Deformation and failure of thin brazed joints—microscopic considerations

Experimental data are presented on the microscopic aspects of the strength and deformation of thin brazed joints. Determination of the shear stress distribution at the braze interface revealed that the interfacial shear intensity increases as the thickness to diameter ratio,t/d, increases. The contribution of geometrical constraint (triaxiality) to joint strengthening was found to increase drastically ast/d decreases whereas the role of strain hardening in joint strengthening was found to change from one of delaying macroscopic instability in thick joints to the microscopic role of delaying microvoid coalescence in thin joints. Stress-strain measurements of both the braze metal and adjacent layers of the base metal showed that increasing triaxiality (lowert/d) results in lower axial strains within the joint for any given axial stress. In addition, base metal yielding was found to cause large increases in plastic strain within the brazed joint.     

Crystallisation of lithium zinc silicates

Metastable phases and phase assemblages are commonly encountered in the Li₄SiO₄-Zn₂SiO₄ system. Typically, the metastable states arise from a failure of the system to remain at equilibrium upon cooling from higher temperatures. Physical data, including X-ray powder patterns, are presented to characterise the metastable phases. The crystallo-chemical relationships between the metastable and stable phases are discussed and used to explain why metastable phases may arise. Many of the features of the metastable phase assemblages can be represented on phase non-equilibrium diagrams.The possibilities of encountering these and structurally related phases in glass-ceramics are discussed.     

The solid electrolyte system,Li3PO4Li4SiO4

The phase diagram of the system Li₄SiO₄Li₃PO₄ has been studied. At subsolidus temperatures, ? 1000°C, Li₄SiO₄ forms a short range of equilibrium solid solutions between 0 and ～ 12 mole % Li₃PO₄; γ-Li₃PO₄ forms a range of equilibrium solid solutions between ～ 58 and 100% Li₃PO₄. In addition to these equilibrium solid solutions, Li₄SiO₄ forms an extensive range of metastable solid solutions containing up to ～ 60% Li₃PO₄, on quenching melts from ? 1050°C. Hence compositions around 60% Li₃PO₄, 40% Li₄SiO₄ may be prepared in two structural forms, i.e. as solid solutions of either Li₄SiO₄ or γ Li₃PO₄. Conductivity measurements show that, at these compositions, the two solid solution structures have similar, high conductivity of Li⁺ ions.     

Runner flow in injection moulds

Runner flow in injection moulding has been investigated employing pressure drop, coloured tracer and birefringence measurements. Runners having a variety of lengths and numbers of elbows were employed and it was found that the results obtained could be explained in terms of a general non-Newtonian fluid model with local heat generation. The characteristics of this type of flow are significantly different from isothermal laminar shear flow and suggest that practical advantages can result from the use of long runners containing a number of elbows in certain cases.     

Phase equilibria in the system Li2O-TiO2

The system Li₂O-TiO₂ contains four stable phases: Li₄TiO₄, Li₂TiO₃, Li₄Ti₅O₁₂ and Li₂Ti₃O₇, and one metastable phase, H. Li₂TiO₃ undergoes an order-disorder phase transition at 1215°C. High Li₂TiO₃ forms an extensive range of solid solution between ～44 and 66 mole % TiO₂ and low Li₂TiO₃ forms a more limited range of solid solution between ～47 and 51% TiO₂. The temperature of the order-disorder transition decreases to either side of the Li₂TiO₃ composition. The spinel phase Li₄Ti₅O₁₂, has an upper limit of stability at 1015 ± 5°C, above which it decomposes to high Li₂TiO₃ ss and Li₂Ti₃O₇. Li₂Ti₃O₇ has a lower limit of stability at 957 ± 20°C, below which it decomposes to Li₄Ti₅O₁₂ and rutile. During this decomposition of Li₂Ti₃O₇, phase H, a metastable phase of unknown composition, forms as an intermediate. Li₂Ti₃O₇ forms a short range of solid solutions between ～74 and 76% TiO₂. A phase diagram for the system Li₂O-TiO₂ has been constructed using a combination of results determined here and those reported by GICQUEL, MAYER and BOUAZIZ. X-ray powder diffraction data are given for Li₂Ti₃O₇, Li₄Ti₅O₁₂ and phase H.     

Microstructural changes produced in a multifilamentary Nb-Ti composite by cold work and heat treatment

The microstructural changes produced by cold work and heat treatment of a full-scale filamentary Nb-Ti superconducting composite have been investigated using transmission electron microscopy. Full details of the processing conditions used are given, and both longitudinal and transverse sections of the microstructure have been examined. Heat treatments are found to give a complex precipitate morphology; the precipitates produced by heat treatments at 648 K (375 °C) were found to range from a thin boundary film 3 to 6 nm thick, through small approximately ellipsoidal precipitates (~5 x 10 nm), to larger (~50 to 500 nm) equiaxed precipitates. The larger precipitates could be identified as α-Ti. Cold drawing was found to refine the microstructure, but an even greater degree of refinement was observed when intermediate heat treatments were applied. The observations of this investigation show a strong interdependence between the cold-worked substructure and the precipitate morphology in these heat-treated and heavily cold-worked (ε ~ 5 to 9) composites.     

The reversion of martensite to austenite in certain stainless steels

An investigation has been made of the reversion of martensite () to austenite () in two stainless steels (i) Fe-16 wt% Cr-12 wt% Ni (of low interstitial content) (ii) Fe-15 wt% Cr-8 1/2 wt% Ni-2 wt% Mo-0.09 wt% C. The alloys were refrigerated to produce 12 to 15% martensite () and then heated for short times at various temperatures ranging from below A _s to above A _f. With rapid heating the reversion of to occurs largely by a shear mechanism. In the Fe-16Cr-12Ni alloy individual grains of transform to grains of reversed of similar size and shape. In the carbon-containing alloy there is evidence of break-up of the grains on reversion. An increase in the strength results from reversion and this is attributable mainly to the high dislocation density of the reversed .     

Effects of drinking water temperature on production responses in lactating Holstein cows in summer

During late summer, 24 lactating Holstein cows were offered 10 or 28 degrees C (control) drinking water ad libitum at 1400 h for 10 min to investigate the effects on respiration rates, body temperatures, dry matter intake, and milk production. Experimental design was a 2 X 3 factorial arrangement of the two drinking water temperatures with .8, 1.1, and 1.4% dietary potassium associated with another experiment. Following 1 wk adjustment and 1 wk standardization, cows were blocked by dry matter intake as a percentage of body weight within parity and randomly assigned to treatments within blocks. Cows were denied access to water from 0900 until 1400 h. Respiration rates and rectal temperatures were recorded before and after watering. Tympanic membrane temperatures (8/h) were recorded during the comparison period using 4 cows per water treatment. No interaction occurred between water and potassium. Water at 10 degrees C had a greater cooling effect than 28 degrees C water. No differences were found between treatments in respiration rates and rectal temperatures after drinking water was temperatures after drinking water was offered. Chilled drinking water decreased tympanic membrane temperatures, which remained lower longer. Cows that drank 10 degrees C drinking water increased dry matter intake and milk yield.