Pure Fe Samples Research Articles

Anisotropic deformation mechanism of {110} hexagonal dislocation networks in BCC Iron

Molecular dynamics simulation was performed to study the anisotropic mobility behavior of hexagonal dislocation networks (HDNs) in a series of bicrystalline pure Fe samples under a force-control in-plane shear deformation test. It is found that the mobility of HDN is mainly controlled by the characteristic features of <001> dislocations, which formed in the vicinity of ½<111> dislocations lying at the HDN. Furthermore, we elucidate the underlying mechanism of shearing in HDN as the variation of the length and the core energy of <001> dislocation lines with HDN misorientation angle. The energy barrier analysis of kink activities on the HDN plane is used to address the contribution of these geometrical and structural features to the in-plane shearing anisotropy of the HDN.

Ultrasonic scattering predictions of two-phase polycrystalline materials based on digital microstructures

Many materials found in nature and used in industry consist of multiple phases, and the mechanical performance of such materials is controlled by their material organization. Ultrasonic scattering is one approach to characterize these microstructures nondestructively. In this presentation, previous ultrasonic scattering theories for two-phase materials are discussed and implemented using discrete synthetic three-dimensional microstructures as a means to assess the material statistics. These models predict the ultrasonic wave speed, attenuation, and diffuse ultrasonic backscatter with respect to the volume fraction and grain size distribution of each constituent. The computational approach is then focused on predictions for samples created using spark plasma sintering (SPS) of Cu and Fe powders with varying volume fractions as well as pure Cu and pure Fe samples. DREAM.3D is used to generate digital synthetics representative of the SPS samples as characterized using electron backscatter diffraction (EBSD). A set of 30 realizations for each volume fraction is used for each to quantify the statistical variations expected. The combined theoretical and computational model is used to study the dependence of ultrasonic wave propagation on the material organization for these two-phase materials. [Work supported by Air Force Research Laboratory (AFRL) under prime contract FA8650-15-D-5231.]

Ultrasonic scattering in two-phase polycrystalline materials

Typically, many of the polycrystalline materials found in nature and those created using different manufacturing processes consist of multiple phases. Careful nondestructive characterization of these materials is of fundamental importance for quality assurance because microstructure is strongly correlated with mechanical performance. Ultrasonic scattering measurements have shown high sensitivity to material microstructure such that this approach is of interest for multi-phase materials. A fundamental understanding of scattering from idealized two-phase materials would provide essential information regarding the predictive nature of scattering measurements to quantify such microstructures. For this purpose, samples were created using spark plasma sintering (SPS) from mixtures with three different ratios (with respect to mass) of Cu and Fe powders. These elements do not alloy such that the resulting samples will not have any intermediate phases. Moreover, one pure Cu sample and one pure Fe sample were also sintered using SPS. The samples were imaged using electron backscatter diffraction (EBSD) to quantify the material organization. Ultrasonic backscatter and attenuation measurements were performed on the samples and the results were used for comparison with scattering models. Prospects for nondestructive evaluation of such materials are also discussed. [Work supported by Air Force Research Laboratory (AFRL) under prime contract FA8650-15-D-5231.]

Comparison experiment on the sputtering of EUROFER, RUSFER and CLAM steels by deuterium ions

In this work, the RAFM steels EUROFER, RUSFER and CLAM, along with a reference pure Fe sample, were all exposed to the same source of deuterium and analyzed using the same techniques, allowing a direct comparison of the experimental results. A 200 eV/D mass-selected deuterium ion beam at the SIESTA facility was used to bombard the samples to a fluence of 5 × 1024 Dm−2 at 450 K. The surface morphology of the samples was investigated with Scanning Electron Microscopy. The sputter yield of the samples was determined by weight-loss measurements and confirmed by measurements of the eroded depth. The near-surface enrichment of W and Ta was investigated via Energy-dispersive X-ray spectroscopy, X-ray Photoelectron Spectroscopy and Rutherford Backscattering Spectrometry. Grain-orientation-dependent sputtering was studied with Confocal Laser Scanning Microscopy and Electron Backscatter Diffraction. Lastly, Nuclear Reaction Analysis and Thermal Desorption Spectrometry were employed to analyze deuterium retention in all the samples. The erosion behavior of all three steels under deuterium bombardment was confirmed to be similar. The measured sputter yield was comparable for all three steels, and significantly lower than that of pure Fe. Likewise, all steels develop a needle-like surface morphology under the given exposure conditions and a W- and Ta-enriched layer in the range of few nanometers, while the Fe sample remained smooth. Retained deuterium amounts were also comparable among the steel samples, and were overall larger than the retention measured for the pure Fe sample.

