Yield stress of a copper single crystal containing B2O3 particles

The yield stress of a copper single crystal containing vitreous B₂O₃ particles was measured as a function of temperature (77–1073 K) and strain rate (5.6 × 10^–6–5.6 × 10^–4sec^–1). Although the B₂O₃ particles in the copper matrix are a plastically non-deformable solid at low temperatures, they became liquid-like at high temperatures, above approximately 550 K. The yield stress of the Cu-B₂O₃ alloy at low temperatures was explained by the Orowan mechanism and the modulus-corrected yield stress of the Cu-B₂O₃ alloy at 1073 K was about four-fifths of the values at low temperatures. It was found that the liquid B₂O₃ particles could be the effective hardening centres even at high temperatures. At 873 and 1073 K, the yield stresses of the Cu-B₂O₃ alloy varied with the logarithm of the strain rates.     

Influence of temperature and cyclic loading on hydrogen embrittlement of nickel refractory alloys

We investigate the influence of hydrogen on the mechanical properties of initial and preliminarily deformed (cyclic bending with an amplitude of 1.6% and a frequency of 0.5 Hz in helium and hydrogen under a pressure of 35 MPa) specimens of KhN55MBYu and KhN56MBYuD alloys in the temperature range 293–1073 K. The number of cycles to fracture in low-cycle bending of plane specimens and percentage elongation are most sensitive to the influence of hydrogen (decrease, respectively, by 95–98 and 80–90% of their values in helium). The decreases in the strength and plasticity of KhN55MBYu alloy are maximum at room temperature, minimum in the temperature range 873–973 K, and again substantial at 1073 K. The positive influence of the preliminary cyclic deformation in hydrogen on the ultimate short-term strength and plasticity of both alloys in hydrogen was detected. At room temperature, the percentage elongation of specimens of KhN55MBYu alloy increases from 10 (undeformed specimens) to 29% (deformed by 20% of the low-cycle fatigue life).     

Thermal stability and thermal expansion behavior of FeCoCrNi2Al high entropy alloy

Present work reports the thermal stability and thermal expansion behavior of dual-phase FeCoCrNi₂Al HEA prepared by Mechanical Activated Synthesis and consolidated by hot pressing. The thermal stability of the phases present in FeCoCrNi₂Al HEA has been extensively studied using in-situ high-temperature X-ray diffraction (HT-XRD) in conjunction with dilatometry and differential scanning calorimetry (DSC). The DSC thermogram shows a single endothermic peak at 1430 °C (1703 K) which belongs to the melting point of the alloy. HT-XRD and dilatometry experiments were carried out from room temperature to 1000 °C (1273 K). HT-XRD study has shown that the room temperature FCC + BCC (face-centred cubic + body-centred cubic) phases remains stable up to 1000 °C (1273 K). Although the amount of BCC phase has increased above 800 °C (1073 K), no additional phase formation was observed in HT-XRD. The coefficient of thermal expansion (CTE) curve shows linear increment up to 1000 °C (1273 K) with a slight change in slope beyond 800 °C (1073 K). Theoretical CTE was computed using the lattice parameter of the FCC phase, obtained from HT-XRD, as a function of temperature and compared with experimental CTE. Third-order polynomial equation was fitted to the experimental CTE data and the constants were evaluated which can be used to predict the coefficient of thermal expansion of the alloy.     

Characterization of albumin- and lysozyme–adsorption evaluated on two differently prepared apatites

