As-cast Samples Research Articles

Experimental study and thermodynamic modeling of the Ti–Cu–B system

The Ti–Cu–B ternary system has been systematically studied by experimentation and thermodynamically assessed combining the CALPHAD (CALculation of PHAse Diagram) approach and first-principles calculation. Using seven equilibrated alloys, the isothermal section at 1073 K was established by electron probe micro analyzer equipped with wavelength dispersive spectrometer and X-ray diffraction. Differential scanning calorimetry analysis was performed on all the samples to determine the phase transformation temperatures. Primary solidification phases were also identified from the micrographs of the as-cast samples. Based on all the experimental data obtained in this work, the thermodynamic description of the Ti–Cu–B system was reasonably developed and a set of self-consistent thermodynamic parameters was obtained. The calculated isothermal section, vertical section and liquidus projection account for the experimental data satisfactorily.

Mechanical and damping behavior of artificially aged Al 6061/TiO2 reinforced composites for aerospace applications

In this research, the microstructural and mechanical properties of the as-cast and artificially aged Al6061-TiO2 alloy and its composites developed by the double stir casting process were studied. The reinforcements were added in different weight concentrations and artificial aging was done at 200 °C for 2 h. TiO2 particle reinforcement was adopted because of its better grain refining capacity, high elastic modulus and precipitate pinning effect. Heat treatment was performed for the formation of a high density of fine precipitates which was suitable for stress-bearing applications. The results showed an improvement in the tensile strength and hardness of the heat-treated samples up to 195.2 and 43.68%, respectively, compared to the as-cast samples. After TiO2 addition and age-hardening heat treatment, the SEM fractography showed that the small size dimples were evenly distributed which represented the enhanced ductile nature. The as-cast alloy and its composites had better damping properties compared to the age-hardened specimens. Fracture toughness and elongation showed enhancement in the heat-treated samples than in the as-cast samples. This enhancement is associated with the grain refining effect of TiO2 particles and precipitate formation. Artificially aged Al6061 alloy and its composite showed a better balance of properties.

Manufacturing of high-toughness Al–Si alloy by rolling and friction stir processing: Effect of traverse speed

In this work, the influence of traverse speed on the microstructural evolution and mechanical behavior of Al–7Si alloy fabricated by cold rolling and friction stir processing (FSP) was studied. After the FSP, the needle-shaped silicon and Fe-rich phases were modified to fine particles with a low aspect ratio and high sphericity, and porosity was eliminated. The FSPed samples revealed a uniform dispersion of Si and Fe-rich particles in the aluminum matrix. With the increment of the traverse speed, the average size and sphericity of the Si particles were reduced, while the aspect ratio was increased. The peaks of α-Al, Si, Al 4 FeSi 2 , and Al 5 FeSi phases were observed in all samples, however, the Mg 2 Si peak was not visible due to its low content. With increasing the traverse speed, the peak shifting and lattice strain were decreased due to decreasing the degree of plastic deformation. The as-cast sample had an average hardness higher than the FSPed samples owing to the presence of large second phases. By performing the FSP, the tensile properties were significantly improved owing to the refinement, spheroidization, and uniform distribution of particles. Increasing the tool traverse speed up to 120 mm/min enhanced the strength of the FSPed samples because of decreasing the size of silicon and Fe-rich particles. Further increment of the traverse speed led to a decrease in the strength owing to the presence of cavities. The best strength-ductility belongs to the traverse speed of 120 mm/min which resulted in the highest toughness (57.9 J/cm 3 ). The ductile fracture was the dominant feature on the fracture surface of all FSPed samples.

Impact strength and structural refinement of A380 aluminum alloy produced through gas-induced semi-solid process and Sr addition

Semi-solid processing of A380 aluminum alloy was performed by gas induced semi-solid (GISS) process. The effects of argon inert gas flow rate, starting temperature and duration of gas purging as key GISS parameters and also modification with Sr on the structural refinements, hardness and impact strength of GISS alloys were investigated. Microstructural evolution shows that there is an important effect of the pouring temperature and Sr addition on the morphology and size of primary α(A1) in the alloy to change from coarse dendritic to fine globular structure. The best sample which has fine grains of 51.18 μm in average size and a high level of globularity of 0.89 is achieved from a GISS processing of Sr modified alloy in which the gas purging started at 610 °C. The impact strength of the GISS optimized samples ((4.67±0.18) J/cm2) shows an increase of about 40% with respect to the as-cast sample due to the globular structure and fibrous Si morphology. Moreover, the hardness of the optimized GISS sample ((89.34±2.85) HB) increases to (93.84±3.14) HB by modification with the Sr and GISS process. The fracture surface of Sr modified alloy is also dominated by complex topography showing typical ductile fracture features.

