As-rolled Samples Research Articles

Microstructure and Texture Evolution During Thermomechanical Processing of Al0.25CoCrFeNi High-Entropy Alloy

Microstructure and texture evolution was studied in a Al0.25CoCrFeNi high-entropy alloy after cold work and subsequent isochronal annealing treatments. The alloy was synthesized by arc-melting and the resulting ingots were cold rolled up to two different thickness reductions: 50 pct and 80 pct. The alloy was then annealed for 1 hour at 973 K, 1073 K, 1173 K, and 1273 K. The final microstructures were analyzed using X-ray diffraction, scanning electron microscopy, and electron backscatter diffraction and the results were correlated with hardness measurements. The sample reduced by 80 pct recrystallized at a lower temperature than the sample reduced by 50 pct, confirming the influence of the deformation degree on the rate of nucleation and growth of new grains. The recrystallized microstructures revealed equiaxed grains with a high density of twins, which is typical of metals with low stacking fault energy. Twins were also observed in the as-rolled samples, suggesting that twinning precedes shear banding during deformation of this alloy. This accounts for the strength of the {110} 〈112〉 brass texture component in the cold rolled samples.

Influence of Heat Treatment on Microstructures and Impact Toughness of Mg-Al-Zn Alloy

Microstructures and impact properties of the rolled Mg-8.10Al-0.46Zn-0.18Mn-0.18Ag (wt.%) alloy were investigated under various thermal conditions including as-rolled, solid solution (T4) and solid solution plus aging (T6) states. The results show that the impact toughness of the as-rolled alloy is slightly enhanced after solution treatment but remarkably reduced by the subsequent aging process, exhibiting a similar trend with the elongation of the alloy. Fractography analysis suggests that the impact toughness variations are closely associated with the changes in the deformation mode: the superior impact toughness of the as-rolled and T4 samples are mainly attributed to the occurrence of profuse twins during impact testing, while, in the T6 sample, the twinning activity is significantly suppressed due to the presence of β-Mg17Al12 phases. In addition, the lamellar-shaped β-Mg17Al12 phases are easy to fracture, which accelerates the crack propagation and thus degrades the impact property.

The Mechanical and Corrosion Properties of Hot-Rolled TiB2/Ni Composites

To quickly prepare TiB2/Ni composites at low temperatures, a method combining spark plasma sintering and hot rolling was used. This paper presents the preparation, microstructural and mechanical properties, strengthening mechanism and corrosion properties of TiB2/Ni composites in detail. X-ray diffraction analysis shows that the texture degree of the TiB2/Ni composites after hot rolling greatly differed from that of the as-rolled pure Ni samples. The addition of TiB2 particles limited grain growth in the Ni matrix and led to grain refinement. Dislocation strengthening, grain refinement strengthening and load transfer strengthening contributed to a 30% increase in the tensile strength compared to that of the as-rolled pure Ni. In addition, the strengthening mechanism of the mechanical property reinforcement was analyzed. The electrochemical test results demonstrate that the as-rolled pure Ni exhibited a lower corrosion current density and corrosion resistance than the other as-rolled TiB2/Ni composites fabricated in this paper. This work demonstrates a new approach for fabricating composites in less time at lower preparation temperatures than conventional methods.

Evaluation of fracture toughness and rupture energy absorption capacity of as-rolled LZ71 and LZ91 Mg alloy sheet

