Deformation induced phase transformation during machining of Ti-5553

Ti-5553 is a relatively new titanium alloy with applications particularly in the aerospace industry for such key structural components as landing gear. However, during machining of Ti-5553, the elevated temperature and high strain at tool-workpiece interface may alter workpiece microstructure and result in ß to a phase transformation. During phase transformation, some intermediated phase such as w phase may form which is brittle and hard to machine, and it could reduce the fatigue life of machined components. The aim of this research work is to optimize the machining condition for Ti-5553, in which its hot deformation behavior in terms of ß to a phase transformation could be fully understood. Analysis of variables such as micrographs of phase components and cutting zone temperature demonstrates that the cutting temperature governs the formation of final phase components and to some extent this variation has been quantified to allow for further and more detailed investigation.

Thermoregulation in young athletes exercising in hot environments.

Children are less efficient thermoregulators than are adults. During exercise, sweat evaporation is the most important physiological means of cooling the body. The sweat response in children, however, is less efficient than in adults, so children dissipate less heat though evaporative sweating and more through convection (the loss of heat through the skin) plus radiation. Children and adolescents with high levels of body fat and heavy builds are more susceptible to heat stress because they dissipate body heat less efficiently. Maintaining adequate hydration is crucial for preventing heat stress, Although water is often described as the best choice of fluid, studies on voluntary drinking habits and flavor preferences in children and adolescents suggest that greater consumption occurs when sports drinks are offered instead of water. Although a child's sweat contains less sodium and chloride than an adult's does, there appears to be no evidence that a child's performance improves when given beverages more diluted than those currently recommended for adults, More information is necessary to identify the optimal electrolyte and carbohydrate content of sports drinks for young athletes.

The generation of new high-angle boundaries in aluminium during hot torsion

The crystallographic rotation field for deformation in torsion is such that it is possible for orientations close to stable orientations to rotate away from the stable orientation. A Taylor type model was used to demonstrate that this phenomenon has the potential to transform randomly generated low-angle boundaries into high-angle boundaries. After imposing an equivalent strain of 1.2, up to 40% of the simulated boundaries displayed a disorientation in excess of 15°. These high-angle boundaries were characterised by a disorientation axis close to parallel with the sample radial direction. A series of hot torsion tests was carried out on 1050 aluminium to seek evidence for boundaries formed by this mechanism. A number of deformation-induced high-angle boundaries were identified. Many of these boundaries showed disorientation axes and rotation senses similar to those seen in the simulations. Between 10% and 25% of all the high-angle boundary present in samples twisted to equivalent strains between 2 and 7 could be attributed to the present mechanism.

Ultrafine grained ferrite formed by interrupted hot torsion deformation of plain carbon steel

A plain carbon steel was deformed using a hot torsion deformation simulator. A schedule known to produce strain-induced ferrite was used with the strain interrupted for increasing intervals of time to determine the effect of an isothermal hold on the final microstructure. Microscopy and electron back-scattered diffraction (EBSD) were used to analyse the changes that occurred in the partially transformed microstructure during the hold and the subsequent applied strain. The strain-induced ferrite coarsened during the hold and this coarsened ferrite was refined during the second deformation. These results were compared to those obtained for a different plain carbon steel deformed in single pass rolling close to the Ar3 temperature.

Comparative greenhouse emissions anayalsis of domestic solar hot water systems

It is commonly assumed that solar hot water systems save energy and reduce greenhouse emissions relative to conventional fossil fuel-powered systems. Very rarely has the life-cycle greenhouse emissions (including the embodied greenhouse emissions of manufacture) of solar hot water systems been analysed. The extent to which solar hot water systems can reduce emissions compared with conventional systems can be shown through a comparative life-cycle greenhouse emissions analysis. This method determined the time it takes for these net greenhouse emissions savings to occur, or the 'emissions payback period'. This paper presents the results of a life-cycle greenhouse emissions analysis of solar hot water systems in comparison with conventional hot water systems for a southern (Melbourne) and a northern (Brisbane) Australian city.

Quenched and annealed microstructures of hot worked magnesium AZ31

The microstructures of magnesium AZ31 are examined following hot compression testing and annealing. The grain size, fraction dynamically recrystallized and, in a couple of cases, the crystallographic texture are reported. The progress of dynamic recrystallization and the recrystallized grain size were sensitive to processing conditions, as expected. This effect was more marked in the former than in the latter, compared to other metals. It was also found that, for structures containing between 80 and 95% dynamic recrystallization, abnormal grain growth occurred during annealing. Irrespective of the whether or not abnormal grain growth occurred, the annealing step weakened the crystallographic texture.

Recrystallization during and following hot working of magnesium alloy AZ31

The microstructures of magnesium AZ31 are examined following hot compression testing and annealing. The grain size, fraction dynamically recrystallized and, in a couple of cases, the crystallographic texture are reported. It was found that the progress of dynamic recrystallization is strongly sensitive to processing conditions but that the dynamically
recrystallized grain size was less sensitive to stress than in other metals. It was also found that, for structures containing between 80 and 95 % dynamic recrystallization, abnormal grain growth occurs during annealing. The crystallographic texture produced is also sensitive to the deformation conditions.