Ca2+-deficient hydroxyapatite (r-HAp) originated from cattle bones and stoichiometric hydroxyapatite (s-HAp) derived from reagents were prepared by wet syntheses. The adsorption characteristics of albumin (BSA) and lysozyme (LSZ) on the two HAp surfaces were compared by changing the heating temperature of the powders at 273–1073 K in a stream of water vapour. The saturated amount of adsorption (ASA(B) for BSA and ASA(L) for LSZ) on these HAp powders changed little at 273–673 K (Region I), but at 673–1073 K (Region II), clearly increased with crystallite size growth and transformation of crystal morphology. As far as the surface proportions of HAp for P- and C-adsorption sites (the ratios ASA(L)/ASA(B)) are concerned, r-HAp gave no change in Region I and decreased in Region II, whereas those for s-HAp were kept constant through all regions. The heats of LSZ adsorption, QL, for r-HAp and s-HAp, respectively, increased and decreased in Region II. These differences could be a result of the Ca2+-deficient structure of r-HAp with the OH–-vacancy and loosening surface structure due to segregation of impurities in Region II. r-HAp exhibited a 157% higher heat of BSA adsorption, QB, and a 60% lower QL in Region I than s-HAp. Conclusively, r-HAp can be used as an excellent adsorbent, rather than s-HAp, because of its chromatographic characteristics for the separation of acidic and basic proteins. © 1998 Chapman & Hall     

Characterization of intermetallic precipitates in a Nimonic alloy by ultrasonic velocity measurements

Ultrasonic velocity measurements have been carried out in Nimonic 263 specimens thermally aged at 923 and 1073 K for durations up to 75 h and correlated with the results of hardness measurements and electron microscopy studies. The ultrasonic velocities and hardness results obtained in the specimens thermally aged at both temperatures clearly indicated that ultrasonic velocity is more sensitive to the initiation of the precipitation, whereas the influence of precipitation on hardness can be observed only after the precipitates attain a minimum size to influence the movement of dislocations. Further, ultrasonic velocity measurements also revealed faster kinetics and a lesser amount of precipitation at 1073 K compared to 923 K due to higher solubility of precipitate-forming elements.     

Effect of annealing on the structural,electrical and magnetic properties of Gd-implanted ZnO thin films

We report the results from structural, electrical and magnetic measurements on Gd-implanted ion beam deposited zinc oxide (ZnO) films. 40 keV Gd ions were implanted into 150 nm thick ZnO films with fluence 2.8 × 10¹⁵ cm⁻². RBS spectra reveal the implanted atoms are located in the near-surface region in as-implanted and up to 923 K annealed films, diffusing deeper into the films after 1073 K annealing. SEM images show that the average grain size increases from 10 to 30 nm upon annealing. High-resolution and energy-filtered transmission electron microscopy of a ZnO:Gd sample annealed at 923 K reveal the presence of Gd-rich regions in the film, but no evidence of pure Gd precipitates. Annealing increases the resistivity, and the carrier concentration decreases by as much as six orders of magnitude after annealing at up to 1073 K. All annealed films display a mix of paramagnetic, superparamagnetic and ferromagnetic behaviour extending to temperatures above 300 K that we attribute to the spatially inhomogeneous Gd distribution. The paramagnetic behaviour can be attributed to isolated Gd moments, while the ordered magnetic phases appear to arise from Gd-rich regions within the ZnO. X-ray absorption near edge spectroscopy provides evidence that there exist oxygen vacancies.     

Photocatalytic studies of antimonate compounds prepared by a self-combustion route

Antimonates compounds with 1Ca:1Sb and 2Ca:1Sb:1Al compositions were synthesized by a self-combustion method. For the 1Ca:1Sb composition, a calcination at 1573 K led to a pure Ca₂Sb₂O₇ weberite phase, whose structure was determined using the Rietveld method. In the case of the 2Ca:1Sb:1Al composition, a pure phase was achieved at 1073 K, and the use of higher calcination temperatures led to a mixture of phases. Some of the products (1Ca:1Sb (873 K), 2Ca:1Sb:1Al (1073 K) and Ca₂Sb₂O₇ (1573 K)) were tested as photocatalysts for the methyl orange degradation. The results clearly demonstrated that Ca₂Sb₂O₇ is the catalyst exhibiting the best results for the MO photocatalytic degradation. This fact was interpreted as due to a predominant role of structural features on the photocatalytic activity of the prepared compounds.     

