Average Crystal Grain Research Articles

High (1 1 1) orientation poly-Ge film fabricated by Al induced crystallization without the introduction of AlOx interlayer

High (111) orientation poly-Ge film was fabricated by Al induced crystallization (AIC), where Al and amorphous Ge (a-Ge) layers were continuously deposited by magnetron sputtering, avoiding the deliberate introduction of an AlOx interlayer. To improve the quality of poly-Ge film, the ratio of thicknesses of Al and a-Ge was adjusted. Electron backscattered diffraction (EBSD) results revealed that the (111) fraction of poly-Ge film reached 97% and the average crystal grain size surpassed 100μm.

Effects of homogeneous irradiation of electron beam on crystal growth and thermoelectric properties of nanocrystalline bismuth selenium telluride thin films

The effects of homogeneous irradiation of electron beam (EB) on the crystal growth and thermoelectric properties of nanocrystalline bismuth selenium telluride thin films were investigated. The thin films were prepared using a flash evaporation method, after which EB irradiation was performed under N2 at room temperature at an accelerated voltage of 0.17MeV. SEM revealed that the untreated thin film was composed of a large quantity of rice-like nanostructures. With increasing the EB irradiation dose, a number of nanodots with diameters of less than 10nm became visible on the surface of the rice-like nanostructures. The crystallinity and the crystal orientation were enhanced with increasing EB irradiation dose while the average crystal grain size remained almost the same size as that of the untreated thin film. In terms of thermoelectric properties, the mobility of the thin films was enhanced as the EB irradiation dose was increased while the carrier concentration was not greatly changed. As a result, both the electrical conductivity and the Seebeck coefficient were improved with increasing EB irradiation dose. Consequently, even though there is still room for further improvement, the power factor was enhanced around sevenfold (from 0.14 to 0.96μW/cm/K2) by the EB irradiation treatment.

Nanocrystalline structure and soft magnetic properties of nickel–molybdenum alloy thin films electrodeposited from acidic and alkaline aqueous solutions

Nanocrystalline nickel–molybdenum (Ni–Mo) alloy thin films were electrochemically synthesized in acidic and alkaline aqueous solutions. Transmission electron microscope bright-field images and electron diffraction patterns of the electrodeposits made it obvious that pure Ni consists of a submicron crystalline phase with the grain diameter of several hundred nanometers, while Ni–20 %Mo alloy was composed of a nanocrystalline phase with the grain diameter of a few nanometers. It was estimated that the nanocrystalline phase of electrodeposited Ni–Mo alloy thin films was introduced by the formation of supersaturated Ni–Mo solid solution phase with Mo content in the deposit more than 20 %. Submicron crystalline pure Ni thin films were hardly magnetized in perpendicular direction to the film plane while the nanocrystalline Ni–20 %Mo alloy thin films were isotropically magnetized. It was suggested that the isotropical magnetization behavior was caused by decreasing the demagnetizing field and the magneto crystalline anisotropy with a decrease in the magnetic moment and the average crystal grain size. Coercive force of a submicron crystalline pure Ni thin film electrodeposited from an acidic aqueous solution was ca. 100 Oe while that of a nanocrystalline Ni–20 %Mo alloy thin film electrodeposited from an alkaline aqueous solution was only 1∼2 Oe. Soft magnetic properties of Ni–Mo alloy thin films electrodeposited from an alkaline aqueous solution were better than that from an acidic aqueous solution and it was improved with an increase in Mo content in the deposit. It was estimated that the electrodeposited Ni–Mo alloy catalysts could be easily recovered with magnetic field less than 1 kOe.

