Decrease In Dislocation Density Research Articles

Annealing effect on physical characterisation and sensing properties of nanostructered AgO thin films

Thermal evaporation (TE)was employed to create thin coatings of AgO on glass substrates. The post-annealing temperatures for the deposited films were (100, 150, and 200), respectively. The XRD data demonstrate that when annealing temperature climbed from 100°C to 200°C, the intensity of (100) plane strengthened. Regardless of the temperatures used for post-annealing, the XRD spectra show that the films are polycrystalline and have a cubic structure. The average grain size was 15.39 nm, 16.30 nm, and 17.68 nm for the intended films. When the annealed temperature rises, the dislocation density and strain value decrease. The root mean square (RMS) roughness measured via AFM images decreased from 7.33 nm to 3.64 nm. Due to annealing at 200°C, the average particle size behaved similarly and reduced from 76.9 nm to 46.5 nm. The surface roughness exhibited the same behavior and dropped from 8.77 nm to 4.46 nm at 200 o C. The sample annealed at 200°C had the highest absorbance values, whereas the sample annealed at 100°C had the highest transmittance values. As the film annealing increased, the absorption coefficient rose somewhat. The bandgap of AgO thin films falls from 1.59 eV to 1.44 eV with the rise of annealing. In contrast, the transmittance, refractive index, and Extinction coefficient also lower as the temperature rises. Sensitivity measurements indicated a reduction in sensitivity as the annealing temperature and gas concentration increased.

Effect of Coiling Temperature on Microstructure and Properties of Ferritic-Bainitic Dual-Phase Steels

In this study, a 780 MPa grade ferritic-bainitic dual-phase steel with excellent matching of strength-plasticity and formability was developed using thermomechanical control processing. Optical microscopy, Scanning electron microscopy, and Electron Backscatter Diffraction techniques were used to characterize the microstructure comprehensively, and the effects of coiling temperature on the microstructure, the strength-plasticity, and hole-expansion ratio of the test steels were thoroughly investigated. The results showed that the test steel had an excellent combination of ferrite and bainite at the coiling temperature of 520 °C, 23.7 and 76.3%, respectively, with a hole expansion ratio of 58.5 ± 2.8%. The uniformity of the microstructure was the key to obtaining a high expansion ratio in ferrite-bainite dual-phase steels. The test steels formed granular bainite at low-temperature coiling, while polygonal ferrite was promoted at high-temperature coiling. The effect of coiling temperature on grain size is small. Dislocations were redistributed during high-temperature coiling, resulting in a decrease in dislocation density. The higher elongation and hole expansion rate at higher coiling temperatures were attributed to increased polygonal ferrite content, reduced grain size, and enhanced TRIP effect. When coiling at low temperatures, the agglomeration of polygonal ferrite or granular bainite tends to result in a non-uniform distribution of the soft and hard phases of the matrix. At the same time, the strong texture parallel to the rolling direction has a significant difference in plasticity in different directions, leading to non-uniform deformation, which is liable to stress concentration, causing crack nucleation and extension in the hole expanding process, thus reducing the hole expansion performance.

RF magnetron sputtering of [formula omitted] thin films: Analysis of thermal annealing induced tuning of structural, optical characteristics, and energy band alignments

This correspondence showcases the deposition of ultra-wide bandgap β−Ga2O3 thin films via the utilization of RF magnetron sputtering at an elevated deposition temperature of 400 °C, followed by a comprehensive analysis of their structural, surface and optical properties using X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), Raman, Ultraviolet–Visible Spectroscopy (UV–Vis), and Atomic Force Microscopy (AFM) at 800 °C, 900 °C, and 1000 °C annealed sample. Annealing up to 1000 °C led to a significant enhancement in the film’s crystallinity by 10%, accompanied by a remarkable decrease in dislocation density of up to 93.5%. The study also observed several key trends upon annealing, including a decreasing lattice constant from 12 to 11.97 Å, and an increase in the bandgap from 4.8 to 5.3 eV. Concurrently, crystallite size was consistently increased from 4.07 to 15.77 nm. The conduction band offset (CBO) decreased with higher annealing temperatures. Additionally, the increase in bandgap led to an enhancement in the critical electric field from 8.9 to 11.2 MV/cm. The Electron Density Mapping (EDM) results depicted a covalent bond between the atoms for different annealing processes along with the fundamental structural change in atomic coordinates and unit cell parameters, which has not been reported yet. These findings underline the remarkable material properties of β−Ga2O3 at 1000 °C temperatures. This establishes it as a compelling substitute for materials like SiC and GaN, showcasing its potential across various high-power applications due to a superior Baliga figure of merit and robust sensitivity even under elevated temperatures, positioning it as a promising candidate for optoelectronic applications.

