Pre-annealed Sample Research Articles

Characterization of mechanical and corrosion properties of cryorolled Al 1100 alloy: Effect of annealing and solution treatment

Effect of annealing and solution treatment prior to cryorolling on the formation of initial structure influencing microstructure formation from nano to micron scale and resultant mechanical and corrosion properties in Al 1100 alloy has been studied in detail. Before subjecting to 50% cryorolling, samples were pre-annealed at 250 °C for 2 h and pre-solution treated at 540 °C for 1 h. X-ray diffraction and HRTEM techniques were used to understand the crystallite size, lattice strain and dislocation configuration in the processed alloy. The results indicate that the pre-annealed sample has the highest grain aspect ratio (4.43), the smallest crystallite size (37.53 nm), the highest lattice strain (9.12×10−3) and the highest dislocation density (45.16×1013 m−2) among the tested sample. The pre-annealed sample shows a significant improvement of 43.44%, 24.64% and 20.33% in hardness, ultimate tensile strength and yield strength. Both pre-annealed and pre-solution treated samples show improved corrosion resistance when compared to cryorolled samples without any pre-treatment, with the pre-annealed sample showing the best corrosion resistance.

Microstructure evolution of gadolinium doped cerium oxide under large thermal gradients

The effects of large thermal gradient annealing on the microstructure of 10 mol% gadolinium doped ceria (GDC) were investigated. GDC powder was prepared by solvent deficient method and sintered at 1650 °C for 10 h to achieve dense ceramics with ~8 μm grain size. The densified GDC samples were subsequently annealed using a 60 W infrared laser at over 2100 °C for 1 h under a thermal gradient equivalent to ~0.3–0.5 °C/μm. The post-annealed samples at 2150 °C for 1 h exhibit grains with average length and width of 37 and 28 μm, respectively. Electron backscattered diffraction (EBSD) analysis revealed that the post-annealed sample at 2150 °C consists of grains oriented close to five principal directions (<4 3 10>, <0 0 1> and <13 1 14> on [0 0 1], and <7 6 20> and <7 2 7> on [0 1 0]) within a tolerance angle of ±10°, whereas the grains of the pre-annealed sample are randomly oriented. Gadolinium diffuses 20–30 μm away from the irradiated surface, with the measured composition of regions deeper than 30 μm, Ce0.86Gd0.14O1.93, is close to that of the pre-annealed sample, Ce0.87Gd0.13O1.94. Enhancement of total conductivity of the post-annealed GDC (1.1 × 10-3 S cm-1 at 500 °C, and 2.1 × 10-2 S cm-1 at 700 °C) is observed when compared to the pre-annealed GDC (3.1 × 10-5 S cm-1 at 500 °C, and 1.7 × 10-3 S cm-1 at 700 °C), and points to the decrease in the grain boundary (GB) resistivity. This could be attributed to both the change in GB area and grain alignment.

Optical and structural studies on bio-synthesized ZnO using Citrullus lanatus peel extract

Bio-fabrication of ZnO films using plants, enzymes, and microorganisms has been recognized as an environmentally friendly procedure as an alternative to physical and chemical methods. In this research, the optical and structural properties of ZnO thin film have been investigated using UV-Vis spectrophotometer, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM), respectively. The ZnO films was prepared by spin-coating the mixed solution of Zn(NO3)2 and watermelon (Citrullus lanatus) peel extract on glass substrate. The ZnO films were then annealed at 400°C for 3h. The UV-Vis absorbance spectra show the strong absorption peaks occurs over a range of wavelengths of 220-380nm, and 190-235 nm for pre-annealed and annealed samples, respectively. The optical band gap of the samples was influenced by the heat treatment. The as-prepared samples synthesized at pH 8 is 3.73 eV and increased up to 5.4 eV after annealed at 400 °C for 3 h. This result suggested that pre-annealed sample has better photocatalytic activity compared to the annealed samples. The XRD pattern of the ZnO films exhibits the ZnO diffraction peaks that correspond to the hkl of hexagonal wurtzite structure. SEM image shows that the morphology of ZnO samples are spherical and rod-like microstructure.