Microstructural properties of electrochemically prepared Ni–Fe–W powders

A nanostructured Ni–Fe–W powder was obtained by electrodeposition from ammonium citrate electrolyte within the current density range of 500–1000 mA cm−2 at the electrolyte temperature of 50 °C–70 °C. XRD analysis shows that the powder contains an amorphous matrix having embedded nanocrystals of the FCC solid solution of iron and tungsten in nickel, with an average crystal grain size of 3.4 nm, a high internal microstrain value and a high density of chaotically distributed dislocations. EDS analysis exhibits that the chemical composition of the Ni–24%Fe–11%W powder does not depend upon current density and electrolyte temperature due to the diffusion control of the process of codeposition of nickel, iron and tungsten.SEM micrographs show that the electrodeposition results in the formation of two particle shapes: large cauliflower-like particles and small dendrite particles. The cauliflower-like particles contain deep cavities at hydrogen evolution sites. Cavity density increases with increasing deposition current density. Smaller powder particles are formed at higher temperatures and at higher current densities.During the first heating, relative magnetic permeability decreases reaching the Curie temperature at about 350 °C and after cooling exhibits a 12% increase due to the performed relaxation process. Following the second heating to 500 °C, the magnetic permeability of the powder is about 5% lower than that of the as-prepared powder due to crystallization of the amorphous phase of the powder and the crystal grain growth in FCC phase.

Microstructure of new composite electrocatalyst and its anodic behavior for chlorine and oxygen evolution

The first layer of active coating made from a rutile-structured solid solution of ruthenium and titanium dioxides having an average crystal grain size of 30nm was thermally deposited on an adequately prepared titanium metal substrate. Then, at a temperature of 500°C, the second layer was formed on the first layer from a mixture of amorphous particles of metallic platinum and rutile-structured iridium dioxide nanocrystals having an average crystal grain size of 26nm.Rutile phase nanocrystals are characterized by a high density of chaotically distributed dislocations and high internal microstrain values. The coatings exhibit a compact granular morphology without cracks on the surface. Their catalytic activity is similar to that of conventional DSAs for the anodic oxidation of chloride ions from both concentrated and dilute sodium chloride solutions. The anodic current efficiency both during chlorate formation and active chlorine production was several percentage points higher in electrolyzers containing these anodes than in those containing DSAs. The catalytic activity of anodes having these coatings is about 50mV lower than that of DSAs and about 350mV higher than that of lead/antimony alloy electrodes, for oxygen evolution from acid sulfate solutions (0.5moldm−3 H2SO4) characteristic of processes for the production of some metals. An accelerated corrosion test showed that the stability of the double-layer anodes is about twelve-fold higher than that of conventional DSAs.

Correlation between crystal grain sizes of transparent ceramics and scintillation light yields

Light yields of Y2O3 ceramics are different from specimen to specimen. Nature of this phenomenon is not clear yet. Furthermore, origin of emission peaks for Y2O3 is not well understood. The results reported suggest that the emission derived from trapped excitons originates from the defects accumulated in the grain boundaries of the ceramics. In this paper, average grain size is introduced in order to evaluate defects inside the ceramics. Relationship between average crystal grain size and scintillation light yield is demonstrated.

Large crystal grain niobium thin films deposited by energetic condensation in vacuum arc

This article presents evidence for unprecedented, large crystal grain size in ∼1μm thick Nb films that were grown on sapphire and copper substrates using a vacuum arc process called coaxial energetic deposition CED™. Most other deposition techniques with low adatom energy produce amorphous or small crystal-grain films. Typically, high substrate temperatures and annealing steps are required to form the large, highly connected grains. The CED™ technique deposits from plasma consisting of a nonequilibrium, high energy (50–150eV) ion population produced from the ionized source material. At the substrate these fast ions break up columnar structures, intermix with the first few atomic layers of the substrate to improve adhesion, and form dense films at lower substrate temperatures than are typical for low adatom energy techniques, such as physical vapor deposition (PVD). Nanoscale features of the thin films were examined using electron backscatter diffraction (EBSD). The films’ cryogenic state electrical properties were characterized by their residual resistivity ratio (RRR) and superconducting transition temperature (Tc). RRR of ∼77 and Tc∼9.2K were measured on a Nb thin film deposited on a sapphire substrate. EBSD and x-ray diffraction measurements indicated that the sapphire substrate thin films have single crystal structure, with a Nb {110} crystal plane monolithically aligned and parallel to the sample surface. Nb thin films on an ∼400°C Cu substrate had average crystal grain size of 50μm, which is an order of magnitude larger than that which is typical of films grown by PVD. The crystal structure of CED™ thin films is comparable to that of polycrystalline bulk Nb material, which is the state of the art for superconducting radio frequency (SRF) particle accelerators such as at the Thomas Jefferson National Accelerator Facility (JLab). The films’ novel crystal features suggest that CED™ is a promising technique to coat Nb thin films for lower cost SRF particle accelerators. Further studies of the nanoscale grain boundary features would shed light on the role played by these features in determining the performance of SRF cavities using such thin films on Cu.

