Intermediate Annealing Temperature Research Articles

Thermal Stability and Mechanical Behaviour of Equal Channel Angular Pressed Structural Steel IS2062

The annealing behaviours of the equal channel angular pressed (ECAP) structural steel (hypoeutectoid) were investigated. The sample was processed up to four pass-through routes Bc in 120° angle die at ambient condition. Due to the effect of ECAP process, mechanical properties significantly improved, whereas the ductility drastically decreased in the material. The microstructural and mechanical characterization illustrates that the recovery process occurred at an annealed temperature of 500–525 °C and the recrystallization process occurred when the sample was annealed at 550 °C. When the annealing temperature was 600 °C, the grain growth process occured in the ECAPed sample and the strength, hardness and ductility were almost equivalent to the as-received material. The microstructural analysis was revealed in the TEM micrography. According to the microstructural and mechanical property analysis, the intermediate annealing temperature of 525 °C to 550 °C was suitable for this material to optimize the strength and ductility.

Structure-specific photoluminescence of ZnGa2O4:Eu3+ thin films deposited on sapphire C-plane substrates

1 at. % Eu3+-doped ZnGa2O4 (ZnGa2O4:Eu) thin films were deposited on sapphire C-plane substrates by dual-target sputtering, and the correlation between their crystal structures and luminescent properties was investigated. When deposition was carried out with H2O vapor as the oxygen source gas and subsequently postannealing was done in vacuum, the ZnGa2O4:Eu films consisted of randomly oriented polycrystals. In contrast, ZnGa2O4:Eu films deposited with O2 consisted of (111)-oriented crystallites. The crystallites were epitaxial after postannealing at above 400 °C. At intermediate annealing temperatures between 250 and 400 °C, Ga2O3 and GaO(OH) precipitated as impurity phases with (111)-oriented ZnGa2O4. Upon excitation at 325 nm, the Eu3+ emission intensities from the randomly oriented ZnGa2O4:Eu films were comparable to those of the epitaxial films. The epitaxial films exhibited only the 5D0 → 7F2 transition signal, whereas the randomly oriented polycrystalline films showed considerable emissions from the 5D0 → 7F4 transition as well as 5D0 → 7F2. Furthermore, the emission signal width of the 5D0 → 7F2 transition was narrower for the epitaxial films compared with the polycrystalline films. Such different emission characteristics can be explained from the viewpoint that the single crystal structure allows Eu3+ ions to occupy only a limited number of sites, whereas randomly oriented polycrystalline crystallites formed by incorporating H+ and OH− species have abundant grain boundaries, and defect sites enable larger numbers of structurally and chemically different emission-active sites to hold Eu3+ ions.1 at. % Eu3+-doped ZnGa2O4 (ZnGa2O4:Eu) thin films were deposited on sapphire C-plane substrates by dual-target sputtering, and the correlation between their crystal structures and luminescent properties was investigated. When deposition was carried out with H2O vapor as the oxygen source gas and subsequently postannealing was done in vacuum, the ZnGa2O4:Eu films consisted of randomly oriented polycrystals. In contrast, ZnGa2O4:Eu films deposited with O2 consisted of (111)-oriented crystallites. The crystallites were epitaxial after postannealing at above 400 °C. At intermediate annealing temperatures between 250 and 400 °C, Ga2O3 and GaO(OH) precipitated as impurity phases with (111)-oriented ZnGa2O4. Upon excitation at 325 nm, the Eu3+ emission intensities from the randomly oriented ZnGa2O4:Eu films were comparable to those of the epitaxial films. The epitaxial films exhibited only the 5D0 → 7F2 transition signal, whereas the randomly oriented polycrystalline films showed considerable emissions from the...

High-Quality-Factor AlGaAs-on-Sapphire Microring Resonators

We realize an AlGaAs-on-sapphire platform through Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -assisted direct wafer bonding and substrate removal processes. The direct wafer bonding process is optimized concerning the intermediate layer deposition and annealing temperature to obtain a high bonding strength between the AlGaAs and sapphire wafers. High quality-factor (Q) microring resonators are fabricated using electron-beam lithography in which the charging effect is mitigated by applying a thin aluminum layer, and a smooth pattern sidewall definition is obtained using a multi-pass (exposure) process. We achieve an intrinsic Q of up to ~460,000 which is the highest Q for AlGaAs microring resonators. Taking advantage of such high Q resonators, we demonstrate an ultra-efficient nonlinear four-wave mixing process in this platform and obtain a conversion efficiency of -19.8 dB with continuous-wave pumping at a power level of 380 μW. We also investigate the thermal resonance shift of microring resonators with different substrate layouts and observe superior temperature stability for devices in the AlGaAs-on-sapphire platform. The realization of the AlGaAson-sapphire platform also opens new prospects for AlGaAs devices in nonlinear applications in the mid-infrared wavelength range.

