A study of the dissipative properties of homogeneous materials deposited as coatings. Part 1. Method for the determination of the amplitude dependence of the true vibration decrement of the coating material

A method is proposed for the determination of the amplitude dependence of the true vibration decrement of homogeneous materials deposited as coatings on a substrate of rectangular cross section. The method is based on the self-consistent calculation of energy loss factors for the substrate and coating materials using experimental amplitude dependences of vibration decrement for coated substrate, obtained under the conditions of cantilever specimens of rectangular cross section. The applicability of the method is illustrated by the determination of values of the true vibration decrement of Co-20 wt.% Fe alloy deposited as a coating on VT1-0 titanium alloy. __________ Translated from Problemy Prochnosti, No. 6, pp. 134–143, November–December, 2007.     

Systematic evaluation of the damage to a material during plastic deformation

Aluminum alloy D16 is used as an example to systematically evaluate the damage to metal on the basis of characteristics of its damping capacity (logarithmic vibration decrement), acoustic emission, and weight as determined by a new method developed by the authors. It is shown that the damage sustained by metallic materials during static loading can be estimated from the change in the vibration decrement and certain acoustic-emission parameters. These conclusions are substantiated by similar relations expressing the dependence of these parameters on the dilatation of the material in an evaluation of its volume change. Translated from Problemy Prochnosti, No. 5, pp. 23–30, May, 1996.     

The effect of repeated annealing temperature on the structural,optical, and electrical properties of TiO<Subscript>2</Subscript> thin films prepared by dip-coating sol–gel method

In this study, we have studied the effect of repeated annealing temperatures on TiO₂ thin films prepared by dip-coating sol–gel method onto the glasses and silicon substrates. The TiO₂ thin films coated samples were repeatedly annealed in the air at temperatures 100, 200, and 300 °C for 5 min period. The dipping processes were repeated 5 to 10 times in order to increase the thickness of the films and then the TiO₂ thin films were annealed at a fixed temperature of 500 °C for 1 h period. The effect of repeated annealing temperature on the TiO₂ thin films prepared on glass substrate were investigated by means of UV–VIS spectroscopy, X-ray diffraction (XRD), and atomic force microscopy (AFM). It was observed that the thickness, average crystallite size, and average grain size of TiO₂ samples decreased with increasing pre-heating temperature. On the other hand, thickness, average crystallite size, and average grain size of TiO₂ films were increased with increasing number of the layer. Al/TiO₂/p-Si metal–insulator–semiconductor (MIS) structures were obtained from the films prepared on p-type single silicon wafer substrate. Capacitance–voltage (C–V) and conductance–voltage (G/ω–V) measurements of the prepared MIS structures were conducted at room temperature. Series resistance (R _s) and oxide capacitance (C _ox) of each structures were determined by means of the C–V curves.     

Effect of grain size on the primary and secondary creep behavior of Sn–3 wt.% Bi alloy

The effect of grain size as well as creep temperature on the primary and secondary creep parameters of Sn–3 wt.% Bi alloy has been studied. It was found that the creep parameters α, β, and έ _s were decreased with increasing grain size. This was explained in view of the dislocation interaction with the defects and different inclusions in the matrix. For both the primary and secondary creep, the activation energies estimated indicate that the rate-controlling mechanism is the grain boundary-sliding mechanism.     

Polycrystalline silicon films doped with aluminum during deposition

Aluminum-doped polycrystalline silicon films have been grown by molecular-beam deposition at substrate temperatures between 540 and 600 °C. The grain size increases to 1–8 μm with increasing substrate temperature. High Hall mobilities of the carriers were measured, in the range 30–90 cm²/V·s. Pis’ma Zh. Tekh. Fiz. 23, 83–87 (June 12, 1997)     

Thickness dependent electrical properties of CdO thin films prepared by spray pyrolysis method

