Matrix Planes Research Articles

The crystallography of C-centred monoclinic to body-centred tetragonal polymorphic phase transformation in mixed-phase TiO2(B) and anatase nanocomposite

A detailed invariant line analysis was described on the habit plane and orientation relationship between TiO2(B) and anatase in titania nanocrystalline photocatalyst. It is demonstrated that the predicted habit plane and orientation relationship are coincident well with the observed crystallographic features. The polymorphic phase transformation of C-centred monoclinic structure to body-centred tetragonal structure is proposed to start from an initial Bain lattice correspondence that close-packed plane of matrix is parallel to close-packed plane of product, so is closed-packed direction.

An atom probe tomography study of internal oxidation processes in Alloy 600

Internal oxidation in Alloy 600 (Ni–16Cr–9Fe) involves the inward diffusion of O, which preferentially reacts with solute elements (e.g. Cr, Fe) forming internal oxide precipitates. In this work, the internal oxidation process and its resultant metal-oxide heterostructures are systematically analyzed in 3D at the finest length scales, using atom probe tomography (APT). Internal oxidation is induced by exposure of Alloy 600 to 480 °C hydrogenated steam, with an oxygen partial pressure below the dissociation pressure of the solvent metal oxide, NiO. Following exposure, nodules of metallic Ni are observed on the sample surface, originating from material that is expelled to relieve compressive stresses generated by internal oxidation. Probing the material immediately below the surface reveals these nodules to be directly connected to their parent grains via Ni-rich metal channels. The matrix metal is intertwined with a continuous network of oxides, which are primarily FeCr2O4. The continuous interface between oxides and matrix provides the short-circuit diffusion pathways necessary for Ni expulsion. Deeper below the surface, oxides are observed as particles, rather than a continuous network, and are often aligned on matrix planes. The small oxide particles are Cr2O3, which is also found to be the composition at the centres of many larger FeCr2O4 oxides. This indicates that oxides first precipitate as Cr2O3, then later grow as FeCr2O4 when local depletion of Cr changes which phase is most energetically-favourable. Initial comparisons indicate that some fundamental findings in this work are applicable to known internal oxidation systems at lower and higher temperatures.

Wellbore stability analysis for horizontal wells in shale formations

As a serious problem in drilling operation, wellbore instability restricts efficient development of shale gas, especially in formations with weak bedding planes which have strong strength anisotropies. The occurrence of bedding planes has significant influence on wellbore instability. Triaxial compressive tests have been carried out to study the effects of the orientation angle between the major principal stress direction and the weak bedding plane on the strengths of weak bedding shales. According to the laboratory test data, the strength of rock matrix and the strength of weak bedding planes were acquired, and failure criterion of rock matrix and weak bedding planes were established based on Mohr-Coulomb strength criteria. Based on the poroelasticity theory and rock strength theory, this paper proposed a wellbore instability analysis model for horizontal wells to reveal the combined effects of borehole trajectory, occurrence of stratification, strength of weak plane on wellbore instability. The results show that the shape of curve between peak compressive strength and orientation angle is ‘U-shaped’, and the bedding planes of weakness causing the strong strength anisotropies. When the bedding dip angle is greater than about 45°, the reasonable well azimuth angle would make wellbore stable. In addition, the directions of bedding planes and in-situ stresses pose the significant influences on wellbore instability. This paper provides a method for wellbore stability analysis of weak bedding formations which can help design mud density and well trajectory by elaborating all the effects of various parameters on wellbore stability.

Cohesive model application to micro-crack nucleation and growth

The process of micro-crack nucleation and the first stages of micro-meso-crack propagation are analyzed with the help of a cohesive, finite element model. The loaded material cell containing an inclusion is presented. The model is based on experimental observations. The inclusion–matrix interface and planes of potential crack propagation in the inclusion and matrix are modeled with the cohesive elements implemented in ABAQUS. Both element-based and surface-based approaches are used. The material constants used in the calculations are hypothetical, but based on data relevant to the real materials and reported in the literature. The influence of the cohesive element parameters (that is, peak stress and fracture energy) as well as the influence of constraint on the sequence of events during loading of the material cell are analyzed. Relations between selected parameters of the model leading to inclusion fracture or the debonding process of an inclusion are established.