Microstructural evolution and formability of Ti−6Al−4V alloy sheet during electropulsing-assisted bending

The electropulsing-assisted bending test was carried out on Ti−6Al−4V alloy sheet with the effective current density of 0−3.2 A/mm2 and duty ratio of 10%−70%. The results show that the bending forming displacement increased from 9.15 to 15.60 mm with increasing effective current density from 0 to 2.4 A/mm2. The crack changed to be shallow and small at the same time. Besides, the springback angle decreased as the effective current density increased at the bending displacement of 8 mm. Duty ratio also affected bending angle, where 30% duty ratio led to the lowest bending angle of 135.0°. The thermal stability temperature increased with increasing effective current density and varied non-monotonically with duty ratio. In addition, grain coarsening, {0001} texture strengthening and sub-grain development were observed during electropulsing-assisted bending. The electropulsing decreased dislocation density and accelerated dislocation rearrangement, the rearranged and piled-up dislocation inside α grains promoted sub-grain structure formation, which improved the formability. The contribution of athermal effect made the low-temperature formability of Ti−6Al−4V alloy comparable to that at high temperature.

Microstructure evolution and the deformation mechanism in nanocrystalline superior-deformed tantalum.

The temperature-controlled relationship between the mechanical properties and deformation mechanism of tantalum (Ta) enables the extension of its application potential in various areas of life, including energy and electronics industries. In this work, the microstructure and deformation behavior of nanocrystalline superior-deformed Ta have been investigated in a wide temperature range. The structural analysis revealed that the high-performance Ta consists of several different substructures, with an average size of about 20 nm. The tensile behavior of nanocrystalline Ta (NC-Ta) was analysed and simulated at various temperatures from 100 K to 1500 K by the molecular dynamics (MD) method. It is shown that with increasing average grain size, the elastic modulus of NC-Ta linearly increases, and the impact factor reaches a value close to 1.8. The critical grain size, as obtained from the Hall-Petch relationship, was found to be about 8.2 nm. For larger grains, the flow stress follows the Hall-Petch relationship, and the thermal behavior of twin bands determines the deformation process. On the other hand, when grains are smaller than the critical size, the relationship between the flow stress and structure transforms into the inverse Hall-Petch relationship, and the deformation mechanism is controlled by grain rotation, boundary sliding or atomic migration. The results of numerical simulations revealed that temperature significantly affects the critical grain size for the plastic deformation of NC-Ta. In addition, it is demonstrated that both the elastic modulus and dislocation density decrease with increasing temperature. These findings provide guidance for the design of polycrystalline tantalum materials with tailored mechanical properties for specific industrial applications such as heat exchangers and condensers in aerospace, bone substitutes in biomedicine, and surface acoustic wave filters or capacitors in electronics.

Enhanced Toughness and Ductility of Friction Stir Welded SA516 Gr.70 Steel Joint via Post-Welding Annealing.

