Deformation and crystallization of Zr-based amorphous alloys in homogeneous flow regime

The purpose of this study is to experimentally investigate the interaction of inelastic deformation and microstructural changes of two Zr-based bulk metallic glasses (BMGs): Zr_(41.25)Ti_(13.75)Cu_(12.5)Ni_(10)Be_(22.5) (commercially designated as Vitreloy 1 or Vit1) and Zr_(46.75)Ti_(8.25)Cu_(7.5)Ni_(10)Be_(27.5) (Vitreloy 4, Vit4). High-temperature uniaxial compression tests were performed on the two Zr alloys at various strain rates, followed by structural characterization using differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). Two distinct modes of mechanically induced atomic disordering in the two alloys were observed, with Vit1 featuring clear phase separation and crystallization after deformation as observed with TEM, while Vit4 showing only structural relaxation with no crystallization. The influence of the structural changes on the mechanical behaviors of the two materials was further investigated by jump-in-strain-rate tests, and flow softening was observed in Vit4. A free volume theory was applied to explain the deformation behaviors, and the activation volumes were calculated for both alloys

Triple junction limited grain growth in nanomaterials

Grain growth in nanocrystals can be limited by triple junctions, during both sintering of nanopowders and annealing of dense materials. An analysis is developed to determine experimental conditions under which triple junctions can limit grain growth

Diffusion creep in metals and ceramics: extension to nanocrystals

The fundamental aspects of diffusion creep are examined with reference to creep parameters and microstructural development. It is demonstrated that there is strong microstructural support for diffusion creep, although the theoretical and experimental creep rates are likely to agree only to within an order of magnitude. This discrepancy arises partly from uncertainties in the diffusion coefficients, and also from a lack of consideration of the stochastic nature of grain size distribution. Models developed for creep in nanocrystals are examined critically. Currently, there is no good experimental evidence for the occurrence of conventional diffusion creep in nanocrystals

Bt brinjal: premature approval for cultivation

Komorač je bogat izvor različitih skupina fenolnih spojeva, a za povećanje učinkovitosti njihove ekstrakcije razvijaju se nove tehnike. Stoga je cilj ovog istraživanja bio optimirati uvjete izolacije hidroksicimetnih kiselina, flavonola i flavan-3-ola iz odmašćenih sjemenki gorkog komorača sukcesivnim iscrpljivanjem 30 %-tnom otopinom acetona i 30 %-tnom otopinom metanola primjenom ubrzane ekstrakcije otapalima pri povišenom tlaku (PLE) uz varirane parametre: temperatura (75 i 100 oC) te broj ciklusa (1, 2 i 3 ciklusa). Optimalni PLE uvjeti pri kojima su dobiveni najveći prinosi hidroksicimetnih kiselina bili su ekstrakcija s 30 %-tnim acetonom pri temperaturi od 100 oC i 3 ciklusa te ekstrakcija s 30 %-tnim metanolom pri 100 oC i 2 ciklusa. Najveći prinosi flavonola dobiveni su ekstrakcijom s 30 %-tnim acetonom te 30 %-tnim metanolom pri 100 oC i 3 ciklusa, dok je najveći prinos flavan-3-ola dobiven ekstrakcijom s 30 %-tnim acetonom pri 100 oC te 2 ciklusa.Fennel is a rich source of different groups of phenolic compounds and new techniques are being developed in order to increase the efficiency of their extraction. Therefore, the aim of this study was to optimize the conditions for the isolation of hydroxycinnamic acids, flavonols and flavan-3-ols from defatted bitter fennel seeds by successive exhaustion with 30 % acetone solution and 30 % methanol solution using pressurized liquid extraction (PLE) with varied parameters: temperature (75 and 100 oC) and number of cycles (1, 2 and 3 cycles). The optimal PLE conditions for obtaining the highest yields of hydroxycinnamic acids were extraction with 30 % acetone at 100 oC and 3 cycles and extraction with 30 % methanol at 100 oC and 2 cycles. The highest flavonol yields were obtained by extraction with 30 % acetone and 30 % methanol at 100 oC and 3 cycles, while the highest yield of flavan-3-ols was obtained by extraction with 30% acetone at 100 oC and 2 cycles

Diffusion creep in oxide ceramics

Although the models for diffusion creep were developed over 50 years ago, recently there has been considerable debate in the literature regarding the experimental validity of the models. This report summarizes recent theoretical developments in diffusion creep, with specific emphasis on ceramics. Concomitant microstructural changes during high temperature deformation, such as grain growth and cavitation, frequently interfere with the identification of the rate controlling process. Recent careful experiments coupled with appropriate microstructural characterization will be reviewed in structural oxide ceramics such as alumina and tetragonal zirconia; it will be demonstrated that these oxides deform by diffusion creep. Detailed analysis of the data in tetragonal zirconia will also be utilized to demonstrate the significance of diffusion creep in superplastic ceramics

Superplasticity in advanced materials - ICSAM-97

ICSAM-97 Proceedings of the 1997 International Conference on Superplasticity in Advanced Materials (ICSAM-97), Bangalore, India, January 1997

On the emergence of new surface grains during superplastic deformation

Superplasticity, the ability of some polycrystalline materials to exhibit large elongations to failure offers an attractive and cost effective means for forming some components with complex shapes, and it is being used currently in several aerospace and other applications [1-3]. Although the phenomenon has been studied extensively since the 1960's [1,2,4 -7], the fundamental rate controlling deformation mechanism has not yet been unambiguously identified. One of the key microstructural observations following superplastic deformation is the retention of an equiaxed grain size following large elongations

Unusual stress and grain size dependence for creep in nanocrystalline materials

Analyses of diffusion and dislocation creep in nanocrystals needs to take into account the generally utilized low temperatures, high stresses and very fine grain sizes. In nanocrystals, diffusion creep may be associated with a nonlinear stress dependence and dislocation creep may involve a grain size dependence

An experimental study on the alignment of cavities in a superplastic commercial copper alloy

A detailed study of cavitation was conducted in a commercial copper alloy deformed superplastically at a strain rate of 1.3 × 10-3 s-1. Cavities are observed to form in stringers parallel to the tensile axis due to cavity nucleation around aligned stringers of large cobalt-rich particles present in the as-received alloy. The increase in the number density of cavities and the range of cavity sizes observed indicates that cavities nucleate continuously during superplastic deformation. At large elongations, the interlinkage of cavities in a direction perpendicular to the tensile axis tends to mask the alignment of cavity stringers. It is demonstrated that the present results can rationalize satisfactorily the previous observations of cavity alignment in the superplastic copper alloy