In this study, for the first time, fracture behavior and rupture energy absorption of Mg-Li alloys are evaluated. At the first, dual-phase Mg LZ71 and LZ91 alloys were melted at the temperature of 770 °C under argon atmosphere. After this, high plastic deformation was applied during a warm rolling process to prepare thin sheet from the initial ingot, for the present investigation. Fracture behavior and rupture energy absorption were evaluated through plane stress fracture toughness tests, extracted R-curve and calculated the area below force-displacement curves. Plane stress fracture test and compact tension (CT) were performed according to ASTM E-561 and E-399. Also, microstructure, mechanical properties, and fractography are evaluated using x-ray Diffraction (XRD), Optical Microscopy (OM), microhardness measurement, uniaxial tensile test and Scanning Electron Microscopy (SEM). The optical images and XRD analysis demonstrated that Mg-Li alloys possess a dual-phase microstructure containing β-Mg-Li matrix with Body Centered Cubic (BCC) and partitioned α-Mg phase with Hexagonal Closest Packed (HCP) structures. According to the OM images, HCP phase of as-cast specimens has been observed in lath shape and after rolling process, the α–Mg phase was elongated and arranged in the rolling direction. The results showed that increasing of the lithium mass portion from 7% to 9%, not only did not increase mechanical properties, absorbed energy and fracture toughness, but also all of them decreased. Moreover, results of XRD analysis depict that adding more Li into the alloys chemical composition did not cause to the formation of any new phases. Hence, the ultimate tensile strength, microhardness, absorbed energy and fracture toughness of Mg LZ71 were achieved 1.07, 1.06, 1.91 and 1.51 times higher than LZ91 respectively. Due to the dependence of fracture toughness on two significant parameters, namely strength and ductility, adding lithium into the composition will increase the value of fracture toughness with compared to AZ alloys, because of the fact that a significant increase in ductility compensates the reduced strength. Furthermore, SEM photographs of tensile fracture surfaces of as-rolled LZ71 and LZ91 samples displayed dimples and microvoids which are characterized as a ductile rupture mode. Thus, Mg-Li alloys had ductile fracture, which were consistent with the results of the tensile test.

Preparation of magnetic Fe-Co alloy using texture controlled technique

Microstructure and texture controlled 48Fe-52Co at% alloy was prepared by repeated cold-rolling and recrystallization through heat treatment at temperatures below order-disorder phase transformation using Fe and Co foils. Furthermore, distortion of controlled texture orientated cubic crystal structured 48Fe-52Co at% alloy along the 〈0 0 1〉 direction was attempted by introducing nitrogen interstitially through plasma nitriding. The textural analysis suggested that the microstructure is composed of micron-sized grains randomly aligned along rolling direction (RD). Furthermore, from the results of orientation distribution function (ODF), the dominance γ-fiber was confirmed in as-rolled samples. However, in recrystallized sample, the intensity of rotated-cube orientation increased while the presence of γ-fiber decreased. Furthermore, a complete rotated-cube orientation was realized in nitrided texture. The appearance of the prominent X-ray diffraction peak (2 0 0) in all samples indicated the presence of rotated-cube orientation. However, the FWHM of (2 0 0) peak of the nitrided sample was broader than the rest. This was attributed to the diffusion of nitrogen into the matrix during plasma nitriding and internal nitriding was confirmed from the EDX analysis. However, further investigation is necessary to understand the behavior of nitrogen.Magnetic properties of as-rolled 48Fe-52Co at% alloy inferred from in-plane magnetic hysteresis loops was similar Fe foil. Furthermore, magnetic properties of recrystallized and nitrided 48Fe-52Co at% alloy were different from Fe-Co particles or crushed bulk Fe-Co alloy prepared by arc melting. However, the internal diffusion of nitrogen was not adequate enough to bring about a considerable change in the magnetic properties. We believe that considerable crystal distortion to induce change in the magnetic properties can be exerted by introducing interstitial carbon and the addition of third or fourth elements.