A large number of thin films of cadmium oxide have been prepared on glass substrates by spray pyrolysis method. The prepared films have uniform thickness varying from 200–600 nm and good adherence to the glass substrate. A systematic study has been made on the influence of thickness on resistivity, sheet resistance, carrier concentration and mobility of the films. The resistivity, sheet resistance, carrier concentration and mobility values varied from 1·56–5·72×10⁻³ Ω-cm, 128–189 Ω/□, 1·6–3·9×10²¹ cm⁻³ and 0·3–3 cm²/Vs, respectively for varying film thicknesses. A systematic increase in mobility with grain size clearly indicates the reduction of overall scattering of charge carriers at the grain boundaries. The large concentration of charge carriers and low mobility values have been attributed to the presence of Cd as an impurity in CdO microcrystallites. Using the optical transmission data, the band gap was estimated and found to vary from 2·20–2·42 eV. These films have transmittance around 77% and average reflectance is below 2·6% in the spectral range 350–850 nm. The films aren-type and polycrystalline in nature. SEM micrographs of the CdO films were taken and the films exhibit clear grains and grain boundary formation at a substrate temperature as low as 523 K.     

Vibrodiagnostic parameters of fatigue damage in rectangular plates. Part 3. Through-the-thickness and surface semi-elliptical cracks

The paper addresses the analytical determination of vibrodiagnostic parameters that describe the presence of normal-rupture flat through-the-thickness and surface semi-elliptical central cracks in a rectangular homogeneous plate of constant thickness for various plate fixing conditions and vibration modes. It is shown that the most sensitive vibrodiagnostic damage parameter of a plate is the variation of the logarithmic decrement in the case of a through-the thickness crack and the second-harmonic ratio of the vibration process in superharmonic resonance in the case of a surface crack. __________ Translated from Problemy Prochnosti, No. 5, pp. 27–47, September–October, 2006.     

Phase formation and high dielectric constant of calcium copper titanate using sol–gel route

Nano-sized calcium copper titanate (CCTO) powder was synthesized from a quick and innovative sol–gel process. Calcium nitrate, copper nitrate and titanium isopropoxide were used as the raw materials to synthesize the precursor product. The dried precursor powder was then milled and calcined at 450, 550, 650, 800, 850 and 950 °C for 3 h. The XRD results of the powder calcined at 800 °C indicates the formation of CCTO single phase. AFM studies shows that the average particle size of CCTO powder ranges around 80 nm. From the FTIR spectra the modes observed at 606, 525 and 463 cm⁻¹ was assigned to vibration modes of Ca–O, Cu–O and Ti–O–Ti, respectively. The samples sintered at 1,040 °C shows high density (96%) as compared to the theoretical value. The grain sizes of sintered pellets were determined by FE-SEM and the dielectric properties were studied by LCR meter.     

Synthesis and properties of barium titanate stannate thin films by chemical solution deposition

Barium titanate stannate (BaTi_1−x Sn _x O₃, 0 ≤ x ≤ 0.25) thin films were deposited directly on copper foil substrates via a chelate chemical solution process. The films were subsequently crystallized in a reducing atmosphere such that substrate oxidation was avoided and that the 2-valent state of tin could be stabilized. Despite the stabilization of the low-melting temperature SnO oxidation state at high temperatures, the final grain size was smaller with increased tin incorporation similar to other B-site substituted BaTiO₃ films. Temperature and field-dependent dielectric measurements revealed a reduction in dielectric constant and dielectric tuning with increasing tin concentration. The reduction in permittivity with reduced grain size is consistent with the well-known trends for ceramic barium titanate and in combination with a defect-dipole model involving Sn acceptors, can be used to explain the experimental trends. Phase transition frequency dependence was studied and for compositions containing up to 25 mole percent tin. No phase transition dispersion was observed and thus no strong evidence of relaxor-like character. The phase transition became increasingly diffuse with deviation from Curie–Weiss behavior, but the observed transition temperatures agreed well with bulk reference data.     

Polycrystalline Si1-x Ge x thin film deposition by rapid thermal chemical vapor deposition

Polycrystalline silicon germanium (poly-Si_1−xGe_x) thin films on a-Si film have been deposited by rapid thermal chemical vapor deposition (RTCVD) with SiH₄–GeH₄–H₂. Effect of GeH₄/SiH₄ and deposition temperature on stoichiometry (x), Si-Ge binding character, composition, hydrogen configuration, crystallinity, preferred orientation, grain size, and surface roughness of poly-Si_1−xGe_x films has been investigated. Poly-Si_1−xGe_x deposited on the substrate with amorphous silicon buffer layer on oxide shows better crystallinity and contains the less amount of oxygen than the one deposited directly on the oxide surface. At low temperature region, the Ge–H bond with the small amount of Si–H₂ bond is dominant but all hydrogen bonds are desorbed at high temperature. All films have polycrystalline phase and the grain size and (111) orientation increased with increasing deposition temperature in which Ge content also increases at the fixed gas flow rate of GeH₄ to total source gas. Poly-Si_1−xGe_x/Si thin film transistors (TFT) are fabricated and hydrogen during post-hydrogenation process preferentially is attached to Ge dangling bond and the TFT characteristics could be improved.     