Rejuvenation by triaxial compression in a brittle La-based bulk metallic glass

Rejuvenation was achieved in brittle (La50Ce50)65Co25Al10 bulk metallic glasses (BMGs) by compressing a notched sample. The rejuvenated sample shows low hardness (reduced by 7%), high relaxation enthalpy (increased by 44%) compared with those of as-cast sample. Most importantly, our results show that, in terms of percentage increase in relaxation enthalpy per strain, the rejuvenation ability of La-based BMG is higher than that of Zr-based BMG under plastic deformation. Our findings demonstrated the powerful rejuvenation ability for triaxial compression once again.

Influences of reinforcement size and artificial aging on the compression features of hybrid ceramic filled aluminum syntactic foams

Over the past years, the number of scientific efforts on aluminum matrix syntactic foams (AMSFs) has increased in a noteworthy manner, and different investigation teams have tried to figure out the physical, microstructural, and mechanical properties of AMSFs. In this paper, different from the previous valuable efforts, an industrial-focused cold chamber die casting machine was utilized during the fabrication instead of commonly used lab-scale techniques. Also, the effects of the reinforcement diameter on the compressive features were analyzed for pumice and expanded glass-added hybrid AMSFs. To ascertain the mechanical properties, quasi-static compression tests were conducted and stress–strain curves were obtained. During the compression tests, the deformation styles of the hybrid foams were followed to comprehend their damage mechanisms. Moreover, half of the samples were subjected to artificial aging treatment and the results were checked up with as-cast samples. According to experimental outcomes, it was obvious that the artificial aging treatment caused superior mechanical properties and triggered brittle-style deformation.

An engineering route to synthesize stable bulk nanocrystalline magnesium with an average grain size of 20 nm

A simple and effective route to preparing bulk nanocrystalline (NC) pure Mg with an average grain size of 20 nm is first proposed by hydrogenation-disproportionation-desorption-recombination (HDDR) followed by spark plasma sintering (SPS) and hot extrusion (HE) techniques. NC Mg is thermodynamically super-stable against annealing at 550 °C and straining under compression and tension. Moreover, the as-extruded NC Mg samples show high tensile yield stress (TYS) of 259 MPa and compressive yield strength (CYS) of 157 MPa, which are about 2 times and about 7–10 times higher than those of their coarse-grain counterparts and the as-cast samples, respectively.

Evaluation of optimal processing parameters for a Zn-based eutectoid alloy processed by friction-stir welding

Zn–Al structures offer various benefits, such as high mechanical strength, biocompatibility, good resistance to corrosion, low melting point and low cost. In this work, the study of optimal processing parameters of Zn–22Al–2Cu eutectoid alloy for friction-stir welding is undertaken. Firstly, as-cast plates with a thickness of 3.5 mm were processed considering two different tool geometries (flat and grooved surface), a rotary speed from 1100 to 1500 rpm and a welding speed of 15 mm/s. The metallurgical characterization of the joints was analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and X-ray diffraction. Tensile tests were performed in as-cast and welded samples, detecting a larger value of 280 MPa for as-cast condition. Moreover, Vickers hardness measurements were recorded for different joints and a maximum value of 150 HV was determined. The results showed that the welded Zn–22Al–2Cu joints with a grooved surface at 1100 rpm present superior mechanical properties and non-appearance of tunneling defects. In addition, the welding process was replicated by applying the finite element method in order to achieve numerical results of temperature, strain and stress in the stir zone. Welding microstructures revealed a grain refinement in the stirring zone due to the movement of α and η grains. The dispersed duplex microstructure in Zn–Al alloys prevented excessive grain growth and the tool characteristics played a substantial role in the weld quality preventing tunneling defects in the joint.

