Spectroscopic and fluorescence properties of Sm~(3+)-doped zincfluorophosphate glasses

Optical absorption and fluorescence spectra of Sm3＋-doped zincfluorophosphate glasses with molar composition of 44P2O5＋17K20＋9Al2O3＋（30-χ）ZnF2＋χSm2O3 （χ=0.01 mol.%, 0.05 mol.%, 0.1 mol.%, 0.5 mol.%, 1.0 mol.%, 2.0 and 3.0 mol.%） referred as PKAZFSm were prepared by melt quenching technique and were characterized through Raman, absorption, emission and decay curve analysis. From the absorption spectra, Judd-Ofelt intensity parameters were determined and were used to predict radiative properties such as transition probabilities （AR, radiative lifetimes （τR）, branching ratios （βR）, effective bandwidths （△λeff） and stimulated emission cross-section （σ（λp）） for the excited 4G5/2 luminescent level. The decay curve for the 4G5/2 level was single exponential for lower concentration and became non-exponential for higher concentrations. The non-exponential nature of the decay curves of the 4G5/2 level increased with increase in Sm3＋ ions concentration accompanied by decrease in lifetime due to energy transfer processes among the Sm3＋ ions. The non-exponential decay curves was well fitted to the generalized Inokuti-Hirayama model for S=6, indicating that the energy transfer among optically active ions was of dipole-dipole interaction. The cross-relaxation mechanism responsible for the quenching of lifetimes and the effect of variation of concentration on the spectroscopic properties were also discussed.     

Luminescence of samarium doped hydroxyapatite containing strontium: Effects of doping concentration

A series of samarium (Sm) doped hydroxyapatites containing strontium (Sr) with controllable and adjustable luminescence were designed and prepared via chemical hydrolysis co-precipitation method. The effects of doping concentration of Sm on the structure, composition, photoluminescence (PL), energy transfer, substitute site, fluoresce lifetime and luminescence color of samples were investigated. It is shown that the introduction of Sr ions induces the structure and composition change for Sm doped samples. The typical transitions of Sm³⁺ at 564, 601, 648 and 707 nm due to ⁴G_5/2→⁶H_J/2 (J = 5, 7, 9 and 11) transition under the excitation of 404 nm were detected. The PL intensity is affected by the Sr/Ca ratio and Sm concentration, and the optimal concentration of Sm is 0.8 mol% when Sr/Ca ratio equals 7/3. The non-radiative transitions and energy transfer of Sm ions are the main reason for the quenching, and the interactions among ions are ascribed to dipole–dipole type by theoretical calculation. Besides, the ratio of PL intensity between 601 and 648 nm (r_O/R = I_{601 nm}/I_{648 nm}) indicates the symmetry and substitution process of Sm ions to Ca/Sr ions. The fluorescence lifetime (τ) decreases with the concentration of Sm increasing, which is the result of the decrease of distance and the enhanced interaction between Sm ions. The CIE chromaticity coordinates and luminescence color of samples are in the orange-red region and have close relation with the concentration of Sm. Furthermore, the cytotoxicity evaluation and confocal laser scanning microscopy (CLSM) observation of samples via cells indicate the good biocompatibility and safe use of this kind of bio-based luminescent materials for their potential efficient fluorescence labeling and detection.     

The brittle compressive failure of fresh-water columnar ice under biaxial loading

