Early Stage Of Annealing Research Articles

Enhancement of homogeneity of grain boundary microstructure by magnetic annealing of electrodeposited nanocrystalline nickel

The effect of a magnetic field on grain growth in nanocrystalline nickel produced by electrodeposition was investigated. Magnetic annealing was carried out at 573 K for 120 s to 1.8 ks under a direct current magnetic field of 1.2 MA/m (15 kOe). A magnetic field enhanced grain growth at the early stage of annealing was observed, which produced a homogeneous grain boundary microstructure.

Microstructure and growth kinetics of the Mo 5Si 3 and Mo 3Si layers in MoSi 2/Mo diffusion couple

The microstructures and growth kinetics of the Mo 5Si 3 and Mo 3Si layers in the MoSi 2/Mo diffusion couple was investigated using optical microscopy, field-emission scanning electron microscopy, electron probe microanalyzer, and cross-sectional transmission electron microscopy. The MoSi 2/Mo diffusion couple was made by chemical vapor deposition CVD of Si on a Mo substrate at 1100 °C and annealed at temperatures between 1250 and 1600 °C in an Ar atmosphere. Simultaneous parabolic growth of the Mo 5Si 3 and Mo 3Si layers was observed at the early annealing stage of the MoSi 2/Mo diffusion couple. From the marker experiments using ZrO 2 particles, the growth mechanism of the Mo 5Si 3 and Mo 3Si layers and the dominant diffusion element in each phase were revealed. The difference in the growth rates of Mo 3Si layer between the MoSi 2/Mo diffusion couple and the Mo 5Si 3/Mo diffusion couple was explained by a multiple layer growth model.

Microstructural studies of crystallization of a Zr-based bulk metallic glass

The evolution of the microstructure of a Zr 52.5Ti 5Cu 17.9Ni 14.6Al 10 alloy during isothermal annealing near the glass transition temperature was studied by transmission electron microscopy (TEM), small-angle neutron scattering (SANS), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). In situ SANS experiments show that an interference maximum develops with isothermal annealing, which is attributed to decomposition in the undercooled liquid state. In agreement with these results, TEM observations show the formation of structural inhomogeneities in the glassy alloy in the early stages of annealing, which are correlated with the partially crystalline microstructure in the later stages. The TEM and XRD data show that finally two nanocrystalline phases form after long-term annealing as a result of the decomposition process in the early stages. Direct evidence for decomposition was obtained using Z-contrast imaging technique that showed a systematic variation of the Zr concentration between the two nanocrystalline phases.

Effects of time and temperature on physical aging of polycarbonate

The effects of time and temperature on physical aging of polycarbonate (PC) have been investigated by differential scanning calorimetry (DSC). Aging of PC is a progressive process involving several mechanisms. The results agree with the concept of lateral entanglement. An increase in the density of entanglement with aging stage leads to a more stronger morphology that requires a higher temperature and a higher energy to disentangle. The method used to calculate the excess enthalpy from the DSC scan affects the measurement results and the interpretation of the aging process. The subtraction between the DSC scans of aged and de-aged samples would include the change in both the upper and the lower endothermic peaks. The method of extrapolating the base line above T g back in temperature until it touches the peak would indicate only the change in the upper endothermic peak at the early stage of annealing, when the lower peak is small. During annealing, rejuvenation and aging take place simultaneously. At the early stage of annealing, rejuvenation is more important and can be easily detected by DSC analysis. At a later annealing stage, aging becomes predominant and outweighs the rejuvenation process.

Morphology of Thin Films of Diblock Copolymers on Surfaces Micropatterned with Regions of Different Interfacial Energy

Self-assembled (SA) films of octadecyltrichlorosilane were patterned by exposure to X-rays in air through a mask to produce chemically patterned surfaces. The irradiated regions of the SA films underwent surface chemical modification from nonpolar, hydrophobic surfaces to polar, hydrophilic surfaces. The degree of chemical modification increased with increasing exposure dose. The behavior of thin films of symmetric poly(styrene-b-methyl methacrylate) (P(S-b-MMA)) was investigated on the chemically patterned surfaces exposed to X-rays at doses ranging from 800 to 2000 mJ/cm2. P(S-b-MMA) films exhibited symmetric, neutral, and asymmetric wetting on these surfaces with increasing dose. The area and height of islands and holes that formed on the free surface of the films depended on the interfacial energy between the film and the surface. If the difference in interfacial energies (Δγ) between the surface and both PS and PMMA was small, islands or holes formed that had a smaller average area and smaller step height than islands or holes that formed on surfaces where Δγ was large. Additionally, perpendicular lamellae were detected at the edge of islands when Δγ was small but were not detected at the edge of islands when Δγ was large. The island/hole morphologies observed over regions where Δγ was small were concluded to be the result of slow rates of formation and growth of the topography. Films of initial thickness from 1.75 to 2.75Lo, where Lo is the bulk lamellar period, were studied on chemically patterned surfaces where both exposed and unexposed regions had large values of Δγ. On these surfaces, regions of the film were observed to remain flat and featureless even when the film thickness did not equal a quantized value of the thickness. These flat regions were concluded to be due to either mass transport of excess material from island-forming regions across the pattern boundaries to regions with deficits (hole-forming regions) or deformation of lamellae in the outer layer of the block copolymer film. On surfaces with large values of Δγ, ordering was fast and allowed large-scale cooperation between adjacent regions of the polymer film to set up the film morphology during the very early stages of annealing.