The effect of crystal textures on the anodic oxidization of zirconium in a boiling nitric acid solution

ABSTRACTThe effects of crystal textures and the potentials in the anodic oxidation of zirconium in a boiling nitric acid solution were investigated to study the stress corrosion cracking of zirconium in nitric acid solutions. The test specimen was machined such that the specimen surface was parallel to the rolling surface, arranged with a (0002) crystal texture. The potentials applied for the anodic oxidation of zirconium were set at 1.2, 1.4, and 1.5 V against a saturated KCl–Ag/AgCl electrode (SSE) in boiling 6 M HNO3. The growth of the zirconium oxide film dramatically changed depending on the applied potential at a closed depassivation potential (1.47 V vs. SSE in this study). At 1.5 V, the zirconium oxide film rapidly grows, and its growth exhibits cyclic oxidation kinetics in accordance with a nearly cubic rate law. The zirconium oxide film grows according to the quantity of electric charge and the growth rate does not depend on the crystal texture in the pretransition region before the cyclic oxidation kinetics. However, the growth and cracking under the thick oxide film depend on the crystal texture in the transition region. On the normal direction side, the oxide film thickness decreases on average since some areas of the thick oxide film are separated from the specimen surface owing to the cracks in the thick oxide. On the rolling direction (RD) side, no cracks in the thick oxide film are observed, but cracks are found under the thick oxide film, which deeply propagate in metal matrix along the RD without an external stress. The cracks under the thick oxide film propagate to the center of the oxide layer. The crystal orientation relationship between the oxide layer and the zirconium matrix is (0002)Zr//(111)ZrO2, and the cracks in the oxide layer propagate in the (0002)Zr plane in the zirconium matrix. The oxide layer consists of string-like zirconium oxide and zirconium hydride. The string-like zirconium oxide contains orthorhombic ZrO2 in addition to monoclinic ZrO2. It is not well known why the cracks propagate along the (0002)Zr plane under the thick oxide film. As one assumption for the mechanism of crack initiation and propagation without an external stress, it is considered that the oxidizing zirconium hydrides precipitated in the (0002)Zr plane near the interface of the thick oxide film and the matrix. Then, the phase transformation from orthorhombic ZrO2 to monoclinic ZrO2 in the oxide layer causes the crack propagation in the (0002) plane.

Dislocations in icosahedral quasicrystalline phase embedded in hot-deformed Mg alloys

We perform a systematic structural investigation of the I-phase particles embedded in Mg matrix in I-phase-reinforced Mg–3.5Zn–0.6Gd alloy and offer evidence to the presence of dislocations in the I-phase particles. Such dislocations are found to be formed on the (0001) plane of Mg matrix, which is attributed to their slipping into the 5-fold and 2-fold planes of I-phase particles. We also discuss how deformation conditions of wrought Mg alloys affect the deformation behaviors of the I-phase and how deformation behavior of I-phase affect the mechanical properties of wrought Mg alloys. The bonding between the I-phase and Mg matrix was also confirmed to be strong.

Reuse of Byproduct Alumina Composite Powder from Hydrogen Production Process

Water molecule reacts with aluminium when it is immersed in water, which plays a vital role in hydrogen generation process. This process which uses sodium hydroxide as catalyst produces a byproduct alumina and some other scarce ingredients. This byproduct is mentioned as alumina composite powder (ACP). In an attempt of reutilizing and converting it into a matrix material using a resin polymer as a binder, this work investigates the workability of the product produced by alumina composite matrix. The specimen produced by alumina composite matrix has been tested for its desirable strength, namely, tensile strength, elongation under varied thermal conditions, compression test, flexural test with fiber reinforcement and non fiber reinforcement. The nature of crack formation and the plastic behavior of the specimen during test have been analyzed, based on the crack propagation in failure plane in the alumina composite matrix as a high quality alternative for wood and tiles for high class interior decorations. This research explores the effective use of the byproduct alumina composite matrix and its consistent eco-friendly nature.

Phase Transitions and Elementary Processes in Shape Memory Alloys

Shape memory effect is a peculiar property exhibited by certain alloy systems, and shape memory alloys are recognized to be smart materials. These alloys have important ability to recover the original shape of material after deformation, and they are used as shape memory elements in devices due to this property. The shape memory effect is facilitated by a displacive transformation known as martensitic transformation. Shape memory effect refers to the shape recovery of materials resulting from martensite to austenite transformation when heated above reverse transformation temperature after deforming in the martensitic phase. These alloys also cycle between two certain shapes with changing temperature.Martensitic transformations occur with cooperative movement of atoms by means of lattice invariant shears on a {110} - type plane of austenite matrix which is basal plane of martensite.Copper based alloys exhibit this property in metastable β-phase field. High temperature β-phase bcc-structures martensiticaly undergo the non-conventional structures following two ordered reactions on cooling, and structural changes in nanoscale level govern this transition cooling. Atomic movements are also confined to interatomic lengths due to the diffusionless character of martensitic transformation.