Influences of magnetic treatment on microstructure densification of diamond saw segments

The heated test pieces were treated with alternating magnetic field by self-made experimental facility firstly. And influences of magnetic treatment on microstructure densification of Diamond Saw Segments were studied through hardness testing, ultrasonic testing, metallurgical structure and fracture pattern analysis by comparative method. The mechanism of magnetic treatment is analyzed and discussed in the end. The results show that the hardness of test pieces after magnetized are harder than before, that HRB hardness is improved by 3.58 on average. The sound path and amplitude of echo wave both decrease in test pieces after magnetized. The relative pad value of echo wave is regularly related with the microstructure densification, what is profound to further establish the regularity studying the degree of matrices densification using ultrasonic testing. The pores become few and pore shape gradually spheroidizing with the magnetic treatment, and matrices are more homogeneous and compact than the without by metallographic microscope. The degree of matrices densification is further improved after magnetized. The average crystal grain size is finer than the without, and the reason of grain refining is that densification of diamond saw blade improved. Magnetic treatment can act as one kind of effective technique to improve the microstructure densification of diamond saw segments.

Structure and magnetic properties of bulk nanocrystalline SmCo6.6Nb0.4 permanent magnets

The crystal structure and magnetic properties were studied for the bulk nanostructural permanent magnet SmCo6.6Nb0.4 prepared by spark plasma sintering method. The magnet crystallizes in a single phase with a hexagonal TbCu7-type crystal structure after the sintering process. Rietveld fitting results show that the alloying element of Nb prefers to occupy the 3g site. Microstructure observation indicates that the average crystal grain size is about 30nm. The coercivity decreases almost linearly from 2.8to0.5T with increasing temperature from 300to773K. A remanence enhancement resulting from intergrain exchange coupling among the fine grains was also observed.

2703 RCP加工を施したAZ31マグネシウム合金切削チップ押出固化材における組織と曲げ特性(S19-1 アルミニウム合金,マグネシウム合金(1),S19 アルミニウム合金およびマグネシウム合金の創製と加工技術)

In this study, using the extrude AZ31 magnesium alloys through machine processed chips (machined chips extrusion) and RCP processed chips (RCPed chips extrusion), it was researched the relationship between the twin-crystal occurrence during the bending process and difference of bending property due to the grain size of the extruded magnesium alloys. As a result, under 3μm of average crystal grain size of the machined chips extrusion, it became definite to be possible to bend even on R/t=1 (R:bending radius, t:thickness). But, on the RCPed chips extrusion of average crystal grain size 1.33μm, crack happened during bending test. It is considered that there are many oxide or intermetallic compounds on grain boundary of RCPed extrusion, and these compounds restrain to transform during bending test.

Effects of fundamental process factors on the properties of AZ31 magnesium alloy strip produced by the melt drag process

The purpose of this study is to produce magnesium alloy strip of good quality at lower cost than the conventional rolled sheet. Melt drag process has many advantages such as the low production cost and the improved microstructure because the strip is made directly from molten metal by rapid cooling. In this study, we designed the experimental device for molten magnesium casting and researched the effects of the basic factors such as roll speed, pouring temperature and melt height on surface quality, strip thickness, Vickers hardness and microstructure. The AZ31 magnesium alloy strip was able to be produced at roll speed from 1 m/min to 90 m/min, and the thickness changed from 0.5 mm to 8.8 mm. The higher the pouring temperature, the thinner the strip thickness became. And the higher the melt height, the thicker the strip thickness became. The Vickers hardness is about 47HV. The microstructure of the produced strip was equiaxed and the distribution of crystal grain size was relatively uniform. The average crystal grain size was from 50 μm to 300 μm depending on the experimental conditions.