Microstructure and Texture of Ni7W/Ni12W/Ni7W Composite Substrates at Different Intermediate Annealing Temperatures

Ni7W/Ni12W/Ni7W composite substrates for YBa2Cu3O7-δ coated conductors were prepared by rolling assisted biaxially textured substrates route. A threefold intermediate annealing at different temperatures was introduced in the rolling process of Ni7W/Ni12W/Ni7W composite substrates to optimize the deformation texture. The recovery microstructure and the deformation texture of latitude and longitude section were studied with X-ray diffraction and electron backscattered diffraction to reveal the possible mechanism of temperature effects on rolling and strong cube texture formation processes. The results show that the highest cube area fraction is found in sample intermediately annealed at 600 °C/60 min; in this way Ni7W/Ni12W/Ni7W composite substrates with high cube texture content of 95% (<10°) are obtained at a low recrystallization annealing temperature. Crystal orientation maps reveal that a higher amount of cube orientation exists in its recovery and initial recrystallization samples. Point to point misorientation files confirm the high grain boundary angle of these cube grains, which strongly boost the cube texture formation during subsequent recrystallization.

Effect of Cold Rolling Process on Microstructure, Texture and Properties of Strip Cast Fe-2.6%Si Steel.

The use of twin-roll strip casting for the preparation of non-oriented silicon steel has attracted widespread attention in recent years, but related reports are limited. In this study, both one- and two-stage cold rolling with three intermediate annealing temperatures were employed to produce strip cast non-oriented silicon steel. The evolution of the microstructure and texture through the processing routes and its effect on magnetic properties were studied. Compared with one-stage rolling, two-stage rolling increased the in-grain shear bands and the retention of Cube texture in the cold rolled sheets, thereby promoting the nucleation of favorable Goss and Cube grains and restraining the nucleation of harmful {111}<112> grains. With the increase in intermediate annealing temperature, the η-fiber texture in annealed sheets was gradually enhanced, and the average grain size was increased, leading to significant improvement of magnetic properties.

Factors determining room temperature mechanical properties of bimodal microstructures in Ti-6Al-4V alloy

The bimodal microstructure in Ti-6Al-4V alloy comprised of equiaxed primary α grains and transformed β areas can be regarded as a kind of “dual-phase” structure. In this study, the volume fraction of primary α grains was systematically modified by changing the intercritical annealing temperature in the α + β two phase region and the tensile properties were evaluated at room temperature. It was found for the first time that the relative nano-hardness of the two components changed depending on their volume fractions which were determined by the intercritical annealing temperature. The change in the relative hardness was explained from a viewpoint of solid solution strengthening of α phase by aluminum. Moreover, the change in the relative nano-hardness was found to have a significant influence on mechanical properties of the bimodal microstructures through affecting the strain distribution behavior. A peak uniform elongation (~ 12%) was obtained at an intermediate annealing temperature (910 °C) where the volume fractions of two components were nearly equal and thereby the length density of the interface between them reached a maximum.

Relative strength of perpendicular magnetic anisotropy at bottom and top interfaces in Pt/Co/MgO trilayers

In Pt/Co/MgO trilayers, the contribution to the total perpendicular magnetic anisotropy from the bottom Pt/Co interface is significantly greater than that from the top Co/MgO interface at intermediate annealing temperatures. However, the relative contribution is reversed at the highest annealing temperature examined in this study, 400 °C. These results indicate that as the annealing temperature increases, the quality of the Pt/Co interface deteriorates owing to the intermixing of Pt and Co, whereas the quality of the Co/MgO interface improves as oxygen atoms, which are interpenetrated into the Co layer during the deposition of MgO, are diffused toward the Co/MgO interface.

Ensuring combination of strength, ductility and toughness in medium-manganese steel through optimization of nano-scale metastable austenite

Medium-Mn steel was innovatively designed in terms of alloying elements for medium to heavy steel plates to obtain combination of high strength, good ductility, and excellent low temperature toughness. Martensite was the dominant microstructure in the directly quenched steel plate because of high hardenability obtained by the addition of 5.6wt% Mn. Three intercritical annealing processes were adopted to ensure transformation-induced-plasticity (TRIP) effect through optimization of the volume fraction, morphology, and C and Mn-enriched reversed austenite. On annealing, the dislocation density of martensite plate was decreased because of recovery and recrystallization, and metastable austenite film nucleated at the interface. Both thermal and mechanical stability of austenite decreased with increase in annealing temperature. The high yield strength of 840MPa, good elongation after fracture of 24.3%, and excellent toughness at −60°C of 130.3J was obtained at intermediate annealing temperature of 650°C, and the volume fraction of reversed austenite at room temperature and −80°C was 22% and 17%, respectively. The reversed austenite exhibited different stability with increased tensile strain, leading to improved ductility and delayed necking. Moreover, the crack initiation energy and crack propagation energy were increased via dynamic stress partitioning and relaxation together with the transformation of metastable austenite. Thus, significant degree of TRIP effect induced by moderate stability of austenite played an important role in governing mechanical properties.