Thermal History Dependent Aging Dynamics in a La-Based Metallic Glass

The atomic dynamics in metallic glasses (MGs) are closely related to their stability. Due to weak resistance to nanocrystallization at high temperatures, we interestingly observe the slow atomic dynamics happening in an as-quenched La-Al-Ni MG sample compared with a sub-Tg pre-annealed one when cooling from about 0.99Tg (Tg the glass transition temperature). An intermittent aging behavior also appears in the as-quenched MG sample only on cooling but not on heating, nor does it appear in the pre-annealed sample on both cooling and heating, indicating that it could be thermal history dependent and related to the existence of nanocrystals. Differently, a sudden atomic dynamics transition from fast to slow is observed in the pre-annealed MG sample when the pre-annealing temperature is approached upon cooling, resulting from the configuration recovery to a low energy state created by pre-annealing. Our findings demonstrate that the thermal history can give rise to significantly different aging dynamics of MGs , providing an in-depth understanding of structural relaxation in disordered materials on the atomic level.

Doping of TiO2 nanotubes with nitrogen by annealing in ammonia for visible light activation: Influence of pre- and post-annealing in air

The ∼60 nm wide and ∼2 μm long TiO2 nanotubes were obtained by anodization of Ti films sputtered on F-doped tin oxide glass. For N-doping the samples were annealed in ammonia atmosphere. The effect of pre- and post-annealing in air on the nature and amount of incorporated N was studied by X-ray photoelectron spectroscopy. By measuring the absorption spectra of the obtained samples and interpreting the corresponding Tauc plots it was shown that the sample annealed just in ammonia showed the highest visible light absorption even after sputtering cleaning and a decrease of N amount from 3.8% to 1%. Pre and/or post annealing in air led to smaller amount of incorporated N, that caused less pronounced absorption enhancement and smaller band gap narrowing compared to the sample annealed only in ammonia. By fitting of N 1 s line, the contribution that was assigned to substitutional N was detected only in the samples that did not sustained post-annealing. The study showed that post-annealing in air might lead to partial conversion of N atoms in TiO2 to oxidized nitrogen species that are easily removed with sputtering. It is also possible that substitutional nitrogen was suppressed by oxygen from air to move to interstitial site. Weakly bonded NOx surface species, which are cleaned away by sputtering, can be removed by post-annealing in air. Those surface species could act as sensitizers and when their amounts are reduced, the core absorption properties, as a result of interstitial incorporation of N in TiO2 structure, were revealed. Much lower visible light sensitization was achieved in the case of pre-annealed sample in comparison to sample without pre-annealing, regardless the same quantity and type of incorporated nitrogen.

Study of anisotropy, magnetization reversal and damping in ultrathin Co films on MgO (0 0 1) substrate

Ultrathin Co films of 3nm thickness have been prepared on MgO (001) substrate in presence or absence of substrate pre-annealing. Uniaxial anisotropy is induced in the samples due to the deposition under oblique angle of incidence. Along with the oblique deposition induced anisotropy, another uniaxial anisotropy contribution has been observed due to pre-annealing. However, no cubic anisotropy has been observed here as compared to the thicker films. Angle dependent ferromagnetic resonance (FMR) measurement confirms the presence of two anisotropies in the pre-annealed sample with ∼18° misalignment with each other. The two anisotropy constants were calculated from both superconducting quantum interference device (SQUID) magnetometry and FMR spectroscopy. The magnetization reversal is governed by nucleation dominated aftereffect followed by domain wall motion for the pre-annealed sample. Branched domains are observed for the sample prepared without pre-annealing which indicates grain disorientation of Co. However, in the thicker (25nm) Co films ripple domains were observed in contrary to ultrathin (3nm) films.

X-ray dose response of calcite—A comprehensive analysis for optimal application in TL dosimetry

The effect of various annealing treatments on dosimetric characteristics of orange calcite (CaCO3) mineral has been studied in detail. Quantitative analysis on the dose response shows that the 573K annealed sample showed sublinear dose response from 10mGy to 1Gy. The fading and reproducibility of this sample are also good enough for dosimetric application. However, a specific annealing treatment after irradiation shows some significant improvements in the dosimetric characteristics of the sample. The 773K pre-annealed sample, after X-ray irradiation post-annealing at 340K for 6min provides linear dose response from 10mGy to 3.60Gy, very less fading and good reproducibility. Moreover, this sample after post-annealing at 380K for 6min shows linear dose response from 10mGy to 5.40Gy when analyzed from the ∼408K thermoluminescence (TL) glow peak. Analysis of TL glow curves confirmed that the 1.30eV trap center in calcite crystal is the most effective trapping site for dosimetric application.