Dislocation Loop Generation Differences between Thin Films and Bulk in EFDA Pure Iron under Self-Ion Irradiation at 20 MeV

In the present investigation, high-energy self-ion irradiation experiments (20 MeV Fe+4) were performed on two types of pure Fe samples to evaluate the formation of dislocation loops as a function of material volume. The choice of model material, namely EFDA pure Fe, was made to emulate experiments simulated with computational models that study defect evolution. The experimental conditions were an ion fluence of 4.25 and 8.5 × 1015 ions/cm2 and an irradiation temperature of 350 and 450 °C, respectively. First, the ions pass through the samples, which are thin films of less than 100 nm. With this procedure, the formation of the accumulated damage zone, which is the peak where the ions stop, and the injection of interstitials are prevented. As a result, the effect of two free surfaces on defect formation can be studied. In the second type of experiments, the same irradiations were performed on bulk samples to compare the creation of defects in the first 100 nm depth with the microstructure found in the whole thickness of the thin films. Apparent differences were found between the thin foil irradiation and the first 100 nm in bulk specimens in terms of dislocation loops, even with a similar primary knock-on atom (PKA) spectrum. In thin films, the most loops identified in all four experimental conditions were b ±a0&lt;100&gt;{200} type with sizes of hundreds of nm depending on the experimental conditions, similarly to bulk samples where practically no defects were detected. These important results would help validate computational simulations about the evolution of defects in alpha iron thin films irradiated with energetic ions at large doses, which would predict the dislocation nucleation and growth.

Corrosion, optimization and surface analysis of Fe-Al2O3-CeO2 metal matrix nanocomposites

In the present work, metal matrix nanocomposites are being prepared using Fe as base material reinforced with Al2O3 and doped with CeO2. Nanocomposite specimens were synthesized using powder metallurgy technique. Tafel Polarization, Corrosion Behavior and its optimization using Analysis of Variance (ANOVA) as well as Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS) along with Phase and Microstructure of prepared samples have been investigated. It was observed that corrosion rate and corrosion current density was highest for pure Fe samples whereas 1.0% CeO2 doped Fe-Al2O3 metal matrix nanocomposite system showed the formation of nano amorphous layer on the specimen surface. Analysis of Variance shows that the different compositions of samples have changed outcome on corrosion behavior. Technique for Order of Preference by Similarity to Ideal Solution analysis shows ordered preference of sample as per the readings of corrosion rate.

Effect of grain boundary on the friction coefficient of pure Fe under the oil lubrication

In this study, the effect of grain boundary on the frictional behavior under the oil-lubricated condition was investigated by varying the grain size (crystallite size) of the pure Fe samples prepared via physical vapor deposition. A high fraction of grain boundary in the sample yielded a low friction coefficient μ in the case of a lubrication oil that formed a chemisorbed film on the surface of the material. Thick absorbed layer formed on the surface was observed only in the sample with high fraction of grain boundary. These results indicate that a disordered structure in the vicinity of grain boundary preferentially forms chemisorbed films and reduces μ by protecting the surface of the material.

