Fe Alloy Samples Research Articles

Hot working behaviour of low-cost Ti-3.4Fe bio-implant alloy

This study investigated the hot workability of an experimental, non-toxic, low-cost Ti-3.4Fe alloy using flow stress analysis, constitutive modelling, processing maps and microstructural examination. Hot compression tests were performed on Ti-3.4Fe alloy samples at different deformation temperatures (750, 800, 850 and 900 °C), strain rates (0.05, 0.1, 1 and 10 s−1) and a total strain of 0.6. The compression tests were performed using a Gleeble® 3500 thermomechanical simulator. The isothermally compressed samples were analysed using a scanning electron microscope to assess the microstructure. An Arrhenius-based model was used to derive the constitutive constants. From the results, the stress exponent and activation energy were 4.91 and 611 kJ.mol−1 under the steady-state stress condition and 5.32 and 675 kJ.mol−1 at peak stress. The stress exponents suggested a dislocation climb and glide mechanism controlling deformation. The processing map showed that the optimum conditions to deform Ti-3.4Fe were 850 °C at a strain rate of 0.1 s−1 for both steady-state and peak stresses. The microstructure revealed kinked, rotated and bent lamella at the safe region (850 °C at 0.05 s−1), confirming the dominance of dynamic recovery as the softening mechanism. Instabilities manifested as cracks and inhomogeneity at 750 °C and 1 s−1 and at 850 °C and 10 s−1.

Preparation and properties of multiphase solid-solution strengthened high-performance W–Cu alloys through alloying with Mo, Fe and Ni

In this study, high performance W–Mo–Cu–Ni–Fe alloy samples with additions of Mo (0–6 wt%), Ni and Fe (total content: 2.5 wt% and 5 wt%) were obtained through liquid-phase sintering at lower temperature, with the raw material of ultrafine W–Mo–Cu–Ni–Fe composite powder. Ultrafine W–Mo–Cu–Ni–Fe alloy powder with strong sintering activity and uniform composition was obtained by two-stage reduction means composed of carbothermic pre-reduction and hydrogen deep deoxidation steps. Significantly, the bonding ability of W/Cu phase interface and the wettability of two phases are greatly improved due to the presences of Ni and Fe. Moreover, the addition of appropriate Mo content was advantageous to the formation of W–Mo solid solution. All alloy samples achieved higher densification degrees to guarantee that the sintered blocks possess outstanding overall performances. Especially, by adjusting Ni/Fe ratio, the highest tension strength and elongation of were achieved by W-2wt.%Mo-1.75 wt%Ni-0.75 wt%Fe-27.5 wt%Cu sintered block, which were 567 MPa and 10.37%, respectively. Moreover, owing to the presences of W–Mo and Cu–Ni–Fe solid solutions, this alloy also had the highest microhardness and bending strength of 446 HV and 1473 MPa, respectively. As increasing Mo content from 0 wt% to 6 wt%, the compression strength of sintered blocks was improved, and failure strains of all the sintered blocks are close to 100%, respectively. However, even though the Cu matrix network structure is more evenly distributed as a result of the existences of added Ni and Fe, the electronic movement ability of the sintered blocks was reduced, leading to a significant decrease in conductivity.

Processability and Optimization of Laser Parameters for Densification of Hypereutectic Al–Fe Binary Alloy Manufactured by Laser Powder Bed Fusion

Centimeter-sized samples of hypereutectic Al–15 mass% Fe alloy were manufactured by a laser powder bed fusion (L-PBF) process while systematically varying laser power (P) and scan speed (v). The effects on relative density and melt pool depth of L-PBF-manufactured samples were investigated. In comparison with other Al alloys, a small laser process window of P = 77–128 W and v = 0.4–0.8 ms−1 was found for manufacturing macroscopically crack-free samples. A higher v and P led to the creation of macroscopic cracks propagating parallel to the powder-bed plane. These cracks preferentially propagated along the melt pool boundaries decorated with brittle θ-Al13Fe4 phase, resulting in low L-PBF processability of Al–15%Fe alloy. The deposited energy density model (using P·v−1/2) would be useful for identifying the optimum L-PBF process conditions towards densification of Al–15%Fe alloy samples, in comparison with the volumetric energy density (using P·v−1), however, the validity of the model was reduced for this alloy in comparison with other alloys with high thermal conductivities. This is likely due to inhomogeneous microstructures having numerous coarsened θ–Al13Fe4 phases localized at melt pool boundaries. These results provide insights into achieving sufficient L-PBF processability for manufacturing dense Al–Fe binary alloy samples.