Doping β-Ga2O3 with europium: influence of the implantation and annealing temperature

β-Ga2O3 bulk single crystals were doped by ion implantation at temperatures from room temperature to 1000 °C, using a 300 keV Europium beam with a fluence of 1 × 1015 at cm−2. Rising the implantation temperature from room temperature to 400–600 °C resulted in a significant increase of the substitutional Eu fraction and of the number of Eu ions in the 3+ charge state as well as in a considerable decrease of implantation damage. Eu is found in both charge states 2+ and 3+ and their relative fractions are critically dependent on the implantation and annealing temperature, suggesting that defects play an important role in stabilizing one of the charge states. The damage recovery during post-implant annealing is a complex process and typically defect levels first increase for intermediate annealing temperatures and a significant recovery of the crystal only starts around 1000 °C. Cathodoluminescence spectra are dominated by the sharp Eu3+ related intra-ionic 4f transition lines in the red spectral region. They show a strong increase of the emission intensity with increasing annealing temperature, in particular for samples implanted at elevated temperature, indicating the optical activation of Eu3+ ions. However, no direct correlation of emission intensity and Eu3+ fraction was found, again pointing to the important role of defects on the physical properties of these luminescent materials.

Solar‐Water‐Splitting BiVO4 Thin‐Film Photoanodes Prepared By Using a Sol–Gel Dip‐Coating Technique

AbstractA facile and low cost method to construct a bismuth vanadate thin film photoanode was implemented with the aim of integrating it in a tandem dual water splitting photoelectrochemical cell. Multilayer semi‐transparent thin films of BiVO4 were fabricated by a sol–gel process and deposited by dip‐coating onto transparent conducting oxide substrates with intermediate annealing treatment between layers and final calcination at a low temperature of 450 °C in air. The effect of the intermediate annealing temperature has a great impact on the porosity, and therefore density, of thin layers of BiVO4 when fabricated by sol–gel dip‐coating methods; thus, for optimal activity, the annealing temperature should be kept at 400 °C for thinner layers and 450 °C for thicker layers. The annealing temperature has a direct effect on the size of the crystallites which determines the microstructural density and porosity. In contrast, the final calcination temperature must be 450 °C in order to achieve good electrochemical performances. Optimized BiVO4 photoanodes exhibit a photocurrent of up to 2.1 mA cm−2 with an average Faradic efficiency of 85 % for oxygen evolution in neutral pH potassium phosphate buffer at 1.23 V vs. RHE under 350 mW cm−2 light irradiation.

Strengthening effect of reduced graphene oxide in steel clad copper rod

Reduced graphene oxide has been extensively used as reinforcing agent owing to their high mechanical properties. In this work, an attempt is made to synthesize steel clad copper rod reinforced with reduced graphene oxide (RGO) by the combination of powder-in-tube and intermediate annealing (IA). Experiments show that the Fe/RGO/Cu composites manifest better mechanical properties than Fe/Cu composites. In the process of groove rolling, RGO acts as effective binder, which can greatly improve the adhesive strength of copper scrap and two metals. Moreover, the strengthening effect of RGO is tightly related to its dispersion state. The RGO diffuses much more uniformly on the metallic substrate under the IA temperature of 1100 °C than 800 °C, which can be characterized by less deformation twins appearing at the interface of core copper and the formation of Fe–RGO–Cu transition belt at the bonding interface. In this case, the peak hardness, tensile strength and shear strength of Fe/RGO/Cu composites are 52 HV, 125 and 41 MPa higher than those of the Fe/Cu composites, respectively. The difference of strengthening effect and mechanisms of RGO under 800 and 1100 °C of IA are systematically discussed by referring to experimental results.