Grain size evolution and mechanical properties of thermomechanically processed pure iron for biodegradable medical implant application

A high strength-ductility combination is a critical mechanical property requirement for biodegradable metals such as pure iron (Fe) deployed for cardiovascular implant applications. However, improving strength and ductility simultaneously is a very challenging task because strength and ductility are mutually exclusive. The main target of this work was to achieve homogeneous and fine grain structure in pure iron (Fe) that would enable adequate strengthductility combination via thermomechanical process of cold rolling and recrystallization annealing. Pure Fe samples were subjected to various degrees of cold rolling followed by recrystallization annealing at 550°C, 670°C, 800°C and 900°C, microstructural examination and the mechanical property evaluation. Thermomechanical processing restored ductility, refined microstructure reducing grain size from 29.6 µm to 14.6 µm and 13.8 µm, which led to 44.7% and 48.2% increase in yield strengths for the pure Fe cold rolled to 75% and 85% reduction and annealed at 550°C, respectively.Keywords: grain size evolution, mechanical properties, pure iron, thermomechanical processing, biodegradable.

Study of the Heat Transfer Behavior and Naturally Deposited Films in Strip Casting by Using Droplet Solidification Technique

Oxide films that naturally deposit on the surface of the twin-roll mold during strip casting greatly influence the heat transfer from molten steel pool to the mold wall, which further affect the quality of casting product. In this study, a droplet solidification technique has been developed to simulate the initial process of solidification and film deposition during strip casting process. The results suggest that the maximum heat flux increases firstly (to 5201.5 kW/m2 for industrial pure Fe and to 4242.1 kW/m2 for stainless steel) and then decreases (to 4700.3 kW/m2 for industrial pure Fe and to 2037.8 kW/m2 for stainless steel) with the repeat of dropping tests. Furthermore, the roughness and thickness of the films formed on the surface increase with the successive addition of the solidifying material on the prior film. The compositions of the films are detected mainly as oxides containing O, Fe, Si, Mn, S, and Cu for the industrial pure Fe sample and they are O, Si, S, Mn, Cr, and Cu for the stainless steel sample. The deposited film with a thickness (54 μm for industrial pure Fe and 82 μm for stainless steel) and a roughness (24.5 nm for industrial pure Fe and 36.6 nm for stainless steel) allows a better wetting behavior between the molten steel and mold surface, resulting in an increase of actual contact area, and an enhancement of nucleation rate, which then in turn promote the interfacial heat transfer during the initial solidification of molten steel.

Dislocation loops in ultra-high purity Fe(Cr) alloys after 7.2 MeV proton irradiation

Ultra-high purity Fe(Cr) alloys (from 0 wt% Cr to 14 wt% Cr) were 3D homogeneously irradiated by 0–7.2 MeV protons to 0.3 dpa at nominal temperatures from 270 °C to 500 °C. Microstructural changes were observed by transmission electron microscopy (TEM). The results showed that evolution of dislocation loops depends on the Cr content. Below 300 °C, large ½ a0 <111> loops are dominating. Above 300 °C, a0 <100> loops with a habit plane {100} appear. Loop sizes of both types are more or less the same. At temperatures from 310 °C to 400 °C, a0 <100> loops form clusters with the same {100} habit plane as the one of the loops forming them. This indicates that <100> loops of the same variant start gliding under mutual elastic interaction. At 500 °C, dislocation loops form disc shaped clusters about 1000 nm in diameter and sitting on {111} and/or {100} planes in the pure Fe samples. Based on these observations a quantitative analysis of the dislocation loops configurations and their temperature dependence is made, leading to an understanding of the basic mechanisms of formation of these loops.

Impact of 18 MeV He+ ions on the morphological and structural properties of pure Fe

In the present work, morphological and structural changes induced by 18 MeV He+ ions in pure iron (Fe) matrix have been reported. Pure Fe samples were irradiated by 18 MeV He+ ions at different fluences ranging from 1 × 1013 ions cm−2 to 1 × 1016 ions cm−2 at 300 K under vacuum by using Cyclotron Accelerator. The surface morphology of irradiated samples was studied through field emission scanning electron microscopy (FESEM). The FESEM results revealed the formation and growth of micro-size pits, cavities, voids and incoherent structures at different irradiation fluences. The formation of these pits/incoherent structures was attributed to the melting, re-deposition and sputtering of the irradiated surface. The small size Fe particles were ejected out from the sample’s surface at lower fluence (1 × 1013 ions cm−2) which were then transformed into large size pits/craters at higher fluence (1 × 1016 ions cm−2). The existence of these Fe particles was confirmed through energy dispersive x-ray spectroscopy (EDS). The structural analysis by x-ray diffraction (XRD) indicated a variation in intensities of Fe diffraction peaks, peaks shifting and broadening that became more pronounced with increase of the irradiation fluence. These structural changes were attributed to the accumulation of irradiation induced stresses inside the Fe matrix.

