Room temperature synthesis of high temperature stable lanthanum phosphate–yttria nano composite

A facile aqueous sol–gel route involving precipitation–peptization mechanism followed by electrostatic stabilization is used for synthesizing nanocrystalline composite containing lanthanum phosphate and yttria. Lanthanum phosphate (80 wt%)–yttria (20 wt%) nano composite (LaPO₄–20%Y₂O₃), has an average particle size of ～70 nm after heat treatment of precursor at 600 °C. TG–DTA analysis reveals that stable phase of the composite is formed on heating the precursor at 600 °C. The TEM images of the composite show rod shape morphology of LaPO₄ in which yttria is acquiring near spherical shape. Phase identification of the composite as well as the phase stability up to 1300 °C was carried out using X-ray diffraction technique. With the phases being stable at higher temperatures, the composite synthesized should be a potential material for high temperature applications like thermal barrier coatings and metal melting applications.     

Effects of cyclic stressing,heat treatment and shot-peening pressure on the residual stress distribution in two titanium alloys

Using the method of drilling holes, the residual stress distributions were determined in two titanium alloys, IMI-685 and IMI-318, in the machined, polished, shot-peened and cyclically stressed (MPSC) as well as the heat-treated and quenched (HTQ) conditions. In IMI-318, the effect of shot-peening pressure on the residual stress distribution was also studied. Tensile cyclic stressing relaxed the shot-peen induced residual stresses in the longitudinal direction and the extent of relaxation depended on the degree of cyclic softening present in the material. In both alloys, in the post- heat-treated and quenched condition, the residual stresses were tensile in nature. In IMI-318, a decrease in the shot-peening pressure led to residual stresses of lower magnitudes. The peak residual stress was present closer to the surface when the shot-peening pressure was increased.     

Kinetics of Crystallization of High-T c Superconductor/Thermoplastic Polymer Composite

Composite of YBa₂Cu₃O_7−x and high-density polyethylene (HDPE) prepared by mixing both materials display improving flexibility and crystallinity with increasing polymer content. Differential scanning calorimetry (DSC) data at different heating rates on the composite is reported and discussed. The crystallization data are interpreted in terms of analyses developed for non-isothermal crystallization. The activation energy of crystallization and dimensionality of growth, which are important parameters for controlling crystallization, are evaluated. The results confirm that the crystallization mechanism of YBCO/HDPE composite is based on three-dimensional growth.     

Thermally assisted deformation of structural superplastics and nanostructured materials: A personal perspective

Optimal structural superplasticity and the deformation of nanostructured materials in the thermally activated region are regarded as being caused by the same physical process. In this analysis, grain/interphase boundary sliding controls the rate of deformation at the level of atomistics. Boundary sliding develops to a mesoscopic level by plane interface formation involving two or more boundaries and at this stage the rate controlling step is boundary migration. In other words, grain/interphase boundary sliding is viewed as a two-scale process. The non-zero, unbalanced shear stresses present at the grain/interphase boundaries ensure that near-random grain rotation is also a non-rate controlling concomitant of this mechanism. Expressions have been derived for the free energy of activation for the atomic scale rate controlling process, the threshold stress that should be crossed for the commencement of mesoscopic boundary sliding, the inverse Hall-Petch effect and the steady state rate equation connecting the strain rate to the independent variables of stress, temperature and grain size. Beyond the point of inflection in the log stress-log strain rate plot, climb controlled multiple dislocation motion within the grains becomes increasingly important and at sufficiently high stresses becomes rate controlling. The predictions have been validated experimentally.     

Strain distribution on the surface of specimen in superplastic compression

Strain distribution on the surface of specimens during superplastic flow in compression is determined. It is shown to be distinctly different from what has been reported for tensile superplasticity. The origins of these differences are discussed.     

Effect of shot peening on the fatigue and fracture behaviour of two titanium alloys

The fatigue and fracture behaviour of two titanium alloys, the near-alpha IMI-685 and alpha-beta IMI-318, were studied in the machined and polished (MP) as well as the machined, polished and shot (glass-bead) peened (MPS) conditions. Glass-bead peening reduced the room-temperature as well as the high-temperature (450°C) fatigue life of alloy IMI-685 at high stress amplitudes, _a, approaching the proof stress, _ps, of the material (LCF region). When the applied stress amplitude (0–770 MPa, HCF region) was comparable to the peen-induced peak longitudinal residual stress, _LP, i.e. (_LP/a)=0.92, an improvement in the room-temperature fatigue life of IMI-685 was observed. When the (_LP/a) ratio was less than this value, decreases in the fatigue life were seen. The room-temperature fatigue behaviour of IMI-318 at high stress amplitudes was similar to that of IMI-685. The decrease in the fatigue life of this alloy, at a stress amplitude (770 MPa) where improvement was observed for IMI-685, could be attributed to the higher relaxation of peen-induced residual stresses in IMI-318 compared with IMI-685. Glass-bead peening improved the hightemperature (450°C) fatigue life of IMI-685 at a low stress amplitude (465 MPa; (_a/PS)=0.87). The crack-initiation sites in the MP and the MPS conditions were at the surface for both the alloys. However, fracture in the surface layers of the alloys appeared more brittle in the peened (MPS) rather than in the unpeened (MP) condition.     