High corrosion resistance and weak corrosion anisotropy of an as-rolled Mg-3Al-1Zn (in wt.%) alloy with strong crystallographic texture

Combining with electrochemical corrosion measurements, immersion and hydrogen evolution testing performed in 0.9 wt.% NaCl solution at 37 °C, the corrosion resistance of an as-rolled Mg-3%Al-1%Zn alloy before and after a 3% compressive strain along the rolling direction was investigated. Results revealed that the corrosion behavior of differently oriented surfaces of the as-rolled samples with a strong basal texture was obviously different. Among them, the corrosion rate of sample surface with the orientation parallel to the normal direction (ND) of the plate was the fastest, the corrosion rate of sample surface with the orientation parallel to the rolling direction (RD) of the plate took the second place and the corrosion rate of sample surface with the orientation parallel to the transverse direction (TD) was the slowest. After being pre-strained, the activation of a high density of {10–12} twins could remarkably reduce the corrosion rate of surrounding α-Mg matrix and simultaneously weaken the corrosion anisotropy between differently oriented samples. The main reason was that similar to grain boundaries, twin boundaries acted as physical barriers to the corrosion attack. Moreover, the activated twins increased the protectiveness of surface films and then suppressed the micro corrosion couples occurred in twinned grains.

Phase transformation kinetics in rolled U-10 wt. % Mo foil: Effect of post-rolling heat treatment and prior γ-UMo grain size

The effect of sub-eutectoid heat treatment on the phase transformation behavior in rolled U-10 wt.% Mo (U10Mo) foils was systematically investigated. The as-cast 5 mm thick foils were initially homogenized at 900 °C for 48 h and were hot rolled to 2 mm and later cold rolled down to 0.2 mm. Three starting microstructures were evaluated: (i) hot + cold-rolled to 0.2 mm (as-rolled condition), (ii) hot + cold-rolled to 0.2 mm + annealed at 700 °C for 1 h, and (iii) hot + cold-rolled to 0.2 mm + annealed at 1000 °C for 60 h. Annealing of as-rolled materials at 700 °C resulted in small grain size (15 ± 9 μm average grain size), while annealing at 1000 °C led to very large grains (156 ± 118 μm average grain size) in rolled U10Mo foils. Later the samples were subjected to sub-eutectoid heat-treatment temperatures of 550 °C, 500 °C, and 400 °C for different durations of time starting from 1 h up to 100 h. U10Mo rolled foils went through various degrees of decomposition when subjected to the sub-eutectoid heat-treatment step and formed a lamellar microstructure through a cellular reaction mostly along the previous γ-UMo grain boundaries. The least amount of cellular reaction was observed in the large-grain microstructure at all temperatures. Conversely, a substantial amount of cellular reaction was observed in both the as-rolled and the small-grain microstructure. After 100 h of heat treatment at 500 °C, the volume fraction of the lamellar phase was found to be 4%, 22%, and 82% in large-grain, as-rolled, and small-grain samples, respectively.

Role of Severe Plastic Deformation in Suppressing Formation of R Phase and Ni4Ti3 Precipitate of NiTi Shape Memory Alloy

Microstructural evolution of NiTi shape memory alloy (SMA) with a nominal composition of Ni50.9Ti49.1 (at %) is investigated on the basis of heat treatment and severe plastic deformation (SPD). As for as-rolled NiTi SMA samples subjected to aging, plenty of R phases appear in the austenite matrix. In terms of as-rolled NiTi SMA samples undergoing solution treatment and aging, Ni4Ti3 precipitates arise in the austenite matrix. In the case of as-rolled NiTi SMA samples subjected to SPD and aging, martensitic twins are observed in the matrix of NiTi SMA. With respect to as-rolled NiTi SMA samples subjected to solution treatment, SPD, and aging, neither R phases nor Ni4Ti3 precipitates are observed in the matrix of NiTi SMA. The dislocation networks play an important role in the formation of the R phase. SPD leads to amorphization of NiTi SMA, and in the case of annealing, amorphous NiTi SMA samples are subjected to crystallization. This contributes to suppressing the occurrence of R phase and Ni4Ti3 precipitate in NiTi SMA.