Simultaneous growth mechanism of intermediate silicides in MoSi 2/Mo system

The simultaneous growth mechanism of the Mo 5Si 3 and Mo 3Si layers in the MoSi 2/Mo diffusion couple was investigated using optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA) and X-ray diffraction (XRD). The MoSi 2/Mo diffusion couple was made by chemical vapor deposition (CVD) of Si on the Mo substrate at 1100°C for 5 h and annealed at temperatures of 1250 and 1600°C, respectively, in an argon atmosphere. Simultaneous parabolic growth of the Mo 5Si 3 and Mo 3Si layers was observed at an early annealing stage of the MoSi 2/Mo diffusion couple. From the location of Kirkendall voids observed in the Mo 5Si 3 layer and the change of columnar diameter and texture of Mo 5Si 3 grains, simultaneous growth mechanism of the Mo 5Si 3 and Mo 3Si layers was found. The phase transformation of MoSi 2 into Mo 5Si 3 and Si contributed to approximately 30% of the total thickness of Mo 5Si 3 layer, but the remainder of Mo 5Si 3 layer and the Mo 3Si layer with small thickness were formed by the diffusion reaction of the released Si and Mo substrate. These results indicated that Si was the only diffusing element in the Mo 5Si 3 phase.

Early Stages of Film Creation in Thin Diblock Copolymer Films

Thin poly(styrene-block-p-methylstyrene) diblock copolymer films on top of silicon substrates were examined right after preparation and during the early stages of annealing. Using specular and off-specular X-ray scattering as well as scanning force microscopy, the film morphology is determined. With the spin-coating technique films are prepared which exhibit a roughness correlation between the substrate and the copolymer surface within a limited film thickness and molecular weight range right after preparation. The transferred part of the roughness spectrum of the substrate is probed and explained as a morphology of a frozen liquid with a surface bending rigidity. During annealing the energetically unfavorable roughness replication decays, and an internal ordering is formed. The decay of long-range correlation is explained by a surface diffusion where diffusion is slowed down as compared to bulk behavior.

Identification of the nitrides formed during the annealing of a low-carbon low-aluminium steel

The precipitation of a low carbon low aluminium steel with a sub-stoichiometric [Al]/[N] atomic ratio was investigated during an annealing at 600°C by Transmission Electron Microscopy (TEM) and chemical analyses by X-ray Energy Dispersive Spectroscopy (EDX) on thin foils and carbon extraction replicas. These studies showed that in this steel, the precipitates which form have a platelet-like morphology associated with a cubic structure (with a = 0.412 ± 0.005 nm) and the following orientation relationship with iron: (001)p // (001)Fe and [110]p // [010]Fe. The EDX microanalyses of these precipitates revealed that they contain, in addition to aluminium and nitrogen, chromium and/or manganese. It was suggested that in the early stages of annealing, the initial precipitates are of CrN or (Cr,Mn)N type. During a prolonged annealing, they serve as nucleation sites for the final precipitates of (Al,Cr)N and (Al,Cr,Mn)N type.

Influence of Deformation Temperature on Microstructure Evolution and Static Recrystallization of Polycrystalline Copper

Static recrystallization was studied in warm and hot deformed polycrystalline copper (99.99%). Samples were compressed to a strain of 0.25 at 573 K and 723 K at a strain rate of 2×10−1 s−1, quenched in water, and subsequently isothermally annealed at 673 K . Static recrystallization kinetics were found to be faster in samples hot-deformed at 723 K in spite of the lower level of stored strain energy. In all cases nucleation at the early stages of annealing takes place by bulging of serrated grain boundaries. Deformation at 723 K introduces higher orientation gradients evolved along serrated grain boundaries than those at 573 K . It is shown that static recrystallization is controlled not only by the level of stored strain energy, but also by the specific features of sub-grain structures formed in local regions.

(Bi,Pb) 2Sr 2Ca 2Cu 3O x phase formation in a silver-sheathed multifilament tape

The 2223 formation is studied on tape samples air-quenched from the annealing temperature. The morphology, dimension and distribution of 2223 phase at the early stage of annealing are revealed by SEM on a scale of several grains. Based on this observation a tentative model of nucleation/growth is proposed.