Microstructure, superplasticity, and mechanical properties of Al–Mg–Er–Zr alloys

Minor additions of rare-earth elements improve the mechanical properties of aluminum-based alloys due to precipitation strengthening, increased recrystallization resistance, and grain refinement effects. This study investigated the microstructure, room temperature mechanical properties, and superplasticity of Al–Mg–Z–Er alloys with the Mg content in a range of 2.1–4.9 wt%. The alloys' microstructure was presented by an Al-based solid solution matrix enriched with Mg, the (Al,Mg) 3 Er phase of solidification origin, and nanoscale secondary precipitates of the Al 3 (Er,Zr) L1 2 –structured phase. The Al 3 (Er,Zr) precipitates provided the Orowan strengthening mechanism, led to a strong recrystallization resistance and the Zener pinning effect during elevated temperature deformation. An increase of the Mg solute resulted in a solid solution strengthening and facilitated dynamic recrystallization at elevated temperatures. In the alloy with 4.9%Mg, a combined effect of fine L1 2 precipitates, high solute Mg, and (Al,Mg) 3 Er particles led to a fine-grained structure formation and superplasticity with the maximum strain rate sensitivity m of 0.51 and the elongation-to-failure of 550–600% at the constant strain rates of (0.8–1) × 10 −2 s −1 . The mechanical properties at room temperature were studied after the post-deformation annealing of the thermomechanically treated alloys and after the superplastic deformation. The developed Arrhenius-type mathematical model of superplastic deformation behavior showed excellent predictability for the studied alloys with different solute Mg. • Microstructure and tensile properties for thermomechanical-treated Al–Mg–Er–Zr alloys were studied. • A L1 2 -Al 3 (Er,Zr) precipitates parameters were studied after annealing of as-cast and rolled samples. • Increase in Mg solute improved solid solution strengthening and superplastic properties. • Model with excellent predictability of the superplastic deformation behavior was developed.

Effect of Y Addition on the Structural Properties and Oxidation Behavior of Fe60Al40-nYn Alloys (n= 1, 3, and 5 at.%)

ABSTRACT The influence of Y addition on the microstructural features, phase relationships, hardness, magnetic behaviour and cyclic oxidation performance of Fe60Al40 − n Y n alloys (n = 1, 3, and 5 at.%) has been examined in detail. Al8Fe4Y phase formed even at 1 at.% Y addition because of the limited solid solubility of Y in the FeAl-based phase. For all the examined compositions, the Al8Fe4Y phase developed a eutectic with the FeAl-based phase and its volume fraction increased with increasing Y up to 5 at.%, which is near the eutectic composition. The mean microhardness values increased with increasing Y content for both as-cast and heat-treated samples. Cyclic oxidation tests revealed that the oxidation rate and scale thickness increased with increasing Y content. α-Al2O3 was the main surface oxide for all compositions. θ-Al2O3 was also formed with relatively low amount. An internal oxidation layer composed of mixed Al/Y oxides was observed beneath the surface layer.

Ambient-temperature time-dependent deformation of cast and additive manufactured Al-Cu-Mg-Ag-TiB2 (A205)

A dual-stage indentation test at ambient temperature including a constant indentation load rate followed by a constant indentation load-hold segment was employed to assess the time-dependent plastic deformation of cast and additive manufactured Al-Cu-Mg-Ag-TiB2 alloys in as-fabricated and T7 conditions at room temperature. Optical microscopy, scanning electron microscopy, electron backscattered diffraction, and transmission electron microscopy techniques were used to study the microstructure of the samples and to correlate the microstructure with the creep properties. That is, the indentation load/displacement/time data from depth-sensing indentation creep were combined with the advanced microstructural assessments to analyze the controlling mechanisms of creep in as-cast, as-built, and T7 samples. Expectedly, the microstructure of samples manufactured by different methods was substantially different in terms of the grain size and the distribution of TiB2 particles. The θ’’, θ’ and Ω phase were formed in all heat-treated samples; however, the density of Ω phase was higher in the cast-T7 samples. Distinct microstructure and precipitation density resulted in different indentation-derived properties, both cast and AM samples at T7 condition showed enhanced creep resistance compared to their as-manufactured counterparts. The main controlling mechanism of creep deformation was found to be dislocation creep based on the indentation-derived creep stress exponent values.

The shock forming process of Cu50Zr50 metallic glasses studied via molecular dynamics simulation

The shock forming process of Cu50Zr50 metallic glasses is investigated via the classical molecular dynamics method. The velocity and density profiles are presented to describe the shock wave propagation, and the displacement vector is used to trace the atomic flow. The shock forming process is accompanied by the evolution of the internal short-range order of the metallic glasses. Beside, the influence of piston velocity and mould size on the shock forming process is explored. It is found that the suitable shock pressure is in the range of 18–30 GPa, with which the filling rate could be higher than 85%. A larger fillet radius or a smaller mould opening size is advantageous to alleviate the residual stress concentration. The sample obtained by shock forming exhibits better plasticity compared with the as-cast sample, which could be explained by the change in the number of the dominated Voronoi polyhedra.