The SA516 Gr.70 steel possessing excellent toughness and plasticity has been widely used in the cryogenic field. However, the appearance of coarse bainite in the heat affected zone (HAZ) of the fusion welded joint deteriorates the toughness and ductility. In this work, 4.5 mm thick SA516 Gr.70 steel was joined using shielded metal arc welding (SMAW) and friction stir welding (FSW), respectively, and the microstructure and mechanical properties of joints were investigated in detail. The Charpy energy in the HAZ in the FSW joint was 80 J/cm2, which was higher than that of the HAZ in the SMAW joint (60 J/cm2) and due to microstructure refinement. In addition, the total elongation (TE) of the SMAW joint was 17.5%, which was higher than that of the FSW joint (12.1%) and caused by a wider nugget zone with high hardness. The post-welding annealing was used to improve the toughness and ductility of the SMAW and FSW joints, and the microstructure and mechanical properties of the joints after annealing were analyzed. The toughness in the HAZ of the SMAW and FSW joints were 80 and 103 J/cm2, and the TE of the SMAW and FSW joints were 18.6% and 25.2%, respectively. Finally, the as-annealed FSW joints exhibited excellent toughness and ductility. The abovementioned excellent mechanical properties were primarily attributed to the appearance of tempering martensite, decrease in dislocation density, and fine grain.

Outstanding thermal stability of cold-rolled Al–Y alloy revealed using in-situ synchrotron X-ray diffraction and ex-situ microscopy

This paper describes the main results from an experimental investigation into the thermal stability of a cold-rolled Al–Y alloy. Tensile tests performed on specimens of the alloy and pure Al in annealed states reveal superior anti-softening properties of the former specimens relative to the latter counterparts. Origins of such thermal stability and underlying recovery and recrystallization kinetics are studied using electron microscopy and high energy X-ray diffraction (HEXRD) techniques. Microscopic observations reveal that recovery and recrystallization begin in the specimens of pure Al at a much lower temperature than in the specimens of Al–Y alloy. Onset of the recovery process in the Al–Y alloy is observed to begin with dislocation rearrangements in the β-Al3Y phases. The onset is followed by more substantial reduction in dislocation density, shrinkage of the β-Al3Y phases, and coarsening of the α-Al grains. The alloy contains stacking faults, which interestingly remain stable during the annealing treatments contributing to the thermal stability. The observed mechanisms are further confirmed by tracking the evolution of peaks under the in-situ synchrotron X-ray diffraction with heating. Onset of recovery was observed at 280 °C in both α-Al and β-Al3Y phases, while substantial shrinkage and spheroidization of β-Al3Y phases and decrease in dislocation density were detected at 400 °C causing loss of the alloy strength. Thermodynamic calculation showed that solubility of Y rapidly increases in α-Al at temperatures above 400 °C explaining the spheroidization and shrinkage of the β-Al3Y phases by diffusion of Y into the Al matrix.

Texture evolution and strengthening mechanism of CuCrZr alloys during cold rolling

The evolution of microstructure and crystallographic texture in Cu–1Cr-0.061Zr alloy strips during multi-pass cold rolling deformation was studied. The results showed that the tensile strength of Cu–1Cr-0.061Zr alloy increased from 507 MPa to 683 MPa with increasing rolling strain, while the conductivity decreased from 84.1 to 68.1 of the International Annealed Copper Standard. When the strain is 1.86–3.85, the elongation is effectively stable at 7.5%–8.5%. The local strain and grain dislocation angle inside the alloy gradually increase with the increase in strain, and the grain orientation distribution becomes more uniform and stronger. The dislocation slip generated during the rolling process leads to the concentration of grain orientation toward the <11−1> direction, causing the Goss texture ({110}<001>) to gradually transform into a Copper texture ({112}<11−1>) with relatively stable grain orientation, which significantly improves the mechanical properties at the macro level. In addition, the heat generated during the cold rolling process causes the cancellation of heterologous dislocations on a certain slip surface, resulting in a decreased dislocation density and a slight growth of nanoprecipitates. Nanoprecipitation strengthening and grain boundary strengthening are the main strengthening mechanisms in the Cu–1Cr-0.061Zr alloy, while the strength contribution of banded Cr phase dispersion is relatively small.