Characterization of Tin disulphide thin films prepared at different substrate temperature using spray pyrolysis technique

Thin films of tin disulphide on glass substrates were prepared by spray pyrolysis technique using precursor solutions of SnCl₂·2H₂O and n–n dimethyl thiourea at different substrate temperatures varied in the range 348–423 K. Using the hot probe technique the type of conductivity is found to be n type. X ray diffraction analysis revealed the polycrystalline nature with increasing crystallinity with respect to substrate temperature. The preferential orientation growth of SnS₂ compound having hexagonal structure along (002) plane increased with the substrate temperature. The size of the tin disulphide crystallites with nano dimension were determined using the Full Width Half Maximum values of the Bragg peaks and found to increase with the substrate temperature. The surface morphology had been observed on the surface of these films using scanning electron microscope. The optical absorption and transmittance spectra have been recorded for these films in the wavelength range 400–800 nm. Thickness of these films was found using surface roughness profilometer. The absorption coefficient (α) was determined for all the films. Direct band gap values were found to exist in all the films deposited at different substrate temperatures. The value of room temperature resistivity in dark decreased from 5.95 × 10³ Ω cm for the amorphous film deposited at low temperature (348 K) to 2.22 × 10³ Ω cm for the polycrystalline film deposited at high temperature (423 K) whereas the resistivity values in light decreased from 1.48 × 10³ to 0.55 × 10³ Ω cm respectively, which is determined using the four probe method. Activation energy of these thin films was determined by Arrhenius plot.     

Galvanostatic electrodeposition and microstructure of copper (I) oxide film

 Polycrystalline copper (I) oxide films were deposited on stainless steel substrate by galvanostatic electrodeposition method and were characterized by X-ray diffraction and scanning electron microscopy. The effect of bath temperature, bath pH and current density on the compositon, grain size, surface texture and surface morphology of the electrodeposited films were investigated. The films deposited at low bath pH (≤7) consisted of copper (I) oxide and metallic copper; while the films deposited at bath pH between 8 and 12 and bath temperature of 60°C were pure copper (I) oxide. The preferred orientation of the copper (I) oxide films depended on the relative growth rate of {111} and {200} faces and could be controlled by adjusting the bath pH and/or the cathodic current density. (100)-oriented copper (I) oxide films could be deposited at pH=9 and current densities in the range of 0.25–1 mA/cm², while (111)-oriented films could be prepared at pH=12 or at pH=9 using the current densities between 1.5–2.5 mA/cm². Computer simulated crystallite shapes showed that the crystal shape changed from octahedral for (100)-oriented film to trucated pyramids and cubs for (111)-oriented film. And they were approved by scanning electron microscopy. Received: 1 December 1997 / Accepted: 13 December 1997     

Hot deformation behavior of an 8% Cr cold roller steel

An 8% Cr cold roller steel was compressed in the temperature range 900–1200 °C and strain rate range 0.01–10 s⁻¹. The mechanical behavior has been characterized using stress–strain curve analysis, kinetic analysis, processing maps, etc. Metallographic investigation was performed to evaluate the microstructure evolution and the mechanism of flow instability. It was found that the work hardening rate and flow stress decreased with increasing deformation temperature and decreasing strain rate in 8% Cr steel; the efficiency of power dissipation decreased with increasing Z value; flow instability was observed at higher Z-value conditions and manifested as flow localization near the grain boundary. The hot deformation equation and the dependences of critical stress for dynamic recrystallization and dynamic recrystallization grain size on Z value were obtained. The suggested processing window is in the temperature range 1050–1200 °C and strain rate range 0.1–1 s⁻¹ in the hot processing of 8% Cr steel.     