Relationships governing deformation and failure of an iron-nickel alloy in creep in vacuum and in air

Conclusions The investigations into the creep and long-term strength of the iron-nickel alloy in the temperature range 873–1073°K for up to 1000 h showed that in this temperature range we can define three differing typical regions of creep strain cumulation in relation to temperature and stress. The time to failure of the batch I specimens at a temperature of 1073°K and a stress of 200 MPa in air is five times longer, than the time to failure in vacuum.Institute of Strength Problems, Academy of Sciences of the Ukrainian SSR, Kiev. Moscow, Translated from Problemy Prochnosti, No. 1, pp. 43–48, January, 1986.     

Influence of Al content on thermal stability of nanocrystalline AlxCoCrFeNi high entropy alloys at low and intermediate temperatures

Thermal stability of mechanically alloyed nanocrystalline Al_xCoCrFeNi (x = 0, 0.3, 0.6, 1 mol) high entropy alloys (HEAs) has been investigated for the low and intermediate temperature range of 673–1073 K. Single phase FCC structure is observed in the as milled CoCrFeNi. A mixture of FCC and BCC phases is exhibited by × = 0.3, 0.6 and 1, alloys where the volume fraction of BCC increases with increasing Al content. Phase evolution in heat-treated Al_xCoCrFeNi HEAs proceeds via increasing BCC fraction at 673 K, followed by subsequent reduction at elevated temperatures. For each alloy, the major phase observed in as milled condition and it is retained even after prolonged exposure at the 1073 K. Al favors the formation of the BCC phase due to its high affinity to form ordered B2 structures with constituent elements Co, Fe and Ni. Thermal exposure of Al_xCoCrFeNi HEAs also leads to the formation of Cr₇C₃, owing to the higher negative free energy of carbide formation for Cr among other constituents. Transmission electron microscopy (TEM) investigations substantiated that nanostructure of milled powder is maintained even after the heat treatment. Grain growth factor for quinary HEAs is relatively lower than quaternary CoCrFeNi owing to their slower rates of diffusion.     

Synthesis and characterization of NiWO4 crystals

Nickel tungstate (NiWO₄) catalyst has been synthesized by reacting ammonium metatungstate and nickel nitrate as a function of temperature from 673 to 1073 K and of 1-h reaction time. It was found that NiWO₄ is formed from 823 to 1073 K. The yield of 99% was obtained from 903 K to higher temperatures. The average crystal sizes have been determined by the Scherrer analysis and the surface area was measured by the Brunauer–Emmett–Teller (BET) method. The former increase from 55 to 112 nm, while the second decrease from 16 to 3 m² g⁻¹ in both cases, as the reaction temperature increases from 823 to 1073 K. Elemental composition and morphological structure were studied by energy dispersive spectroscopy (EDS) and scanning electron microscopy (SEM). The structural characterization has been performed using X-ray diffraction (XRD).     

Microstructure and elevated temperature properties of a refractory TaNbHfZrTi alloy

Compression properties of a refractory multi-component alloy, Ta₂₀Nb₂₀Hf₂₀Zr₂₀Ti₂₀, were determined in the temperature range of 296–1473 K and strain rate range of 10⁻¹–10⁻⁵ s⁻¹. The properties were correlated with the microstructure developed during compression testing. The alloy was produced by vacuum arc melting, and it was hot isostatically pressed (HIPd) and homogenized at 1473 K for 24 h prior to testing. It had a single-phase body-centered cubic structure with the lattice parameter a = 340.4 pm. The grain size was in the range of 100–200 μm. During compression at a strain rate of έ = 10⁻³ s⁻¹, the alloy had the yield strength of 929 MPa at 296 K, 790 MPa at 673 K, 675 MPa at 873 K, 535 MPa at 1073 K, 295 MPa at 1273 K and 92 MPa at 1473 K. Continuous strain hardening and good ductility (ε ≥ 50%) were observed in the temperature range from 296 to 873 K. Deformation at T = 1073 K and έ ≥ 10⁻³ s⁻¹ was accompanied by intergranular cracking and cavitation, which was explained by insufficient dislocation and diffusion mobility to accommodate grain boundary sliding activated at this temperature. The intergranular cracking and cavitation disappeared with an increase in the deformation temperature to 1273 and 1473 K or a decrease in the strain rate to ~10⁻⁵ s⁻¹. At these high temperatures and/or low-strain rates the alloy deformed homogeneously and showed steady-state flow at a nearly constant flow stress. Partial dynamic recrystallization, leading to formation of fine equiaxed grains near grain boundaries, was observed in the specimens deformed at 1073 and 1273 K and completed dynamic recrystallization was observed at 1473 K.     

