132 research outputs found
The grain-refinement mechanism during heavy cold-rolling of commercial-purity titanium
Microstructure evolution in heavily-cold-rolled (≥40 pct.) commercial-purity titanium was determined to be governed by a continuous-dynamic-recrystallization mechanism. This process was shown to be closely linked with mechanical twinning occurring at lower rolling strain
The Effect of Hot Deformation Parameters on Microstructure Evolution of the α-Phase in Ti-6Al-4V
The effect of high-temperature deformation and the influence of hot working parameters on microstructure evolution during isothermal hot forging of Ti-6Al-4V in the alpha phase field were investigated. A series of hot isothermal axis-symmetric compression tests were carried out at temperatures both low and high in the alpha stability field [(1153 K and 1223 K (880 °C and 950 °C), respectively], using three strain rates (0.01, 0.1 and 1.0/s) relevant to industrial press forging. The microstructures and orientation of the alpha laths were determined using optical microscopy and electron backscatter diffraction techniques. The experimental results show that there is a change in lath morphology of the secondary α phase under the influence of the deformation parameters, and that α lath thickness appears to have little influence on flow behavior
Microstructure response of cryogenically-rolled Cu-30Zn brass to electric-current pulsing
The effect of transient electric-current pulses (ECP) on the evolution of microstructure and texture of cryogenically-rolled Cu-30Zn brass was determined. The pulsing was shown to lead to recrystallization followed by grain growth. The mean grain size in the recrystallized material was 0.5 μm, thus indicating that cryogenic rolling coupled with ECP is suitable for the production of an ultrafine-grain microstructure in Cu-30Zn brass. The differences in the recrystallization texture in pulsed versus statically-annealed conditions suggested a distinct recrystallization mechanism during ECP
Phonon densities of states of face-centered-cubic Ni-Fe alloys
Inelastic neutron scattering and nuclear resonant inelastic x-ray scattering were used to determine the phonon densities of states of face-centered-cubic Ni-Fe alloys. Increasing Fe concentration results in an average softening of the phonon modes. Chemical ordering of the Ni_(0.72)Fe_(0.28) alloy results in a reduction of the partial vibrational entropy of the Fe atoms but does not significantly change the partial vibrational entropy of the Ni atoms. Changes in the phonon densities of states with composition and chemical ordering are discussed and analyzed with a cluster expansion method
Electronic structure and vibrational entropies of fcc Au-Fe alloys
Phonon density of states (DOS) curves were measured on alloys of face-centered-cubic (fcc) Au-Fe using nuclear resonant inelastic x-ray scattering (NRIXS) and inelastic neutron scattering (INS). The NRIXS and INS results were combined to obtain the total phonon DOS and the partial phonon DOS curves of Au and Fe atoms from which vibrational entropies were calculated. The main effect on the vibrational entropy of alloying comes from a stiffening of the Au partial phonon DOS with Fe concentration. Force constants were calculated from first principles for several compositions and show a local stiffening of Au-Au bonds close to Fe atoms. The calculated phonon DOS curves reproduce the experimental trend. The stiffening is attributed to two main effects comparable in magnitude: (i) an increase in electron density in the free-electron-like states and (ii) stronger sd hybridization
Comparison of gamma-gamma Phase Coarsening Responses of Three Powder Metal Disk Superalloys
The phase microstructures of several powder metal (PM) disk superalloys were quantitatively evaluated. Contents, chemistries, and lattice parameters of gamma and gamma strengthening phase were determined for conventionally heat treated Alloy 10, LSHR, and ME3 superalloys, after electrolytic phase extractions. Several of long term heat treatments were then performed, to allow quantification of the precipitation, content, and size distribution of gamma at a long time interval to approximate equilibrium conditions. Additional coarsening heat treatments were performed at multiple temperatures and shorter time intervals, to allow quantification of the precipitation, contents and size distributions of gamma at conditions diverging from equilibrium. Modest differences in gamma and gamma lattice parameters and their mismatch were observed among the alloys, which varied with heat treatment. Yet, gamma coarsening rates were very similar for all three alloys in the heat treatment conditions examined. Alloy 10 had higher gamma dissolution and formation temperatures than LSHR and ME3, but a lower lattice mismatch, which was slightly positive for all three alloys at room temperature. The gamma precipitates of Alloy 10 appeared to remain coherent at higher temperatures than for LSHR and ME3. Higher coarsening rates were observed for gamma precipitates residing along grain boundaries than for those within grains in all three alloys, during slow-moderate quenching from supersolvus solution heat treatments, and during aging at temperatures of 843 C and higher
The Kinetics of Primary Alpha Plate Growth in Titanium Alloys
The kinetics of primary alpha-Ti colony/Widmanstatten plate growth from the
beta are examined, comparing model to experiment. The plate growth velocity
depends sensitively both on the diffusivity D(T) of the rate-limiting species
and on the supersaturation around the growing plate. These result in a maxima
in growth velocity around 40 K below the transus, once sufficient
supersaturation is available to drive plate growth. In Ti-6246, the plate
growth velocity was found to be around 0.32 um min-1 at 850 oC, which was in
good agreement with the model prediction of 0.36 um min-1 . The solute field
around the growing plates, and the plate thickness, was found to be quite
variable, due to the intergrowth of plates and soft impingement. This solute
field was found to extend to up to 30 nm, and the interface concentration in
the beta was found to be around 6.4 at.% Mo. It was found that increasing O
content will have minimal effect on the plate lengths expected during
continuous cooling; in contrast, Mo approximately doubles the plate lengths
obtained for every 2 wt.% Mo reduction. Alloys using V as the beta stabiliser
instead of Mo are expected to have much faster plate growth kinetics at
nominally equivalent V contents. These findings will provide a useful tool for
the integrated design of alloys and process routes to achieve tailored
microstructures.Comment: Revised version resubmitted to journa
Applying a new concept of embedding qualitative research: An example from a quantitative study of carers of people in later stage dementia
BACKGROUND: Qualitative methods are increasingly included in larger studies to provide a richer understanding of people's experience. This paper explores the potential of using a novel approach to embedded qualitative design as part of an observational study examining the effectiveness of home support for people in later stage dementia in England. The method involved collecting and analysing unsolicited conversational comments made by participants as they completed standardised measures. An evaluation of the method is presented using the voices of participants to illustrate its potential. METHODS: The conversations of 17 carers recruited to an observational study were audio recorded to gather commentary made while completing a structured interview. Data were interrogated using thematic analysis to investigate the feasibility of conducting an embedded qualitative study, the potential richness of the material and participants' reactions to formal questioning and participating in research. RESULTS: The findings revealed that qualitative data were available from this approach. Analysis generated three themes from carers: conflicting carer emotions; the importance of maintaining normality and agency within day-to-day life; and tensions between these desires and making use of formal services. Important issues for carers were revealed establishing the benefit of using the method. The advantages of exploiting unsolicited conversation included enhancing understanding of people's lived experience, reducing participant burden in research and easing the process of data collection. In addition, it provided an opportunity to evaluate individuals' experience of the research process. CONCLUSIONS: The findings demonstrate how unsolicited comments during structured interviews may appear incidental but can reveal important aspects of living with dementia. The method also emphasised methodological challenges for research in dementia, including the influence and impact of the research context. Further research is required to evaluate the method with other groups including people with dementia themselves
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