Some physical properties of copper oxide films: The effect of substrate temperature

In this work, copper oxide films were deposited at different substrate temperatures of 200, 250, 300 and 350 ± 5 °C by ultrasonic spray pyrolysis technique and the effect of substrate temperature on the structural, surface, optical and electrical properties of the films was presented. The film structures were studied by X-ray diffraction (XRD). To obtain information about structural properties in detail, the grain size (D), dislocation density (δ) and lattice parameters (a = b = c for cubic structure) for preferential orientations were calculated. The surface properties and elemental analyses were characterised using scanning electron microscopy and energy dispersive X-ray spectroscopy, respectively. Optical properties of the films were analyzed by transmission, linear absorption coefficient and reflection spectra, and the optical method was used to determine the band gaps of the films. The current–voltage values were measured with two-probe technique, and the electrical conductivities were calculated. Consequently, it was determined that substrate temperature has a strong effect on the structural, surface, optical and electrical properties of copper oxide films.     

Effect of microstructural evolution on magnetic properties of Ni thin films

The magnetic properties of Ni thin films, in the range 20–500 nm, at the crystalline-nanocrystalline interface are reported. The effect of thickness, substrate and substrate temperature has been studied. For the films deposited at ambient temperatures on borosilicate glass substrates, the crystallite size, coercive field and magnetization energy density first increase and achieve a maximum at a critical value of thickness and decrease thereafter. At a thickness of 50 nm, the films deposited at ambient temperature onto borosilicate glass, MgO and silicon do not exhibit long-range order but are magnetic as is evident from the non-zero coercive field and magnetization energy. Phase contrast microscopy revealed that the grain sizes increase from a value of 30–50 nm at ambient temperature to 120–150 nm at 503 K and remain approximately constant in this range up to 593 K. The existence of grain boundary walls of width 30–50 nm is demonstrated using phase contrast images. The grain boundary area also stagnates at higher substrate temperature. There is pronounced shape anisotropy as evidenced by the increased aspect ratio of the grains as a function of substrate temperature. Nickel thin films of 50 nm show the absence of long-range crystalline order at ambient temperature growth conditions and a preferred [111] orientation at higher substrate temperatures. Thin films are found to be thermally relaxed at elevated deposition temperature and having large compressive strain at ambient temperature. This transition from nanocrystalline to crystalline order causes a peak in the coercive field in the region of transition as a function of thickness and substrate temperature. The saturation magnetization on the other hand increases with increase in substrate temperature.     

Effects of heating rate and DC electric field during sintering on the grain size distribution in fully sintered tetragonal zirconia polycrystals stabilized with 3% molar yttria (3Y-TZP)

The effects of sintering temperature rate ([(T)\dot] (\dot{T} = 1.5–50 °C/min) without and with an initial applied dc electric field (E _o = 14 V/cm) on the grain size distribution (GSD) of fully sintered 3 mol%, yttria-stabilized tetragonal zirconia (3Y-TZP) was determined from SEM micrographs of fractured and polished-and-etched surfaces. No clear difference between the measurements on the two surfaces was detected. The grain size parameters characterizing the GSD tended to decrease with [(T)\dot] \dot{T} and with E _o. All of the GSD’s however fit a single curve based on the Bitti–Di Nunzio grain coarsening model. This fit along with other considerations also give that the heating rate and electric field applied during sintering did not have a significant effect on the grain shape or the grain boundary energy in the fully sintered specimens. It is proposed that the decrease in grain size in the fully sintered condition by the application of an electric field during prior sintering results primarily from its effect on the driving force for grain growth, while the effect of the heating rate is on the grain mobility.     

Optical and structural characterization of r.f. sputtered CeO2 thin films

The optical and structural properties of r.f. sputtered CeO2 thin films deposited on Pyrex substrates have been studied as a function of substrate temperature during deposition. The refractive index, n, extinction coefficient, k, and bandgap of the films were calculated from reflectance, R, and transmittance, T, spectra in the wavelength range 340–900 nm. The refractive index of CeO2 films at 550 nm comprises values from about 2.25–2.4 depending on the substrate temperature during deposition. The extinction coefficient was negligible for wavelength values higher than 400 nm. The value obtained for the bandgap was 3.1 eV. The X-ray diffraction patterns showed the same (f c c) cubic structure with preferential orientation depending on substrate temperature during deposition. The scanning force microscope measurements showed that the roughness and grain size of the CeO2 films increase with increasing substrate temperature. This revised version was published online in November 2006 with corrections to the Cover Date.     