Etude de la solution solide Pb2O(S1−xWxO4) et structure cristalline de la variete alpha du monooxodiplomb (II) tetraoxotungstate (VI) Pb2O(WO4) par diffraction X sur poudres

The Pb₂O(S_1?xW_xO₄) solid solution has been investigated by X-ray diffraction in the 0<x<1 range. Direct synthesis of monooxodilead(II)tetraoxotungstate(VI) by heating 2PbO+WO₃ mixtures at different temperatures, reveals the existence of two polymorphs: alpha-Pb₂ O(WO₄) is obtained for 823<T<833K and beta-Pb₂ O(WO₄) for T>1073K. For 833<T<1073K, mixtures of both polymorphs are obtained. In the present work the alpha-Pb₂O(WO₄) species is characterized for the first time, and crystal structure investigations by X-ray diffraction on polycristalline samples show that this phase is isostructural with its Pb₂O(AO₄) homologues for A = S, Cr and Mo (1).     

Effect of sintering temperature on the properties of Cu-Co ferrites prepared by oxalate precipitation method

Polycrystalline Cu-Co ferrite powder was synthesized following oxalate precipitation method. The samples of the compound Cu_0.5Co_0.5Fe₂O₄ were heated at different temperatures in the range of 773-1173 K and were characterized by X-ray diffraction and SEM techniques. The results of XRD show the formation of single-phase cubic spinel structure. The lattice parameter showed a minimum value for the sample heated at 1073 K. It has been observed that grain size increases with the increase in temperature and is maximum (3.2 μm) for the powder sintered at 1173 K.     

Interaction between liquid aluminum and NiO single crystals

The wetting behavior of NiO single crystal by liquid aluminum has been studied by the sessile drop method under vacuum at 973–1273 K for 2 h. Optical microscopy, SEM, EDS and X-ray analysis were applied to characterize the structure and chemistry of solidified cross-sectioned sessile drop couples. Under tested conditions, molten Al wets and reacts with NiO to form Al₂O₃ and Ni. This leads to alloying of the initially pure Al drop with Ni to the hypereutectic composition and to the formation of a thick reaction product region inside the NiO substrate, whose structure presents interpenetrated networks of fine alumina precipitates and an Al–Ni matrix. After solidification the Al–Ni matrix and the drop have the same phase composition, which is in agreement with Al–Ni phase diagram, showing the formation of Al₃Ni at T < 1128 K and Al₃Ni₂ at 1128 K < T < 1406 K. The strong reactivity of Al/NiO couples, accompanied with the drop deformation, fragmentation of the reaction product region and development of a crater under the drop, contributes to the perturbation of the triple line and to the formation of apparent contact angles at 1073–1273 K. This leads to unusual changes of measured contact angles with temperature, decreasing from 84^° at 973 K to 36^° at 1073 K, and then increasing to 75^° at 1273 K, while structural analysis suggests complete wetting at 1073 K.     

Investigation on the mechanism of the photoluminescence of MCM-41

Pure siliceous MCM-41 sample was synthesized in ethylenediamine (EDA) medium. MCM-41 sample calcined at 813 K showed the most strong photoluminescent (PL) effect, while those calcined at 1073 K and 1323 K only showed weak photoluminescence. The intensity of photoluminescence decreased as the calcined temperature increased. By nuclear magnetic resonance (NMR) spectroscopy and infrared (IR) investigation, it was demonstrated that both the Al-depleted defect sites and silanol contents were responsible for the strong PL effect of the investigated MCM-41 samples. It was also suggested that the mesoporous channel structure of MCM-41 influences the investigated PL effect.     