Corrosion Behavior of Heat-Treated Nickel-Aluminum Bronze and Manganese-Aluminum Bronze in Natural Waters

Nickel Aluminum Bronze (NAB) and Manganese Aluminum Bronze (MAB) are high-alloyed bronzes that are increasingly employed in several industrial sectors, mainly related to hostile environments due to their excellent properties against corrosion, cavitation, erosion and improved mechanical properties in relation to other copper-based alloys. These materials are very sensitive against thermal treatments due to a multiphase microstructure in as-cast condition. To contribute to the knowledge of the behavior of both alloys, the effect of thermal treatments on the corrosion behavior of NAB (CuAl10Fe5Ni5) and MAB (CuMn12Al8Fe4Ni2) was studied. As-cast material was subjected to various combinations of quenching and quenching and tempering at 850 °C and 600 °C. Corrosion testing was carried out using simulated sea and fresh water. The microstructures of the as-cast and heat-treated samples were characterized by metallography using two chemical agents with FeCl3 and NH4OH solutions and examination by optical and scanning electron microscopy. The major effect of thermal treatments on corrosion was found in influencing the amount and distribution of β-phase, which is prone to selective corrosion in both electrolytes.

Production and characterization of the Cr35Fe35V16.5Mo6Ti7.5 high entropy alloy

The microstructure, thermal stability, and mechanical properties of a novel Cr35Fe35V16.5Mo6Ti7.5 high-entropy alloy were studied. The mechanical properties were mapped by nanoindentation, and the results correlated with the microstructure and the Vickers microhardness measurements. The alloy was produced by arc melting in a low pressure He atmosphere. Thermal treatments were performed to study the thermal stability of the alloy. The as-cast microstructure of the alloy exhibited a body-centered cubic phase with morphology of dendrites, outlined by a very thin interdendritic phase with a crystallographic structure compatible with Fe2Ti. The presence of the intermetallic particles was predicted by a free-energy based model, in contrast with the single solid solution alloy predicted by a parameter-based model. The volume fraction of the dendrites in the alloy is ∼ 94 % after arc melting. A small fraction of sparse Ti-rich particles, ∼0.4 vol%, was observed. The thermal treatments produced an increase of the population of Ti-rich particles, the formation of a σ-phase and nucleation of precipitates enriched with Fe and Ti into the previous dendrites. The material in as-cast condition exhibited a microhardness value of 6.2 ± 0.3 GPa, while the alloy aged at 960 °C resulted in 7.1 ± 0.4 GPa. Nanoindentations maps showed an excellent correlation with the microstructure, and their statistical analyses yielded a nanohardness mean value of 8.2 ± 0.4 GPa in the dendritic BCC regions of the as-cast and thermal treated samples and 14.1 ± 0.6 GPa for the σ-phase. The onset of the plastic behavior has been studied by analyzing the pop-in phenomenon observed in the nanoindentation loading curves. For the as-cast alloy, this analysis showed that the elastic-to-plastic transition seems to be triggered by dislocation nucleation. The alloy has a low thermal diffusivity in the measured temperature range that increases on increasing temperature.

Strain-hardening under uniaxial tension in a rejuvenated bulk metallic glass

A rejuvenated Zr-based bulk metallic glass is tested in tension: it shows strain-hardening and reaches 0.9% plastic strain at failure. The initial rate of increase of flow stress with strain is 73 GPa, much higher than normal for polycrystalline metals and alloys. This hardening rate and its decay with increasing strain are compared with published data on a representative range of conventional and novel alloys. Taking the onset of necking as failure, and using Considère's analysis, we conclude that the metallic glass, however much rejuvenated, is limited to tensile plastic strains of approximately 1%, because of the rapid decay of hardening rate with strain. Rejuvenation of the metallic glass blocks early catastrophic failure in a predominant shear orientation. In comparison with as-cast samples, the fracture surface of the rejuvenated sample is more rugged and the characteristic vein pattern is denser. The effects of rejuvenation on abrasive-wear behavior are also examined.

A re-examination of the liquidus surface of the Al–Fe–Ti system

Abstract The liquidus surface of the Al –Fe –Ti system has been reexamined. 34 different alloys have been studied by differential thermal analysis, and the temperatures of invariant reactions have been determined. By examining the as-cast samples by optical microscopy, X-ray diffraction and energy-dispersive spectrometry in a scanning electron microscope, the crystal structures and chemical compositions of the primary phases and two-phase aggregates have been established. In some cases, additional investigations were carried out in the transmission electron microscope. From the combined results of these investigations the solidification paths of the alloys were established leading to a revised representation of the liquidus surface of the Al –Fe –Ti system. A reaction scheme has been set up which shows phase equilibria that are consistent with previous solid-state isothermal sections.

