Transient analysis of bang?bang phase locked loops

This work gives insight into the behaviour of second-order bang-bang phase locked loops in the far from lock region. This region, while largely unexplored, is of particular interest as PLL behaviour in this region determines locking time and capture range. By analysing PLL cycle slipping behaviour in this region, the transient response for the system is derived. Expressions for first-order system stability and locking time are also presented.     

Numerical analysis of liquid fraction in solid–liquid phase transformation of semisolid alloy

Abstract

The non-linear mathematical expression of liquid fraction in solid–liquid phase transformation of semisolid alloy was derived by thermodynamic equations, and the numerical solution of the non-linear mathematical expression was obtained by the Gauss Newton iteration algorithm. The solid–liquid phase transformation of hypereutectic Al–20Si–3Fe–1Mn–4Cu–1Mg alloy was studied by differential scanning calorimetry, and it was used for the expression reliability validation and compared with the Scheil linear regression expression. The results showed that the liquid fraction of the semisolid alloy was not increased linearly with the heating temperature increasing, but increased non-linearly, which was not consistent with the Scheil expression, and the growth rate of liquid fraction was not entirely the same in different temperature ranges. The non-linear mathematical expression data fit well with the experimental data, and the non-linear mathematical expression had a smaller discrete degree and higher credibility compared with the Scheil linear regression expression. The relationship of liquid fraction and heating temperature of the semisolid alloy can be reflected by means of the non-linear mathematical expression in the case of solid–liquid phase transformation.     

X-ray quantitative phase analysis of super α2 alloy through thermochemical processing with hydrogen

The effect of hydrogen on the phase constitution of super ₂ alloy was studied by means of X-ray quantitative phase analysis. The results showed that the alloy consists of ₂, B₂ and O phases, and the volume fraction of O phase in the alloy increases with hydrogen content.     

Application of dilatometric analysis to the study of solid–solid phase transformations in steels

This article outlines the use of dilatometry in solid–solid phase transformation research in steel. It describes how dilatometric data are interpreted, with an emphasis on continuous heating and cooling transformation diagrams. These diagrams show the microstructural constituents that result from given heating and cooling conditions, and are an invaluable tool for the metallurgist in characterizing steels with respect to their response to heat treatments. Several practical examples and applications of dilatometry in steel research are briefly described in this work.     

Choice of a γ-emission source for phase analysis of a material by nuclear γ-resonance

Consideration is given to the influence of nonresonance attenuation of resonance -quanta by the lattice of a -emission source, on the shape of a monoline in the Mössbauer spectrum. It is shown that this effect leads to increased error in the phase analysis of a material in nuclear -resonance spectroscopy. Criteria are determined for the suitability of a -emission source for use in the phase analysis of materials by this method. The actuality of the problem is shown for the most widely used Mossbauer isotopes.Translated from Izmeritel'naya Tekhnika, No. 6, pp. 55–57, June, 1994.     

Specific analysis of EBSD data to study the texture inheritance due to the β → α phase transformation

A specific processing of EBSD data is proposed to study the texture inheritance of titanium or zirconium alloys. A non standard misorientation map is calculated to localise the colonies inherited from the same parent grain. The calculation of the parent orientation from its inherited variants detailed in previous works has been adapted to the data obtained from an automated EBSD analysis. Finally, a method to derive the orientation map of the parent phase from that of the inherited phase is proposed. The resulting and COMs are used to study some aspects of the variant selection occurring in the transformation of a T40 sample.     

Displacement measurement of concrete bridges by the sampling Moiré method based on phase analysis of repeated pattern

Measuring accurate deformation distribution of large-scale structures inexpensively and efficiently is a crucial challenge of structural health monitoring. Phase-based imaging technique has great potential for accurate and robust multipoint displacement measurement in the field. In this study, the sampling Moiré method—one of the promising optical techniques—was applied to the displacement measurement of a concrete bridge for the high-speed railway in Japan. Using retroreflective Moiré markers, the two-dimensional in-plane displacements at multiple locations could be easily measured from recorded digital images at a distance of 20 m regardless of day and night. Results of the dynamic deflection obtained from the sampling Moiré method were in good agreement with those from a conventional laser Doppler vibrometer. The time series of two-dimensional displacement analyses when the outbound or inbound trains passed at the speed of 150 or 320 km/h through the bridge revealed that the points at the centre and the quarter of the bridge span demonstrated complex deformation behaviour showing elliptical rotation. The effects of random noise of the recorded image were quantitatively investigated, and the air fluctuation was discussed from the field experiments. We proved that measurements using the sampling Moiré method could be more stable at night than daytime.     