Effects of gradient heat treatment on Te-rich CdZnTe crystal

The gradient heat treatment was performed on Te-rich CZT crystal grown by the vertical Bridgman (VB) method, which was under the temperature of 1073 K and the temperature gradient of 2 K/mm and the velocity of 1.8 mm/h. IR transmission, IR microscope, I-V curves and glow discharge mass spectrometry (GDMS) revealed that Te inclusions moved towards the last-to-freeze region in CZT ingot, which proved that the gradient heat treatment has the possibility to purify the CZT ingot. Finally, after the gradient heat treatment, the resistivity of the CZT ingot was enhanced, and the IR transmittance was also improved.     

Measurement of Nb3Ge heat capacity

The heat capacity of massive Nb₃Ge specimens (cast, annealed, and rapidly quenched) is measured by the adiabatic calorimetry method with periodic heat supply over the temperature range 5–30°K. Measurements and data collection were completely automated.Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 41, No. 6, pp. 1073–1077, December, 1981.     

Preparation of New Composite Magnetocaloric Compounds by Modifying the Annealing Temperature of La0.8Ca0.2?x □ x MnO3 Perovskite

In this paper, a new method to broaden the range of the magnetic refrigeration temperature by changing the annealing temperature was proposed. Series of La_0.8Ca_0.2?x ?? _x MnO₃(0.00??x??0.20) compounds were prepared by solid-state reaction and annealed firstly at a temperature of 1473 K (S1) and then at 1073 K (S2). Morphologic and structural studies have revealed that the decrease of the annealing temperature modifies the grain size and the structure of these compounds. The magnetic measurements have shown that the annealing at low temperature (1073 K) increases the magnetization and enhances the one-electron bandwidth, which induces an increase of the Curie temperature for 183 K (S1) to 241 K (S2) for the x=0.00 sample. The magnetocaloric investigation has exposed that the decrease of the annealing temperature induces a change from a second-order magnetic phase transition to first-order one for S1 and S2 compounds, respectively. Also, we have found that the Relative Cooling Power (RCP) factor remains almost constant as a function of calcium-deficiency concentration (x) and the annealing temperature. Finally, we have deduced that we can use composite magnetocaloric compounds, exploiting a mixing of the same compounds annealed at two different temperatures (1473 K; S1) and (1073?K; S2), for refrigeration over the temperature range 175?C264?K.     

Microstructure control on thermoelectric properties of Ca0.96Sm0.04MnO3 synthesised by co-precipitation technique

Nanopowder of Ca_0.96Sm_0.04MnO₃ (CSM) perovskite was prepared by chemical co-precipitation technique. It was characterized and studied by X-ray diffraction and Transmission Electron Microscopy. Nano-crystalline CSM phase having grain size of 60-70 nm can be prepared by calcination at 1073 K for 6 h in air. The obtained nanopowder was pressed, sintered at 1373 K for 24 h to obtain a dense sample. In comparison, CSM samples prepared from normal powder need sintering temperature of 1623 K to reach a similar microstructure, showing the efficiency of nanopowder to decrease the sintering temperature. The thermoelectric properties of samples prepared with two different processes were studied. The Seebeck coefficient and the thermal conductivity slightly decrease by using the nanopowder while the value of the electrical resistivity does not change. This results in the same figures of merit for the two materials.     

The effect of strong magnetic field treatment on microstructure and room temperature compressive properties of NiAl–Cr(Mo)–Hf eutectic alloy

The Ni–33Al–28Cr–6Mo–0.2Hf (at.%) eutectic alloy was treated in a 10 T strong magnetic field at 1073 K, 1173 K and 1273 K for 1 h, respectively. Microstructure examination reveals that after the strong magnetic field treatment, Heusler particles (Ni₂AlHf) along eutectic cell boundaries distribute more uniformly, and moreover most Heusler particles have changed into Hf solid solution. In addition, after strong magnetic field treatment at 1173 K and 1273 K, the original eutectic cellular morphology is changed greatly; Cr(Mo) plates become spheroidizing and trend to align to the direction of strong magnetic field. The compression tests show that room temperature compressive ductility of the alloys with strong magnetic field treatment improves significantly, compared with the heat-treated alloy. The fracture characteristics change from debonding into transgranular cleavage, which indicates that the cohesion of grain boundaries get significant improvement.