Volume 15, Issue 4
August 1992, pages 289-387
pp 289-296 August 1992
Texture plays an important role in the commercial acceptability of Zr-2·5 wt% Nb pressure tubes used in nuclear reactors. A modified flow sheet for the fabrication of these pressure tubes involves a few additional steps viz. stress relieving, cold working and annealing, as compared to the conventional route. The evolution of texture during sequential fabrication steps of extrusion, stress relieving, cold working and annealing was studied in terms of texture coefficients and inverse pole figures. It was observed that crystallographic texture primarily developed during hot extrusion and the additional steps of stress relieving, cold working and annealing did not alter the texture significantly. The texture developed was one having a majority of the basal plane normals along the tangential direction of the tube.
pp 297-310 August 1992
Considerable anisotropy in the mechanical properties of quaternary Al-Li-Cu-Mg alloys was observed in both plate and sheet products. These alloys showed more than 100% increase in tensile ductility in the test direction oriented at 45–60° to the rolling direction as compared to that in the rolling direction (longitudinal, L). A concomitant decrease in strength was also found. These alloys exhibit superior low cycle fatigue resistance in the long-transverse (LT) direction as compared to the longitudinal (L) direction. Another observation is the occurrence of strength differential (S-D), which is seen to be directional. The trends in S-D are similar under monotonic as well as cyclic loading conditions. The fracture resistance is also highly anisotropic. An attempt is made here to correlate the observed anisotropy in the mechanical behaviour of these alloys with the microstructure and crystallographic texture.
pp 311-319 August 1992
Cathodic hydrogen charging in 3·5% NaCl solution altered the mechanical properties of 2091-T351 (Al-Cu-Li-Mg-Zr) determined by a slow (10−3/s) strain rate tensile testing technique. UTS and YS decreased in the case of 2091-T351 and 2014-T6(Al-Cu-Mn-Si-Mg) with increase in charging current density. Elongation showed a decrease with increase in charging current density for both the alloys. However, elongation occurring throughout the gauge length in uncharged specimens changed over to localized deformation, thus increasing the reduction in area in charged specimens. A transition in fracture mode from surface (brittle) to the core (ductile) was observed. The presence of hydrogen increased the hardness, mostly indicative of solution strengthening and it decreased with depth confirming the existence of hydrogen concentration gradient. The effects were similar in 2014-T6, but to a slightly smaller extent.
pp 321-331 August 1992
The paper describes a computer-based methodology for evaluating various strain and stress components within the body of a material undergoing plastic deformation. The strategy uses as input the grid distortion data, which provides the magnitudes of macroscopic particle velocities at discrete (nodal) points. To facilitate computation of the various strain-rate and strain components by explicit differentiation, B-spline functional relationships have been established for this data employing interpolating techniques. Numerical solutions obtained using this methodology have been compared with FEM predictions, which indicate that the results are in good agreement. Further, using plasticity theory, a set of partial differential equations have been established to describe the stress gradients induced due to materials processing. The mathematical formulations in the work are described only in polar coordinates, but the program VISIO can also handle the nodal displacements prescribed in rectangular coordinates too.
pp 333-338 August 1992
Microhardness studies were carried out on (100) faces of gel-grown ADP and KDP single crystals. Slip lines were observed on (100) face of ADP crystal at the corners of the impressions. Microcracks around the indentation were found on (100) face of KDP crystal from 10g load which spread out as the load increased. Vickers hardness numberHv decreased with increase in load. ΔHv at 50g load for solution-grown crystals and gel-grown crystals (present case) was determined. Work hardening indexn for both ADP and KDP crystals was less than 2 showing soft-material characteristics. Using Wooster’s empirical relation, values of C11 from hardness were calculated and found to be close to the reported ones.
pp 339-347 August 1992
Barium copper oxalate was grown in silica hydrogel at ambient temperature. The effect of various parameters like gel pH, gel density, gel aging and concentrations of reactants on the growth of these crystals was studied. The crystals grown were characterized by chemical analysis, X-ray powder diffractometry, infrared spectroscopy, thermogravimetric and differential thermal analysis. The results of these observations are described and discussed.
pp 349-353 August 1992
Molybdate crystals doped with rare-earth ions are finding immense use as laser materials. Rare-earth mixed single crystals of samarium barium molybdate grown in silica gel are important for use in optical equipment and electronic and acoustic studies. These octahedral bipyramidal crystals of samarium barium molybdates are characterized by IR, EDAX and thermal analyses.
pp 355-362 August 1992
Single crystals of LiNaSO4 were grown without adjusting the pH value of equimolar aqueous solution containing Li2SO4·H2O and NaHSO4 at 30°C. As-grown crystals were characterized using X-ray, IR, Raman and other crystal perfection studies such as chemical etching, scanning electron micrograph and microhardness measurements. Atomic absorption technique was adopted to verify the composition of Li+ and Na+ ion content and these were found to be consistent with the desired composition to within ± 6 mol%.
pp 363-366 August 1992
Glass-silver microcomposites have been prepared through sol-gel route by reducing the gel-containing AgNO3 with alkaline formaldehyde solution. The product has been characterized by atomic absorption spectroscopy and X-ray diffraction technique. Optical spectroscopy of thin films has been studied.
pp 367-375 August 1992
A low-temperature route for the synthesis of Ag2S, Ag2Te and their solid solutions Ag2S1 −xTex(0 ≤x ≤ 1) is reported. Ag2S is prepared by the direct addition of silver nitrate solution to thiourea, while Ag2 Te is prepared by reacting silver nitrate solution with tellurium in nitric acid and subsequently reducing it with hydrazine hydrate. The solid solutions of Ag2S and Ag2Te are obtained by the addition of nitrate solutions of silver and tellurium to thiourea followed by its reduction with hydrazine hydrate. The method enables the synthesis of low-temperature crystalline phase of Ag2S1 −xTex solid solutions. The powder X-ray diffraction studies suggest that the solid solutions of compositionsx 〈 0·3 have a phase akin toα-Ag2S and those with compositionsx 〉 0·6 are similar toα-Ag2 Te. In the intermediate range of compositions (x=0·4 and 0·5), the solid solutions are found to be mixtures ofα-Ag2S andα-Ag2 Te phases which transform totally toα-Ag2S phase on prolonged annealing at about 473 K.
pp 377-384 August 1992
Superconducting thin films of Y1Ba2Cu3 O7 −x have been deposited on (100) Y-ZrO2 substrates by pulsed excimer laser ablation from anunreacted mixture of Y2O3, BaCO3 and CuO. The films deposited at substrate temperature of 680°C and oxygen partial pressure of 200 mtorr were found to be superconducting with zero resistive transition temperature of 89 K and critical current density of over 3 × 105 A/cm2 at 77 K. These results are compared with those obtained by laser ablation from a sintered superconducting pellet.
pp 385-387 August 1992
X-ray powder analysis of solid solution of NaH2PO4 and KH2PO4 with H3BO3 was carried out. Both the systems were observed to be tetragonal. The crystallographic data are reported.
Volume 42 | Issue 6
Click here for Editorial Note on CAP Mode