Texture development and deformation mechanisms during uniaxial straining of U–Nb shape-memory alloys

The shape–memory effect is well documented in uranium–niobium alloys near the α″–γ^o metastable phase boundary. In situ neutron diffraction measurements during uniaxial loading indicate that U–14?at.%?Nb (in the α″ monoclinic phase field) deforms by stress–induced twin reorientation. Alternatively, U–16?at.%?Nb (initially γ^o tetragonal) undergoes a stress–induced phase transformation to the α″ monoclinic phase. The crystallographic texture of the monoclinic phase of both compositions has been measured and qualitatively interpreted by considering the orientation relationship between the most favoured α′′ variant and the parent phase. In addition, previously published observations of deformation structures within the shape–memory regime of a U–13?at.%?Nb alloy are discussed within the context of the same model.     

Texture development and deformation mechanisms during uniaxial straining of U–Nb shape-memory alloys

The shape-memory effect is well documented in uranium–niobium alloys near the α″–γ^o metastable phase boundary. In situ neutron diffraction measurements during uniaxial loading indicate that U–14?at.%?Nb (in the α″ monoclinic phase field) deforms by stress-induced twin reorientation. Alternatively, U–16?at.%?Nb (initially γ^o tetragonal) undergoes a stress-induced phase transformation to the α″ monoclinic phase. The crystallographic texture of the monoclinic phase of both compositions has been measured and qualitatively interpreted by considering the orientation relationship between the most favoured α′′ variant and the parent phase. In addition, previously published observations of deformation structures within the shape-memory regime of a U–13?at.%?Nb alloy are discussed within the context of the same model.     

Analysis of auto-ignition of heated hydrogen–air mixtures with different detailed reaction mechanisms

Auto-ignition processes of hydrogen, diluted with nitrogen, in heated air are numerically investigated by means of an unsteady laminar flamelet approach in mixture fraction space. The focus is on the auto-ignition delay time and the most reactive mixture fraction as obtained with five chemical mechanisms. Two strongly different levels of dilution, corresponding to experiments in the open literature, are considered. This concerns low-temperature chemistry at atmospheric pressure. The temperature of the air stream is much higher than the temperature of the fuel stream in the cases under study. We extensively investigate the effect of the co-flow temperature, the conditional scalar dissipation rate and the resolution in mixture fraction space for one case. With respect to the conditional scalar dissipation rate, we discuss the Amplitude Mapping Closure (AMC) model with imposed maximum scalar dissipation rate at mixture fraction equal to 0.5, as well as a constant conditional scalar dissipation rate value over the entire mixture fraction value range. We also illustrate that an auto-ignition criterion, based on a temperature rise, leads to similar results as an auto-ignition criterion, based on OH mass fraction, provided that the hydrogen is not too strongly diluted.     

New aspects of the plastic deformation of silicon – prerequisites for the reshaping of silicon microelements

New shapes of silicon microelements which can be partially situated outside the wafer plane can be created by the combination of wet anisotropic etching and plastic deformation at high temperatures. Therefore new applications become possible. In order to characterize the plastic behaviour of the silicon microelements bending tests in the 3-point manner were carried out at monocrystalline, differently orientated beams with variation of temperature, bending rate and maximum bending. Additionally the fracture strength at room temperature of deformed and undeformed beams was determined. The dislocation content introduced during the deformation was analysed by the etch pit technique. The deformation is characterized by the formation of dislocations, a pronounced yield point effect, and an orientation-dependent strengthening. The yield points depend strongly on temperature. Because of the strong dependence on the deformation parameters it is possible to create the same amount of irreversible deformation at different stages of the stress–bend diagrams resulting in different dislocation contents and therefore different properties. The analysis of the fracture strength values by means of the Weibull statistics shows a slightly decreased average fracture strength of the deformed material in comparison to the undeformed silicon but a strongly increased Weibull modulus. Received: 22 September 1998 / Accepted: 29 January 1999 / Published online: 28 April 1999     

The deformation texture ofβ-Sn III. Derivation of texture from elements of plastic deformation

The theoretical derivation of compression and rolling textures in -tin has been carried out for a different part in the deformation by slip and twinning for two different sets of slip systems given in the literature. The textures derived theoretically were compared with the compression and rolling textures measured in -tin in [6] and [7]. The dependence of the texture produced on the temperature of deformation is explained.     

A new methodology for identification of β-transus temperature in α + β and β titanium alloys using ultrasonic velocity measurement

A new methodology has been established for identification of β-transus temperature in α + β and β titanium alloys by ultrasonic velocity measurements in a single specimen in one microstructural condition only. This methodology is based on a linear correlation obtained for the variation in β-transus temperature with ultrasonic longitudinal wave velocity in various titanium alloys specimens, β-heat-treated followed by water quenching. Furthermore, it has been demonstrated for the first time that ultrasonic velocity in α′ martensitic structure increases with the addition of α-stabilizing elements and decreases with the addition of β-stabilizing elements for α + β titanium-alloys.     