The brittle compressive failure of fresh-water, columnar ice was investigated under biaxial loading at a strain rate of ϵ = 10^⇔2s⁻¹ at temperatures of −10 and −40°C. Tests were performed through proportional loading over the range 0 ⩽R<1 where R is the ration of the major to major comprehensive stress, i.e. R = σ₂/σ₁. Two types of confinement were considered, across the long axis of the columnar grains (type-A) and along the columns (type-B). For both types the major stress was orthogonal to the columns. The results reveal two failure regimes under cross-column loading: the failure stress first increases rapidly with increasing R_A in the range 0 ⩽R_A ⩽ R_t, and then decreases as R_A increases further. The transition ratio, R_t, decreases from ∼0.2 at −10°C to ∼0.1 at −40°C. Correspondingly, the failure mode changes from splitting along the columns along the loading direction at zero confinement to shear faulting in the loading plane at 0 < R_A ⩽ R_t to a combined mode of splitting across the columns and shear faulting out of the loading plane at R_A >R_t. The failure envelope at both temperatures resembles a truncated Coulomb envelope. Under along-column confinement (type-B) neither the failure stress nor the failure mode depends upon the confining stress. High-speed photography and thin-section examinations revealed that wing cracking and localized fragmentation are important elements in the failure process. The observations ae explained in terms of two failure mechanisms; viz. frictional crack sliding and contact tensile fractures.     

Morphological and structural studies of thermoelastic martensites in a Ag-38 At. Pct Zn alloy

Thermoelastic martensites formed upon subzero cooling a Ag-38 at. pct Zn alloy have been studied by means of optical and electron microscopy, electron diffraction, and electrical resistivityvs temperature measurements. Two different morphologies, slender banded and spear shaped, are observed in cooled bulk specimens, both being thermoelastic. The slender banded martensite is retained at room temperature in thin foils after subzero cooling and possesses the 9R type long period stacking order structure with internal stacking faults on the basal plane. This 9R martensite is “normal” with an orthorhombic lattice:a=4.81,b=2.82 andc=20.5Å (a:b:c=1.71:1:7.27). The spear shaped martensite is also retained at room temperature in subzero cooled thin foils and in shape memory cycled ribbons as well. This morphology exhibits a monoclinic 3R type stacking order structure with internal twins and stacking faults. Lattice parameters of the 3R martensite area=4.83,b=2.87,c=6.94Å and β=87.4 deg (a:b:c=1.68:1:2.41). This structure is equivalent to that of AuCuI (L1₀, fct) with lattice parametersa=4.07,c=3.89, andc/a=0.96. The twin and stacking fault planes in the 3R martensite are the (201) and (001) planes respectively. The basal planes of the 9R and 3R martensites are common, being generated from the {110} plane of the CsCl type parent phase, and the two martensites differ only in the shuffling mode on the {110} plane upon transformation. The thermelastic nature of the 3R martensite is slightly different from that of the 9R one.     

Correlation of mechanical anisotropy with fine grain strengthening for Sm2Co17-type sintered permanent magnets

The as-solution-treated Sm₂Co₁₇-type magnets exhibiting a single 1:7H phase with different average grain sizes (D) were designed. Anisotropy of bending strength (R_bb) and compressive strength (R_mc) of the magnets were investigated. Moreover, the R_bb increases from 86 to 173 MPa with D decreasing from ～52 to ～18 μm for group c//h samples. The Hall–Petch correlation was employed to reveal the effect of grain size on mechanical properties of the magnets, giving deep understanding of the mechanical anisotropy characteristics. The relatively high Hall–Petch coefficient K^Rbb (0.79 MPa?m^1/2) gives rise to the largest R_bb (173 MPa) for group c//h samples. The mechanical anisotropy of the samples is well explained based on crystal structure and grain size features (grain boundaries). Grain refinement is an effective way to enhance the mechanical properties of Sm₂Co₁₇-type sintered magnets.     

Abnormal grain growth in pure materials

Thompson et al. [Acta metall.35, 887 (1987)] have proved that if a large grain of size R_A is introduced in a matrix which has Hillert's [Acta metall.13, 227 (1965)] quasi-stationary grain size distribution this large grain will decrease its size relative to the critical radius of the distribution, R_Cr, so that d(R_A/R_Cr)/dt < 0. In the present work the effect of having a matrix distribution different from Hillert's is examined. It is shown that in such case the behaviour of an abnormally large grain is more complex and either d(R_A/R_Cr)/dt < 0 or d(R_A/R_Cr)/dt > 0 are initially possible. The present analysis is applied to lognormal distributions with different values of side deviation.     