Grain size distribution effects on the degradation and mechanical behaviours of biodegradable metallic biomaterials

Event Abstract Back to Event Grain size distribution effects on the degradation and mechanical behaviours of biodegradable metallic biomaterials Camillus Obayi1, 2, Ranna Tolouei2, Boniface Okorie1, Daniel Obikwelu1 and Diego Mantovani2 1 University of Nigeria, Metallurgical & Materials Engineering, Nigeria 2 Laval University, Lab. Biomaterials and Bioengineering, CRC-I, Dept Min-Met-Materials Eng & CHU de Québec Research Cen, Canada Introduction: The study of the degradation and mechanical behaviours is a critical aspect of biodegradable metallic biomaterials science. Results of theoretical materials’ models indicate that besides average grain size and grain orientation, another microstructural parameter-grain size distribution (gsd) could impact corrosion[1] and mechanical behaviours of polycrystalline metals[2]. This outcome could be of importance to researchers in biodegradable metals (BMs) who are seeking for non-chemical techniques for adjusting and controlling corrosion behaviours of biometals in physiological fluids. It could also enable the optimization of degradation and mechanical behaviours of BMs so as to obtain degradation rate that matches tissue healing rate, preventing earlier-than-expected mechanical failure and preserving the biocompability of BMs. This work investigated the influence of gsd on the degradation and mechanical behaviours of pure iron and considering its importance while developing standards for biodegradable medical implant application. Materials and Methods: Thermomechanical processing route of cold rolling and annealing was used to induce different average grain sizes and grain size distributions in pure iron. Annealing was carried out in a tube furnace in the temperature range of 550 οC – 1000 οC, under high purity argon atmosphere. The grain sizes and gsd were measured with optical microscope. The mechanical properties of yield strength and ductility were evaluated using tensile testing while the corrosion rates were determined in Hanks’ solution using potentiodynamic polarization method. An X-ray diffractometer was utilized to identify the constituent phases of the samples. Results and Discussions: Figure 1 shows the micrographs and grain size distributions of as-received and some of the annealed pure iron samples subjected to both tensile testing and potentiodynamic polarization tests in Hanks’ solution. Table 1 shows the effect of both average grain size and gsd on the mechanical and degradation properties of the pure Fe samples. Figure 2 shows the cumulative effects of gsd on degradation and mechanical properties of the pure Fe samples. The results demonstrate that the degradation rate increases while the yield strength decreases as the gsd increases. An increase in gsd is accompanied by an increase in residual stress [2], which lowers strength, but increases corrosion rate due to more active sites of low activation energy[3]. Both behaviours are also grain size dependent. Conclusions: This work is the first to evaluate the effect of the gsd on corrosion behaviour of any biometal in simulated body fluid and it adds to the emerging knowledge on the use of microstructure to control the degradation and mechanical behaviours of biodegradable metallic implant materials. These results open a new research direction to optimize the corrosion rates and mechanical properties of pure Fe as a candidate BM material without the changing the base alloy chemistry. This work was partially supported by NSERC-Canada, CIHR-Canada, CFI-Canada, FRQ-NT-Quebec, MRI-Quebec, Canadian Commonwealth Scholarship Program and University of Nigeria.

Effect of grain sizes on mechanical properties and biodegradation behavior of pure iron for cardiovascular stent application.