Combining HAADF STEM tomography and electron diffraction for studies of α-Al(Fe,Mn)Si dispersoids in 3xxx aluminium alloys

A new methodology to study the precipitation crystallography of dispersoids in an Al matrix is proposed. By combining high angle annular dark field tomography and electron diffraction studies, the three-dimensional morphology, orientation relationship (OR) with Al matrix and habit planes of the dispersoids can be achieved simultaneously. This approach has been applied to investigate the -Al(Mn,Fe)Si dispersoids precipitated in an AA3xxx alloy. Most dispersoids have a plate-shaped morphology after low-temperature homogenization at 450C. The largest proportion of the dispersoids follows the previously described OR with the Al matrix . Two plate-shaped dispersoids have been studied in detail. The dispersoid following the commonly observed orientation had habit planes . The dispersoid not following the commonly observed OR had habit planes , with (OR) , .

A pseudo-3D approach based on electron backscatter diffraction and backscatter electron imaging to study the character of phase boundaries between Mg and long period stacking ordered phase in a Mg–2Y–Zn alloy

In Mg–2at.% Y–1at.% Zn alloys, the LPSO (Long Period Stacking Ordered) phase is important to improve mechanical properties of the material. The aim of this paper is to present a study on the phase boundary character in these two-phase alloys. Using EBSD pattern analysis it was found that the 24R structure is the dominant LPSO phase structure in the current alloy. The phase boundary character between the Mg matrix and the LPSO phase was investigated using an improved pseudo-3D EBSD (electron backscatter diffraction) technique in combination with BSE or SE (backscatter or secondary electron) imaging. A large amount of very low-angle phase boundaries was detected. The (0 0 0 2) plane in the Mg matrix which is parallel to the (0 0 0 24) plane in the LPSO phase was found to be the most frequent plane for these phase boundaries. This plane is supposed to be the habit plane of the eutectic co-solidification of the Mg matrix and the LPSO phase.

Structure of collagen-glycosaminoglycan matrix and the influence to its integrity and stability.

Glycosaminoglycan (GAG) is a chain-like disaccharide that is linked to polypeptide core to connect two collagen fibrils/fibers and provide the intermolecular force in Collagen-GAG matrix (C-G matrix). Thus, the distribution of GAG in C-G matrix contributes to the integrity and mechanical properties of the matrix and related tissue. This paper analyzes the transverse isotropic distribution of GAG in C-G matrix. The angle of GAGs related to collagen fibrils is used as parameters to qualify the GAGs isotropic characteristic in both 3D and 2D rendering. Statistical results included that over one third of GAGs were perpendicular directed to collagen fibril with symmetrical distribution for both 3D matrix and 2D plane cross through collagen fibrils. The three factors tested in this paper: collagen radius, collagen distribution, and GAGs density, were not statistically significant for the strength of Collagen-GAG matrix in 3D rendering. However in 2D rendering, a significant factor found was the radius of collagen in matrix for the GAGs directed to orthogonal plane of Collagen-GAG matrix. Between two cross-section selected from Collagen-GAG matrix model, the plane cross through collagen fibrils was symmetrically distributed but the total percentage of perpendicular directed GAG was deducted by decreasing collagen radius. There were some symmetry features of GAGs angle distribution in selected 2D plane that passed through space between collagen fibrils, but most models showed multiple peaks in GAGs angle distribution. With less GAGs directed to perpendicular of collagen fibril, strength in collagen cross-section weakened. Collagen distribution was also a factor that influences GAGs angle distribution in 2D rendering. True hexagonal collagen packaging is reported in this paper to have less strength at collagen cross-section compared to quasi-hexagonal collagen arrangement. In this work focus is on GAGs matrix within the collagen and its relevance to anisotropy.

The reason for red streaks on dermoscopy in the distal part of a subungual hemorrhage.

The reason for red streaks on dermoscopy in the distal part of a subungual hemorrhage.

