Short-time Annealing Research Articles

Effect of intermediate annealing time on microstructure, texture and mechanical properties of Al-Mg-Si-Cu alloy

The effect of intermediate annealing time on the microstructure, texture and mechanical properties of Al-Mg-Si-Cu alloys was studied by mechanical properties, microstructure and texture characterization in the present study. The results show that the intermediate annealing time has some influence on the microstructure, recrystallization texture, and final mechanical properties. After the pre-aging treatment and natural aging treatment (T4P treatment), in contrast to the sheet with short intermediate annealing time, the sheet with long intermediate annealing time possesses higher plastic strain ratio r value. Strength has no positive correlation with annealing time, and when applying the annealing time of 16 h, the strength is highest. Before solution treatment, the sheet with long intermediate annealing time has more particles with a larger average size, compared with the sheet with short intermediate annealing time. After solution treatment, they possess the similar recrystallization equiaxed grain structure and recrystallization texture. The sheet with short intermediate annealing time is comprised of CubeND {001} 〈310〉, Goss {110}〈001〉 and P {011}〈122〉 orientations, while the sheet with long intermediate annealing time possesses weak texture including CubeND {001}〈310〉, Goss {110}〈001〉 and {015}〈751〉 orientations. Finally, a particle dissolution model during solution treatment is proposed to explain the variation of strength with annealing time.

Design and fabrication of a low modulus β-type Ti–Nb–Zr alloy by controlling martensitic transformation

In this paper, high density of dislocations, grain boundaries and nanometer-scale α precipitates were introduced to a metastable Ti–36Nb–5Zr alloy (wt%) through a thermo-mechanical approach including severe cold rolling and short-time annealing treatment. The martensitic transformation was retarded, and the β phase with low content of β stabilizers was retained at room temperature after the thermo-mechanical treatment. As a result, both low modulus (57 GPa) and high strength (950 MPa) are obtained. The results indicate that it is a feasible strategy to control martensitic transformation start temperature through microstructure optimization instead of composition design, with the aim of fabricating low modulus β-type Ti alloy.

Achieving bimodal microstructure and enhanced tensile properties of Mg–9Al–1Zn alloy by tailoring deformation temperature during hard plate rolling (HPR)

In the present work, we investigated the influence of deformation temperature on the formation of a bimodal microstructure and tensile properties of a Mg–9Al–1Zn (AZ91) alloy processed by a single pass hard plate rolling (HPR) with a thickness reduction of 55% followed by a short time annealing. Microstructural examinations by electron backscatter diffraction (EBSD) reveal that there exists a narrow deformation temperature window, i.e. it is only feasible to achieve a desired bimodal grain structure in the AZ91 alloy when HPRed at ∼350 °C. It is mainly because that partial dynamic recrystallization (DRX) occurs easily in the sample HPRed at ∼ 350 °C, facilitating the formation of a bimodal microstructure consisting of coarse un–recrystallized grains (>∼70 μm) and fine recrystallized grains (<∼5 μm). In contrast, reducing deformation temperature to ∼300 °C results in a coarse unrecrystallized microstructure containing substantial sub structure, while elevating the deformation temperature to ∼400 °C leads to an almost uniform recrystallized grain structure. Especially, the formation mechanism for the bimodal grain structure at the optimum deformation temperature is explored in terms of Schmidt factors analysis for basal slips (SFbasal) for grains of different size scales. Moreover, the 350 °C HPRed AZ91 sample exhibits a better combination of strength (ultimate tensile strength = ∼374 MPa) and ductility (elongation = ∼19.6%), as compared to the 300 and 400 °C samples. It is mainly attributed to the typical bimodal grain structure and the relatively high SFbasal featured by the fine recrystallized grains as well as the nanometer spherical particles distributing in fine grain interiors.