Phase variation of manganese oxide in the MnO@ZnO nanocomposite with calcination temperature and its effect on structural and biological activities

Having powerful antibacterial and antioxidant effects, zinc oxide and manganese oxide nanomaterials are of great interest. Here we have synthesized manganese oxide decorated zinc oxide (MZO) nanocomposites by co-precipitation method, calcined at different temperatures (300–750 °C) and studied various properties. Here the crystalline structure of the nanocomposite and phase change of the manganese oxide are observed with calcination temperature. The average crystalline size increases and the dislocation density and microstrain decrease with the increase in calcined temperature for the same structural features. The formation of composites was confirmed by XRD pattern and SEM images. EDAX spectra proved the high purity of the composites. Here, different biological properties change with the calcination temperature for different shapes, sizes and structures of the nanocomposite. Nanomaterial calcined at 750 °C provides the best anti-microbial activity against Escherichia coli, Salmonella typhimurium, Shigella flexneri (gram-negative), Bacillus subtilis and Bacillus megaterium (gram-positive) bacterial strain at 300 µg/mL concentration. The nanomaterial with calcination temperatures of 300 °C and 450 °C provided better antioxidant properties.

The cyclic deformation behavior and microstructural evolution of 304L steel manufactured by selective laser melting under various temperatures

The low cycle fatigue (LCF) tests with strain-controlled are carried out to investigate the cyclic deformation behavior of 304L steel manufactured by selective laser melting (SLM 304L) at room temperature (RT), 300 °C, and 650 °C. According to the experimental results, the continuous cyclic softening behavior of SLM 304L is presented at different temperatures. Meanwhile, due to the external force during the fatigue test, the substructure morphology is changed from the elongated cellular substructure of the as-built SLM 304L to the cell substructure of the failure sample at different temperatures. Moreover, since the dislocation rearrangement process is a net decrease in dislocation density, the continuous cyclic softening behavior is presented. Besides, the dynamic recovery and recrystallization promote the cyclic softening behavior of SLM 304L at high temperatures. Additionally, when the multiplication and annihilation of dislocations research the equilibrium state, the dislocation density has no obvious change in the microstructure, leading to the steady state of the cyclic response curve. Finally, considering the influence of the crack closure effect, a new fatigue life prediction model is proposed and discussed.

Pengaruh Variasi Temperatur Tempering Terhadap Struktur Mikro Dan Struktur Kristal Pada Baja Karbon Sebagai Bahan Mandrill

This writing begins with a mandrill that cannot be modified in a company, so the author wants to know the crystal structure and microstructure of the steel, as well as explain the composition contained in the steel being tested. Tests were carried out by observing the crystal structure using an X-Ray Diffractometer (XRD), observing the microstructure and material composition using Scanning Electron Microscopy – Energy Dispersive X-ray (SEM-EDX). The results show that the crystal structure and microstructure are strongly influenced by the quenching and tempering processes. The increase in crystal size occurred after the tempering process at 425° C from 34.33 nm to 52.31 nm. There was a decrease in dislocation density after tempering at 425° C from 0.00085 lines/mm2 to 0.00085 lines/mm2. Likewise, the micro strain after the tempering process at 425°C decreased from 0.25 (ε) to 0.19 (ε). The test material has several compositions such as iron (Fe), oxygen (O), manganese (Mn), sodium (Na), chromium (Cr), calcium (Ca) and carbon (C). Microstructure testing showed a decrease in iron Fe atoms after the tempering process from 65.79% to 42.96%, a decrease in atoms also occurred in manganese from 0.51% to 0.34% after the tempering process. There was an increase in oxygen atoms after the tempering process from 33.31% to 54.23%, an increase in the atomic presentation also occurred in sodium (Na) from 0.33% to 2.46% after the tempering process

Tailoring high-temperature mechanical properties of laser powder bed fusion Ti-6.5Al-2Zr-1Mo-1 V alloy via microstructure design

The microstructure of Ti-6.5Al-2Zr-1Mo-1 V (TA15) alloy fabricated by laser powder bed fusion (LPBF) is characterized by the ultrafine α′ martensite with a high density of dislocations and twins, which is distinct to that of conventionally forged TA15 alloy. The α′ martensite in the as-built alloy transforms to stable α phase when annealing below the β transus, and meanwhile the dislocation density decreases and the α lamellae coarsen with increasing of annealing temperature. An excellent synergy of strength and ductility was achieved in the sample after designated heat treatments, which is better than that of the forged counterpart at both room temperature and 500 °C. In-situ tensile test at 500 °C demonstrated that the plasticity of as-built TA15 alloy was dominated by the formation of microscale shear bands (MSBs) between the α′ lamellae, which results in pronounced strain localization and limited tensile ductility. In the sample with coarsened α lamellae, it was found that the activation of pyramidal < c + a > slip system at 500 °C effectively alleviated the strain localization and cracking tendency during mechanical loading, which is essential to achieve a desired balance of strength and ductility. These findings are helpful to promote the practical applications of LPBF near-α titanium alloys.