Effects of compressive stresses on torsional fatigue

Rolling contact fatigue (RCF) is the dominant failure mode in properly installed and maintained ball and roller element bearings. Lundberg and Palmgren in their seminal publication indicated that this failure is due to the alternating component of shear stress. Thus, torsional fatigue experiments have been used to predict the RCF behavior of bearing materials. In non-conformal contacts, due to Hertzian pressure the contact experiences large compressive stresses. Hence, it is critical to take into account the effect of these large compressive stresses in torsional fatigue to better simulate RCF conditions. This paper presents an investigation of torsional fatigue of bearing steels, while the effects of combined compressive stress and its relevance to material behavior in rolling contact fatigue is examined. An MTS test rig was used to investigate the fatigue life of several bearing steels and their failure mechanisms were evaluated through fractography. Then the effects of compressive stresses on torsional fatigue were investigated. A set of custom designed clamp fixtures were designed, developed and used to apply Hertzian pressures of up to 2.5GPa on the torsion specimens. The experimental results indicate that at high cycle fatigue, a combination of shear and biaxial compression, by application of Hertzian contact, is more detrimental to fatigue life than shear alone; however, as expected it has little to negligible effects in the low cycle fatigue regime. Also the failure mode changes such that fracture planes form a cup and cone pair with multiple internal cracks as opposed to helical planes observed in pure torsion which are formed by a single crack. A 3D finite element model (using ABAQUS) was developed to investigate the fatigue damage accumulation, crack initiation, and propagation in the material. The topology of steel microstructure is modeled employing a randomly generated Voronoi tessellation wherein each Voronoi cell represents a material grain and the boundaries between the cells are assumed to represent the weak plane in the steel matrix. Continuum damage mechanics (CDM) was used to model material degradation during the fatigue process. A comprehensive damage evolution equation is developed to account for the effect of mean stress on fatigue. The model predicts the fatigue lives and crack patterns successfully both in presence and absence of compressive stresses.

Newly observed prismatic Mg2Sn laths in a Mg–Sn–Zn–Mn alloy

Lath-shaped Mg2Sn precipitates with their habit planes parallel to the prismatic planes of the Mg matrix are characterized in a Mg–Sn–Zn–Mn alloy. The orientation relationships (ORs) between these β-Mg2Sn precipitates and α-Mg matrix are [0 1 1]β//[0 1 −1 0]α and (0 1 −1)β deviating 0.36° to 1.20° from (0 0 0 1)α, in which the deviation angle of 0.39° is most frequently observed. Although the ORs vary, the laths always exhibit four side facets bearing fixed relationships with g vectors in reciprocal space. Their major side facets incline to the basal plane of Mg matrix from 4.3° to 14.3°.

Precipitation process and its effects on properties of aging Cu–Ni–Be alloy

The precipitation process of aged Cu–Ni–Be alloy was investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM), and high-resolution transmission electron microscopy (HRTEM). The tensile strength, yield strength, and electronic conductivity of this alloy after aging were also studied. The precipitation sequence of the C17510 alloy aged at 525 °C is supersaturated solid solution→ G.P zones→ γ″→ γ′→ γ. This transformation can be achieved by the accumulation of Be-atom layers. The G.P zones are composed of disk-shaped monolayers of Be atoms, which are formed on (001) matrix planes. The intermediate γ″ precipitate is nucleated in the G.P zones. The γ″ and γ′ precipitates have the same orientation relationship with matrix, e.g., (110)P‖(100)M,[001]P‖[001]M. The tensile strength of specimen shows a maximum during the aging process and then continuously decreases if the specimen is over aged. The strengthening effect of γ′ phase precipitated in aging at 525 °C for 4 h is calculated to be 436 MPa according to the Orowan strengthening, which is quite consistent with the experimental data.

Complex cylindrical vector beam excludes the orientation dependence of the intensity of scanning fluorescence images of single molecules

A polarization inhomogeneous vector beam, which is the complex superposition of radially and azimuthally polarized beams, has been studied computationally and theoretically in application to scanning fluorescence microscopy of single molecules. It has been shown that its application makes it possible to almost exclude the dependence of the intensity maximum of the scanning fluorescence image of a single molecule on its orientation. It has been demonstrated that the scanning of one horizontal plane of a solid matrix containing impurity luminescent molecules provides images of all molecules located in a 1-μm-thick layer, replacing three-dimensional scanning. Recommendations on the technical implementation of the proposed beam have been given.