Effect of Processing Techniques on Precipitation Behavior of Secondary Phase Particles in Zr-1Nb-0.01Cu Alloy

The precipitation behavior of secondary phase particles (SPPs) was investigated in Zr-1Nb-0.01Cu alloy prepared by various processing techniques. The results show that with the decrease of cold rolling and annealing steps, intermediate annealing temperatures, final annealing temperatures and time, the average sizes of SPPs decrease accordingly. The β -Zr phase formed at the intermediate annealing temperature (higher than 640 °C) is hard to dissolve in the matrix after final annealing treatment. During the long-time final annealing process, the SPPs with smaller size coalesce into larger particles by diffusion through the matrix gradually because of Ostwald ripening mechanism. It shows that the decrease of intermediate annealing temperature is more effective than other processing techniques for minimizing the size of SPPs. The average particle size smaller than 50 nm can be achieved by low intermediate/final annealing temperature (≤520 °C) or short annealing time (≤2 h) treatment. The investigations in the present paper are very meaningful to control the SPPs in Zr-Nb based alloys.

Influence of Temperature on Typical Texture Distribution in Primary Recrystallization Matrix of 3% Si CGO Silicon Steel

OM (optical microscopy) and EBSD (electron backscatter diffraction) techniques were used to study microstructure and texture distribution during primary recrystallization under different intermediate annealing temperatures in CGO silicon steels. The effect of intermediate annealing temperature on texture distribution in 3% Si electrical steel was analyzed. The results indicate that the microstructure in primary recrystallization matrix of CGO silicon steel is comprised of equiaxed ferrite grains. Mean grain size of primary recrystallization increases with the rising of intermediate annealing temperature.γ-fiber texture is the dominant component in primary recrystallization matrix. With higher intermediate annealing temperature,111121texture and111110texture increase and111121texture is stronger than111110texture. Goss texture was observed to be decreased firstly and then increased. The content of high angle grain boundaries in primary recrystallization matrix are affected by intermediate annealing temperature. When intermediate annealing temperature is increased, high angle grain boundaries are increased firstly and then decreased. Misorientation distribution in primary recrystallized matrix is affected by primary recrystallization annealing temperature either. The content of high angle grain boundaries are increased owing to higher primary recrystallization annealing temperature, which can be a benefit to the abnormal growth of Goss grains in secondary recrystallization.

Effect of Post Deposition Annealing Treatments on Properties of AZO Thin Films for Schottky Diode Applications.

High-quality aluminum (Al) doped ZnO (AZO) thin films were deposited on silicon substrates by RF sputtering at room temperature. The deposited films were annealed from the temperatures 350 °C to 650 °C in pure nitrogen (N₂) ambient. The effects of annealing on the microstructural, optical and electrical properties of the AZO films were investigated. A detailed analysis by X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), Four Probe and Hall measurements was performed to study the properties of these AZO thin films. It was observed that all of the as-deposited and annealed AZO films have homogenous surfaces and hexagonal wurtzite structures with good crystalline quality. The study also suggested that there was an intermediate post annealing temperature (450 °C) at which the deposited ZnO film exhibit best surface characteristics. Pd/AZO Schottky devices were fabricated with 450 °C annealed AZO thin films and the parameters of Schottky devices were extracted from I-V characteristics. These results indicated that the Pd/AZO films were very much suitable for various optoelectronics applications particularly for metal semiconductor metal based UV detector application.

High temperature recrystallization of kersterite Cu2ZnSnS4 towards enhanced photocatalytic H2 evolution

Kesterite Cu2ZnSnS4 (CZTS) with different crystallinities were obtained by high temperature recrystallization of as-prepared kesterite CZTS nanocrystals under elevated temperature. The effect of temperature on the crystallinity, crystallite size and specific surface area, thus the photocatalytic H2 evolution activity were discussed in detail. The maximum photocatalytic H2 evolution rate was achieved under an intermediate annealing temperature (450 and 550 °C), which show moderate crystallinity and specific surface area. However, the surface specific activity of CZTS, namely the amount of H2 evolution per surface area, show the highest value when the annealing temperature increased up to 750 °C. A rapid cooling process which induces the improvement of crystallinity without significant loss of specific surface area was used to further enhance the photocatalytic H2 evolution activity of CZTS.

The dependence of final microstructure, texture evolution and mechanical properties of Al–Mg–Si–Cu alloy sheets on the intermediate annealing

Effect of intermediate annealing on the microstructure, texture and mechanical properties of Al–Mg–Si–Cu alloy sheet in the different conditions was investigated by means of tensile test, microstructure characterization and texture measurement in this study. The results show that, three different intermediate annealing treatments (no annealing, low temperature annealing, high temperature annealing) have a great influence on the evolution of microstructure and texture, and final mechanical properties. Compared with the high temperature annealing and no intermediate annealing, the low temperature annealing is most beneficial to improve mechanical properties, especially for improving the average Lankford coefficient r and reducing Δr values, and to form the uniform recrystallization structure and the finer recrystallization grains. Although the intermediate annealing temperature only affects the intensities of textures formed by annealing treatments, and the intensities of β fibers formed by the following cold rolling, yet, the texture components are quite different in the three alloy sheets in the T4P state, and only the CubeND orientation produced by PSN effect appears in the alloy sheet treated by the low temperature annealing. Additionally, the relationship between texture, r value and yield strength was analyzed by VPSC model and slip theory in this paper.