Influence of Austempering Conditions on Hardness and Microstructure of Bainite in Low-Alloyed Steel

The influence of austempering temperature and time on the microstructure and hardness of a low-alloyed bainitic steel is investigated in the temperature range 275 °C to 375 °C for up to 24 hours. It is shown that the dislocation density and coarseness of the bainitic microstructure are affected by the austempering temperature, while only the dislocation density is significantly affected by the austempering time. The hardness of the steel is estimated based on microstructure–property relations and is in good agreement with the measured hardness. In conclusion, the decrease in dislocation density is the main reason for loss in hardness upon increasing austempering temperature and/or time for the studied temperature range.

Effect of microstructure modification on magnetic and mechanical properties of high-grade non-oriented silicon steel during annealing treatment

The optimization of magnetic and mechanical properties by microstructure modification is tremendously challenging for high-grade non-oriented silicon steel. In the current study, the microstructure of cold-rolled high-grade non-oriented silicon steel was modified by recrystallization annealing to achieve high strength and good magnetic properties. The results indicate that recrystallization annealing significantly improved the magnetic properties, while negatively impacting its mechanical properties. At the early stage of annealing (<2 min), recrystallization nucleation occurred in the deformation matrix, leading to a significant decrease in dislocation density. This decrease in dislocation density resulted in a notable reduction in coercivity and hence enhancement in magnetic properties. However, the mechanical properties deteriorated due to the elimination of dislocations. With further increasing the annealing time (>2 min), the recrystallization grains grew within the fully recrystallized matrix. There was a slight decrease in both dislocation density and grain boundary density, leading to a slight decrease in iron loss and yield strength. The magnetic induction intensity of the fully recrystallized annealed sheets was primarily influenced by the recrystallization texture. Thus, the critical annealing time was 2 min to meet the demands of both magnetic and mechanical properties for the studied high-grade non-oriented silicon steel.

Effect of Sm and Ce content on microstructure and mechanical property of newly developed Mg-Sm-Ce-Mn based alloy

In this work, the effect of Sm and Ce contents on mechanical property of Mg-Sm-Ce-Mn based alloy have been investigated, and it is found that both the strength and ductility increased continuously with the increase of solute contents. In the as-extruded Mg-1.6Sm-0.8Ce-0.4Mn alloy, a high strength-ductility synergy was obtained, with yield strength (YS) of 269 MPa and an elongation (EL) of 21%. The increase of Sm and Ce elements introduces the high density of micro-sized and nano-sized second phases as well as the Sm segregation at grain boundaries, which leads to an increase in the recrystallization fraction, more evident dynamic recrystallized (DRXed) grain refinement, and also the texture weakening. The increased density of nano-phases and the DRXed grains refinement lead to the higher strength, and the decrease in dislocation density and texture weakening contribute to the excellent ductility. The relevant work can shed light on designing other low-cost and high-performance Mg wrought alloys containing the cheap light rare-earth elements.

Strengthening Effect of Decreased Dislocation Density After Annealing in Pure Aluminum or Copper

Strengthening Effect of Decreased Dislocation Density After Annealing in Pure Aluminum or Copper

A study on as-welded microstructure and mechanical properties of thick-walled 9Cr3W3Co1CuVNbBN martensitic steel weldment

A systematic study on the microstructure evolutions and their relationships with mechanical properties of thick-walled 9Cr3W3Co1CuVNbBN martensitic steel pipe joint welded by narrow-gap automatic argon arc welding was carried out. The results showed that a narrow equiaxed grain zone (EGZ) and a significantly wide inter-critical zone (ICZ) were formed in the heat affected zone (HAZ) due to the larger grain size and lower VN precipitates in base metal (BM). The refined grains formed in WM and the higher solid solubility of C, Cr and W in EGZ and ICZ were the main factors leading to their higher hardness than that of BM. The decrease of dislocation density in over-tempered zone (OTZ) immediately adjacent to ICZ not only significantly improved the impact toughness of HAZ, but also led to a significantly lower hardness than that of BM. Nevertheless, the room/high temperature tensile fracture of the welded joints occurred in the BM zone, which was attributed to the cross-sectional shrinkage of the OTZ restrained by the nearby high hardness region ICZ, and the preferential formation of cavities near the coarse Cr23C6 carbides in BM.