Fundamental frequency patterns of Chinesein different speech modes

I.IntroductionTheF,patternsofspeechareimportantnotonlyforthcprosodicfeaturesbuta1soforvoicesourcecharactcristics.Nowmoreandmorespeechscientistsrecognizedthatvoiceexcitationsourceintcxt-to-spccchsystemsp1aysanimportantro1elnbothintclligibilityandnaturalnessorsynthcticspcech.Espccially,forChinese,atone1anguagewithmulti-tonesystem,thetonalpatternswhicharcmainlydcmonstratedintheF,con-tourscarry1exicalmeaning.SomecomparativestudiesoftheF,pattcrnsinbetweentonelanguage(Chinese)andstress1anguage(En…     

Short-range order clustering in BCC Fe–Mn alloys induced by severe plastic deformation

The effect of severe plastic deformation, namely, high-pressure torsion (HPT) at different temperatures and ball milling (BM) at different time intervals, has been investigated by means of Mössbauer spectroscopy in Fe_100–xMn_x (x = 4.1, 6.8, 9) alloys. Deformation affects the short-range clustering (SRC) in BCC lattice. Two processes occur: destruction of SRC by moving dislocations and enhancement of the SRC by migration of non-equilibrium defects. Destruction of SRC prevails during HPT at 80–293 K; whereas enhancement of SRC dominates at 473–573 K. BM starts enhancing the SRC formation at as low as 293 K due to local heating at impacts. The efficiency of HPT in terms of enhancing SRC increases with increasing temperature. The authors suppose that at low temperatures, a significant fraction of vacancies are excluded from enhancing SRC because of formation of mobile bi- and tri-vacancies having low efficiency of enhancing SRC as compared to that of mono vacancies. Milling of BCC Fe_100–xMn_x alloys stabilises the BCC phase with respect to α → γ transition at subsequent isothermal annealing because of a high degree of work hardening and formation of composition inhomogeneity.     

Compositional dependence of the deformation behaviour of ultrahigh-purity Ti–Al alloys

The present study is concerned with the effect of the O and Al concentrations on the deformation behaviour of ultrahigh-purity (UHP) Ti–(48,?50,?52)?at.%?Al alloys using UHP Ti with 30?wt?ppm?O. It has been shown that yield strength increases with increasing O content. Stoichiometric Ti–50?at.%?Al alloys had the lowest yield strength and the highest ductility when the O content was sufficiently low. It is suggested that the deformation mechanism of UHP binary Ti–Al is strongly related to the Al concentration. The deformation substructure of UHP Ti–48?at.%?Al is shown to be dominated by ordinary dislocation as well as deformation twinning and a small portion of superdislocations. The deformation substructure of UHP Ti–50?at.%?Al alloy was similar to that of Ti–48?at.%?Al, but deformation twinning was not observed. Most of dislocation structures of UHP Ti–52?at.%?Al alloy consisted of faulted dipoles. The major deformation mode of UHP Ti–48?at.%?Al and UHP Ti–50?at.%?Al alloys was ordinary dislocation in deformation orientation, which takes advantage of ordinary dislocation slip. However, the major deformation mode in this orientation for UHP Ti–52?at.%?Al alloys was superdislocation slip.     

Solidification mechanisms of unmodified and strontium-modified hypereutectic aluminium–silicon alloys

The effects of strontium on the solidification mode of hypereutectic aluminium–silicon alloys have been studied. Samples were prepared from an aluminium–17?wt% silicon-based alloy and strontium was added at several different concentrations. The development of the microstructure was investigated by cooling curve analysis, interrupted solidification experiments and optical and scanning electron microscopy. It was found that nucleation of primary silicon is suppressed by additions of strontium. The suppressed nucleation results in supersaturation of the liquid prior to nucleation, and an increased growth rate after nucleation. As a result, the silicon crystals become less faceted and more dendritic with increasing strontium additions. Increasing the strontium concentration slightly refined the eutectic spacing and introduced a small amount of fibrous silicon. Electron back-scatter diffraction measurements were performed to determine the crystallographic relation between the primary and eutectic silicon phases. The eutectic silicon in the unmodified alloy does not have any crystallographic relationship with the primary silicon crystals. In contrast, the eutectic silicon crystals in the strontium-modified alloys often share an identical or twin relationship with nearby primary silicon crystals. The incidence of twinning within primary silicon crystals was relatively low and did not appear to increase with strontium additions.     