Synthesis and Structure–Property Relationship of Biobased Biodegradable Poly(butylene carbonate-co-furandicarboxylate)

A series of biobased poly(butylene carbonate-co-furandicarboxylate) (PBCF), are synthesized through a two-step polycondensation reaction. Chemical structures, thermal properties, crystallization behaviors, mechanical properties, barrier properties, and enzymatic degradation of PBCFs are investigated. The linear variation of the glass transition temperatures with the content ratio confirms the good miscibility between butylene carbonate (BC) and butylene furandicarboxylate (BF) units. BF segments could crystallize in most contents under different temperatures. Consequently, mechanical properties of these copolymers depend not only on the composition but also on the annealing conditions. Long-time annealing at room temperature or short-time annealing under high temperature could tremendously increase the tensile modulus. For room-temperature annealing, the formation of less perfect crystals of the poly(butylene furandicarboxylate) (PBF) could interpret the enhancement of modulus. On the other hand, the high...

Microstructure evolution of Cu–30Zn during friction stir welding

The microstructure evolution of Cu–30Zn during the deformation and cooling stages of friction stir welding was separately investigated by employing the in-process rapid cooling, tool “stop action”, and subsequent short-time annealing. A pure copper foil was inserted into the butting surfaces of the two workpieces to show the microstructure evolution path. The microstructure along the material flow path was investigated by the EBSD technique. At the weld’s upper part, continuous material flow occurs nearly over the whole range of the shoulder. The initial coarse grains are refined by the discontinuous dynamic recrystallization (DDRX) accompanied by the annealing twinning. During the material flow, the grain structure evolution is dominated by the annealing twinning during the thermally activated grain boundary migration and the subsequent twin destruction due to further deformation, resulting in a nearly constant grain size. Finally, normal grain growth occurs at the cooling period. At the lower part, the material transfers in a very thin layer near the probe surface and rapidly forms stable band structures. Due to the lower heat generation and higher strain rate, the mechanical twinning occurs in front of the probe. These deformation twins can provide additional nucleation sites for the DDRX via the twin destruction caused by further deformation. The higher strain rate in the weld’s lower part contributes to the finer grains than that of the upper part grains. However, due to the shoulder’s coverage, the lower part undergoes a longer cooling period than the upper part, and thus more significant grain growth occurs.

Tuning the Structure and the Mechanical Properties of Ultrafine Grain Al–Zn Alloys by Short Time Annealing

Abstract Solid solution treated Al-Zn alloys with different Zn contents (10 and 30 wt.%) have been nanostructured by severe plastic deformation (SPD) via equal-channel angular pressing method. In-situ transmission electron microscopy observations have been used to follow microstructure evolutions upon annealing. It was shown that SPD leads to the precipitation of Zn particles and that this partial solid solution decomposition was more pronounced in the Al- 30%Zn alloy. Annealing at temperatures in range of 200 to 250 °C led to visible dissolution of Zn particles in both alloys and to formation of extensive grain boundary segregations of Zn. This approach helped to design short term annealing treatments leading to specific ultrafine grain structures that could be achieved by static annealing on bulk samples. Last, the tensile behavior of these materials has been investigated with a special emphasis on the influence of the strain rate on the yield stress and on the elongation to failure. It is shown that in any case the yield stress is mainly controlled by the grain size, while a low volume fraction of Zn phase leads to a relatively modest ductility.

Annealing-Induced Grain Rotation In Ultrafine-Grained Aluminum Alloy

Abstract Results of in situ transmission electron microscopic studies of annealing-induced evolution of grain boundary misorientations in ultrafine-grained aluminum alloy Al-4%Cu-0.5%Zr (wt.%) processed by high pressure torsion are presented. An experimental procedure based on the single reflection technique was applied for the measurements of orientations of individual grains before and after annealing that allowed for determining misorientations between them. The measurements revealed that relaxation processes occurring in non-equilibrium grain boundaries during short-time annealing are accompanied by a change of grain boundary misorientations, grain rotation, grain migration as well as grain growth. Obtained results were compared with theoretical studies considering the kinetics of grain rotation in discrete-dislocation as well as continuum approaches.