Role of boron diffusion in CoFeB/MgO magnetic tunnel junctions

Several scientific issues concerning the latest generation read heads for magnetic storage devices, based on CoFeB/MgO/CoFeBmagnetic tunnel junctions (MTJs) are known to be controversial, including such fundamental questions as to the behavior and the role of B in optimizing the physical properties of these devices. Quantitatively establishing the internal structures of several such devices with different annealing conditions using hard x-ray photoelectron spectroscopy, we resolve these controversies and establish that the B diffusion is controlled by the capping Ta layer, though Ta is physically separated from the layer with B by several nanometers. While explaining this unusual phenomenon, we also provide insight into why the tunneling magnetoresistance (TMR) is optimized at an intermediate annealing temperature, relating it to B diffusion, coupled with our studies based on x-ray diffraction and magnetic studies.

Influence of annealing temperature on structural, electrical and optical properties of undoped zinc oxide thin films

The undoped zinc oxide thin films were grown on quartz substrate at a substrate temperature of 750 °C by radio frequency magnetron sputtering and post annealed at different temperatures (600–800 °C) for a period of 30 min. The influence of annealing temperature on the structure, electrical and optical properties of undoped ZnO thin films was investigated by X-ray diffraction, Hall-effect, photoluminescence and optical transmission measurements. Results indicated that the electrical properties of the thin films were extremely sensitive to the annealing temperature and the conduction type could be changed dramatically from n-type to p-type, and finally changed to weak p-type when the temperature increased from 600 to 800 °C. Electrical and photoluminescence results indicate that native defects, such as oxygen and zinc vacancies, could play an important role in determining the conductivity of these nominally undoped ZnO thin films. The conversion of the conduction type was attributed to the competition between Zn vacancy acceptor and oxygen vacancy and interstitial Zn donors. At an intermediate annealing temperature of 750 °C, the film behaves the best p-type characteristic, which has the lowest resistivity of 12 Ωcm, hall mobility of 2.0 cm2/V s and carrier concentration of 1.5 × 1017 cm−3. The photoluminescence results indicated that the Zn vacancy might be responsible for the intrinsic better p-type characteristic in ZnO thin films.

Influence of intermediate annealing on the microstructure and texture of Ni-9.3at%W substrates

The effects of intermediate annealing (IA) on the microstructure and texture of Ni-9.3at%W substrates have been investigated by using electron backscattering diffraction and X-ray diffraction. Results suggest that IA can optimize the homogeneity of deformation microstructure. Higher IA temperatures (without undergoing recrystallization during IA) will increase the copper-type components of deformation texture and improve the content of cube texture after recrystallization. Sharp cube texture (97.2%) can be obtained at the optimum IA temperature of 650°C. The mechanism underlying the transition of deformation texture can be interpreted as that IA increases the dislocation slipping ability and suppresses the twinning deformation of Copper orientation in the subsequent rolling process. The observed strengthening of cube texture as a result of IA treatment is presumably attributed to the reduction of noncube nucleation and the optimization of preferential growth surrounding the cube nuclei.

Influence of annealing temperature on properties of nitrogen-doped zinc oxide films deposited by magnetron sputtering

Nitrogen-doped p-type zinc oxide films have been realized by radio frequency (rf) magnetron sputtering and post-annealing techniques. The effect of annealing temperature on the structural, electrical and optical properties of nitrogen-doped zinc oxide films was investigated by X-ray diffraction, Hall-effect, photoluminescence measurements. The nitrogen-doped p-type zinc oxide film with good structural, electrical and optical properties can be obtained at an intermediate annealing temperature region (e.g., 650°C). The nitrogen-doped p-type zinc oxide had the lowest resistivity of 2.9Ωcm, Hall mobility of 18cm2/Vs and carrier concentration of 1.3×1017cm−3. The p-type conduction behavior of the nitrogen-doped zinc oxide film was confirmed by the rectifying I–V characteristies of a ZnO homojunction. The chemical bonding states of nitrogen doped in ZnO film were examined by XPS analysis. Mechanism of the p-type conductivity was discussed in the present work.