Pure iron has been demonstrated as a potential candidate for biodegradable metal stents due to its appropriate biocompatibility, suitable mechanical properties and uniform biodegradation behavior. The competing parameters that control the safety and the performance of BMS include proper strength-ductility combination, biocompatibility along with matching rate of corrosion with healing rate of arteries. Being a micrometre-scale biomedical device, the mentioned variables have been found to be governed by the average grain size of the bulk material. Thermo-mechanical processing techniques of the cold rolling and annealing were used to grain-refine the pure iron. Pure Fe samples were unidirectionally cold rolled and then isochronally annealed at different temperatures with the intention of inducing different ranges of grain size. The effect of thermo-mechanical treatment on mechanical properties and corrosion rates of the samples were investigated, correspondingly. Mechanical properties of pure Fe samples improved significantly with decrease in grain size while the corrosion rate decreased marginally with decrease in the average grain sizes. These findings could lead to the optimization of the properties to attain an adequate biodegradation-strength-ductility balance.

Facile immobilization of heparin on bioabsorbable iron via mussel adhesive protein (MAPs)

Motivated by adhesive proteins in mussels, strategies using dopamine to modified surface have become particularly attractive. In the present work, we developed a novel and convenient method to modify the biodegradable Fe plates with heparin. Iron was first treated by a facile one-step pH-induced polymerization of dopamine, and then a high density heparin was successfully grafted onto the surface via coupling with polydopamine (PDA) active layer. Heparin immobilization contributed much longer blood clotting coagulation time than the pure Fe sample, and hence reduced the risk of thrombosis. Cell viability tests suggested that the heparin modified Fe plates were more favorable to the proliferation of ECV304 cells. In summary, the heparin modified Fe plates with good anti-thrombus properties and inhibiting the proliferation of VSMC cells provide great prospects for biodegradable iron.

Rapid in situ fabrication of Fe/SiC bulk nanocomposites by selective laser melting directly from a mixed powder of microsized Fe and SiC

Fe/SiC bulk nanocomposites were fabricated by selective laser melting (SLM) directly from a simple mixture of microsized Fe and SiC. Uniformly dispersed nanosized SiC particles with a mean particle size of 78 nm were obtained and fine homogeneous needle-shaped martensite and partial pearlitic microstructures were observed in different planes of the SLM-fabricated Fe/SiC composites. The Fe/SiC nanocomposite exhibits much higher strength than pure Fe sample, with an ultimate tensile strength of up to 753 ± 49 MPa.

In-situ positron lifetime spectroscopy of radiation damage by simultaneous irradiation of slow-positron and ion beams

An in-situ positron analysis system has been developed for positron annihilation lifetime spectroscopy during ion beam irradiation. An electron linear accelerator was used to produce a slow positron beam for this system. Positron lifetime spectroscopy of SiO2/Si and annealed pure Fe samples was successfully demonstrated during simultaneous irradiation with a 150 keV Ar+ beam. The lifetime spectra changed with increasing ion dose, indicating a decrease in ortho-positronium intensity (SiO2) and the decrease in positron diffusion length (Fe).

Effects of copper precipitates on microdefects in deformed Fe-1.5 wt%Cu alloy

As-annealed Fe–1.5 wt%Cu alloys were deformed by cold rolling. Positron annihilation lifetime spectroscopy (PALS) and Doppler broadening spectra (DBS) were used to analyze the microdefects in the alloy induced by deformation. Cu precipitates were formed uniformly in the alloy after annealing at 1173 K. To investigate the effects of Cu precipitates on the formation and migration of defects, well-annealed pure Fe samples were prepared as a reference. PALS results show that the value of positron lifetime (both long lifetime τ2 and mean lifetime τm) in the alloy is smaller than in pure Fe during deformation. This indicates that Cu precipitates restrain the growth of vacancy clusters. Results of DBS show that the S parameter in pure Fe is larger than in the alloy, and more deformation is needed for the S parameter to be saturated in the alloy.