Effects of Al content on grain growth of solid solution (Ti,Al)N films

Substitutional solid solution (Ti1−xAlx)N films with different Al contents (0⩽x⩽0.41) were deposited onto unheated Si(100) substrates by reactive unbalanced close-field magnetron sputtering in an Ar–N2 gas mixture. The effect of Al atomic concentration on the sizes of crystal grains during deposition was investigated. X-ray diffraction analysis revealed that the incorporated Al atoms had an obvious impact on the grain growth of (Ti1−xAlx)N films and the average crystal grain size showed an exponential decay with Al atomic concentration. A phenomenological model was proposed to analyze this solute-drag effect occurring during film deposition. It was found that the presence of solute drag in normal grain growth resulted in a low kinetic growth exponent, and the exponential decay in average grain size with solute atomic concentration could be reproduced in our calculations.

Characterization of Pearl Luster Pigments

AbstractThis paper presents current developments in pearl luster pigments. After a short introduction on the application of pigments, the synthesis and characterization of a ZrO2/SiO2 based pearlescent pigment will be described. The applied methods for characterization were ex situ x‐ray diffraction (XRD) of dried and calcined pigment powders, in situ XRD in a temperature range from 100°C up to 850°C and transmission electron microscopy (TEM) of thin cross‐sections. The XRD measurements were used for phase analysis, determination of cell parameters and average crystal grain sizes. A special preparation method was developed for TEM cross section specimens for platy like pigment particles. The microstructure, the interface between substrate and coating material and the particle sizes are described with high resolution TEM pictures of cross section specimens. The basic interest is the behaviour of the zirconium dioxide coating during sintering in order to achieve a condensation of the film without any further crystal grain growth.

A New Form of Nanosized SrTiO3 Material for Near-Human-Body Temperature Oxygen Sensing Applications

A new form of nanosized SrTiO3 semiconducting oxide material with an average crystal grain size of 27 nm has been synthesized using the physical high-energy ball milling technique. The unique presence of the singly charged “O-” ions in the lattice oxygen sites of the nano-range crystal grain material has been observed in the XPS study. This unprecedented and interesting discovery has expounded on the new oxygen sensing mechanism for the near 1/2 slope gradient (the best value ever reported) in the logarithmic relationship of the electrical conductance with the oxygen partial pressure. The derived SrTiO3 oxygen gas sensors were found to operate at 40 °C (the lowest temperature ever reported for an SrTiO3-based sensor) that is near to the human body temperature.

EXAFS study on amorphous and nanocrystalline M–W (M=Fe,Ni) alloys produced by electrodeposition

Ductile amorphous and nanocrystalline M–W (M=Fe,Ni) alloys were produced by electrodeposition. Structural studies of these alloys were made by using EXAFS and SAXS methods. The crystal structure of the electrodeposited Ni–W alloy was similar to that of the Ni 4W crystal phase. The nearest Ni–Ni distance was determined to be 2.49 Å; the Ni–W distance was determined to be 2.50 Å. The atomic distances in the nanocrystalline Ni–W alloys increases with the tungsten concentration. The average crystal grain size of the Ni–W alloy was estimated at about 2.5 nm from a Guinier plot of the SAXS spectra. The electrodeposited amorphous Fe–21.6 at.% W alloy has only short range order, and no medium range order.

Ｘ線材料強度 高マンガンオーステナイト鋳鋼の疲労き裂進展挙動とＸ線フラクトグラフィ

Fatigue crack growth tests were carried out using a high manganese austenitic cast steel under constant amplitude loading. Average crystal grain sizes of the material are 200 micro-meters and 1000 micro-meters. For this material, threshold stress intensity factor range (ΔKth) is about 8MPa√m which is quite large as compared to the ΔKth of general structural steels. The crack growth rate is lower than the general structural steels especially in the lower ΔK region. The reasons of this behaviour are crack closure due to bridging and fretting oxide, decreasing of the stress concentration near the crack tip due to secondary crack and slip on crystal plane. X-ray fractography can be applied to the fatigue fracture surface of the material which has large grain by using oscillation of X-ray beam and in-plane oscillation on the fracture surface. The half-value breadth of the diffraction profile on the fracture surface increases with increase in the effective stress intensity factor range. The relationship between the half-value breadth and the effective stress intensity factor range was represented by a narrow band regardless of the stress ratio.Therefore, the effective stress intensity factor range can be estimated from this relation in fractured surface of actual components.

