Showing papers on "Annealing (metallurgy) published in 2015"
TL;DR: In this article, an equiatomic CoCrFeMnNi high-entropy alloy (HEA), produced by arc melting and drop casting, was subjected to severe plastic deformation (SPD) using high pressure torsion.
887 citations
TL;DR: An easy and flexible two-step method consisting of hydrothermal and subsequent annealing process have been developed to synthesize the porous 3-D flower-like Co/CoO and it is found that the suitable heat treatment temperature played a vital role on the flower- like structure, composition, and electromagnetic absorption properties.
Abstract: The porous three-dimensional (3-D) flower structures assembled by numerous ultrathin flakes were favor for strengthen electromagnetic absorption capability. However, it still remains a big challenge to fabricate such kind of materials. In this study, an easy and flexible two-step method consisting of hydrothermal and subsequent annealing process have been developed to synthesize the porous 3-D flower-like Co/CoO. Interestingly, we found that the suitable heat treatment temperature played a vital role on the flower-like structure, composition, and electromagnetic absorption properties. In detail, only in the composite treated with 400 °C can we gain the porous 3-D flower structure. If the annealing temperature were heated to 300 °C, the Co element was unable to generate. Moreover, when the annealing temperature increased from 400 to 500 °C, these flower-like structures were unable to be kept because the enlarged porous diameter would wreck the flower frame. Moreover, these 3-D porous flower-like structures...
489 citations
TL;DR: In this article, the in-plane and cross-plane thermal conductivity of reduced graphene oxide films subjected to a high-temperature treatment of up to 1000 °C was investigated.
Abstract: Thermal conductivity of free-standing reduced graphene oxide films subjected to a high-temperature treatment of up to 1000 °C is investigated. It is found that the high-temperature annealing dramatically increases the in-plane thermal conductivity, K, of the films from ≈3 to ≈61 W m−1 K−1 at room temperature. The cross-plane thermal conductivity, K⊥, reveals an interesting opposite trend of decreasing to a very small value of ≈0.09 W m−1 K−1 in the reduced graphene oxide films annealed at 1000 °C. The obtained films demonstrate an exceptionally strong anisotropy of the thermal conductivity, K/K⊥ ≈ 675, which is substantially larger even than in the high-quality graphite. The electrical resistivity of the annealed films reduces to 1–19 Ω □−1. The observed modifications of the in-plane and cross-plane thermal conductivity components resulting in an unusual K/K⊥ anisotropy are explained theoretically. The theoretical analysis suggests that K can reach as high as ≈500 W m−1 K−1 with the increase in the sp2 domain size and further reduction of the oxygen content. The strongly anisotropic heat conduction properties of these films can be useful for applications in thermal management.
457 citations
TL;DR: A low-density, nanocrystalline high-entropy alloy, Al20Li20Mg10Sc20Ti30 was produced by mechanical alloying as discussed by the authors, which formed a single phase fcc structure during ball milling and transformed to single phase hcp upon annealing.
Abstract: A low-density, nanocrystalline high-entropy alloy, Al20Li20Mg10Sc20Ti30 was produced by mechanical alloying. It formed a single-phase fcc structure during ball milling and transformed to single-phase hcp upon annealing. The alloy has an estimated strength-to-weight ratio that is significantly higher than other nanocrystalline alloys and is comparable to ceramics. High hardness is retained after annealing.
448 citations
TL;DR: The ferroelectric properties and crystal structure of doped HfO2 thin films were investigated for different thicknesses, electrode materials, and annealing conditions in this paper.
Abstract: The ferroelectric properties and crystal structure of doped HfO2 thin films were investigated for different thicknesses, electrode materials, and annealing conditions Metal-ferroelectric-metal capacitors containing Gd:HfO2 showed no reduction of the polarization within the studied thickness range, in contrast to hafnia films with other dopants A qualitative model describing the influence of basic process parameters on the crystal structure of HfO2 was proposed The influence of different structural parameters on the field cycling behavior was examined This revealed the wake-up effect in doped HfO2 to be dominated by interface induced effects, rather than a field induced phase transition TaN electrodes were shown to considerably enhance the stabilization of the ferroelectric phase in HfO2 compared to TiN electrodes, yielding a Pr of up to 35 μC/cm2 This effect was attributed to the interface oxidation of the electrodes during annealing, resulting in a different density of oxygen vacancies in the Gd:Hf
404 citations
TL;DR: In this paper, the electrical response to NO 2 and other gases of resistive type gas sensors based on liquid chemically exfoliated (in N-methyl pyrrolidone, NMP) MoS 2 flakes annealed in air either at 150°C or at 250°C.