Magnetic properties and structure of Fe50Pd50-xNix alloys (x = 4 and 8) in the as-deformed and annealed state

The structural and hysteresis properties of ternary Fe50Pd50-xNix (x = 4 and 8) alloys have been studied. In order to accelerate the formation of the hard magnetic L10 phase in these alloys, they were deformed by rolling with a reduction of 96% and by the method of high-pressure torsion (HPT). The annealing treatment for ordering for up to 100 h was performed at 400–500°С. It is shown that the structure transformation of the initial fcc phase into the ordered tetragonal phase at 400°С proceeds very slowly. After annealing for 100 h at this temperature, the Fe50Pd46Ni4 and Fe50Pd42Ni8 alloys are multiphase and contain residues of the cubic phase (Fm3¯m), cubic phase ordered by the L12 type (Pm3¯m), and tetragonal phase L10* appropriately described by the symmetry space group C4/mmm. The isothermal annealing at 400–500 °C for up to 100 h does not result in the maximum of Hc for the as-rolled Fe50Pd46Ni4 and Fe50Pd42Ni8 alloys. Implementation of the annealing routine with a temperature decreasing stepwise from 500 to 400 °C allowed us to increase Hc to 851 and 527 Oe for as-rolled samples and to 1192 and 980 Oe for the HPT samples of the Fe50Pd46Ni4 and Fe50Pd42Ni8 alloys, respectively.

X線ラインプロファイル解析と透過電子顕微鏡観察による強圧下冷間圧延された純鉄，Fe-0.3 mass%Si合金，Fe-0.3 mass%Al合金の再結晶に伴う転位組織変化の評価

The change in dislocation structure with recovery and recrystallization of 99.8% cold-rolled pure iron, Fe-0.3 mass%Al and Fe-0.3 mass%Si alloys was investigated by means of X-ray line profile analysis (XLPA) and TEM observation. In as-rolled samples of Fe-Al and Fe-Si alloys, the fraction of edge dislocation density increased in comparison with that in pure iron. In the early stage of recovery, dislocation densities with both edge and screw components remarkably decreased in pure iron, whereas in the Fe-Al and Fe-Si alloys, only the edge dislocation density distinctively decreased. This suggests that edge dislocations with relatively high density in as-rolled Fe-Si and Fe-Al alloys are easily annihilated by the climbing up motion of edge dislocations. In the late stage of recovery, the dislocation density of Fe-Si alloy did not decrease. No structural changes were observed by TEM which suggests that the recovery of Fe-Si alloy is strongly retarded, since Si hinders dislocation movement. In the early stage of recrystallization of pure iron, the formation of large subgrains was clearly confirmed in the lamellar structure. The subgrains show a similar orientation to the neighboring unrecrystallized grains, which represents similar behavior regarded as continuous recrystallization. Fe-Al alloy is similar to pure iron. Whereas, Fe-Si alloy exhibits discontinuous recrystallization in the sense that grains with low dislocation density were confirmed in the unrecovered lamellar structure with high driving force for recrystallization. This is because the Si strongly hinders dislocation movement. This effect agrees with the behavior of dislocation in Fe-Si alloy confirmed by XLPA.

Effects of particle distribution on microstructural evolution and mechanical properties of TiB2/AZ31 composite sheets

In-situ TiB2/AZ31 composites were prepared by self-propagating high-temperature synthesis reaction assisted with the coupled-field dispersion treatment. The samples of as-cast AZ31 alloy and in-situ TiB2/AZ31 composites with and without the coupled-field dispersion treatment were thermal deformed by cross-rolling. The influence of TiB2 particle distribution on the microstructures and mechanical properties of the composites was investigated. It was found that the as-cast microstructure of AZ31 matrix was refined by TiB2 particles. The uniform dispersion of the TiB2 particles is favor of further refinement. All as-rolled samples were composed of recrystallized small grain streams and relatively coarse grains. The improvement of reinforcement dispersion made the grain streams thinner and increased their amount, but had little influence on the texture evolution. The strength and elongation of TiB2/AZ31 composites increased simultaneously due to the promotion of particle distribution induced by coupled-field dispersion treatment.