Laser powder bed fusion of a near-eutectic Al–Fe binary alloy: Processing and microstructure

•This study focused on additive manufacturing (AM) of the Al–Fe binary alloy samples with a near-eutectic composition of 2.5 mass% Fe using the laser powder bed fusion (LPBF) process. The melt pool depth, relative density, and hardness of LPBF-fabricated Al–2.5Fe alloy samples under different laser power (P) and scan speed (v) conditions were systematically examined. The results provided optimum laser parameter sets (P = 204 W, v ≤ 800 mm s−1) for the fabrication of dense alloy samples with high relative densities >99%. Additionally, Pv-1/2, which is based on the deposited energy density model, was found to be a more appropriate parameter for additively manufacturing Al–2.5Fe alloy samples, and using it to simplify the relative densities of the samples made the determination of a threshold value for the laser parameters required to fabricate dense alloy samples. The microstructural and crystallographic characterization of the LPBF-built Al–2.5Fe alloy samples revealed a characteristic microstructure consisting of multi-scan melt pools that resulted from local melting and rapid solidification owing to laser irradiation during the LPBF process. Furthermore, a number of columnar grains with a mean width of ∼21 μm elongated along the building direction were also observed in the α-Al matrix. Numerous nano-sized particles of the metastable Al6Fe intermetallic phase with a mean size <100 nm were finely dispersed in the α-Al matrix. The hardness of the refined microstructure produced by the LPBF process was high at ∼90 HV, which is more than twofold higher than that of conventionally casted alloys that contain the coarsened plate-shaped Al13Fe4 intermetallic phase in equilibrium with the α-Al matrix.

The corrosion behavior of porous Ni–Cr–Fe alloy in 2 mol L−1 alkaline solution

Abstract Ni–Cr–Fe alloy samples with different porosities were prepared via the Kirkendall effect, with a reactive synthesis of Ni, Cr, and Fe elemental powders. The microstructure, surface morphology and the compositions were analyzed with X-ray diffraction and scanning electron microscopy. The corrosion behavior was explored in a 2 mol L−1 KOH solution using electrochemical methods and an immersion test. The polarization resistance indicated that the free corrosion potential and the lower corrosion current of the porous Ni–Cr–Fe alloy were −0.18528 V and 3.5998 × 10−7 A cm−2. The immersion test showed that after 25 days of immersion, the weight change of porous Ni–Cr–Fe alloy was 0.132 %, which was less than the porous Ni (0.346 %). X-ray photoelectron spectroscopy results revealed the corrosion products of the porous Ni–Cr–Fe alloy and the porous Ni. The corrosion mechanism of the porous Ni–Cr–Fe alloy was discussed.

Thixoforming of an Fe-Rich Al-Si-Cu Alloy—Thermodynamic Characterization, Microstructural Evolution, and Rheological Behavior

Thixoforming depends on three factors: (a) the thermodynamic stability of the solid-to-liquid transformation in the presence of temperature fluctuations; (b) the size and morphology of the solid particles in the liquid in the semisolid state; and (c) the rheology of the semisolid slurry during formation. In this study, these parameters were characterized for an Al-Si-Cu alloy with a high Fe content (B319+Fe alloy). Fe is usually found in raw metal produced by recycling, and its removal increases processing costs. This study is an attempt to use this lower-cost alloy for the thixoforming route. Thermodynamic analysis was performed by numerical simulation (under Scheil conditions) and the application of the differentiation method (DM) to differential scanning calorimetry (DSC) curves recorded during heating cycles up to 700 °C at 5, 10, 15, 20, and 25 °C/min. The processing window was evaluated by comparing the results of the DM and those of the analysis of open-die thixoforged samples after isothermal heat treatment at 575, 582, 591, and 595 °C for 0, 30, 60, and 90 s. The microstructural and rheological behavior of the semisolid slurry was analyzed at 591 and 595 °C for all four soak times. Isothermal heat treatment caused the refinement and spheroidization of the solid phase. Good agreement between the predicted thermodynamic behavior and the microstructural behavior of the thixoformed B319+Fe alloy samples was observed. Although the alloy exhibited a coarse microstructure, it was microstructurally and rheologically stable at all temperatures and for all the soak times studied, indicating that B319+Fe is a promising raw material for thixoforming.