Microstructures and mechanical properties of a hot-extruded Mg−8Zn−6Al−1Gd (wt%) alloy

Microstructural evolution and mechanical properties of a Mg−8Zn−6Al−1Gd (wt%) alloy were thoroughly investigated in this work. The results indicate that the dominant intermetallic phases in the as-cast sample are ϕ-Al2Mg5Zn2, τ-Mg32(Al,Zn)49, i-Mg44Al15Zn41 and Al2Gd phases and almost free Gd was detected in the former three phases. After extrusion, the sample has a fully recrystallized microstructure with the average grain size being ~1.5 µm, and exhibits a weak rare earth texture. Additionally, fine particles were approximately homogeneously dispersed in the fine-grained structure. Most of them are quasicrystal phase (i-phase) but have no identical orientation relationship with Mg matrix regardless of whether they distribute at grain boundaries or inside grains. Finally, the as-extruded sample exhibits good strength-ductility balance in both tension and compression and simultaneously has a slight reverse tension/compression asymmetry. Microstructural observations indicate that the excellent mechanical performance of the studied alloy is highly related to its fine grains, weak RE texture, and numerous homogeneously distributed fine particles.

Annealing Effect on Domain Wall Dynamics in Wires With Induced Gradient of Perpendicular Anisotropy

Amorphous glass-coated Fe-Si-B-P microwires with an induced gradient of perpendicular magnetic anisotropy are studied. The angular dependence of the domain wall mobility in the perpendicular magnetic field is present in as-cast sample. After thermal annealing below the crystallization temperature, the effect of the perpendicular magnetic field is suppressed due to the relaxation of internal mechanical stresses. Moreover, the domain wall mobility decreases, and the critical field increases. The results are explained in terms of the release of mechanical stresses induced during production after annealing. Furthermore, a new mechanical stress distribution is induced due to the slow cooling rate after thermal annealing. Scanning electron microscopy images of annealed samples below and above the crystallization temperature suggest the presence of the gradient of perpendicular magnetic anisotropy. Directional growth of the crystals after annealing above the crystallization temperature follows the induced stresses and shell-like structure in the cross section is recognized.

Effect of heat treatment on the mechanical and biocorrosion behaviour of two Mg-Zn-Ca alloys

The effect of heat treatment on the mechanical and biocorrosion behaviour of the Mg-1 wt.% Zn-1 wt.% Ca (ZX11) and Mg-3 wt.% Zn-0.4 wt.% Ca (ZX30) alloys was evaluated. For this purpose, three-point bending tests as well as electrochemical and immersion tests in Hank's solution were performed on both alloys in four different thermal conditions: as-cast, solution-treated, peak-aged and over-aged. Microstructural examinations revealed that the as-cast ZX11 and ZX30 alloys exhibit a microstructure composed of α-Mg grains separated by large Mg2Ca and Ca2Mg6Zn3 particles and by large Ca2Mg6Zn3 particles, respectively. During solution treatment, the Ca2Mg6Zn3 precipitates at the grain boundaries (GBs) are fully dissolved in the ZX11 alloy, but mainly redistributed to form a more connected configuration in the ZX30 alloy, showing a poor age-hardening response. Consequently, after solution-treatment, galvanic corrosion and corrosion rate decreases in the former, but increases in the latter. The peak-aged condition displays the highest corrosion rate for both alloys, maybe due to an excessive number density of fine Ca2Mg6Zn3 particles acting as cathodic sites. However, the over-aged condition shows the lowest corrosion rate for the ZX11 alloy and a very similar one to that of the as-cast sample for the ZX30 alloy. The ZX11 alloy shows generally better biocorrosion behaviour than the ZX30 alloy to its lower content in the Ca2Mg6Zn3 phase and thus reduced galvanic corrosion. The Mg2Ca phase present in the studied ZX11 alloy has been proved to exhibit an increased corrosion potential, which has been related to an observed enrichment with Zn.

Transition from spin glass to paramagnetism in the magnetic properties of PrAu2Si2

It is unexpected that a spin-glass (SG) transition, which generally occurs only in systems with some form of disorder, was observed in the ThCr2Si2-type compound PrAu2Si2 at a temperature of ∼3 K. This puzzling phenomenon was later explained based on a novel dynamic frustration model that does not involve static disorder. We present the results of re-verification of the reported SG behaviors by measuring the physical properties of three polycrystalline PrAu2Si2 samples annealed under different conditions. Indeed, in the sample annealed at 827 °C for one week, a SG transition does occur at a temperature of T f ∼ 2.8 K as that reported previously in the literature. However, it is newly found that the SG effect is actually more pronounced in the as-cast sample, and almost completely disappears in the well-annealed (at 850 °C for four weeks) sample. The annealing effect observed in PrAu2Si2, that is, SG to paramagnetism transition is discussed by comparing with earlier results reported on the same system and other isomorphic compounds.