Thermal expansion in the Ni−Cr−Al and Co−Cr−Al systems to 1200°C determined by high-temperature X-ray diffraction

The effect of temperature on the lattice parameters of phases in twelve nickel-chromium-aluminum (Ni?Cr?Al) alloys and nine cobalt-chromium-aluminum (Co?Cr?Al) alloys was determined using high temperature diffraction (HTXRD). The temperature range was from 25 to 1200°C. The data for each phase of each alloy were computer fit to an empirical thermal expansion equation developed in this study: \(LP_T = LP_{25^\circ C} (1 + R)^{(1 + T/273)^{1.5} } \) and a value forR was derived for each. Excellent fits were obtained for nearly all cases. A comparison ofR values revealed that for a given phase (ψ/ψ′, β and α in Ni?Cr?Al and αCo and β in Co?Cr?Al),R was independent of alloy composition. In the Ni?Cr?Al systemR for γ/γ′ was 19.2×10^?4,R for β was 19.9×10^?4 andR for αCr was 13.4×10^?4. In the Co?Cr?Al system theR value for αCo was 20.9×10^?4 and theR for β was 17.8×10^?4. Of all of the phases only the αCr in the Ni?Cr?Al system had anR sufficiently low to reduce to an unimportant level the stress generated from thermal expansion mismatch between Al₂O₃ and substrate or coating and substrate with either Ni?Al or Co?Al coatings on a γ/γ′-δ substrate.     

Synthesis and luminescence properties of a novel red-emitting phosphor SrCaSiO_4：Eu~（3＋） for ultraviolet white light-emitting diodes

A novel red phosphor based on Eu3+-activated SrCaSiO4 was successfully synthesized by conventional solid state reaction method and the photoluminescence properties were investigated. X-ray diffraction (XRD) patterns indicated that SrCaSiO4:Eu3+ phosphors belong to orthorhombic crystal system (space group=Pmnb). The photoluminescence (PL) excitation spectrum showed broad-band absorption and the strongest excitation peak at 397 nm contributed to the 7F0→5L6 transition which matched well with the emission of a...     

Microroughness evolution of the inner surface of copper pipes under drawing

The microroughness evolution of the inner surface of copper pipes under drawing is considered. The roughness parameter R _a is measured on the internal surface of pipes after pressing and drawing. It is revealed that R _a is minimal for hot-pressed pipes. Deformation by drawing to a logarithmic degree of deformation in 0.417 is accompanied by a rise in average parameter R _a from 0.20 to 6.16 μm, i.e., approximately 30 times. The highest growth rate of R _a is noted in the early pass of drawing. The increase in the dispersion of the value measured over drawing pass is also ascertained. The resulting phenomenon is explained by the effect of the copper grain turn.     

The use of young’s modulus for predicting the plastic-strain ratio of low-carbon steel sheets

The variation in Young’s modulus,E, and plastic-strain ratio,R, with angle to the rolling direction, ø, was measured for 35 samples of cold-rolled and annealed low carbon steel sheets. Functions ofE andR were fitted to an empirical expression and correlations were made from which it was possible to predict not only the average plastic-strain ratio, ?R, but also the planar anisotropy, ΔR, and the dependence ofR on ø Calculations were made of the orientation dependence ofE and the quantity R/(R + 1) for single crystals of α-Fe. Although these calculations show that the correlations made for polycrystalline samples are reasonable, they offer little guidance as to the probable limits of applicability of the correlations. The limiting drawing ratio (LDR) was determined_for 12 sheet samples by Swift-cup testing. For these limited results, the average modulus, ?E, and the average strain ratio, ?R, correlate equally well with the LDR. Use of E(ø), to predict deep drawability and earing, should reduce the effort required to characterize the formability of. low-carbon steel sheets.     