Formation of intermetallic phases in AlSi7Fe1 alloy processed under microgravity and forced fluid flow conditions and their influence on the permeability

Ternary Al-6.5wt.%Si-0.93wt.%Fe alloy samples were directionally solidified on-board of the International Space Station ISS in the ESA payload Materials Science Laboratory (MSL) equipped with Low Gradient Furnace (LGF) under both purely diffusive and stimulated convective conditions induced by a rotating magnetic field. Using different analysis techniques the shape and distribution of the intermetallic phase β-Al5SiFe in the dendritic microstructure was investigated, to study the influence of solidification velocity and fluid flow on the size and spatial arrangement of intermetallics. Deep etching as well as 3-dimensional computer tomography measurements characterized the size and the shape of β-Al5SiFe platelets: Diffusive growth results in a rather homogeneous distribution of intermetallic phases, whereas forced flow promotes an increase in the amount and the size of β-Al5SiFe platelets in the centre region of the samples. The β-Al5SiFe intermetallics can form not only simple platelets, but also be curved, branched, crossed, interacting with dendrites and porosity located. This leads to formation of large and complex groups of Fe-rich intermetallics, which reduce the melt flow between dendrites leading to lower permeability of the mushy zone and might significantly decrease feeding ability in castings.

An analytical model for solidification of undercooled metallic melts

A model has been proposed for describing the solidification of undercooled metallic melts, on the basis that the solidification is considered as the sum of a liquid/solid cooling process without latent heat release and a latent heat releasing process without cooling. Application of the model to undercooled solidification of nickel, cobalt, zirconium, and Al–11.3Si–2Cu–0.4Fe alloy samples shows good fits to the temperature curves, and the fitting results of solid fraction curves are consistent with that from the available methods.

Structural and magnetic investigations on metastable Ag–Fe nanophase alloy

Nanocrystalline Ag–Fe alloy samples of various compositions were synthesized by chemical reduction method using sodium borohydride as the reducing agent. The structure analysis of the as prepared and the annealed samples were carried out. The fcc structure of the as prepared samples was stable up to 400°C. As bulk Ag and Fe are immiscible metals, nanophase alloy formation of these two metals was studied from the broad exothermic peak observed and the enthalpy changes were calculated from the differential scanning calorimetric analysis. The presence of Ag and Fe in their metallic form was verified by performing X-ray photoelectron microscopy studies. The microstructure of these samples reveals that the particles are nanosized. The results of the magnetic characterization of the as synthesized and annealed Ag50Fe50 sample and the conclusions drawn there from are in correlation with the metastable nature of the samples up to 400°C and the phase changes in the sample annealed at 500°C.

Laser remelting of Al–1.5 wt%Fe alloy surfaces: Numerical and experimental analyses

A 3D heat transfer mathematical model based on the finite element method is applied to the laser surface remelting (LSR) process with a view to simulating temperature fields and melt pool dimensions. The theoretical predictions furnished by the model are validated against LSR experimental results from tests carried out in the present study with Al–1.5wt%Fe alloy samples. The work also encompasses an analysis of microstructural and microhardness variations throughout the resulting treated and untreated zones. A remarkable effect of the LSR treatment on the mechanical and corrosion resistance of the treated samples is shown.

