The evolution of grain boundary character during superplastic deformation of an Al-6 pct Cu-0.4 pct Zr alloy

The evolution of microstructure, texture, and microtexture in an Al-6 pct Cu-0.4 pct Zr alloy was studied during mechanical testing at 480 °C and a strain rate of 5·10⁻⁴ s⁻¹. The as-processed material had an elongated, banded microstructure and a deformation texture with orientation distribution along the β-orientation fiber. The true strain vs true stress curve exhibited three stages: I, II, and III. Work hardening occurred in stages I and III, whereas nearly steady-state behavior was observed in stage II. A bimodal distribution of boundary disorientation angles was evident in as-processed material and persisted into stage I, with peaks at 5–15 deg in the low-angle boundary (LAB) regime and at 45–60 deg in the high-angle boundary (HAB) regime. An increase in strain rate sensitivity coefficient, m, in stage I was accompanied by fragmentation of the initial microstructure, leading to the formation of new grains. During stage II the strain rate sensitivity coefficient, m, attained a value of 0.5, which is consistent with the onset of grain boundary sliding. In stage III, the texture and the grain boundary disorientation distribution became randomized while the m value decreased. Grain elongation and cavity formation at second-phase particles and along grain boundaries were seen in samples deformed to failure. The as-processed microstructure is described in terms of deformation banding, and a model for the evolution of such a structure during superplastic deformation is proposed.     

Relationship between changes in the total concentration of acetic acid bacteria and major volatile compounds during the acetic acid fermentation of white wine

BACKGROUND: In the scope of the wine vinegar production, this paper provides comprehensive information about the evolution of some volatile compounds during the biological acetification cycle. These data were compared with the acidity, cell concentration and ethanol concentration. Such information may allow a better understanding of the complex biological processes involved. RESULTS: The volatile compounds 2‐phenylethanol, diethyl succinate (diethyl butanedioate), meso‐2,3‐butanediol (meso‐butane‐2,3‐diol), levo‐2,3‐butanediol (levo‐butane‐2,3‐diol), methanol and ethyl acetate exhibited no significant changes between the starting wine and produced vinegar, whereas the rest [acetoin (3‐hydroxybutan‐2‐one) excepted] ethyl lactate (ethyl 2‐hydroxypropanoate), isoamyl alcohols (3‐methylbutan‐1‐ol and 2‐methylbutan‐1‐ol), isobutanol (2‐methylpropan‐1‐ol), 1‐propanol (propan‐1‐ol), and acetaldehyde were consumed in substantial amounts during the process. Additionally, their specific evolution patterns alongside bacterial cell concentrations, acidity and ethanol concentration are shown. CONCLUSION: Concentrations of acetic acid bacteria at the end of the acetification cycle were found to vary because of cell lysis, a result of the high acidity and low ethanol concentration of the medium. Variations were similar to those in some volatile compounds, which suggests their involvement in the metabolism of acetic bacteria. The results testify to the usefulness of this pioneering study and suggest that there should be interest in similar, more detailed studies for a better knowledge of the presence of certain volatile compounds and metabolic activity in cells effecting the acetification of wine. Copyright © 2010 Society of Chemical Industry     

Adaptive system for blood flow estimation

Adaptive estimation of blood flow signals is performed resorting to a framework developed to support research on Doppler blood flow signals' analysis. Real time spectral estimation methods, real time performance evaluation and run-time adjustment of the estimation methods parameters are bound together allowing the system to adapt itself to varying signal characteristics that are caused by physiological reasons.     

Superplasticity in a magnesium alloy prepared with bimodal grain size distributions developed by dynamic recrystallisation

In the present work the influence of bimodal grain size distributions on superplastic behavior, of a magnesium alloy, was investigated. Samples with different volume fraction of fine grains have been prepared, and their strain rate-stress relation during superplasticity has been measured. Additionally, the predictions of two deformation models, based on the isostrain and the isostress conditions, were compared with the experimental data. The isostrain model allows the major experimental observations to be readily explained and predicted.     

Microtexture evolution during annealing and superplastic deformation of Al-5 pct Ca-5 pct Zn

The microtexture and grain boundary misorientation distributions (i.e., mesotexture) of the superplastic alloy Al-5 pct Ca-5 pct Zn have been investigated in the as-processed condition, after annealing at 520 °C (for times ranging from 7 minutes to 90 hours) and after tensile straining in the transverse direction (TD). Three different superplastic straining conditions were considered: 550 °C/10⁻² s⁻¹, 550 °C/10⁻¹ s⁻¹, and 400 °C/10⁻² s⁻¹. Microtexture data were obtained by means of computer-aided electron backscatter diffraction analysis methods. The retention of the deformation texture of the as-received material and the development of an increasingly bimodal grain boundary misorientation distribution following static annealing are consistent with the occurrence of recovery and continuous recrystallization. During superplastic straining, deformation texture components are also retained, but with a change in the grain boundary misorientation distribution toward random, indicating that grain switching occurs during grain boundary sliding (GBS). At the midlayer, however, a change from an initial texture component near the Cu-type texture component toward the Brass texture component, {011}〈211〉, was observed even as the misorientation distribution became more random. This change in texture component is associated with the occurrence of single slip during superplastic flow.     

Cost/benefit criterion for selection of pulsed Doppler ultrasoundspectral mean frequency and bandwidth estimators

A flexible selection criterion for spectral estimators based on the weighted statistical accuracy (benefit) of estimation of decisive spectral parameters under the constraint of low computational complexity (cost) is proposed. This new cost/benefit criterion also selects the model order for parametric spectral estimators-selecting model orders significantly lower than those determined by accepted criteria. The importance of different Doppler signal parameters (e.g., mean frequency and spectral bandwidth) and their accuracy of estimation is incorporated by the use of weighting factors. The use of this method with simulated Doppler signals led to the selection of the modified covariance Alt estimator     

Critical Analysis of Threshold Stresses in the Creep Mechanisms of a Powder Metallurgy Magnesium Alloy AZ31

Metallurgical and Materials Transactions A - In this work, tensile tests were conducted on two powder metallurgy materials based on the AZ31 magnesium alloy. The first material, named AZ31-PM, was...     

Microstructure Evolution during Recrystallization of Newly Developed Low Ni High Mn‐N Stainless Steels

Low cost stainless steels where nickel is replaced in a conventional Fe‐Cr‐Ni stainless steel by manganese and nitrogen were studied. In this work, three new steels based on the system (mass %) Fe‐18Cr‐15Mn‐2Ni‐2Mo‐XN were prepared and their microstructure after each treatment was evaluated by optical and scanning electron microscopy, and X‐ray diffraction. A good correlation between texture and microstructure evolution during annealing was established. A randomization of the texture during recrystallization of the austenite was observed. Recrystallization starts at temperatures above 850°C, and after annealing for 0.5 h at 900°C, the austenite is completely recrystallized, reaching the orientation density a value near 1. Precipitation of σ ‐ phase was observed in the samples annealed at temperatures ranging from 700 to 950°C.