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     

Theoretical error analysis of the sampling moiré method and phase compensation methodology for single-shot phase analysis

Recently, a rapid and accurate single-shot phase measurement technique called the sampling moiré method has been developed for small-displacement distribution measurements. In this study, the theoretical phase error of the sampling moiré method caused by linear intensity interpolation in the case of a mismatch between the sampling pitch and the original grating pitch is analyzed. The periodic phase error is proportional to the square of the spatial angular frequency of the moiré fringe. Moreover, an effective phase compensation methodology is developed to reduce the periodic phase error. Single-shot phase analysis can perform accurately even when the sampling pitch is not matched to the original grating pitch exactly. The primary simulation results demonstrate the effectiveness of the proposed phase compensation methodology.     

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.     

The α/β silicon nitride phase transformation

The literature on the / silicon nitride transformation is reviewed briefly. Data are presented on the kinetics of the tranformation of 1600° C on low and high purity silicon nitride powders. The addition of magnesia increased the rate of transformation while the addition of yttria had no effect. Scanning electron photomicrographs show clearly the morphology changes that accompany the transformation. It is concluded that the transformation occurs via a solution-precipitation mechanism and that and are probably low and high temperature forms of silicon nitride.     

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.     

Influence of the α/β-SiC phase transformation on microstructural development and mechanical properties of liquid phase sintered silicon carbide

The transformation kinetics and microstructural development of liquid phase sintered silicon carbide ceramics (LPS-SiC) are investigated. Complete densification is achieved by pressureless and gas pressure sintering in argon and nitrogen atmospheres with Y2O3 and AlN as sintering additives. Studies of the phase transformation from to -SiC reveals a dependency on the initial -content and the sintering atmosphere. The transformation rate decreases with an increasing -content in the starting powder and in presence of nitrogen. The transformation is completely supressed for pure -SiC starting powders when the additive system consists of 10.34 wt% Y2O3 and 2.95 wt% AlN. Materials without phase transformation showed a homogeneous microstructure with equiaxed grains, whereas microstructures with elongated grains were developed from SiC powders with a high initial /-ratio (>1:9) when phase transformation occurs. Since liquid phase sintered silicon carbide reveals predominantly an intergranular fracture mode, the grain size and shape has a significant influence on the mechanical properties. The toughness of materials with platelet-like grains is about twice as high as for materials with equiaxed grains. Materials exhibiting elongated microstructures show also a higher bending strength after post-HIPing.     

Self-accommodated defect structures modifying the growth of Laves phase

Laves phases,with the topologically close-packed structure and a chemical formula of Ab₂,constitute the largest single class of intermetallics.Planar defects in Laves phases are widely investigated,especially for stacking behavior transformations through synchroshear.Here,we report the coexistence of C14,C36 and C15 structures in MgZn_2 precipitates by using atomic resolution scanning transmission electron microscopy,verifying the previously predicted Laves phase transformation sequence of C14→C36→C15 also applies to MgZn_2.One type of stacking fault couple in precipitates has been found to alone reduce the lattice mismatch with matrix,while some other stacking fault couples need to self-accommodate with irregular planar defects(rhombic units and flattened hexagonal units),or with five-fold symmetry structures to relieve the strain concentration.Precipitates thus grow towards an equiaxed or even round morphology,rather than the plate morphology as conventionally believed.Molecular dynamics calculations are performed to support our analysis.These findings reveal the principles governing the concurrent occurrence of various defects in laves structures,acting as an update of the widely accepted perception of random occurrence of defects during crystal growth.     

Nanoscale control of phase variants in strain-engineered BiFeO₃

Development of magnetoelectric, electromechanical, and photovoltaic devices based on mixed-phase rhombohedral-tetragonal (R-T) BiFeO(3) (BFO) systems is possible only if the control of the engineered R phase variants is realized. Accordingly, we explore the mechanism of a bias induced phase transformation in this system. Single point spectroscopy demonstrates that the T → R transition is activated at lower voltages compared to T → -T polarization switching. With phase field modeling, the transition is shown to be electrically driven. We further demonstrate that symmetry of formed R-phase rosettes can be broken by a proximal probe motion, allowing controlled creation of R variants with defined orientation. This approach opens a pathway to designing next-generation magnetoelectronic and data storage devices in the nanoscale.     