Role of Cu on hydrogen embrittlement behavior in Fe–Mn–C–Cu TWIP steel

The effect of a Cu addition on a hydrogen embrittlement (HE) was studied in Fe–17Mn-0.8C TWIP steels with 0–2 mass% of Cu. As-rolled and hydrogen-charged samples were investigated by examining their microstructures, tensile properties, fracture behaviors, and hydrogen-related characteristics. Diffusible hydrogen was mainly trapped at the grain boundaries in the present steels, the amount of which was similar regardless of the Cu composition. However, the Cu addition clearly enhanced the HE resistance of the alloys. It was revealed that the Cu addition did not change the HE mechanism but affected the HE rates. The hydrogen-charged steels exhibited heterogeneous intergranular fractures due to the limited diffusion of hydrogen. The mechanism of the retarded HE in Fe–Mn–C–Cu TWIP steels was the mitigation of the applied stress on grain boundaries and the uniform distribution of hydrogen. These mechanisms were wholly different from those reported in Fe–Mn–C–Al TWIP steels in spite of the similar improvements in the HE resistance.

Microstructure and mechanical properties relation in cold rolled Al 2024 alloy determined by X-ray line profile analysis

Solution treated aluminum 2024 alloy sheets were subjected to rolling at room and cryogenic temperatures. Aging time and mechanical properties were evaluated by microhardness measurements and tensile test, respectively. Microstructural parameters were assessed by applying modified Williamson–Hall and modified Warren–Averbach methods to the X-ray diffraction patterns. Interestingly, the mechanical behavior of the different as-rolled and post-roll aged samples was in correlation with the sub-grain sizes and dislocation densities. The sub-grain sizes of the as-rolled samples were smaller than 40 nm, and the dislocation densities were larger than 7.7×1015 m−2, which is related to the high strength of the as-rolled samples. After aging treatment, the ductility of the rolled samples increased significantly, this was justified by the decline in the dislocation density.

Mechanical properties and deformation kinetics of bulk Cu–Al–Zn alloy subjected to rolling and annealing

Tensile and stress relaxation experiments were used to study the mechanical properties and deformation kinetics of Cu–12.1at%Al–4.1at%Zn alloy processed by cold rolling and followed annealing. Samples rolled at liquid nitrogen temperature exhibit higher tensile strength and better ductility compared to the ones rolled at room temperature, and the low temperature annealing resulted in an increase of the strength for all as-rolled samples. The analysis of strain rate sensitivity, activation volume and mobile dislocations indicates that the thermally activated deformation mechanism in the as-rolled and low temperature annealed samples is different from that of the coarse grains.

Tensile and Charpy impact properties of an ODS ferritic/martensitic steel 9Cr–1.8W–0.5Ti–0.35Y2O3

A 9Cr-ODS ferritic/martensitic steel with a composition of 9Cr–1.8W–0.5Ti–0.35Y2O3 was fabricated by mechanical alloying and hot isostatic pressing, followed by hot rolling. Tensile properties were measured at room temperature (23°C) and 700°C in the rolling direction (LT) and the transverse direction (TL). The ultimate tensile strength (UTS) of the as-rolled samples in both directions reached 990MPa at 23°C, and still maintained at 260MPa at 700°C. The tensile strength and elongation of the rolling direction was greater than that of the transverse direction. The Charpy impact was tested from −100 to 100°C in the LT direction. The lower shelf energy (LSE) was more than 65% of the upper shelf energy (USE). The total absorbed energy was separated into the energies for crack initiation and propagation. The propagation energy was always higher than the initiation energy in the range of temperatures tested. The ductile-to-brittle transition temperature (DBTT) of the rolled 9Cr ODS evaluated by an absorbed energy curve was about 0°C. However, the high LSE and the fracture surface that still contained dimples at lower shelf indicated good toughness of the as-rolled 9Cr ODS steels at temperature of −60°C.