Quantitative X-ray diffraction analysis of development of Z phase in 12%Cr–Nb–V–N steel

Abstract

To study the evolution of nitrides (Nb,V)N, (V,Nb)N and Cr₂N, and in particular the formation of the Z phase Cr(V, Nb)N, a model alloy with composition similar to that of 12%Cr steels for high temperature applications, microalloyed with Nb and V but with a very low carbon content, has been designed. A quantitative determination of the volume fractions of the extracted nitrides that had formed after aging treatments at 650°C for up to 10 000 h was carried out by an X-ray diffraction procedure, based on the Rietveld approach. The investigation of the Z phase evolution by the Johnson–Mehl–Avrami–Kolmogorov kinetics at 650 and 700°C revealed that, as the kinetic exponent is very close to unity, the formation mechanism of this phase is not associated with a conventional process of nucleation but hints at a gradual diffusion controlled transformation of the pre-existing V and Nb nitrides.     

Intergrowth of C phase within μ phase in a Re-containing Ni-base single crystal superalloy

Precipitation of topologically close-packed phases in a Re-containing Ni-base single crystal superalloy was studied under elevated temperature by in situ transmission electron microscopy.Above 1150?C,a new intergrowth structure called C phase was found within μ phase with a defined crystallographic orientation relationship.Elements mapping analysis reveals that C phase has a similar element composition as μ phase,but contains a lower level of Cr,W and Re.With increasing temperature,the proportion of C phase increases gradually.At 1250?C,C phase becomes the dominant precipitate.It is demonstrated that C phase is more thermodynamically stable than μ phase above 1150?C that leads to an intergrowth pathway from μ phase to C phase.     

The“gene”of reversible phase transformation of phase change materials:Octahedral motif

Nonvolatile phase change random access memory(PCRAM)is regarded as one of promising candidates for next-generation memory in the era of Big Data.The phase transition mechanism of phase change materials is the key scientific issue to be addressed for phase change memory.Moreover,obtaining homogeneous phase change materials with high speed,low power consumption,long life and good thermal stability is still the ultimate challenge for high-density three-dimensional(3D)PCRAM.In this paper,starting from the octahedral structure motifs(octahedrons)which are considered as the"gene"of phase change materials,a new view on the phase transition mechanism is proposed.Based on this mechanism,a homogeneous phase change material is developed by constructing three matched octahedrons,which achieved an overall improvement in performance,showing 180℃ten-year data retention,6 ns SET speed,one order of magnitude longer life time and 75%reduced power consumption compared with traditional Ge₂Sb₂Te₅(GST)devices.It is of great significance to use it in 3D PCRAM chip and multi-level brain-inspired computing chip in the future.     

Morphologies of Si phase and La-rich phase in as-cast hypereutectic Al–Si–xLa alloys

In the present study, the diversified morphologies of Si phase and La-rich phase in as-casted hypereutectic Al–Si–xLa alloys are presented and investigated. The morphological features were examined using conventional optical microscopy and SEM for observations conducted on the optical samples and deep-etched samples, respectively. The results show that primary Si crystals show several morphologies, such as feathery, star-shaped, faceted polygonal, platelet and so on. There are three types of fivefolded Si crystals existing in the present study, fivefold symmetry as radial growth alone: thin-branched, coarse-branched and well-defined star-shaped growing from the preferred growth from the tips of branches. The eutectic Si in unmodified Al–Si alloys appears only in fibrous morphology, while discrete and interconnected coral and rodlike eutectic Si particles were observed in alloys with the addition of La. The La-rich phase also grows into a variety of morphologies, such as needlelike, broken rodlike in pores, spherical, and flat platelet. In optical microscopy, La-rich phase is observed to envelope some small polygonal Si crystals.     

Al–Ti–C phase diagram

Abstract

Equilibrium experiments have been performed at 1373, 1173, and 973 K, with alloys of compositions within the aluminium rich corner of the Al–Ti–C phase diagram. The samples have been metallographically investigated using light optical microscopy and a scanning electron microscope equipped with a system for energy dispersive spectrometry. Equilibrium phases, as well as effects of cooling, have been identified. Dynamic effects originating from cooling are discussed and a tentative phase diagram is proposed. It was predicted theoretically and confirmed experimentally that a class II reaction involving four phases occurs, i.e. Al(l) + TiC(s)?Al₃Ti(s) + Al₄C₃(s), below 1100 K.

MST/1807     

Combined atomistic–crystal plasticity analysis of the effect of beta phase precipitates on deformation and fracture of lamellar γ + α2 titanium aluminide