Abstract: We report on the fabrication, the morphological, structural, and chemical characterization, and the study of the electrical response to NO 2 and other gases of resistive type gas sensors based on liquid chemically exfoliated (in N-methyl pyrrolidone, NMP) MoS 2 flakes annealed in air either at 150 °C or at 250 °C. The active material has been analyzed by scanning electron microscopy (SEM), and micro Raman and X-ray core level photoemission spectroscopies. SEM shows that MoS 2 exfoliated flakes are interconnected between electrodes of the sensing device to form percolation paths. Raman spectroscopy of the flakes before annealing demonstrates that the flakes are constituted by crystalline MoS 2 , while, annealing at 250 °C, does not introduce a detectable bulk contamination in the expected form of MoO 3 . The sensor obtained by thermal annealing in air at 150 °C exhibits a peculiar p -type response under exposure to NO 2 . In line with core level spectroscopy evidences, this behavior is potentially ascribed to nitrogen substitutional doping of S vacancies in the MoS 2 surface (nitrogen atoms being likely provided by the intercalated NMP). Thermal annealing the MoS 2 flakes in air at 250 °C irreversibly sets an n -type behavior of the gas sensing device, with a NO 2 detection limit of 20 ppb. This behavior is assigned, in line with core level spectroscopy data, to a significant presence of S vacancies in the MoS 2 annealed flakes and to the surface co-existence of MoO 3 arising from the partial oxidation of the flakes surface. Both p- and n -type sensors have been demonstrated to be sensitive also to relative humidity. The n -type sensor shows good electrical response under H 2 exposure.
326 citations
TL;DR: In this paper, a review summarises the important results of previous studies about the effects of both intercritical annealing conditions and alloying elements on the microstructure and tensile properties of medium Mn steels.
Abstract: Medium Mn steels have been actively investigated due to their excellent balance between material cost and mechanical properties. The steels possess a single α′ martensite phase in hot and cold rolled states and multiphases after intercritical annealing. Many studies have focused on investigating the influences of chemical composition and annealing conditions on the microstructure, particularly the grain size and retained γ (γR), and on the tensile properties. The steels exhibit high strength and good ductility due to transformation induced plasticity occurring in γR, whose volume fraction is approximately 0·2–0·4. The present review summarises the important results of previous studies about the effects of both intercritical annealing conditions and alloying elements on the microstructure and tensile properties of medium Mn steels.
300 citations
TL;DR: In this paper, a refractory high-entropy alloy HfNbTaTiZr was successfully rolled at room temperature up to 86.4% reduction in thickness (true thickness strain is −2.3).
291 citations
TL;DR: It was found that both the molecular ratio of Ni to Co and the annealing temperature had significant effects on their porous structure and electrochemical properties, and the effect of the Ni/Co ratio on the pseudocapacitive properties of the binary oxide was investigated.
Abstract: Nickel–cobalt oxides were prepared by coprecipitation of their hydroxides precursors and a following thermal treatment under a moderate temperature. The preformed nickel-cobalt bimetallic hydroxide exhibited a flower-like morphology with single crystalline nature and composed of many interconnected nanosheets. The ratio of Ni to Co in the oxides could easily be controlled by adjusting the composition of the original reactants for the preparation of hydroxide precursors. It was found that both the molecular ratio of Ni to Co and the annealing temperature had significant effects on their porous structure and electrochemical properties. The effect of the Ni/Co ratio on the pseudocapacitive properties of the binary oxide was investigated in this work. The binary metal oxide with the exact molar ratio of Ni:Co = 0.8:1 annealed at 300 °C, showing an optimum specific capacitance of 750 F/g. However, too high an annealing temperature would lead to a large crystal size, a low specific surface area, as well as a mu...
231 citations
TL;DR: The synthesis of centimeter-scale, uniform 1T'- and 2H-MoTe2 thin films via the tellurization of Mo thin films is reported.
Abstract: We report the synthesis of centimeter-scale, uniform 1T′- and 2H-MoTe2 thin films via the tellurization of Mo thin films. 1T′-MoTe2 was initially grown and converted gradually to 2H-MoTe2 over a prolonged growth time under a Te atmosphere. Maintaining excessive Te was essential for obtaining the stable stoichiometric 2H-MoTe2 phase. Further annealing under a lower partial pressure of Te at the same temperature, followed by a rapid quenching, led to the reverse phase transition from 2H-MoTe2 to 1T′-MoTe2. The orientation of the 2H-MoTe2 film was determined by the tellurization rate. Slow tellurization was the key for obtaining a highly oriented 2H-MoTe2 film over the entire area, while fast tellurization led to a 2H-MoTe2 film with a randomly oriented c-axis.