Abstract Interfaces for Data Analysis —Component Architecture for Data Analysis Tools

The fast turnover of software technologies,in particular in the domain of in teractivity(covering user interface and visualisation)makes it difficult for a small group of people to produce complete and polished software-tools before the underlying technologies make them obsolete.At the HepVis ‘99 workshop,a working group has been formed to improve the rpoduction of software tools for data analysis in HENP.Beside promoting a distributed development organisation,one goal of the group is to systematically design a set of abstract interfaces based on using modern OO analysis and OO design techniques.An initial domain analysis has come up with several categories(componets)found in typical data analysis tools:historams,Ntuples,Functions,Vectors,Fitter,Plotter,Analyzer and Controller,Special Emphasis was put on reducing the couplings between the categories to a minimum,thus optimising re-use and maintainability of any component individually.The interfaces have been defined in Java and C and implementations exist in the form of libraries and tools using C (Anaphe/Lizard,Openscientist)and Java(Java Analysis Studio),A special implementation aims at accessing the Java Liraries(through their Abstract Interfaces)from C .This paper giver an overview of the architecture and design of the various components for data analysis as discussed in AIDA.     

Ferromagnetism caused by severe plastic deformation of the Fe – 35% Al alloy

Results of investigations into the structure and temperature dependence of magnetization of the Fe – 35% Al alloy subjected to severe plastic deformation are presented. It is demonstrated that after plastic deformation, this alloy becomes ferromagnetic, though before deformation it was non-ferromagnetic. The temperature interval of the ferromagnetic order stability arising due to plastic deformation is established. The revealed effect is explained.     

Analysis of generation of cumulative second harmonics of Lamb modes in a layered planar structure

11mroductlon AI叫ered planar structure m叫 be encoumered In ma叫 practical situations,and cansupport propagation ofplate wave modes known as the generallied La汕 modes.These modescan be used for the nondestructl、e、luatlon（NDE）oflayered Planar structures[‘,‘].In recenty6ars ere has been a growing awareness that the nonlinear elastl帅ODenglneering mater灿can be a very sensitive Indicator ofsome de炉ct states that are difficult to detect by othermeans In particular,the nonlinear elastic…     

Combinational-deformable-mirror adaptive optics system for compensation of high-order modes of wavefront

A new kind of adaptive optics(AO)system,in which several low spatial frequency deformable mirrors (DMs)with optical conjugation relationship are combined to correct high-order aberrations,is proposed. The phase compensation principle and the control method of the combinational AO system are introduced. The numerical simulations for the AO system with two 60-element DMs are presented.The results indicate that the combinational DM in the AO system can correct different aberrations effectively as one single DM with more actuators,and there is no change of control method.This technique can be applied to a large telescope AO system to improve the spatial compensation capability for wavefront by using current DM.     

Analysis of nonlinear dynamic response for delaminated fiber–metal laminated beam under unsteady temperature field

The nonlinear dynamic response problems of fiber–metal laminated beams with delamination are studied in this paper. Basing on the Timoshenko beam theory, and considering geometric nonlinearity, transverse shear deformation, temperature effect and contact effect, the nonlinear governing equations of motion for fiber–metal laminated beams under unsteady temperature field are established, which are solved by the differential quadrature method, Nermark-β method and iterative method. In numerical examples, the effects of delamination length, delamination depth, temperature field, geometric nonlinearity and transverse shear deformation on the nonlinear dynamic response of the glass reinforced aluminum laminated beam with delamination are discussed in details.     

High temperature materials for aerospace applications: Ni-based superalloys and γ-TiAl alloys

Two outstanding aerospace-oriented high-temperature materials, the single-crystal nickel-based superalloys for high-pressure turbine blades and the γ-TiAl-based alloys for low pressure turbine blades, are being presented here. In both cases, the optimisation of their mechanical properties is based on a high knowledge of metallurgy, mixing together different aspects such as processes, alloy design, deformation mechanisms, impact of oxidative environment or interaction between protective layers and protected alloy. Historical evolutions are recalled and put into perspective with more recent research activities.     

Surface tension estimation of high temperature melts of the binary alloys Ag–Au

Abstract

Surface tension calculation of the binary alloys Ag–Au at the temperature of 1381 K, where Ag and Au have similar electronic structures and their atomic radii are comparable, are carried out in this study using several equations over entire composition range of Au. Apparently, the deviations from ideality of the bulk solutions, such as activities of Ag and Au are small and the maximum excess Gibbs free energy of mixing of the liquid phase is for instance ?4500 J/mol at X_Au = 0.5. Besides, the results obtained in Ag–Au alloys that at a constant temperature the surface tension increases with increasing composition while the surface tension decreases as the temperature increases for entire composition range of Au. Although data about surface tension of the Ag–Au alloy are limited, it was possible to make a comparison for the calculated results for the surface tension in this study with the available experimental data. Taken together, the average standard error analysis that especially the improved Guggenheim model in the other models gives the best agreement along with the experimental results at temperature 1383 K although almost all models are mutually in agreement with the other one.