Formation of SnS phase obtained by thermal vacuum annealing of SnS2 thin films and its application in solar cells

We demonstrate a simple approach to fabricate single-phase SnS thin films by thermal vacuum annealing of SnS2 layers obtained by the close-spaced vacuum sublimation method. It was found that the initial non-annealed SnS2 films exhibit typical chemical composition for SnS2 with ratio of Sn/S = 0.49. The structural quality of the SnS2 phase was studied by X-ray diffraction and Raman spectroscopy measurements. In particular, it was established that films have a hexagonal 2H-SnS2 crystal structure. The field emission scanning electron microscope analysis of the surface and cross-section shows plate-like crystallites with an average size of 2 µm. Annealing of the SnS2 samples was carried out at 300, 400, and 500 °C for 30, 60, and 90 min for each temperature, and at 600 °C for 30 min. It was shown that concentration of S gradually decreases with increasing annealing temperature and time. The samples annealed at 500 °C for 30, 60, and 90 min demonstrate a typical SnS composition ratio of Sn/S = 0.96. Further, by using X-ray diffraction, Raman, and energy dispersive X-ray analysis, we found that annealing of the samples at 500 °C for 30, 60, and 90 min provides a phase transition from hexagonal SnS2 to orthorhombic SnS. The shorter annealing time and temperature leads to the mixed SnS, Sn2S3, and SnS2 phase composition. The shape and size of plate-like crystallites remains the same after annealing. However, randomly distributed nano-pores were observed. Transmittance and reflectance measurements of the SnS2 and SnS films show both direct and indirect optical band gaps in the materials. For SnS films a large absorption coefficient of 104–105 cm−1 above the band gap was found. The current-voltage characteristic of the ITO/SnS2/Sn structure shows small rectification current, while the current-voltage curve of ITO/SnS/Sn is linear. The dark resistivity was found to be 1.01 × 105 Ω cm and 1.18 × 103 Ω cm for SnS2 and SnS films, respectively. The heterojunction structure was obtained by annealing of the SnS2 deposited on the ITO/CdS structure to obtain the SnS phase. The p-SnS/n-CdS heterojunction shows weak photovoltaic response under illumination at AM 1.5 conditions, namely, open circuit voltage (Voc), short circuit current density (Jsc), and fill factor (FF) of 0.35 V, 34.08 µA/cm2, and 0.42, respectively.

Investigation of temperature dependent microstructure evolution of pure iron during friction stir welding using liquid CO2 rapid cooling

The microstructure evolution of pure iron during friction stir welding was reconstructed by an ingenious experimental design, in which the rapid cooling friction stir welding combined with the tool “stop action” technique and the subsequent short-time annealing were adopted to “freeze” the transient microstructure during the stirring and reproduce the normal cooling during conventional friction stir welding, respectively. The microstructure evolution during the stirring and normal cooling was investigated along the material flow path and in the annealed “frozen” weld zone by high-resolution electron-backscatter-diffraction technique. The results show that the continuous and discontinuous dynamic recrystallizations occur simultaneously at the severe deformation stage in front of the tool both under low and high heat input conditions. However, during the material flow, the microstructure evolution involves the plastic deformation, recrystallization, high angle boundaries migration and dynamic recovery under the low heat input condition, while in a dynamic balance of deformation, recrystallization and grain growth under the high heat input conditions. At the cooling stage, normal grain growth occurs both for the low and high heat input welding conditions, while it is very limited for the low heat input condition.

Impact of short-time annealing of methylammonium lead iodide on the performance of perovskite solar cells prepared under a high humidity condition

ABSTRACTIn this work, the effects of annealing temperature and time for one-step fabrication of mixed metal halide perovskite films were investigated. The photovoltaic performance of perovskite solar cells (PSCs) improved from 8.30 to 10.85% after being annealed at 100 °C for 10 min and exhibited negligible photocurrent hysteresis when prepared at an ambient humidity of 70%. Besides, a high annealing temperature for a short time (150 °C; 1 min) shows comparable power conversion efficiency with perovskite annealed at 100 °C for 10 min. The electronic properties of PSCs were characterized by photo induced charge extraction via linearly increasing the voltage (photo-CELIV), impedance, and intensity modulated photovoltage spectroscopy. Our finding suggests that the improvement in photovoltaic performance is correlated to the improved charge mobility, suppressed charge trapping, and prolonged recombination lifetime.