211 citations
TL;DR: Annealing of these nanocomposite foils at 300°C, neither causes grain growth of the Cu matrix nor deteriorates the mechanical properties, indicating the role of graphene as an excellent reinforcement material as well as a grain growth inhibitor.
Abstract: Graphene has proved its significant role as a reinforcement material in improving the strength of polymers as well as metal matrix composites due to its excellent mechanical properties. In addition, graphene is also shown to block dislocation motion in a nanolayered metal-graphene composites resulting in ultra high strength. In the present paper, we demonstrate the synthesis of very hard Cu-Graphene composite foils by a simple, scalable and economical pulse reverse electrodeposition method with a well designed pulse profile. Optimization of pulse parameters and current density resulted in composite foils with well dispersed graphene, exhibiting a high hardness of ~2.5 GPa and an increased elastic modulus of ~137 GPa while exhibiting an electrical conductivity comparable to that of pure Cu. The pulse parameters are designed in such a way to have finer grain size of Cu matrix as well as uniform dispersion of graphene throughout the matrix, contributing to high hardness and modulus. Annealing of these nanocomposite foils at 300°C, neither causes grain growth of the Cu matrix nor deteriorates the mechanical properties, indicating the role of graphene as an excellent reinforcement material as well as a grain growth inhibitor.
TL;DR: In this article, the phase changes in heat treated samples were characterized using X-ray diffraction (XRD) and electron back scattering diffraction(EBSD) using a focused Nd:YAG laser beam.
11 Jun 2015-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, an equiatomic NiFeCrCoMn alloy, two non-equiatomic NIFeCrCMn alloys optimized for low stacking fault energy were produced by arc melting and tested at a strain rate of 7.3×10−4−s−1.
Abstract: An equiatomic NiFeCrCoMn alloy, two non-equiatomic NiFeCrCoMn alloys optimized for low stacking fault energy, and an equiatomic NiFeCrCo alloy were produced by arc melting. Samples were homogenized, cold rolled, and annealed at temperatures between 575 and 1100 °C. Samples annealed at a moderate temperature near their recrystallization temperature (625–675 °C) and 1100 °C were cut into flat tensile samples and tested at a strain rate of 7.3×10−4 s−1. Equiatomic NiFeCrCo had the highest ductility and toughness after annealing at both temperatures, followed by Ni18.5Fe18.5Cr18.5Co26Mn18.5. Ni14Fe20Cr26Co20Mn20 exhibited poor thermal stability, forming σ-phase intermetallics at temperatures below 1100 °C. Observation of the fracture surfaces suggested that the high performance of NiFeCrCo might be due to the absence of oxide particles that form in the Mn-containing alloys. The strain-hardening rate and exponent were calculated from the results, showing a large deviation from typical behavior and significant grain size dependence.
TL;DR: In this article, a laminate structure with a nanostructured Cu-10Zn layer sandwiched between two coarse-grained Cu layers was produced by high-pressure torsion, rolling and annealing.
TL;DR: It is found that the crystal formation is kinetically driven by the annealing atmosphere, time and temperature, which indicates a critical impact of the atmosphere upon crystallization and the ultimate device performance.
Abstract: Recently, solution-processable organic–inorganic metal halide perovskites have come to the fore as a result of their high power-conversion efficiencies (PCE) in photovoltaics, exceeding 17%. To attain reproducibility in the performance, one of the critical factors is the processing conditions of the perovskite film, which directly influences the photophysical properties and hence the device performance. Here we study the effect of annealing parameters on the crystal structure of the perovskite films and correlate these changes with its photophysical properties. We find that the crystal formation is kinetically driven by the annealing atmosphere, time and temperature. Annealing in air produces an improved crystallinity and large grain domains as compared to nitrogen. Lower photoluminescence quantum efficiency (PLQE) and shorter photoluminescence (PL) lifetimes are observed for nitrogen annealed perovskite films as compared to the air-annealed counterparts. We note that the limiting nonradiative pathways (i...
TL;DR: It is demonstrated that good devices can only be achieved in low temperature, solution-processed oxides if a significant concentration of acceptor states below the conduction band minimum is compensated or passivated by shallow hydrogen and oxygen vacancy-induced donor levels.