Atomistic simulations based on the use of interatomic potentials and a finite element method based on the crystal plasticity theory are combined to investigate the deformation and fracture behaviour of polycrystalline lamellar -TiAl + ₂-Ti₃Al material containing 10 vol % of body centred cubic beta phase precipitates. The effects of both stable beta phase precipitates, which deform by slip, and metastable beta phase precipitates, which deform by a combination of stress-induced martensitic transformation and slip, are studied. To model the cracking along the grain boundaries and the matrix–precipitate interfaces, the grain boundaries and interfaces are modelled using a cohesive zone approach. The grain boundary–interface potentials are determined by carrying out atomistic simulations of the grain boundary–interface normal separation (decohesion) and sliding.The results obtained suggest that incompatibilities in the plastic flow between the adjacent grains in the single-phase material give rise to a large build-up in tensile hydrostatic stress in the region surrounding certain three-grain junctions, which, in turn, leads to nucleation of the grain boundary cracks and ultimate failure. The stable beta phase precipitates located at the three-grain junctions in the two-phase material help accommodate the incompatibilities in plastic flow, doubling the strain to failure. The lattice expansion, which accompanies martensitic transformation in the metastable beta phase precipitates, further delays nucleation of the grain boundary–interface cracks giving rise to an additional increase in the fracture strain.     

A novel phase retrieval method from three-wavelength in-line phase-shifting interferograms based on positive negative 2π phase shifts

A new method to extract quantitative phases for each wavelength from three-wavelength in-line phase-shifting interferograms is proposed. Firstly, seven interferograms with positive negative 2π phase shifts are sequentially captured by using the phase-shifting technique. Secondly, six dc-term suppressed intensities can be achieved by the use of the algebraic algorithm. Finally, the wrapped phases at the three wavelengths can be acquired simultaneously from these six interferograms add-subtracting by employing the trigonometric function method. The surface morphology with increased ambiguity-free range at synthetic beat wavelength can be obtained, while maintaining the low noise precision of the single wavelength measurement, by combining this method with three-wavelength phase unwrapping method. We illustrate the principle of this algorithm, and the simulated experiments of the spherical cap and the HeLa cell are conducted to prove our proposed method, respectively.     

Comparison of multiple prompt γ-ray analysis and prompt γ-ray analysis for the elemental analysis of geological and cosmochemical samples

Multiple prompt γ-ray analysis (MPGA) and conventional neutron-induced prompt γ-ray analysis (PGA) are nondestructive analytical methods for bulk chemical compositions, and their analytical capabilities were compared for elemental analyses of geological and cosmochemical samples. Detection sensitivities of PGA are often restricted by poor signal-to-noise ratios and interferences from different origins. MPGA can substantially reduce the background level, especially for hydrogenous samples, relative to PGA, which opens up a possibility to use lower energy prompt γ-rays of some trace elements. Although it is one of the major constituent elements of rock samples, Mg is hard to be determined by PGA. With MPGA, Mg contents could be determined with reasonable consistency with their corresponding recommended values in geological and cosmochemical samples by carefully selecting suitable coincident prompt γ-ray energy pairs without interference correction. MPGA was applied to a hydrogenous meteorite, Ivuna, which contains H at 2% mass level. MPGA detection limits for most of the elements studied can be reduced up to 1 order of magnitude when compared with PGA detection limits under the present experimental conditions.     

Accurate phase–height mapping algorithm for PMP

In phase measurement profilometry (PMP), the projector can be regarded as another camera according to the reversibility of the light path principle. The relationship of projecting spatial points to image plane of camera and projector is studied, and the phase–height mapping equation without projector distortion is obtained. The equation is then expanded to a polynomial for the convenience of calibration. Furthermore, the relation between the distortion value and the phase is investigated. Finally the phase–height mapping algorithm considering projector distortion and its polynomial expression are acquired. The accuracy of approximation is studied and compared with another two existing algorithms by computer simulation. It is revealed that the absolute error of the new algorithm expressed with quartic polynomial reaches 5.380× 10^?3 mm and its standard deviation reaches 3.354× 10^?4 mm under general lens distortion. The accuracy of the new algorithm is the highest among the three algorithms. In experiment, the standard deviation of the measurement reaches 0.04 mm even though the result is affected by measurement error.     

Distinct dendritic α phase emerging on the surface of primary α phase in a compressed near-α titanium alloy

The characteristic of the surface morphology of primary α phase was studied in a deformed near-α titanium alloy. Dendritic α phase emerged on the surfaces of primary α phase when the alloy was air-cooled in α + β phase field after deformation. The dendritic α grain has the same orientation with its original primary α grain. The formation of the dendritic α phase could be explained by interface instability in epitaxial growth process of the primary α phase. The dislocations induced by deformation could facilitate the formation of dendritic α phase leading to the dendritic α phase and more obvious with the increase of strain. The growth of dendritic α phase was finally limited by the nucleation of second α phase with cooling.     

Thermal stresses in two‐phase composite media

Abstract

Based on the concept of rhermoelasticity in a single‐phase elastic solid, we have investigated thermal stresses in a two‐phase composite media. A two‐phase composite slab and a concentric solid sphere were considered. The temperature distribution has been obtained by means of the Laplace transform. General formulas of thermal stresses in two‐phase composite are derived, and numerical examples are provided. For a constant average temperature and a constant surface temperature, the maximum transverse (or tangential) stress is located at the surface for both slab and sphere.