Analysis of Interface Microstructure Evolution in Separation by IMplanted OXygen (SIMOX) Wafers

We have examined the evolution of interface microstructures in Separation by IMplanted OXygen (SIMOX) wafers during annealing, and have proposed a model that can reasonably explain the kinetics of interface evolution. There are two dominant mechanisms in the evolution of a square microstructure: coalescence in the early stage of annealing and diffusion after a sufficient period of annealing. The diffusion of oxygen is the driving force in the evolution of interface flatness.

Transfer of a chemical substrate pattern into an island-forming diblock copolymer film

We investigate the transfer of a chemical pattern on a substrate into a symmetric diblock copolymer thin film of poly(styrene-2-vinylpyridine) (PS-PVP). The substrates have patterns of self-assembled monolayers (SAMs) produced by microcontact printing H3C-terminated (H3C-) SAM stripes alternating with HO-terminated (HO-) SAM stripes. The PS-PVP lamellae over the H3C-SAM have a defect structure that attracts excess PS-PVP that would normally form islands on a uniform HO-SAM stripe. We seek to understand the process that limits our ability to accommodate all excess polymers on top of the H3C-SAM. In the early stages of annealing, waves of thickness develop from the H3C/HO-SAM boundary and propagate into the film over the HO-SAM. For very short annealing times, the wavelength λ of these thickness waves is constant at any given time for all grating periodicities. Large amplitude patterns develop when λ=2d/(2n−1), where d is the width of the HO-SAM stripe and n is an integer ⩾1. Such patterns suggest constructive interference of the thickness waves and indeed much lower amplitudes over the HO-SAM stripes are observed when λ=d/n (destructive interference). This behavior seems close to that seen for surface-directed spinodal decomposition waves in thin films of binary polymer mixtures. We achieve more complete transfer of excess copolymers from the HO-SAM stripe to the H3C-SAM ones if the film is preordered under a confining layer that does not permit the formation of surface features.

Grain growth kinetics in nanostructured nickel

Grain growth kinetics for nanostructured nickel was studied by means of isothermal and isochronal annealing and TEM. The range of temperature for the isothermal and isochronal annealing has been selected between 603K and 683K. The isothermal curves for grain size show that an explosive grain growth occurs in the early stage of annealing, but the growth returns normal beyond grain size of 600 nm. The change in microstructure in the annealed specimens has been investigated by TEM. The activation energy for the grain growth was found to be 102 kJ/mol from the plot of grain growth rate vs. 1/T, which is comparable to the activation energy for diffusion at the grain boundaries. The time exponent was obtained from the plot of grain size difference vs. annealing time, and found to be in the range of 1/6–1/7.

Reduction of copper oxide with graphite by mechanical alloying

The reduction of CuO with different amounts of C (CuO:C = 2:1, 2:1.5, and 2:2 molar ratios) driven by mechanical alloying was examined by x-ray diffraction and transmission electron microscopy. It was found that reduction behaviors are closely related to the carbon content. The reduction of CuO for the mixture with 1 mol of carbon follows a two-step process; i.e., CuO → Cu → Cu2O. However, the CuO can be completely converted to Cu for the mixtures with higher carbon content. A tentative model in terms of solid-state reactions at the interfaces is proposed to explain the effect of carbon content. Additionally, the thermal responses of the premilled mixtures were investigated by thermogravity and differential thermal analysis followed by x-ray identification. Contrary to mechanical alloying, reduction of CuO during thermal treatment follows a transition sequence of CuO → Cu2O → Cu. The preferential formation of Cu2O at the early annealing stage is probably due to the involvement of gaseous reduction.

Structural development in the early stages of annealing of sol–gel prepared lead zirconate titanate thin films

Lead zirconate titanate (PZT) thin films on platinized silicon were fabricated and their structural development upon annealing was characterized by x-ray diffraction and transmission electron microscopy (TEM). The amount of a transient intermetallic phase Pt3Pb was found initially to increase with annealing time and to decay after reaching a maximum. The kinetic process of growth and decay was simulated by using the Avrami equation. The Avrami coefficient n and growth rate constant k were determined by comparing the experimental results and the simulated curves, from which activation energies of 40 and 145 kJ/mol were obtained for the growth and decay of the intermetallic Pt3Pb phase, respectively. The perovskite PZT was found by using TEM to nucleate epitaxially on top of the Pt3Pb phase. Evidence is presented that the Pt3Pb phase plays a major role in determining the crystallite’s orientation at the nucleation stage of the perovskite PZT. This depends strongly on the annealing temperature and the orientation changes little during the following growth process.