Use of Hot Rolling for Generating Low Deviation Twins and a Disconnected Random Boundary Network in Inconel 600 Alloy

In this investigation, Inconel 600 alloy was thermomechanically processed to different strains via hot rolling followed by a short-time annealing treatment to determine an appropriate thermomechanical process to achieve a high fraction of low-Σ CSL boundaries. Experimental results demonstrate that a certain level of deformation is necessary to obtain effective “grain boundary engineering”; i.e., the deformation must be sufficiently high to provide the required driving force for postdeformation static recrystallization, yet it should be low enough to retain a large fraction of original twin boundaries. Samples processed in such a fashion exhibited 77 pct length fraction of low-Σ CSL boundaries, a dominant fraction of which was from Σ3 (~ 64 pct), the latter with very low deviation from its theoretical misorientation. The application of hot rolling also resulted in a very low fraction of Σ1 (~ 1 pct) boundaries, as desired. The process also leads to so-called “triple junction engineering” with the generation of special triple junctions, which are very effective in disrupting the connectivity of the random grain boundary network.

Nickel oxide films by thermal annealing of ion-beam-sputtered Ni: Structure and electro-optical properties

Nickel oxide films were prepared by thermal annealing of Ni deposited by ion beam sputtering on Si (or glass) substrates. The annealing was carried out in a laboratory furnace open to air at temperatures 350°C–500°C with annealing time 1–7h (1-h step). For as-deposited Ni films the sheet resistance RS was found to be 8.39Ω/⧠ and no significant XRD diffraction peaks were observed. The thermal annealing resulted in significant changes in composition and electrical, structural and optical properties. The oxidation process led to a rapid growth of RS up to 109Ω/⧠, appearance of the optical absorption edge for oxidized Ni, and the formation of a polycrystalline NiO structure with the main NiO (111) diffraction peak. At 350°C the annealing yielded 3-stage behavior of the sheet resistance due to limited oxidation during short time annealing. Longer processing times (>3h) were necessary to successfully oxidize the deposited Ni film, after 1h annealing the oxygen content (analyzed by nuclear resonance analysis) showed a significantly lower concentration within the depth of a sample; more uniform composition was found after prolonged annealing. XPS analysis showed the formation of a significant amount of nickel hydroxide at the surface. It was confirmed by ERDA. The optical properties were studied by Photothermal Deflection Spectroscopy (PDS). The data correlate with the 3-stage behavior of sheet resistance at 350°C, suggesting lower oxidation during short-term annealing, while transparent nickel oxide films were formed during longer annealing and at higher temperatures. Based on analysis of the obtained experimental data (from measurement of the sheet resistance, XRD diffraction and optical absorption spectra), the temperature of 400°C was found to be optimal for the formation of the fully oxidized NiO films.

Formation of InxGa1−xAs nanocrystals in thin Si layers by ion implantation and flash lamp annealing

The integration of high-mobility III–V compound semiconductors emerges as a promising route for Si device technologies to overcome the limits of further down-scaling. In this paper, a non-conventional approach of the combination of ion beam implantation with short-time flash lamp annealing is employed to fabricate InxGa1−xAs nanocrystals and to study their crystallization process in thin Si layers. The implantation fluence ratio of Ga and In ions has been varied to tailor the final nanocrystal composition. Raman spectroscopy and x-ray diffraction analyses verify the formation of ternary III–V nanocrystals within the Si layer. Transmission electron microscopy reveals single-crystalline precipitates with a low number of defects. A liquid epitaxy mechanism is used to describe the formation process of III–V nanocrystals after melting of the implanted thin Si layer by flash lamp annealing. The fabricated InxGa1−xAs nanocrystals are mainly Ga-rich with respect to the implanted Ga/In ratio.