Calculation of Flux Density Distribution in Multi-pole Ring

We have developed an analytical model for estimating the flux density distribution of multi-pole ring. The flux density could be estimated as long as the valves R_r and R_m and pole pairs and B_r are known, where R_r and R_m are the outer and inner radius of the multi-pole ring and B_r is the remanence of the multi-pole ring, respectively. The calculations show that the peak flux density is going up with increasing the pole pairs then going down with increasing the pole pairs when R/R_m is constant and the peak flux density increases with the R_r/R_m when the pole pairs are constant for both internal and external flux density of the multi-pole ring.     

Optical and luminescence characteristics of Eu3+-doped B2O3:SiO2:Y2O3:CaO glasses for visible red laser and scintillation material applications

Europium(Eu~(3+)) doped glasses of chemical compositions(55-x)B_2O_3:10 SiO_2:25 Y_2O_3:10CaO:xEu_2O_3,where x denotes mol% and ranges 0≤ x ≤ 2.5, were synthesized by adopting conventional melt quenching technique, Physical properties like density, molar volume, polaron radius, inter-ionic distance and field strength of the glass samples were investigated to assess the impact of Eu_2O_3. Optical and luminescence properties of the glasses were characterized with optical absorption, photoluminescence,X-ray induced emission spectra, temperature dependence emission spectra and decay times. Judd-Ofelt(JO) intensity parameters(Ω_λ) of the glasses were evaluated based on the absorption spectrum of 0.5 mol%. JO parameters, calculated from absorption spectra with thermal corrections on oscillator strength, were used to evaluate radiative properties such as radiative transition probability(A_R),branching ratio(β_R), stimulated cross section emission(σ) and radiative lifetime(τ_R) for ~5D_0→~7 F_J(J = 0,1,2,3 and 4) transitions. The decay rate of ~5D_0 fluorescent level for all the glass samples was single exponential. Lifetimes of the ~5D_0 level were decreased with increasing concentrations of Eu~(3+)ions from 0.05 mol% to 2.5 mol% which might be due to energy transfer through cross-relaxation in the glasses. The chromaticity coordinates(x, y) were similar for all BSYCaEu glasses and were located at the red region of CIE 1931 color chromaticity diagram. Hence, these results confirm that the Eu~(3+) doped BSYCaEu glasses could be useful for visible red lasers and glass scintillation applications.     

Fatigue crack growth behavior of 4340 steels

Fatigue crack growth behavior of 4340 steels was investigated in four gaseous environments; laboratory air, wet hydrogen, dry hydrogen and dry helium. Specimen orientation does not affect crack propagation rate results. The effects of R-ratio (load ratio) and environment on crack growth rate properties are interrelated. Increasing R -ratio increases the rates of near-threshold crack propagation. Nevertheless, the effect of R-ratio on crack growth rates in air is much more significant than that in the two dry environments. Interestingly, the R-ratio effect in wet hydrogen is comparable to that in dry environments. At an R-ratio of 0.1, the rates of crack propagation in air are slower than those in dry environments while crack growth rates are essentially identical in wet hydrogen and dry environments. Increasing R -ratio was found to decrease the environmental effect. Furthermore, increasing yield strength from 700 to 1040 MPa does not affect crack propagation behavior. While surface roughness-induced crack closure is thought to be minimal in affecting gaseous-environment near-threshold crack growth behavior of 4340 steels, oxide-induced crack closure governs crack propagation kinetics. It is suggested that in moisture-containing environments, thick oxide deposits measured on fracture surfaces may not result in high crack closure levels. Nevertheless, oxide-induced crack closure rationalized the effects of R-ratio and environment on near-threshold crack growth rate properties. Furthermore, hydrogen embrittlement is believed not to play an important role in influencing wet-hydrogen environment near-threshold crack propagation behavior. At higher ΔK levels (⩾ 12 MPa √m), an “intrinsic” dry hydrogen effect seems to be present, and crack closure, however, cannot account for the environmental effect.     