Studi Transformasi Fasa Sistem Besi Karbon Dengan Pengamatan Thermal Diferensial

Phase Transformation Studies of Fe-C System with Differential Thermal Analyzer: Phase transformation studies for ironcarbon (Fe-C) system have been done by means of Differential Thermal Analyzer, DTA. Fe-C samples of nominal compositions for respectively low carbon containing alloy (0.1 wt.%), hypo eutectoid (0.4 wt.%), and eutectoid (0.8 wt.%) were prepared by powder metallurgy process using pure Fe and C powder materials (>99 %) as the feed stock. Measurement by DTA in the temperature range 25 oC–1100 oC for the samples indicated that there are two endothermic temperatures transition in pure Fe sample respectively at 773.8 oC associated with phase transformation of ferromagnetic (α) to paramagnetic (β) and at 930 oC due to a phase transformation of β-ferrite to austenite (γ). The two transition temperature was also consistently observed in all Fe-C samples but with one additional temperature transition at about 753 oC associated with a phase transformation of pearlite to austenite. Data of heat change measurement in the temperature range 25 oC-1100 oC were subsequently used for determination of heat capacity, Cp for the Fe-C samples as the function of T. Cp (T) curves when fi tted by polynomial regression have resulted in regression coeffi cients between 0.8 and 1.0. Keywords: Pearlite, eutectoid, ferromagnetic, entalphy, iron-carbon system, phase transformation

In situ observation of the oxidation and reduction processes on Fe-Cr alloys

We present atomic force microscopy (AFM) observations on the micron and submicron scale of the surface morphology evolution of Fe-Cr alloys during oxidation-reduction cycles. Industrial Fe-17%Cr, which contains impurity inclusions, exhibits a specific type of corrosion behaviour during the initial stages of oxidation. The inclusions, which are rich in silicon, undergo a very rapid oxidation process which leads to a large increase in their volume. This in turn leads in many cases to the ejection of the enlarged precipitates from the sample, leaving a pitted surface. Purer material is free from this type of attack. Apart from the precipitate behaviour, the oxidation-reduction cycle appears to proceed in most cases similarly in the pure and industrial Fe-17%Cr alloys. Both also contain Cr-rich particles which behave differently from the rest of the sample. Fe-5%Cr and pure Fe samples do not exhibit enhanced activity compared to the 17% samples either during oxidation or reduction. Indeed, in the case of the pure Fe sample it is often quite difficult to observe any changes at all. For these mechanically polished surfaces, which are similar to those used in most electrochemical studies and encountered in real corrosion problems, the AFM observations at the scale of a few microns illustrate that chemical heterogeneities on this scale have more influence than polishing scratches, but that other heterogeneous effects sometimes exist which do not appear to be connected with either property. The usefulness of in situ observations carried out on this scale is underlined.

Uniaxial stress-induced symmetry breaking for muon sites in Fe.

Uniaxial stress has been used on Fe single crystals to induce muon-precession frequency shifts. The frequency shift for a nominally pure Fe sample at 302 K was -0.34\ifmmode\pm\else\textpm\fi{}0.023 MHz per 100 microstrain (\ensuremath{\mu}\ensuremath{\epsilon}) along the 〈100〉 magnetization axis. This corresponds to a change of magnetic field at the muon of 25.1\ifmmode\pm\else\textpm\fi{}1.6 G/100 \ensuremath{\mu}\ensuremath{\epsilon}. For an Fe (3 wt. % Si) single crystal, the shifts were -0.348\ifmmode\pm\else\textpm\fi{}0.008 MHz/100 \ensuremath{\mu}\ensuremath{\epsilon} (25.7\ifmmode\pm\else\textpm\fi{}0.5 G/100 \ensuremath{\mu}\ensuremath{\epsilon} at 300 K), and -0.279\ifmmode\pm\else\textpm\fi{}0.010 MHz/100 \ensuremath{\mu}\ensuremath{\epsilon} (20.6\ifmmode\pm\else\textpm\fi{}0.7 G/100 \ensuremath{\mu}\ensuremath{\epsilon} at 360 K). The agreement between the shifts for Fe and Fe (3 wt. % Si) shows the effect to be intrinsic to iron and not strongly impurity sensitive. These shifts and their temperature dependence (1/T) are dominated by the effect of strain-induced population shifts between crystallographically equivalent, but magnetically inequivalent sites. Their magnitudes are in good agreement with theoretical predictions by Jena, Manninen, Niemenin, and Puska and by extrapolation from calculations on Nb and V by Sugimoto and Fukai, especially if both 4T(0) and 1T sites con- tribute comparably.