Abstract: The electronic structure of low temperature, solution-processed indium–zinc oxide thin-film transistors is complex and remains insufficiently understood. As commonly observed, high device performance with mobility >1 cm2 V−1 s−1 is achievable after annealing in air above typically 250 °C but performance decreases rapidly when annealing temperatures ≤200 °C are used. Here, the electronic structure of low temperature, solution-processed oxide thin films as a function of annealing temperature and environment using a combination of X-ray photoelectron spectroscopy, ultraviolet photoelectron spectroscopy, and photothermal deflection spectroscopy is investigated. The drop-off in performance at temperatures ≤200 °C to incomplete conversion of metal hydroxide species into the fully coordinated oxide is attributed. The effect of an additional vacuum annealing step, which is beneficial if performed for short times at low temperatures, but leads to catastrophic device failure if performed at too high temperatures or for too long is also investigated. Evidence is found that during vacuum annealing, the workfunction increases and a large concentration of sub-bandgap defect states (re)appears. These results demonstrate that good devices can only be achieved in low temperature, solution-processed oxides if a significant concentration of acceptor states below the conduction band minimum is compensated or passivated by shallow hydrogen and oxygen vacancy-induced donor levels.
TL;DR: In this paper, hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5×10−6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K).
Abstract: Hole conducting, optically transparent Cu2O thin films on glass substrates have been synthesized by vacuum annealing (5×10−6 mbar at 700 K for 1 hour) of magnetron sputtered (at 300 K) CuO thin films. The Cu2O thin films are p-type and show enhanced properties: grain size (54.7 nm), optical transmission 72% (at 600 nm) and Hall mobility 51 cm2/Vs. The bulk and surface Valence band spectra of Cu2O and CuO thin films are studied by temperature dependent Hall effect and Ultra violet photo electron Spectroscopy (UPS). CuO thin films show a significant band bending downwards (due to higher hole concentration) than Cu2O thin films.
11 Mar 2015-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, two different morphologies of martensite in dual phase (DP) steel were obtained using two different processing routes: intermediate quenching and inter-critical annealing.
Abstract: Two different morphologies of martensite in dual phase (DP) steel were obtained using two different processing routes. In one case, intermediate quenching (IQ) was adapted, where DP steel was water-quenched to obtain martensite phase, followed by inter-critical annealing. In the second case, the steel was cold rolled, followed by inter-critical annealing (CR-IA). For IQ and CR-IA steels, the inter-critical temperatures varied from 750 °C to 850 °C to obtain different volume fractions of martensite. An understanding of structure–property was obtained using a combination of scanning electron microscope (SEM), transmission electron microscope (TEM), and tensile tests. It was observed that fibrous martensite presented in IQ samples, gradually transformed to blocky martensite with increase in inter-critical temperature, resembling the CR-IA steels. The fibrous martensite encouraged martensite cracking, however, the martensite cracking was dramatically decreased in the IQ samples with increase in martensite fraction. The strain hardening behavior studied using the differential C – J model indicated multistage depending on the fraction of martensite. The low volume fraction of martensite in the DP steel provided high ductility–toughness combination and improved strain hardening ability due to the presence of soft ferrite phase in DP steel. Fibrous martensite in DP steel resulted in less strain hardening than blocky martensite, prior to exceeding a threshold volume fraction. The threshold value was significantly smaller for DP steel with blocky martensite.
TL;DR: In this article, high temperature annealing of pure tungsten irradiated by self-ions was conducted to elucidate microstructural and defect evolution in temperature ranges relevant to fusion reactor applications.
TL;DR: In this article, a simple magnetron sputtering process was used to fabricate β tungsten thin films, which are capable of generating giant spin Hall effect, and analyzed the structure and grain size of both β- and α-W thin films.
Abstract: We use a simple magnetron sputtering process to fabricate beta (β) tungsten thin films, which are capable of generating giant spin Hall effect. As-deposited thin films are always in the metastable β-W phase from 3.0 to 26.7 nm. The β-W phase remains intact below a critical thickness of 22.1 nm even after magnetic thermal annealing at 280 °C, which is required to induce perpendicular magnetic anisotropy (PMA) in a layered structure of β-W/Co40Fe40B20/MgO. Intensive annealing transforms the thicker films (>22.1 nm) into the stable α-W phase. We analyze the structure and grain size of both β- and α-W thin films. Electron transport in terms of resistivity and normal Hall effect is studied over a broad temperature range of 10 K to at least 300 K on all samples. Very low switching current densities are achieved in β-W/Co40Fe40B20/MgO with PMA. These basic properties reveal useful behaviors in β-W thin films, making them technologically promising for spintronic magnetic random access memories and spin-logic devices.