Grain growth in 18Ni 1800 MPa maraging steel

The grain-growth behaviour in 18Ni8Co5MoO.4Ti maraging steel was investigated in the temperature range 1123–1323 K. Grain sizes were estimated by measuring the diameter of the equivalent area of the individual grains directly on the optical microscope using a calibrated digital eyepiece. Grain-boundary migrations and substructure analyses were done using an electron microscope. These studies indicate that the overall grain growth in the steel follows the relationship ΔD=ktⁿ where ΔD is the increase in the grain size. However, during the initial stage, a “time lag” for the grain growth to start is observed which is attributed to the presence of highly dislocated austenitic matrix on annealing. Evidence of abnormal grain growth is also seen after annealing at 1173 K for 480 min and at 1123 K for 300 min. The growth exponents for the normal and abnormal grain growth were found to be 0.40–0.44 and 0.90–2.0, respectively. One significant deviation observed in the study wasn decreasing from 0.44-0.40 at higher temperatures during the normal growth. This has been critically discussed in the light of the unique transformation characteristics of the steel. The activation energy for growth was calculated to be 60.0–62.5 kcal mol⁻¹, indicating the overall growth is controlled by self diffusion in γ-iron.     

Determination of the parent grain orientation and habit plane normals for β′1 martensite in a Cu–Al–Ni–Mn shape memory alloy

Martensite plates in β′₁ shape memory alloys commonly form self-accommodating groups of four plate variants with habit plane normals clustered about a {1 1 0} pole of the parent phase. In the present work, the crystallography of martensitic transformation in a Cu–Al–Ni–Mn shape memory alloy has been investigated with particular emphasis on accurate habit plane determination. The characteristically high martensite start (M _s) temperature of β′₁ alloys makes it impossible to analyse samples containing isolated plates within a β₁ grain at ambient temperature. However, the parent β₁ grain orientation has been determined in this work by means of a new method of junction plane trace analysis, which is based on the knowledge that the junction planes are precisely {1 1 0}_β1 planes. The mutual consistency of the experimental results indicates that this technique of junction plane traces analysis is a viable method for determining the parent β₁ grain orientation. Habit plane normals were determined by two surface trace measurements and referred to the parent crystal basis by using the β₁ grain orientation matrix. The habit plane normal was determined to be close to {1 5 5}_β1 with the scatter in a series of mean value determinations being less than ± 1.2°. This revised version was published online in November 2006 with corrections to the Cover Date.     

Transient liquid phase diffusion bonding of 6061-13 vol.% SiCp composite using Cu powder interlayer: mechanism and interface characterization

Transient liquid phase diffusion bonding of an extruded 6061-13 vol.% SiCp composite at 560 °C, 0.2 MPa, using a 50-μm thick copper powder interlayer with 20 min, 1 h, 2 h, 3 h, and 6 h hold times has been investigated. The isothermal solidification and homogenization of the bond region occurred with 3 and 6 h holding, respectively. During isothermal solidification, smaller SiC particles (size range: 11–13 μm) were pushed by the moving solid/liquid interface and segregated around the bond centerline, whereas bigger SiC particles (size range: 24–33 μm) were engulfed. During isothermal solidification, the bigger SiC particles locally hindered the solidification front movement causing grain refinement. The kinetics of isothermal solidification, representing the displacement of the solid/liquid interface (y, in μm) as a function of time (t, in s), followed a power-law relationship: y = 35 t ^0.22. According to this kinetic equation, the effective diffusivity of copper in composite system was found to be about 10⁵ times higher than the lattice diffusivity indicating the dominance of short circuit diffusion through the defect-rich particle/matrix interface. Ultrasonic investigation of the bond interface indicated that the signal attenuation was strongly correlated with the width of the segregated layer-a feature that decreased with the increasing bonding time. The completion of isothermal solidification was indicated by a sharp rise in the received signal amplitude with a negligible attenuation.