Oxygen related donors in Czochralski-grown silicon annealed at 465–650°C

Generation of new donors (NDs) as a result of annealing of boron-doped CZ-silicon at 650°C under a nitrogen ambient for different durations was studied. The results of the influence of oxygen and carbon on donors generated as a result of annealing treatment to the oxygen rich and carbon lean CZ–Si samples with different resistivities are reported. Behaviour of oxygen related donors from thermal donors (TDs) to NDs in the transition region (465°C–540°C) are also studied. It was found the donor generation rate is very rapid in the early stage of annealing and decreases later on. Carbon and oxygen precipitations as a function of annealing time showed that the donor generation depends on both carbon and oxygen concentration. It was found that carbon enhances the ND formation [1] which is higher in the sample with less carbon concentration. Donors generated as a function of carbon reduction were also studied and a steep rise in the donors generated is attributable to the saturation of carbon reduction.

Evolution of Ge islands on Si(001) during annealing

The evolution of the shape and size distributions of Ge islands on Si(001) during annealing after deposition has been studied at different temperatures and effective coverages. The initial distributions of square-based pyramids, elongated “hut” structures, faceted “dome-shaped” islands, and much larger “superdomes” depends on the deposition conditions. During annealing after deposition, the islands coarsen over a limited range of times and temperatures. Those pyramidal-shaped islands that grow transform to faceted, dome-shaped islands as they become larger. Initially dome-shaped islands that dissolve transform to a pyramidal shape as they become smaller during the process of dissolving. Outside of this coarsening regime, the islands can achieve a relatively stable, steady-state configuration, especially at lower temperatures. At higher temperatures, intermixing of Si into the Ge islands dominates, decreasing the strain energy and allowing larger islands to form. At lower and intermediate temperatures, the initial wetting layer is metastable, and some Ge transfers to the islands during the early stages of annealing.

Morphological development with time for immiscible polymer blends with an in situ compatibilizer under controlled shear conditions

We have studied morphological development with time under controlled shear condition for 75/25 wt/wt poly(butylene terephthalate) (PBT) and polystyrene (PS) blend having various amounts of poly(styrene- ran-glycidyl methacrylate) (PS-GMA) as an in situ compatibilizer prepared by solution blending method. The morphology of the blend without PS-GMA develops via a coarsening process during an annealing at higher temperatures. However, the dispersed domain size of the blend with PS-GMA increases slowly at an early stage of annealing, and then levels off. This is due to the in situ formation of graft copolymers at the interface. As the initial amount of PS-GMA in the blend increases, enough of the copolymers for the dispersed domain size in the blend to be levelled off are formed at shorter times. An oscillatory shearing with the frequency range 0.5–10 rad s −1 can induce the coalescence of the dispersed domain in the blend without PS-GMA. However, for the blend with PS-GMA the shear-induced coalescence of the dispersed domain is successfully suppressed by the graft copolymers formed in situ at the interface. The time evolutions of shear storage modulus ( G′) and complex viscosity ( η*) for blends with PS-GMA are strongly affected by the blend morphology which in turn depends on the initial amount of PS-GMA in the blend.

Effects of Annealing on the Magnetic Properties and Structures of Sputtered Co–Pt Alloy Thin Films

The effects of annealing on the in-plane coercivity and the crystal structure have been investigated for sputtered Co–Pt alloy thin films with Pt content between 0 and 50 at.%. The coercivity of a Co50Pt50 film drastically increases at annealing temperatures above 800 K. The coercivity increase corresponds to the formation of an L10 ordered phase, which is formed by the annealing at 940 K in less than 1 h. A maximum coercivity of 920 kA/m (11.5 kOe) is more than that reported for a bulk Co–Pt alloy. The grain size drastically increases in the early stage of annealing. (The grain size should be decreased for the use of the Co–Pt films as high-density recording media.)

Fabrication of silicon nitride–Silicon oxynitride in-situ composites

Fine-grained β-Si 3N 4 ceramics were fabricated from fine and uniform β-powder by hot-pressing at 1700–1750°C using different sintering aids (cordierite, Y 2O 3–MgO, and Y 2O 3–Al 2O 3). The microstructural development of hot-pressed bodies was studied in annealing at 1750°C for 0·5 to 8 h. When Y 2O 3–MgO and Y 2O 3–Al 2O 3 were used as sintering aids, fine and uniform microstructures were maintained because of the low driving force for grain growth of β-Si 3N 4. When cordierite was used as an aid, β-Si 3N 4 reacted with the SiO 2 in the additive and developed a bimodal microstructure with large Si 2N 2O grains in fine β-Si 3N 4 matrix grains after annealing. Local segregation of β-Si 3N 4 grains was observed after hot-pressing. Nucleation of Si 2N 2O occurred at a part of the segregation surface in the early stage of annealing. Si 2N 2O grains grew selectively with annealing time, resulting in improved fracture toughness.