Improved age-hardening behavior of Mg–Sn–Mn alloy by addition of Ag and Zn

The effect of 0.5at% Ag and its combination with 0.4at% Zn on the precipitation hardening behavior of Mg–1.5Sn–0.5Mn (at%) alloy have been investigated using hardness measurements and transmission electron microscopy (TEM). The results show that sole addition of Ag can remarkably improve the peak hardness from 58HV to 77HV after ageing at 200°C, which is attributed to the increased number density, the size and so the volume fraction of the Mg2Sn lath precipitates. A combination addition of Ag and Zn further improves the peak-hardness to 83HV and the time to peak hardness has been reduced from 120h to 100h. The joint addition of Ag and Zn both increases the number density and refines the Mg2Sn precipitates. Zn also promotes the Mg2Sn precipitates lying on the non-basal plane of matrix, as well as the blocky Mg54Ag17 phase which has an orientation relationship with α-Mg matrix as (001)ɛ′//(0001)α, [200]ɛ′//[−1−120]α, [0−20]ɛ′//[1−100]α. In the peak-aged Ag modified alloys, Ag atoms are segregated in the Mg2Sn precipitates. Nucleation, growth and coarsening of the Mg2Sn precipitates simultaneously occur as the ageing proceeds. The growth of Mg2Sn precipitates exhibits a significant anisotropic behavior. Addition of Ag can promote the precipitation process during the underage period and retarding the growth of Mg2Sn during the overage period, leading to a more thermal stable microstructure of the Ag and Ag+Zn modified alloys, from which only a small hardness decrease after 700h ageing is detected.

Martensitic Transformation and Microstructural Characteristics in Copper Based Shape Memory Alloys

Martensitic transformations are first order solid state phase transitions and occur in the materials on cooling from high temperature. Shape memory effect is an unusual property exhibited by certain alloy systems, and based on martensitic transformation. The shape memory property is characterized by the recoverability of previously defined shape or dimension when they are subjected to variation of temperature. The shape memory effect is facilitated by martensitic transformation, and shape memory properties are intimately related to the microstructures of the materials. Martensitic transformations occur as martensite variant with the cooperative movement of atoms on {110}β - type plane of austenite matrix. Martensitic transformations have diffusionless character, and the atomic movement is confined to interatomic lengths in the materials. The basic factors which govern the martensitic transformation are Bain distortion and homogeneous shears. Copper based alloys exhibit this property in metastable β-phase field.

In situ formation of superhard Cu–B based composite by reducing reaction

In this work, superhard Cu–B based composite has been prepared by reducing reaction of B2O3 with Cu–Al melt. Moreover, the microstructure, microhardness, resistivity and CTE of Cu–B based composites has been studied. It has been found that B-rich compounds can be formed by reducing reaction occurred in the Cu–Al melt: [Al]+B2O3→[B]+Al2O3. The precipitation of B-rich compound may change the preferential growth plane of Cu matrix in Cu–B based composite. The average microhardness of the B-rich compound in Cu–10B alloy is 2763HV, which is much higher than that of pure Cu. Moreover, CTE of Cu–10B alloy is much smaller than that of pure Cu, and the Cu–B composite has pretty good resistivity.

Precipitation microstructure and their strengthening effects of an Mg–2.8Nd–0.6Zn–0.4Zr alloy with a 0.2 wt.% Y addition

Abstract A micro-alloy addition of Y (0.2 wt.%) produced a significant improvement in the tensile yield strength of an Mg–2.8Nd–0.6Zn–0.4Zr (wt.%) alloy at 200 °C, with a 28% increase from 143 MPa to 183 MPa. APT characterisation confirmed that small solute clusters in a high number density were present in the as-quenched sample. TEM examinations revealed that β-type precipitates habiting on prism { 1 1 2 ¯ 0 } planes were dominant in the sample after aged for 14 h at 200 °C, and they co-existed with γ-type precipitates on the basal plane of Mg matrix. The precipitation sequence of β-type precipitates is solute clusters → β″ → β′ → β1 before the peak hardness. There was significant clustering of solutes in the Y-containing alloy, but Y did not clearly partition into clusters or precipitates and remained in the Mg matrix. β″, β′ and β1 were measured with stoichiometric Mg9(Nd,Zn), Mg4(Nd,Zn) and Mg2(Nd,Zn), respectively.