TL;DR: In this paper, the processing parameters which govern the evolution of microstructure and texture during rotary swaging and subsequent heat treatments were studied in an equiatomic single-phase CoCrFeMnNi high-entropy alloy.
TL;DR: In this paper, the authors investigated the variation of the work function properties of MoS2 films prepared with chemical vapor deposition (CVD) on SiO2 substrates with the number of film layers.
Abstract: The electrical properties of two-dimensional atomic sheets exhibit remarkable dependences on layer thickness and surface chemistry. Here, we investigated the variation of the work function properties of MoS2 films prepared with chemical vapor deposition (CVD) on SiO2 substrates with the number of film layers. Wafer-scale CVD MoS2 films with 2, 4, and 12 layers were fabricated on SiO2, and their properties were evaluated by using Raman and photoluminescence spectroscopies. In accordance with our X-ray photoelectron spectroscopy results, our Kelvin probe force microscopy investigation found that the surface potential of the MoS2 films increases by ∼0.15 eV when the number of layers is increased from 2 to 12. Photoemission spectroscopy (PES) with in-situ annealing under ultra high vacuum conditions was used to directly demonstrate that this work function shift is associated with the screening effects of oxygen or water molecules adsorbed on the film surface. After annealing, it was found with PES that the su...
TL;DR: In this article, a water-inducement technique for the fabrication of oxide thin-fi lm transistors at low annealing temperatures is reported, where the solvent is composed of water without additional organic additives and catalysts.
Abstract: Here, a simple, nontoxic, and inexpensive “water-inducement” technique for the fabrication of oxide thin fi lms at low annealing temperatures is reported. For water-induced (WI) precursor solution, the solvent is composed of water without additional organic additives and catalysts. The thermogravimetric analysis indicates that the annealing temperature can be lowered by prolonging the annealing time. A systematic study is carried out to reveal the annealing condition dependence on the performance of the thin-fi lm transistors (TFTs). The WI indium-zinc oxide (IZO) TFT integrated on SiO 2 dielectric, annealed at 300 °C for 2 h, exhibits a saturation mobility of 3.35 cm 2 V −1 s −1 and an on-to-off current ratio of ≈10 8 . Interestingly, through prolonging the annealing time to 4 h, the electrical parameters of IZO TFTs annealed at 230 °C are comparable with the TFTs annealed at 300 °C. Finally, fully WI IZO TFT based on YO x dielectric is integrated and investigated. This TFT device can be regarded as “green electronics” in a true sense, because no organicrelated additives are used during the whole device fabrication process. The as-fabricated IZO/YO x TFT exhibits excellent electron transport characteristics with low operating voltage (≈1.5 V), small subthreshold swing voltage of 65 mV dec −1 and the mobility in excess of 25 cm 2 V −1 s −1 .
TL;DR: In this article, the effect of nitrogen flow rate on film resistivity was investigated and it was found that film orientation can influence the resistivity with (111) oriented film more resistive than (200) oriented films.
TL;DR: In this article, the dependence of grain size on deformation mechanisms and deformation-induced microstructural changes was investigated in nanograined (NG) and coarse-grained (CG) stainless steel.
TL;DR: In this paper, the structural changes along the thermal annealing pathway of a poly(furfuryl alcohol) (PFA) derived nanoporous carbon (NPC) were investigated using multi-wavelength Raman spectroscopy.
TL;DR: In this paper, a new ultra-high-strength (ferrite+austenite) duplex lightweight steels containing a low-density element of Al, which exhibit strength above 1 GPa and tensile elongation of 46%, have been developed.
TL;DR: In this article, the impact of the temperature-dependent Dy diffusion processes on both the magnetic properties and the microstructure of permanent magnets has been studied, and it was found that the Dy-shell formation is attributed to the melting/solidification of a heavy-rare-earth-rich intermediate phase during high-temperature annealing.
TL;DR: In this article, the anisotropy of laser melting deposition additive manufacturing Ti−6.5Al−3.5Mo−1.5Zr−0.3Si was studied by microstructure observation and room tensile properties testing.
TL;DR: In this paper, the effect of annealing on the evolution of interface microstructure and mechanical properties of composite plates was investigated, and the results demonstrated that the AZ31B/AA6061 composite plates were bonding well.