Alignment of Fe-rich Primary Phase in Cu–Fe Alloy Solidified under a High Magnetic Field

Cu-11 mass% Fe alloy samples were solidified with and without a high magnetic field. The influence of a high magnetic field and cooling rate on the morphology, alignment and distribution of primarily precipitated Fe-rich phase has been investigated. We found that the primary phase of Fe-rich was equiaxed dendrites or columnar dendrites under the combinations effect of magnetic field and initial cooling rate. And Fe-rich primary phase with random alignment was mainly observed in the upper region of the sample solidified without the magnetic field. In the case of the sample solidified with the magnetic field of 7.5 T, however, Fe-rich phase was uniformly distributed and the Fe-rich phase at some areas was aligned parallel to the direction of the magnetic field. Furthermore, slower cooling rate was beneficial to the alignment but was not to the uniform distribution. These phenomena were well discussed from the viewpoint of magnetic shape anisotropy and convection under the high magnetic field.

Experimental Observations of Dendrite Coarsening &amp; Al-Si Eutectic Growth in Progressively Quenched Structures of Al-Si-Cu Casting Alloys

Computer controlled thermal heating and cooling curve cycles of the W319 (Al-7.5Si-3.5Cu-0.3Fe) and the WA328 (Al-9Si-lCu-0.3Fe) alloy samples were studied in this work. Both alloys contain residual levels of Sr (∼ 20 ppm max) and are processed with no grain refiner. From the cooling curve portion of the thermal cycle the characteristic temperature points that represent phase nucleation and growth are established. Once characteristic temperatures in the alloy samples are known, strategic quench points can be chosen to reveal the evolving mushy state using metallographic examination. In particular the growth kinetics of primary α-Al dendrites in quenched and unquenched alloys are studied and discussed in this work. In addition, growth modes for the Al-Si eutectic lamellae and polyhedral Si particles were also observed from quenched test samples during and post the Al-Si nucleation temperature event.

The effect of annealing on deformation and fracture of a nanocrystalline fcc metal

The tensile deformation and fracture behavior of electrodeposited nanocrystalline Ni–15% Fe alloy samples after annealing for 90 min at 250, 400 and 500 °C temperatures were investigated. The structure of the samples was studied using TEM and XRD techniques and the fracture surfaces were investigated employing SEM. The results of this study indicated that annealing at 250 °C modified grain size distribution slightly but resulted in a significant increase in the initial strain hardening rate. While the average grain size in the 400 °C sample was increased to 59 nm, its yield strength was comparable to the as-deposited alloy with a 9 nm grain size. The plastic tensile elongation of all annealed samples was lowered significantly to less than 1% from approximately 6% in the as-deposited state. These results are discussed in terms of the inhomogeneity of plastic deformation and the evolution of internal stresses in nanocrystalline materials.

Corrosion Behavior of Biomedical Titanium Alloy Ti-5Al-2.5Fe Processed by MIM.

Corrosion behavior plays a decisive role for biocompatibility of titanium alloy implants. In this study, Ti-5Al-2.5Fe alloy samples were formed through metal powder injection molding (MIM) process and their potentiodynamic tests were carried out in a phosphate buffered solution with and without HCl. Experimental results showed that the slope of current potential curves increased within the passive region. In comparison to results of samples processed by vacuum arc melting followed by annealing, existence of micro pores was considered to be a main factor for observed corrosion behavior of MIM processed sample. The observations were further discussed in detail based upon a model of electrochemical reaction system and quantitative equations for quasi-passive state.

Origin of the satellites in the high resolution KLL Auger spectra of the 3d metals, Cu and Ni, and their alloys

The understanding of the structure of high energy Auger spectra in metals and alloys of practical interest is relevant for studying solid state effects on core potentials, charge transfer and localization in these systems. In previous work evidence was found for the presence of intrinsic satellites in the LMM Auger spectra of 4d metals. Here we report the results of a study of the satellite structure identified in the high resolution KLL spectra of 3d metals Cu, Ni and some of their alloys. KLL spectra excited by Cu X-rays from polycrystalline Cu, Cu–noble metal and Ni–Fe alloy samples, were measured by a high luminosity hemispherical electron spectrometer. The satellite structures revealed in the spectra are compared to the structures obtainable on the basis of the spectator vacancy model. For the case of these metals and alloys, our results show that the KLL satellites can be attributed to intra-atomic 3d shake-up processes.