On the transformations of the ψ-AlCuFe icosahedral phase

In the present investigation, different alloy compositions close to the ternary composition values, where the icosahedral phase in AlFeCu is obtained, have been studied. The specimens were obtained using a rapid solidification technique with subsequent thermal treatments of 600°C, 700°C, 800°C and 900°C. The obtained specimens were characterized with X-ray diffraction patterns (XRD) and transmission electron microscopy (TEM). The experimental results show different transformations of the icosahedral phase to crystalline phases between 800°C and 700°C .The cubic β-phase is a solid solution which regulates the formation and decomposition of the ψ-Al₆Cu₂Fe phase to different crystalline phases such as the tetragonal (Al₇Cu₂Fe) and monoclinic (Al₁₃Fe₄) phases.     

Plastic deformation of ß and γ phase silver-tin alloys

The plastic deformation of and phase silver-tin alloys, which are of significance in the formulation of dental amalgam, has been studied using transmission electron microscopy and electron channelling. Deformation twinning in the ordered orthorhombic phase on {0 1 1} planes has been confirmed and another twin plane {2 1 1} has been identified. The phase was also found to deform by slip on {0 0 1} and {0 1 0} planes; superlattice dislocations with Burgers vectors 1/2[1 0 0 ] have been identified on the (0 0 1) plane. The disordered h c p phase deforms essentially by slip on the basal (0 0 0 1) plane by glide of 1/3¯2 1 1 0 dislocations.     

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.     

Superionic solid: composite electrolyte phase – an overview

A general overview on the field of solid state ionics, including materials and transport property, is presented. Superionic systems in the composite electrolyte phase are discussed in great detail. Possible theoretical models suggested to understand the ion-transport mechanism in these systems are reviewed extensively.     

Spatially resolved phase objects using Mach–Zehnder interferometry

Phase characterization with a good spatial resolution is crucial for focused beams in nonlinear media. The phase-shifting interferometry technique, using the least-squares error criterion for several interferograms, is implemented using a reflective spatial light modulator (SLM). The method provides a convenient calibration for any phase-shift steps. The reliability of the proposed method is checked by direct comparison with results obtained by the Fourier transform method as well as using a previously characterized circular phase object.     

Serrated yielding in Nb–V dual phase steel

Abstract

The characteristics of serrated yielding (the Portevin–Le Chatelier effect) in a Nb–V dual phase steel have been studied in the temperature range 85–210°C at strain rates between 1·2 × 10^?5 and 1·2 × 10^?2 s^?1. Serrated yielding was found to initiate only after a critical strain ?_c was reached. The strain between two successive serrations ??_s increases almost linearly with strain, while the stress drop ?σ_c increases with strain up to ?σ_max, then decreases. The exponent β in the mobile dislocation density–plastic strain relationship (ρ_m= ?^β) is 1·09 in the temperature range 85–140°C and 1·34 in the temperature range 140–210°C. The results also indicate that in the same temperature ranges there are two values of activation energy for type A serrations, i.e. 79 and 119 kJ mol^?1 respectively. The results are discussed in terms of substitutional–interstitial solute atom interaction and changes of concentration of interstitial atoms.

MST/934     

Longitudinal–differential phase distribution near the focus of a high numerical aperture lens: study of wavefront spacing and Gouy phase

The longitudinal–differential (LD) phase distribution was investigated near the focus of a high numerical aperture (NA = 0.9) aplanatic lens illuminated with a linearly polarized monochromatic plane wave. The Richards and Wolf method was used to compute field distributions. The LD phase map was obtained by analyzing the deviation of the phase of the simulated wave to the phase of a referential plane wave. The irregular wavefront spacing that is linked to the Guoy phase is discussed and subtle details of the phase features with respect to the spatial domain relative to the focal point are disclosed. The LD phase is used to revisit different definitions of the focal region. The definition is eventually identified that is in agreement with the Gouy phase in the focal region. Our work paves the way towards a coherent notion to quantify the optical action of high NA optical elements that are increasingly important for many applications.