Microstructural and magnetic properties study of Fe–P rolled sheet alloys

In the work presented here, the soft magnetic properties of Fe1−xPx (x=0.36, 0.7, 1.1at%) rolled sheet alloys were investigated. In this respect, the as-rolled sheets were subjected to a two steps annealing processes; the first one between 800 and 1000°C for 1h referred as first stage annealing and the second one at lower temperatures (500 and 600°C) for 30min, referred as second step annealing. BH tracer measurements at 50Hz showed that for all of the phosphorous containing alloys, in general, the magnitude of coercivity decreased by applying these two annealing steps compared to those of as-rolled samples. For all of the studied samples, the B50 values measured at 50Hz were in the range of 1.6–1.7 tesla (T). Samples having highest amount of phosphorous (1.1at%) exhibited lower eddy current loss compared to the rest of the specimens due to the increased electrical resistivity. Besides, microstructural studies revealed that the prepared samples were free from Fe3P phase precipitation and the average grain size increased (~three times) with increasing the phosphorous content giving rise to the decrease of hysteresis losses. Further, amongst the whole prepared samples, the alloy containing 1.1at% P showed the lowest hysteresis loss (6.99W/kg), eddy current loss (9.25W/kg) as well as the highest magnetic induction (1.7T) at 5000 A/M (B50).

Effect of ceramic rolling on the mechanical properties of Zr54Cu38Al8 bulk metallic glass

Plastic deformation of Zr54Cu38Al8 bulk metallic glass (BMG) was subjected to a novel ceramic rolling process. Mechanical properties, shear bands morphology and thermodynamic parameter of the as-cast and as-rolled samples were investigated by compression test, micro-hardness test, scanning electron microscopy (SEM) and differential scanning calorimeter (DSC), respectively. The results show that the metallic glass exhibits a large plastic deformation without fracture through ceramic rolling at room temperature and high strain rates. Especially, when the alloy is rolled to a diameter reduction of 10%, the ductility and strength of the alloy is significantly improved.

Microstructure and mechanical properties of the hot-rolled Mg–Y–Nd–Zr alloy

Abstract

High strength and ductile ultrafine-grained Cu–Ag alloy through bimodal grain size, dislocation density and solute distribution

Ultrafine-grained materials produced by different severe plastic deformation methods show very high strengths but their tensile ductility is often very low. In the present work, we demonstrate an approach for retaining high strength while recovering ductility in a Cu–3at.% Ag alloy through cold rolling and short-time annealing. X-ray line profile analysis of cold-rolled and annealed samples reveals the development of a heterogeneous solute atom distribution due to the dissolution of nanosized Ag particles in some regions of the matrix. In regions with higher solute (Ag) content, the high dislocation density present following rolling is stabilized, while in other volumes the dislocation density is decreased. High-resolution scanning electron microscopy confirms the presence of regions of varying Ag content in the matrix. Microstructure analysis of the rolled and annealed samples revealed bimodal grain size, dislocation density and solute Ag distributions as well as nanosized Ag precipitation. The as-rolled samples exhibit high tensile strengths of ∼600–700MPa with negligible uniform elongation (∼1%). After short-time annealing the strength decreases only slightly to ∼550–620MPa with significant improvement in uniform elongation (from 1 to 10%); this is mainly attributed to the bimodal microstructure.

The pitting corrosion behavior of shear bands in a Zr-based bulk metallic glass

Multiple nearly parallel shear bands were induced by cold-rolling Zr64.13Cu15.75Ni10.12Al10 bulk metallic glass. Immersion measurements, chronopotentiometry and anodic polarization tests for as-rolled samples before and after annealing or electropolishing are conducted to analyze the pitting behavior on shear bands. It is demonstrated that the shear bands indeed act as preferential sites for pitting initiation under certain conditions, a finding attributed mainly to the structural changes in shear bands rather than surface shear offset or residual stress.