High-Temperature-Short-Time Annealing Process for High-Performance Large-Area Perovskite Solar Cells.

Organic-inorganic hybrid metal halide perovskite solar cells (PSCs) are attracting tremendous research interest due to their high solar-to-electric power conversion efficiency with a high possibility of cost-effective fabrication and certified power conversion efficiency now exceeding 22%. Although many effective methods for their application have been developed over the past decade, their practical transition to large-size devices has been restricted by difficulties in achieving high performance. Here we report on the development of a simple and cost-effective production method with high-temperature and short-time annealing processing to obtain uniform, smooth, and large-size grain domains of perovskite films over large areas. With high-temperature short-time annealing at 400 °C for 4 s, the perovskite film with an average domain size of 1 μm was obtained, which resulted in fast solvent evaporation. Solar cells fabricated using this processing technique had a maximum power conversion efficiency exceeding 20% over a 0.1 cm2 active area and 18% over a 1 cm2 active area. We believe our approach will enable the realization of highly efficient large-area PCSs for practical development with a very simple and short-time procedure. This simple method should lead the field toward the fabrication of uniform large-scale perovskite films, which are necessary for the production of high-efficiency solar cells that may also be applicable to several other material systems for more widespread practical deployment.

Microstructure and magnetocaloric properties of non-stoichiometric La1.5Fe12.2-xCo0.8Six alloys

In this work, we have investigated the influence of annealing temperature and Si content on the microstructure and magnetocaloric properties of non-stoichiometric La1.5Fe12.2-xCo0.8Six (x = 1.0, 1.1, 1.2, 1.4) alloys. A high content of La(Fe,Co,Si)13 phase (∼80 vol.%) can be achieved after annealing at 1000 °C for 24 h. The morphology of the 1:13 phase evolves from facet to granule accompanying the aggregation of the α-Fe particles. The Curie temperature increases with increasing annealing temperature and decreases with the increase of nominal Si content. In addition, large entropy change values of 8.4 J/kg K and 8.0 J/kg K at 2 T are obtained for La1.5Fe11.1Co0.8Si1.1 and La1.5Fe11.1Co0.8Si1.2, respectively. The large entropy change, tunable transition temperature and short-time annealing make the currently studied non-stoichiometric La-Fe-Co-Si a promising magnetic cooling material.

Clarification of microstructure evolution of aluminum during friction stir welding using liquid CO2 rapid cooling

The microstructure evolution of aluminum during friction stir welding was reconstructed using tool “stop action” technique. Simultaneous liquid CO2 was used to “freeze” the weld microstructure and the transient microstructure after “stop action”. Subsequent short-time annealing produced a situation similar to the normal cooling. The microstructure evolution during the deformation and annealing stages was investigated along the material flow and in the “frozen” weld zone, respectively, by high-resolution electron-backscatter-diffraction technique. The results showed that the base material evolved into microstructures containing large amount of low angle grain boundaries (44.8%) with strong (7.9 times) B/B− shear texture at the initial welding stage. With the increasing of welding strain, lamellar grain structure with strong (6.1 times) A/A− shear texture was developed. Next, continuous dynamic recrystallization via lattice rotation with the grain 〈101〉 orientation as the rotation axis occurred under the strain relaxation condition, leading to lamellar grains conversion into equiaxed grains. Meanwhile, the strong A/A− texture transformed into weak (2.9 times) β-fiber textures (dominated by B/B− and C components). At the cooling stage, preferred grain growth along {112}〈110〉 occurred, forming relatively strong (3.8 times) B/B− texture, which is generally observed during the friction stir welding of aluminum alloys at higher welding temperatures.

