains experimentally observed sharp cracks in...
Pulsed plasma nitriding (PPN) is used to nitride super duplex stainless steel (SDSS). Different analytical techniques are used to characterize the nitride layer on both ferrite and austenite phases existing in the SDSS. In-situ electrochemical nanoindentation is used to examine the effect of electrochemically charged hydrogen on the mechanical prop...
In order to evaluate the effect of chromium concentration on the mechanical properties of single phase iron aluminum intermetallics, specifically those containing 26 at.% Al, a nano-indentation technique was used. The grain orientations of samples were revealed with the aid of Electron Backscatter Diffraction (EBSD) technique. Additionally, the sur...
Electron backscattered diffraction study was used to determine the preferred orientations of the crystals and texture evolution as a consequence of nitrogen diffusion. In the current study, the nitrided layer on a steel substrate was selected as a model material to investigate the distribution of different phases as well as their crystallographic r...
A combination of experimental and molecular dynamics (MD) simulations is used to investigate the interaction of dislocations with a selected grain boundary (GB) in bicrystalline pillars (BCPs) with component crystals oriented for single slip and multiple slip. As a reference, single-crystalline pillars with the same orientations are also tested and...
Pulsed Plasma Nitriding (PPN) of high-strength low-alloy steels used for offshore applications is a promising approach for controlling erosion, corrosion and hydrogen embrittlement under service conditions. In this work, the microstructure, composition and hardness of the nitride layer produced by an optimized PPN process on 2.25Cr–1Mo steel were e...
In situ electrochemical nanoindentation is used to examine the effect of electrochemically charged hydrogen on mechanical properties of the nitride layer on low-alloy 2.25Cr-1Mo martensitic structural steel. By application of this method, we were able to trace the changes in the mechanical properties due to the absorption of atomic hydrogen to diff...
Appropriate methods of testing are a key element in the prevention of hydrogen embrittlement (He) of high performance metals in energy systems in gaseous hydrogen environments. A range of test methods, which are based on monotonic loading, is available to screen out materials which are susceptible to He and to quantitatively predict long-term servi...
Dislocation nucleation in solid solutions of body-centered-cubic intermetallic Fe3Al alloys was investigated by means of nanoindentation and measurement of the pop-in load of samples with different Cr content. It is clearly shown that the Cr solute element in the Fe3Al intermetallic alloy increases the pop-in load, i.e. shear stress, required for d...
Most of what is known about the local interaction of dislocations with grain boundaries and hydrogen is based on transmission electron microscopy studies, which suffer from the distinct disadvantage that only extremely thin samples can be used. Recently, micropillar compression testing has become a popular means by which investigation of the size e...
In this work, the nitrided layer on austenitic AISI 316L stainless steels were examined by means of in situ electrochemical nanoindentation, and the effect of electrochemically charged hydrogen on the mechanical properties were investigated. By using this method, changes in the mechanical properties due to the absorption of atomic hydrogen at diffe...
Electrochemical nanoindentation is used to study the in situ effect of electrochemically charged hydrogen on the mechanical properties of austenitic stainless steel (ASS). In addition to the observed reduction of the pop-in load and the increase of the hardness, a novel analysis method based on the Taylor assumption and the indentation size effect...
The crucial role of dislocations in the nanomechanical response of high-purity aluminum was studied. The dislocation density in cold-worked aluminum is characterized by means of electron channeling contrast and post-image processing. Further in situ heat treatment inside the chamber of a scanning electron microscope was performed to reduce the disl...