In-situ XRD investigation of re-crystallization and selenization of CZTS nanoparticles

Cu2ZnSnS4 nanoparticles have been produced by a facile and high-yield wet-chemical method at low synthesis temperature. In order to remove the organic residues the synthesis was followed by a pre-annealing procedure at 250 °C in nitrogen atmosphere. Data evaluation of ex-situ XRD measurements on the pre-annealed sample showed, that the diffraction pattern of the as-synthesized powder can be well modeled by diffraction of a hexagonal and a disordered cubic CZTS structure. The CZTS nanoparticles were annealed under nitrogen atmosphere up to 550 °C without and with the addition of selenium powder and diffraction patterns were recorded in-situ as a function of temperature in order to investigate the structural phase transitions during the re-crystallization and selenization of the powders. The in-situ XRD measurements showed a structural phase transition into the tetragonal CZTS structure for pure CZTS and with the addition of selenium. With the addition of selenium, an exchange reaction between sulfur and selenium during the heating process was observed by the shift in the diffraction peaks and subsequent refinement of the lattice parameters of the crystal structures.

Fractographic Analysis of 5052 Al-Mg Alloys Processed by Equal Channel Angular Pressing

In this work, ECAP technique has been applied to 5052 Al-Mg alloys where the alloys find wide application in building and construction, automotive, cryogenic and marine applications. The alloy samples extruded by ECAP with four different deformation routes for 4 passes each were tensile tested and the observation of the fracture surfaces were carried out by using digital camera and Scanning Electron Microscope (SEM). The experimental results showed that the initial pre-annealed sample showed cup and cone shape of fracture, whereas the fractured ECAPed samples of all deformation routes exhibited shear feature in which the fracture surface made an angle with pressing direction of ECAP. The change of size and shape of dimples fracture from larger and irregular shape dimples in initial sample to much smaller and grains-look like dimples in ECAPed sample indicating the grain refinement occurred after ECAP. Among the ECAP deformation routes applied, route BC resulted in smallest dimples size, i.e. about below 2 mm in average. The post annealing subjected to ECAP samples recovered almost completely the fracture feature and fracture morphology to that of the initial one, which was achieved after annealing at 300°C.

Coexistence of antiferromagnetism and ferromagnetism in Mn2+/CdS nanocrystals and their photophysical properties

Manganous ion doped CdS nanocrystals with different concentrations of Mn2+ have been synthesized by a chemical synthesis route. The as-synthesized Mn2+/CdS nanocrystals evince interesting optical emission properties; the intensity of cadmium vacancy emissions VCd decreases on the addition of the dopant ion, proving the displacement of cadmium by manganese which is accompanied by the appearance and enhancement of the Mn2+ d–d emission, 4T1 → 6A1. However, the intensity of the latter emission decreases on further increase in [Mn2+] due to strong cluster formation, such as Mn2+–Mn2+. The low temperature electron paramagnetic resonance measurements suggest strong antiferromagnetism due to strong exchange coupling between the spins of nearby Mn2+ centres both in pre- and post-annealed 5% Mn2+/CdS samples. These magnetic properties for pre- and post-annealed 5% Mn2+/CdS samples are explained by a core/shell (antiferromagnetism/ferromagnetism) model. The pre-annealed sample, on one hand, shows antiferromagnetic behavior with weak ferromagnetism below the Neel temperature, the latter due to uncompensated surface spins. On the other hand, annealing leads to the formation of more Mn2+–Mn2+ dimers or clusters due to ionic migration. This will result in increased antiferromagnetic character as compared to the pre-annealed sample. Both are confirmed by magnetization hysteresis curves at various temperatures. The electron microscopy images confirm the morphology prediction by XRD.

Dislocation engineering and its effect on the oxidation behaviour

Shot-peening of the surface of steel prior to oxidation can have a beneficial effect. Shot-peening can improve the oxidation resistance by introducing a localised plastic deformation in the near surface region resulting in an increase of the dislocation density. These dislocations can act in Cr-containing steels as fast diffusion paths for Cr promoting the formation of protective Cr-oxides. However, the effect of shot-peening has some limitations such as working temperature and microstructure. It has different effects on austenitic steels and ferritic martensitic steels. The effect of shot-peening can become futile due to recovery and recrystallisation of the alloy when subjected to higher temperatures for longer periods. In the present work, the main emphasis is put on the type of dislocation arrangement promoting the positive effect on the oxidation behaviour. Dislocation engineering was applied on shot-peened samples by means of some pre-annealing procedures resulting in a recovery process. During the process, dislocations were assumed to rearrange and form certain combinations nearer to the alloy grain boundaries. These arrays of dislocations can result in different oxidation behaviour. In the present study, 18 wt% Cr and 12 wt% Cr steels were shot-peened and vacuum annealed at 750°C for 1 h, 2 h, 3 h, 5 h and 15 h. Subsequently these steels were oxidised at 750°C. The mass gain in all cases is different for both steels, and in the case of both 12 wt% Cr and 18 wt% Cr steels the best oxidation resistance was achieved for the shot-peened +1 h pre-annealed sample.