A Taylor Model Based Description of the proof stress of magnesium AZ31 during hot working

A series of hot-compression tests and Taylor-model simulations were carried out with the intention of developing a simple expression for the proof stress of magnesium alloy AZ31 during hot working. A crude approximation of wrought textures as a mixture of a single ideal texture component and a random background was employed. The shears carried by each deformation system were calculated using a full-constraint Taylor model for a selection of ideal orientations as well as for random textures. These shears, in combination with the measured proof stresses, were employed to estimate the critical resolved shear stresses for basal slip, prismatic slip, ⟨c+a⟩ second-order pyramidal slip, and { } twinning. The model thus established provides a semianalytical estimation of the proof stress (a one-off Taylor simulation is required) and also indicates whether or not twinning is expected. The approach is valid for temperatures between ∼150 °C and ∼450 °C, depending on the texture, strain rate, and strain path.

Hot working microstructure map for magnesium AZ31

A thermomechanical processing (TMP) structure map is proposed that plots the critical strains required for dynamic recrystallization along with the grain sizes that result. These maps are useful in identifying the limits to grain refinement and designing hot working processes. They are readily constructed for well studied alloys such as plain carbon steel. In light of the recent interest in the hot working of magnesium, initial steps are taken here to construct a TMP structure map for the most common wrought magnesium alloy, AZ31. The completion of dynamic recrystallization is estimated using a geometrical approach and a twinning region is identified.

Too hot to trot? exploring potential links between climate change, physical activity and health

Based on an analysis of existing literature, this paper explores the links between climate change, physical activity and health. It highlights the importance of physical activity for health, explores current understandings of factors influencing participation in sport and physical activity, and develops some hypotheses about the ways in which climate change may impact on the factors influencing physical activity and thereby on the level of participation in physical activity. The paper argues that climate change has the potential to be a barrier to participation in physical activity, particularly in areas where temperatures are already relatively high, and that a reduction in physical activity across the population is likely to have detrimental health impacts. The need for research to clarify the nature and extent of the threat posed to physical activity participation is highlighted, as is the need to take into account the direct and indirect costs of any changes or reductions in physical activity in any assessment of the costs of climate change and/or its mitigation.

Influence of grain size on hot working stresses and microstructures in Mg-3A1-1Zn

The influence of the grain size on the deformation of Mg–3Al–1Zn was examined in compression at 300 °C. At low strains the flow stress increases with increasing grain size. This is interpreted in terms of dynamic recrystallization. Empirical models of dynamic recrystallization are developed and employed to generate a microstructure map.

Net energy analysis of solar and conventional domestic hot water systems in Melbourne, Australia

It is commonly assumed that solar hot water systems save energy and reduce greenhouse gas emissions. The net energy requirement of solar hot water systems has rarely been analysed, including their embodied energy. The extent to which solar hot water systems save energy compared to conventional systems in Melbourne, Australia, is shown through a comparative net energy analysis. It was shown that the embodied energy component of the net energy requirement of solar and conventional hot water systems was insignificant. The solar hot water systems provided a net energy saving compared to the conventional systems after 0.5–2 years, for electric- and gas-boosted systems respectively.

Formation of ultrafine grained microstructures in steel through strain induced transformation during single pass hot rolling

In the present study, wedge-shape samples were used to study the effect of strain induced transformation on the formation of ultrafine grained structures in steel by single pass rolling. The results showed two different transition strains for bainite formation and ultrafine ferrite (UFF) formation in the surface layer of strip at reductions of 40% and 70%, respectively, in a plain carbon steel. The bainitic microstructure formed by strain induced bainitic transformation during single pass rolling was also very fine. The evolution of UFF formation in the surface layer showed that ferrite coarsening is significantly reduced through strain induced transformation combined with rapid cooling in comparison with the centre of the strip. In the surface, the ferrite coarsening mostly occurred for intragranular nucleated grains (IG) rather than grain boundary (GB) ferrite grains. The results suggest that normal grain growth occurred during overall transformation in the GB ferrite grains. In the centre of the strip, there was significantly more coarsening of ferrite grains nucleated on the prior austenite grain boundaries.

Effect of thermomechanical parameters on the critical strain for ultrafine ferrite formation through hot torsion testing

A C–Mn–V steel was used to study ultrafine ferrite formation (1–3 μm) through dynamic strain-induced transformation (DSIT) using hot torsion experiments. A systematic study determined the critical strain for the start of DSIT (C,DSIT), although this may not lead to a fully ultrafine microstructure. Therefore, the strain to produce an ultrafine ferrite (UFF) as final microstructure (C,UFF) during deformation was also determined. In addition, the effect of thermomechanical parameters such as deformation temperature, prior austenite grain size, strain rate and cooling rate on C,DSIT and C,UFF has been evaluated. DSIT ferrite nucleated on prior austenite grain boundaries at an early stage of straining followed by intragranular nucleation at higher strains. The prior austenite grain size affected the distribution of DSIT ferrite nucleation sites at an early stage of transformation and the subsequent coarsening behaviour of the grain boundary and intragranular ferrite grains during post-deformation cooling. Also, C,DSIT and C,UFF increased with an increase in the prior austenite grain size and deformation temperature. The post-deformation cooling had a strong effect not only on C,UFF but also the UFF microstructure (i.e. final ferrite grain size and second phase characteristics).