Anisotropic corrosion behavior of sintered (Ce0.15Nd0.85)30FebalB permanent magnets

In this work, the corrosion behavior of the surface parallel to the oriented c-axis(c‖) and perpendicular to c-axis(c⊥)in the(Ce_(0.15)Nd_(0.85))_(30)Fe_(bal)B dual main phase magnet was studied. With the addition of Ce,the volume fraction of RE-rich phase shown in the backscattered electron(BSE) images is basically approximate on the two surfaces. The free corrosion potential(E_(corr)) of the c‖ surface is more negative,which shows the worse corrosion resistance from the perspective of thermodynamics. While the reaction kinetics parameters with the smaller free corrosion current(i_(corr)) and the larger transfer resistance(R_(ct)) react the opposite conclusion in 3.5 wt% NaCl solution. Moreover, the c‖ surface performs smaller ions concentration of corrosion product and less damaged corrosion morphology compared to c⊥ surface after the free corrosion. The inconformity is not affected by the RE-rich phase, but by the anisotropy of the grains that the c‖ surface has larger density of the atoms and the lower ratio of(Nd, Ce)/Fe.     

Experimental R-curve behavior in partially stabilized zirconia using moiré interferometry

Moiré interferometry is employed to study toughening in partially stabilized zirconia (PSZ). Energy to fracture as a function of crack growth curves (R-curves) is derived from mode I compliance calculations and from near tip fitting of the moiré fringes. The effect of the tetragonal to monoclinic phase transformation in the zirconia is found by comparing the bulk compliance R-curves to the locally derived moiré R-curve. Localized strain field plots are produced from the moiré data for the PSZ zirconia. The observed transformation zone height compares favorably with that predicted by Okada et al. [Acta metall. mater.40, 1421 (1992)] in a companion paper, as does the qualitative nature of the R-curve with predictions by Stump and Budiansky [Acta metall.37, 3297 (1989)].     

Kinetics of fluorescence properties of Eu~(3+) ion in strontium-aluminiumbismuth-borate glasses

Eu3＋ doped strontium-aluminium-bismuth-borate glasses with the chemical composition（50–x）B2O3＋20Bi2O3＋7Al F3＋ 8Sr O＋15Sr F2＋x Eu2O3（where x=0.1 mol.%, 0.5 mol.%, 1.0 mol.% and 1.5 mol.%） were prepared by the conventional melt quenching technique.Structural properties of the prepared glasses were analysed through X-ray diffraction（XRD）, scanning electron microscopy（SEM）, energy dispersive spectroscopy（EDS） and Raman spectral techniques.Thermal stability of glass was analysed by differential thermal analysis（DTA） curve.Photoluminescence characteristics were studied using excitation, emission spectra and decay curves of Eu3＋ doped strontium-aluminium-bismuth-borate glasses.The Judd-Ofelt（J-O） intensity parameters, Ωλ（λ=2, 4 and 6） were obtained using emission spectra and was used to identify the nature of Eu3＋ ions with their surrounding ligands.Using J-O parameters the transition probabilities（A）, stimulated emission cross-sections σE p, branching ratios（βR） and radiative lifetimes（τmeas and τcal） were evaluated for the 5D0→7F J（J=0, 1, 2, 3 and 4） transition of Eu3＋ ions in the present glasses.The decay profiles were found to be non exponential for all the concentrations and the measured lifetimes（τmeas） were obtained from the decay profiles.The higher values of A, σE p, βR and quantum efficiency（η） for 5D0→7F2 emission transition at 617 nm confirmed the present glass was as active medium for red laser emission applications.     