Effect of pre-annealing treatment on the compressive deformation and damage behavior of ultrafine-grained copper

Abstract The effect of short-term pre-annealing treatment on the compressive deformation and damage behavior of ultrafine-grained (UFG) copper produced by equal channel angular pressing (ECAP) has been studied by mechanical tests and microstructural observations. It is found that a controlled 10-min pre-annealing treatment on the UFG copper below the recrystallization temperature can result obviously in a higher strength (higher flow stress level) and a higher flow stability (lower stress softening rate) under uniaxial compression, as compared to the case of as-ECAPed sample. Observations of surface and interior deformation damage features indicate that, compared to the as-ECAPed copper sample, the pre-annealed ECAPed copper at less than recrystallization temperature may exhibit a better compressive plastic deformation capacity, namely, the destructive deformation morphology of large-scale shear bands normally observed in compressed as-produced UFG copper sample would not appear in compressed pre-annealed sample, except for a relatively smooth surface morphology featuring some ‘step’ reliefs with a few discontinuous shear bands and non-propagation voids. Finally, the deformation mechanism of different kinds of severe plastic deformation (SPD) processed UFG materials as well as their pre-annealing effects are further discussed, and a general rule is summarized as follows: an appropriate selection of pre-annealing temperature and annealing time is needed for improving both strength and ductility of SPDed materials with a microstructure comprising equiaxed grains and well-defined grain boundaries.

Enhancement of the Electron Spin Resonance of Single-Walled Carbon Nanotubes by Oxygen Removal

We have observed a nearly 4-fold increase in the electron spin resonance (ESR) signal from an ensemble of single-walled carbon nanotubes (SWCNTs) due to oxygen desorption. By performing temperature-dependent ESR spectroscopy both before and after thermal annealing, we found that the ESR in SWCNTs can be reversibly altered via the molecular oxygen content in the samples. Independent of the presence of adsorbed oxygen, a Curie law (spin susceptibility ∝ 1/T) is seen from ~4 to 300 K, indicating that the probed spins are finite-level species. For both the pre-annealed and post-annealed sample conditions, the ESR line width decreased as the temperature was increased, a phenomenon we identify as motional narrowing. From the temperature dependence of the line width, we extracted an estimate of the intertube hopping energy; for both sample conditions, we found this hopping energy to be ~1.2 meV. Since the spin hopping energy changes only slightly when oxygen is desorbed, we conclude that only the spin susceptibility, not spin transport, is affected by the presence of physisorbed molecular oxygen in SWCNT ensembles. Surprisingly, no line width change is observed when the amount of oxygen in the SWCNT sample is altered, contrary to other carbonaceous systems and certain 1D conducting polymers. We hypothesize that physisorbed molecular oxygen acts as an acceptor (p-type), compensating the donor-like (n-type) defects that are responsible for the ESR signal in bulk SWCNTs.

Dislocation engineering and its effect on the oxidation behaviour

Shot-peening of the surface of steel prior to oxidation can have a beneficial effect. Shot-peening can improve the oxidation resistance by introducing a localised plastic deformation in the near surface region resulting in an increase of the dislocation density. These dislocations can act in Cr-containing steels as fast diffusion paths for Cr promoting the formation of protective Cr-oxides. However, the effect of shot-peening has some limitations such as working temperature and microstructure. It has different effects on austenitic steels and ferritic martensitic steels. The effect of shot-peening can become futile due to recovery and recrystallisation of the alloy when subjected to higher temperatures for longer periods. In the present work, the main emphasis is put on the type of dislocation arrangement promoting the positive effect on the oxidation behaviour. Dislocation engineering was applied on shot-peened samples by means of some pre-annealing procedures resulting in a recovery process. During the process, dislocations were assumed to rearrange and form certain combinations nearer to the alloy grain boundaries. These arrays of dislocations can result in different oxidation behaviour. In the present study, 18 wt% Cr and 12 wt% Cr steels were shot-peened and vacuum annealed at 750°C for 1 h, 2 h, 3 h, 5 h and 15 h. Subsequently these steels were oxidised at 750°C. The mass gain in all cases is different for both steels, and in the case of both 12 wt% Cr and 18 wt% Cr steels the best oxidation resistance was achieved for the shot-peened +1 h pre-annealed sample.