Ag nanoparticle assisted vertically aligned β-Ga2O3 nanowire deposited by GLAD technique for ultrafast photodetection

In this study, we report the fabrication of Silver (Ag) nanoparticle (NP) assisted vertically oriented β-Ga2O3 nanowires on Silicon (Si) - substrate by the Glancing angle deposition (GLAD) technique. The fabricated samples were annealed at 900 °C. The optoelectronic properties of both As-deposited and annealed devices are studied thoroughly. The sample shows an increase in average crystallite size upon annealing with a decrease in lattice strain and dislocation density. FEG-SEM image confirms the growth of well-aligned vertically oriented nanowires with Ag NP in the midway of each nanowire. The UV–Vis absorption spectra show that Ag NP's presence results in the appearance of a significant absorption hump in the visible range, thereby broadening the light absorption capability of β-Ga2O3. The improvement in crystalline quality and reduction in defects after annealing resulted in a better response for the annealed device. These results indicate that annealing the Ag NP-assisted β-Ga2O3 NW device could become a feasible option for high-speed photodetectors, as it demonstrates a faster photoresponse time and a lower turn-on voltage.

Machining hardening and dislocation modeling of magnesium alloys based on Fields-Backofen equation

Abstract Magnesium alloys are now widely used, and the Fields-Backofen equation is combined with an investigation of the properties of common magnesium alloys in order to be able to better analyze them. In this paper, some properties, applications and superiority of magnesium alloys are first analyzed, in which the plastic deformation mechanism slip and twinning of magnesium alloys are particularly explored in detail. Focusing on the stages and model of machining hardening dislocations of magnesium alloy, and combined with Fields-Backofen equation, a model of machining hardening and dislocations of magnesium alloy based on Fields-Backofen optimization is constructed. Then the constructed model was applied to stage III of machining hardening dislocations in magnesium alloy for performance testing. The predicted and actual maximum values of the model were 132MPa and 30MPa, which were in basic agreement with 130MPa and 32MPa. The saturation stresses ranged from 50 MPa to 6 MPa for temperatures from 100°C to 500°C when the strain rate of the dislocation processing stage was 10−2 s−1, and from 55 MPa to 10 MPa for temperatures from 100°C to 500°C at a strain rate of 10−3 s −1. Finally, only basal slip and twin initiation with higher saturation stresses were obtained at lower temperatures. As the temperature continues to increase, the dislocation density decreases, plastic deformation becomes easier, and then the saturation stress decreases.

Overcoming the trade-off between strength and ductility in austenitic stainless steel using a high-density pulsed electric current

This paper presents a method to overcome the trade-off between the strength and ductility in metals and clarifies its mechanism via a crystal structure analysis on type 316 austenitic stainless steel subjected to high-density pulsed electric current (HDPEC) treatment. Because of the HDPEC treatment, the fractions of low-angle grain boundaries (LAGBs) and high-angle grain boundaries (HAGBs) increased, while those of ∑ 3 twin boundaries (TBs) decreased significantly. An increase in the number of HAGBs and the formation of new LAGBs, which leads to achieving refined grains, was achieved by virtue of the change of misorientation angles and dislocation formation. Furthermore, the dissolution of Cr-rich precipitates occurred in the grain surroundings, which led to an increase in ductility of the material. The dislocation density, measured by the mean kernel average misorientation values, decreased because of the dislocation motion induced by HDPEC. The strengthening of the material was attributed to the grain refinement, and the increased ductility was attributed to the decreased dislocation density and decreased content of Cr-rich precipitates, which prevented precipitation hardening. The combination of these advantages contributed to overcoming the trade-off between strength and ductility.