Fatigue crack growth behavior in inconel 706 at 297 K and 4.2 K

The near-threshold fatigue crack growth rate (FCGR) behavior of Inconel 706 was investigated at ambient (297K) and liquid helium (4.2 K) temperatures, respectively. Specimen orientation did not affect the FCGR properties of Inconel 706. At 297 K, a significant influence of R-ratio on the rates of crack propagation was observed while at 4.2 K, the R -ratio effect was minimal. The extent of oxide-induced crack closure was shown to be insignificant in influencing near-threshold crack growth kinetics of Inconel 706 at both temperatures of 297 and 4.2 K. Roughness-induced crack closure was believed to be the dominant mechanism responsible for the influence of R -ratio on the FCGR properties of Inconel 706; this was proved quantitatively by direct crack closure measurements conducted at 297 and 4.2 K. A greater degree of roughness-induced crack closure was observed at 297 K than at 4.2 K; this correlated with the more pronounced R-ratio effect at 297 K. Decreasing the temperature from 297 to 4.2 K decreased the growth rates of fatigue cracks in Inconel 706. The effect of temperature on crack propagation behavior increased with increasing R-ratio. Crack closure could not rationalize this temperature effect. Moreover, the increase in material strength or Young's modulus on cooling from 297 to 4.2 K could not totally account for the influence of temperature on the near-threshold FCGR properties. Dislocation dynamics appears to offer a qualitative explanation for this temperature effect.     

Oxidation of Aluminum Melts with Rare-Earth Metals

Thermogravimetry studies show that the oxidation of aluminum–rare-earth metal (R) melts obeys a parabolic law. The true oxidation rate of the melts is on the order of 10^–4–10^–3 kg/(m² s). In the Al–R systems, the minimum oxidation rate corresponds to the compositions of intermetallic compounds. The oxidation rate of a melt is shown to increase with temperature. It is found by IRS (infrared spectroscopy) and XRD (X-ray diffraction) that the melt oxidation products consist of γ-Al₂O₃, R₂O₃ (R = La, Ce, Pr, Nd, Y, Sc), CeO₂, and rare-earth metal monoaluminates RAlO₃ (CeAlO₃, LaAlO₃, NdAlO₃).     

Rare-earth metals (REMs) in nickel aluminide-based alloys: I. Physicochemical laws of interaction in the Ni-Al-REM and Ni<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Al<Subscript><Emphasis Type="Italic">y</Emphasis></Subscript>-REM-AE (alloying element) systems

The data on the Ni-Al-R (R = REM Sc, Y, La, lanthanides) binary and ternary systems and the interactions of three rare-earth metals (yttrium, lanthanum, cerium) with the main alloying elements (Ti (Zr, Hf), Cr (Mo, W) that are introduced into Ni₃Al-based VKNA alloys are analyzed. The binary aluminides of REMs in the Ni-Al-R ternary systems are shown to be in equilibrium with neither NiAl nor Ni₃Al. The solid solution of aluminum in RNi₅, which penetrates deep into these ternary systems, is the most stable phase in equilibrium with Ni₃Al. In the NiAl (Ni₃Al)-AE-R systems, REM precipitation (segregation) on various defects and interfaces in nickel aluminides is likely to be the most probable, and REMs are thought to interact with the most active impurities in real alloys (C, O, N), since REMs have a large atomic radius and, thus, are virtually undissolved in nickel, aluminum, and nickel aluminides.     

Asymmetric Rolling of Interstitial-Free Steel Using Differential Roll Diameters. Part II: Microstructure and Annealing Effects

The effects of annealing on the microstructure, texture, tensile properties, and R value evolution of an IF steel sheet after room-temperature symmetric and asymmetric rolling were examined. Simulations were carried out to obtain R values from the experimental textures using the viscoplastic self-consistent polycrystal plasticity model. The investigation revealed the variations in the textures due to annealing and symmetric/asymmetric rolling and showed that the R values correlate strongly with the evolution of the texture. An optimum heat treatment for the balance of strength, ductility, and deep drawability was found to be at 873 K (600 °C) for 30 minutes.