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The microstructure of Ti-64 strongly affects the forming and in-service behaviour of aerospace components. The development of microstructure, including crystallographic texture, during thermomechanical processing involves changes caused by deformation, annealing and phase transformation. Recently, it has been reported that deformation and transformation occur concurrently, in a dynamic α → β transformation process, driven by the net flow softening it produces. Here, we present the results of an in-situ synchrotron diffraction experiment that aimed to detect and measure the extent of dynamic phase transformation during hot deformation and its contribution to the crystallographic texture of the alloy. Forged Ti-64 samples were deformed in uniaxial tension at 950°C and a strain rate of about 0.02 s-1, using an electro-thermal mechanical tester (ETMT) mounted on the I12: JEEP beamline at Diamond Light Source. By using a high energy 89 keV synchrotron X-ray beam and a fast acquisition rate (10 Hz) we were able to measure, during deformation, the internal elastic lattice strains in the two phases, the crystallographic texture of both phases and the α → β phase fraction. The results show, for the first time, direct evidence of dynamic transformation during isothermal hot deformation.

In his classic 1976 article on the state of policy studies in Canada, Richard Simeon explicitly warned against following the path toward a policy science. Simeon was suspicious of the normative agenda embedded in the policy sciences project and worried that it would submerge politics in a broader set of interdisciplinary concerns. Was Simeon right? The policy sciences have not developed the way their principal proponent, Harold Lasswell, had anticipated or hoped, but neither has the study of public policy developed exactly as Simeon advocated. Both Lasswell and Simeon believed strongly in an empirical orientation and Lasswell, more than Simeon, focused on creating a tool kit of techniques. Schools of public policy have moved beyond both critique and technique to estimate risk, ameliorate error and mobilize knowledge. This new agenda requires students of public policy to acquire and employ practical knowledge steeped in the particular and instructed by policy narratives. [ABSTRACT FROM PUBLISHER]

Near-α Ti-alloys such as TIMETAL® 834 are known for their superior mechanical properties at high temperature, and as such are found in applications where high strength and improved fatigue performance at elevated temperatures (>450°C) are required. However, these alloys can be susceptible to cold-dwell fatigue; a failure mechanism that is not well understood. The present work investigates the strain localisation behaviour during cold creep and the implications it has in terms of dwell susceptibility for two different bi-modal microstructures. Slip traces and strain distributions have been analysed for different material conditions by employing High-Resolution Digital Image Correlation (HRDIC) in combination with orientation mapping. Using this approach, it was possible to distinguish deformation patterns in primary α grains and transformed-β colonies, loaded incrementally to stress levels of 70%, 80% and 90% of the yield stress. Different prior β-grain morphologies didn’t affect the average strains when stresses are low; but strain distributions have been affected by the β-grain morphology. Material with coarse transformation product accumulated larger amounts of plastic strain compared to material with fine transformation product, at the same relative stress levels. At low stress levels, slip bands have been detected both in primary α, as well in the transformed-β phase, cutting through the lamellae, for the material condition with a coarse transformation product; on the other hand, for the material conditions with a fine transformation product, slip bands are localised only in primary α grains at low stress levels. It was also found for both conditions that at low stress levels slip bands are found in grains that are well oriented for basal slip. Based on these observations it is discussed if b-ligaments are significant obstacles to dislocation movement. Finally, the requirement of crystal-plasticity modelling to take into account differences in crystallographic orientations and the elastic and plastic anisotropy of HCP-titanium will be discussed and considered.