Microstructure Stability of a Fine-Grained AZ31 Magnesium Alloy Processed by Constrained Groove Pressing During Isothermal Annealing

In this study, an AZ31 magnesium alloy plate was processed by constrained groove pressing (CGP) under three deformation cycles at temperatures from 503 to 448 K. The process resulted in a homogeneous fine grain microstructure with an average grain size of 1.8 μm. The as-processed microstructure contained a high fraction of low-angle grain boundaries (LAGB) of subgrains and dislocation boundaries that remained in the structure due to incomplete dynamic recovery and recrystallization. The material's yield strength was found to have increased from 175 to 242 MPa and with a significant weakening of its initial basal texture. The microstructure stability of the CGP-processed material was further investigated by isothermal annealing at temperature from 473 to 623 K and for different time. Abnormal grain growth was observed at 623 K, and this was associated with an increased in nonbasal grains at the expense of basal grains. The effect of annealing temperature and time on the grain growth kinetics was interpreted by using the grain growth equation, Dn+D0n=kt, and Arrhenius equation, k=k0 exp (−(Q/RT)). The activation energy (Q) was estimated to be 27.8 kJ/mol which was significantly lower than the activation energy for lattice self-diffusion (QL = 135 kJ/mol) and grain boundary diffusion (Qgb = 92 kJ/mol) in pure magnesium. The result shows that grain growth is rapid but average grain size still remained smaller than the as-received material, especially at the shorter annealing time.

Effect of Annealing Process on the Performance of Pressure of the φ3.5mm×8.75mm Cylindrical Copper Cylinder

By using different annealing processes to anneal the pressure-measuring cylindrical copper cylinder, playing some static experiments on different copper cylinders, the difference of pressure measuring performance of copper cylinder was analyzed. Results show that, by using current annealing processes all can achieve the purpose of full softening the material of the copper cylinder and the deformation of copper is not significantly affected by the different temperatures. Some copper cylinders which use short holding time have poor linear sensitivity, but their measurement deviation is better than those which use longer holding time. So, in the actual production of copper, we should use shorter annealing time to improve their measuring accuracy.

Influence of long-lasting heat treatments on the structure and properties of the zirconium-steel bond

The explosive welding technology is related to the dynamic impact of the clad onto base material. These results in significant microstructural changes of the bonded materials, the increase of internal stresses and the strain hardening of layers near the interface. In order to eliminate these unfavorable effects, it is advisable to carry out proper heat treatment. The paper presents the results of structural examinations and mechanical properties of bimetal zirconium - carbon steel, after long-lasting heat treatment. Bimetallic samples were annealed at 600 o C for 1, 10, 100, 500, 1000 hours. Microscopic examination were used to the analysis of microstructural changes, whereas systematic microhardness measurements and static tensile test to evaluation of the mechanical properties. It was found that the temperature has a beneficial effect on the changes in the bond zone and for longer annealing times a systematic decrease of the strength properties of the tested bimetal was observed. However, essential for the clad mechanical properties changes were observed in carbon steel plate. After short annealing (times of 1h and 10h) only small microstructural changes due to processes of recovery and recrystallization were observed in layers near the interface. The increase of annealing time was conducive to grain growth and carbon diffusion in the interfacial layer from steel towards zirconium.

Perfectly Ordered Patterns Formed by a Heterogeneous Nucleation Process of Block Copolymer Self-Assembly Under Rectangular Confinement.

The heterogeneous nucleation process during the phase separation of binary blends of the AB diblock and the C homopolymer induced by rectangular confinement is studied by cell dynamics simulation based on the time-dependent Ginzburg-Landau theory. The main goal is to yield large-scale ordered hexagonal patterns by tailoring the surface potentials of the sidewalls. Our study reveals a crucial condition to induce the desired heterogeneous nucleation process in which the nucleated domain grains grow and merge into a defect-free pattern. Specifically, nucleations are induced simultaneously by two parallel sidewalls with a strong surface potential, whereas the spontaneous nucleation and the heterogeneous nucleation at the other two walls with a weak surface potential are suppressed. Moreover, the confinement effect of the other two walls can ensure that the two rows of nucleated domains have correlated positions. Importantly, we find that the ordering process under the crucial condition exhibits a high tolerance to the rectangular sizes. Only a few defects in thousands of domains are occasionally caused that are observed to be annihilated in a short-annealing time via various mechanisms. This study may provide a facile route to prepare large-scale ordered patterns via a simple rectangular confinement.