Transmission electron microscopy studies of thermomechanically control processed multiphase medium-carbon microalloyed steel: Forged, rolled, and low-cycle fatigued microstructures

A ferrite-bainite-martensite (F-B-M) microstructure was produced in a medium-carbon microalloyed (MA) steel through two routes, namely, low-temperature finish forging and rolling, followed by a two-step cooling (TSC) and annealing. Transmission electron microscopy (TEM) was employed to study the microstructural evolution in control forged and rolled material after TSC followed by annealing (TSCA). A TEM investigation was also carried out on samples low-cycle fatigue (LCF) tested at low and high total strain amplitudes of 0.4 and 0.7 pct in case of the forged steel (F-B-M(F)TSCA) and 0.55 and 0.8 pct for the rolled steel (F-B-M(R)TSCA), respectively. Microstructural changes accompanying the LCF testing were identified. The two-step cooled microstructure processed through forging (F-B-M(F)TSC) as well as rolling (F-B-M(R)TSC) revealed a complex multiphase microstructure, along with films and blocks of retained austenite. In both microstructural conditions, vanadium carbide precipitates were too fine to be identified after the TSC treatment. Annealing after TSC produced a stress-free microstructure. The F-B-M(F)TSCA microstructure predominantly consisted of granular/lower bainite, lath martensite, and polygonal ferrite with interlath films as well as blocks of retained austenite, while the F-B-M(R)TSCA microstructure predominantly consisted of lath martensite, granular/lower bainite, and polygonal ferrite with interlath strips/films of retained austenite. Lath martensite content was higher in the F-B-M(R)TSCA condition than in the F-B-M(R)TSCA condition. In both conditions, vanadium carbide precipitates could be seen after annealing. Fatigue-tested F-B-M(F)TSCA microstructure up to a total strain amplitude of 0.4 pct and F-B-M(F)TSCA microstructure up to a total strain amplitude of 0.55 pct were stable. Lath martensite did not undergo deformation and in both microstructural conditions dislocation cell structures were not observed in the ferrite or bainite regions. The interlath retained austenite strips/films played a significant role in preventing the softening during fatigue loading. First, it was stable up to a total strain amplitude of 0.4 and 0.55 pct in the respective microstructures. Second, it underwent heavy deformation during fatigue loading at high total strain amplitudes, thereby accommodating the strain. Fatigue-tested F-B-M(F)TSCA microstructure at a total strain amplitude of 0.7 pct and F-B-M(R)TSCA microstructure at a total strain amplitude of 0.8 pct revealed deformed bainite/martensite laths, dislocation cells, and slip bands in the ferrite regions, which are characteristic features of cyclic softening. The retained austenite transformed to martensite through a strain-induced transformation mechanism and, at that stage, the microstructure contained in addition dislocation-rich bainite and ferrite.     

Dilated Networks for Photonic Switching

We present some novel architectures for rearrangeably nonblocking multistage photonic space switches implemented using arrays ofTi:LiNbO_{3}directional couplers. Multistage networks, studied mostly in the electronic domain, are obtained by minimizing the number of 2 × 2 elements needed to implement a switch. Unfortunately, straightforward extensions of these networks to the photonic domain show that the switch size has to be severely limited by the crosstalk in each of theTi:LiNbO_{3} 2 times 2switching elements. Our networks, on the other hand, have a controllable (including almost zero) amount of crosstalk, low optical path loss, and an asymptotically optimal number of directional coupler switches for a given switch size. In addition, the switch has a simple control algorithm and its performance for light loading appears very promising. The switch is easily decomposable into smaller arrays of no more than two types, making it easy to partition the switch into chips. At the cost of a slight increase in crosstalk, the switch can be made single fault tolerant in terms of its ability to connect any input to any output.     

Glycoform composition of serum gonadotrophins through the normal menstrual cycle and in the post-menopausal state

The heterogeneity of follicle stimulating hormone (FSH) and luteinizing hormone (LH) was investigated in five women aged 29.4 +/- 3.2 years (mean +/- SD) throughout their menstrual cycles and in five post-menopausal women aged 53.8 +/- 5.6 years. Chromatofocusing (pH range 7-4) revealed menstrual cycle stage- and postmenopausal-related differences in the serum gonadotrophin charge. There were differences in the proportion of FSH with an isoelectric point (pl) > 4.3 across phases of the menstrual cycle (P = 0.019): midcycle (MC) 50%; early to mid-follicular (EMF) 36%; late follicular (LF) 37%, luteal (L) 29% and following the menopause (PM) 17%. There was no significant difference in the proportion of LH with pl > 6.55 between midcycle (53%) and EMF, LF or L phases (36, 43 and 32% respectively); although all were greater than that found in the menopause (13%). Concanavalin A chromatography revealed less (P < 0.005) complex FSH and LH glycoforms at midcycle (63 and 13%) than in the EMF, LF and L phases (90 and 18; 90 and 20 and 93 and 24% respectively). Menopausal gonadotrophins were least complex (FSH 34%, LH 4%). There was a direct relationship between serum FSH and FSH pl/complexity, and less acidic FSH was associated with reduced FSH complexity. Increased oestradiol was associated with basic FSH isoforms during the menstrual cycle and reduced follicular phase FSH complexity. We conclude that changes in gonadotrophin glycoforms occur through the menstrual cycle which are related to changes in the prevailing steroid environment. Following the menopause oestrogenic loss resulted in acidic, relatively simple glycoforms.