The Development of Nanocrystalline CBN for Enhanced Superalloy Grinding Performance

CBN grinding wheels are increasingly used on a wide range of engineering materials. This paper compares the grinding performance of monocrystalline (M-CBN) and polycrystalline (P-CBN) abrasives with a newly developed nanocrystalline (N-CBN) abrasive, when grinding nickel-based superalloys. The N-CBN grits possess average crystal grain diameters less than 1 μm compared to average primary grain diameters of 2.3 μm for P-CBN. It was found that the nanocrystalline CBN grits possess higher fracture strength which give reduced wear rates and yield an order of magnitude increase in grinding wheel life. Analysis of the cutting edge distribution shows that the reduced wear rate of N-CBN is due to the predominance of a micro-fracturing mode of abrasive wear. The size of this micro-fracturing is considerably smaller in N-CBN than in P-CBN.

Microtexture of highly crystallized graphite as studied by galvanomagnetic properties and electron channeling contrast effect

The relationship between microtexture and crystallinity of highly crystallized graphites with the residual resistivity ratio ρ300K/ρ4.2K of 3.45–5.50 was investigated. The graphite crystals studied were kish graphite (KG), highly oriented pyrolytic graphite (HOPG), and highly crystallized graphite films prepared from carbonized aromatic polyimide films. The study was made by the observations of an electron channeling pattern and electron channeling contrast image (ECI) under scanning electron microscope and the measurements of x-ray diffraction, magnetoresistance, and Hall coefficient. The values of the mean free path of the carriers λ, which approximates the mean crystal grain size, were estimated to be 2.6–6.1 μm from the magnetoresistance at 4.2 K for the highly crystallized graphites. The values of the average crystal grain diameter D in the basal plane evaluated from ECI were several hundred microns or more for KG, 60 μm for HOPG, and 6 and 12 μm for the graphite films. The difference between the values of λ and D for each crystallized graphite was discussed in relation to other results obtained.

Grinding Characteristics of Polycrystalline CBN Abrasive Grits Having an Ultrafine Crystal Structure.

A new type of polycrystalline CBN grit has been developed by direct transformation at high temperature and pressure from hBN of high purity which was produced using a chemical vapour deposition process. This new polycrystalline CBN (N-CBN) grit possesses an average primary crystal grain diameter less than 1 μm and its fracture strength is around 1.5 times higher than conventional polycrystalline CBN (P-CBN) grit. In grinding high-speed tool steel, the grinding ratio of the wheel containing N-CBN grits is 7∼9 times higher than that of the wheel containing P-CBN grits. The estimated tool life of the N-CBN wheel, based on the roughness of the finished surface, is 1 much longer than that of the P-CBN wheel.

In situ growth of layered, spinel, and rock-salt LiCoO2 by laser ablation deposition

A study is reported of the in situ growth of three distinct phases of LiCoO2 by laser ablation deposition on heated substrates in an oxygen background. Films were characterized by x-ray diffraction from which crystal structure, crystal orientation, lattice constants, and phase information were obtained. Electron microscopy was used to investigate crystal grain size and overall film morphology. For deposition under 2000 mTorr O2, substrate temperatures of 22–250 °C resulted in a rock-salt structure, 300–450 °C produced a modified spinel structure (low-temperature LiCoO2), and 680 °C gave a hexagonal layered structure (high-temperature LiCoO2). Growth at 500 and 550 °C produced mixed-phase spinel and layered LiCoO2; however, at 550 °C, reducing the O2 pressure to 100 mTorr resulted in single-phase high-temperature LiCoO2. In the case of the rock-salt phase, modified film stoichiometries of composition Li0.5Co1.5O2 and Li0.75Co1.25O2 were also produced by using ablation targets of the same composition and growing at 150 °C under 200 mTorr O2. Average crystal grain size for all films was found to increase with growth temperature. Ordering of the cations in rock-salt films by heating was unsuccessful.