Quantitative determination of depth carrier profiles in ion-implanted Gallium Nitride

We studied the electrical activation of Si+ ions implanted at multiple energies (80 and 180keV) and with a total fluence up to 2.7×1014cm−2 in heteroepitaxial GaN films on sapphire. Calibrated scanning capacitance microscopy (SCM) is proposed as a method to measure the depth carrier profile after high temperature annealing (1100–1200°C). Si electrically active fractions of 18% and 36% were obtained after low ramp rate furnace annealing at 1100 and 1200°C, respectively. Interestingly, the dopant activation was significantly improved to 63% in the case of a rapid pre-annealing process at 1100°C before the 1200°C furnace annealing process. Furthermore, the ionised carrier fluence obtained by Hall measurements at room temperature exhibits a significant improvement for the 1100°C RTA pre-annealed sample. This value is in good agreement with the ionised fluence calculated from the active Si profile from SCM, considering a ∼20meV ionisation energy for Si donors in GaN.

Effect of annealing on torsion giant impedance of Co-rich amorphous wires with vanishing magnetostriction

Torsion giant impedance (TGI) ratio, (ΔZ/Z)ξ, has been measured in as-cast and annealed (Co0.94Fe0.06)72.5B15Si12.5 amorphous wire. Two-step current annealing has been employed: pre-annealing (550 mA, 2 min) plus current annealing under torsion stress (33 π rad/m, 450 mA, up to tann=105 min). Pre-annealing results in a drastic increase of (ΔZ/Z)ξ (from 155% to 260%) and decrease of the asymmetry. The consequent annealing under torsion of pre-annealed sample gives rise to the appearance of significant asymmetry of the TGI. In this case (ΔZ/Z)ξ has a tendency to achieve rather asymmetric shape with a sharp maximum at certain torsion ξm. The value of ξm depends on the time of annealing under torsion and on the applied torsion during the annealing. The asymmetric shape of the (ΔZ/Z)ξ in as-cast state and after torsion annealing could be ascribed to the spontaneous or induced helical anisotropy, which can be compensated by the application of certain torsion stress. Evolution of (ΔZ/Z)ξ(ξ) and ξm (ξ) as a function of annealing time reflects the kinetic of the induced magnetic anisotropy.

Influence of annealing on the DC-electrical transport in undoped amorphous silicon

In undoped a-Si:H the changes in temperature dependence of dc conductivity due to thermal annealing were measured. It was found that the downward kink originally observed in the Arrhenius plot of conductivity for pre-annealed sample could be gradually erased by subsequent annealing steps of increasing temperature and/or increasing annealing time. Conductivity measurement carried out during annealing showed that even at high temperature (e.g. at 350°C) more than 2 hours were needed to achieve the thermal equilibrium state. Our results show that for samples in which the thermal equilibrium is fully developed the kink is not observable any longer.

Correlation between changes in Curie temperature and electrical resistivity during structural relaxation in Fe27Ni53P14B6 metallic glass

Changes in Curie temperature (ΔTc, electrical resistivity (Δϱ/ϱ) and volume (ΔV/V) caused by isochronal annealing in as-quenched and pre-annealed Fe27Ni53P14B6 metallic glasses were compared. It was found that the ΔTc against annealing temperature (Ta) curves in as-quenched and pre-annealed samples are very similar to the Δϱ/ϱ against Ta curves. Particularly, almost a linear relationship was observed between ΔTc and Δϱ/ϱ in the pre-annealed sample. The results strongly suggest that the origins of both ΔTc and Δϱ/ϱ during structural relaxation in the pre-annealed sample are attributed to identical, reversible, short-range ordering.

Declustering and melting threshold study in laser irradiated Si(As)

The sheet resistivity of 40-keV, 1016 As/cm2-implanted Si decreases by a factor of 3 after irradiation with a suitable energy density of Nd:YAG laser at 1.06 or 0.53 μm. The changes in conductivity occur with the melting and quenching of the surface layer as indicated by profile broadening, and they are associated with the declustering process during solidification. The threshold energy density for melting is studied. At 0.53 μm, the threshold is the same (∼0.4 J/cm2) for both as-implanted and thermally preannealed Si. At 1.06 μm, the threshold for the as-implanted sample is ∼5 J/cm2, while the threshold for the preannealed sample is ∼10 J/cm2. These results are in agreement with the absorption changes due to crystalline structure alterations and dopant.

Laser irradiation of furnace preannealed (111) ion implanted silicon

The regrowth of self-ion implanted amorphous layer on (111) silicon substrate induced by laser pulse is shown to require less energy density in furnace preannealed sample. After 450 °C 30-min thermal treatment, the energy threshold is reduced about 30%. The extended defects near the threshold exhibit different geometrical arrangement.