Fixed Orientation Relationship Research Articles

Characterisation of microstructure, defect and high-cycle-fatigue behaviour in a stainless steel joint processed by brazing

We report the characterisation of microstructures and high-cycle-fatigue (HCF) properties of Type 304 stainless steel joints processed by brazing. Pure copper was applied as the filler metal for brazing at 1120 °C. A two-phase microstructure was obtained within the joint region: the star-shaped precipitates and copper matrix. The precipitates with an average size of 0.43 μm were rich in iron and chromium. A fixed orientation relationship was found between the precipitates and copper matrix. The joint exhibited much higher tensile strength and HCF life when compared to pure copper. The strength enhancement can be attributed to the presence of precipitates. Furthermore, the effect of joint interface roughness as well as defects was critically investigated. The joint interface roughness showed little influence on the HCF lives. Post-examinations revealed that fatigue crack initiation and propagation occurred entirely within the joint region, hence being consistent with the similar HCF lives regardless of the pre-defined interface roughness conditions. In addition, it was found that the HCF lives decreased exponentially with the increase of initial defect area. Fractography analysis revealed that fatigue striation spacings near the crack initiation zone increased with the increase of defect area, suggesting that the larger defects result in higher crack growth rate, hence shorten the overall fatigue life.

New approach to achieve high strength powder metallurgy Ti-6Al-4V alloy through a simplified hydrogenation-dehydrogenation treatment

A simplified hydrogenation-dehydrogenation approach is demonstrated to achieve high strength powder metallurgy Ti-6Al-4V alloy by introducing 0.90 wt.% hydrogen in the green compact, without the help of hydrogen flow. The refined cross-linked network microstructure, where ultra-fine β phase dispersed in between refined α phase, produces a high tensile strength of ∼1062 MPa. A fixed orientation relationship was determined between these refined α phase and ultrafine β phase, which predicts a coherent interface makes the alloy stronger and showing transgranular and ductile fracture, avoiding intergranular fracture along the β grain boundary as in vacuum sintered sample. The influence of hydrogen content on mechanical properties and microstructures is also investigated in detail. The critical hydrogen content of 0.36 wt.% was revealed for presenting the beneficial effect of hydrogen.

Investigation on the crystallographic orientation relationships and interface atomic structures in an in-situ Ti2AlN/TiAl composite

In this research work, 15vol% Ti2AlN particles reinforced TiAl alloy matrix composite was prepared by an in-situ reactive hot processing method using Ti, Al and TiN powders as raw materials. Transmission electron microscope (TEM) coupled with energy-dispersive spectroscopy (EDS) was utilized to investigate the morphology characteristics of Ti2AlN particles. The crystallographic orientation relationships and interface atomic structures between various shaped Ti2AlN particles and TiAl matrix were investigated by the means of selected area electron diffraction (SAED) and high resolution transmission electron microscopy (HRTEM). The results show that four kinds of Ti2AlN particles presented in the composite, which include vast majority of elliptical and polygonal Ti2AlN particles with the sizes of 4μm, few hexagonal Ti2AlN particles with the sizes of 4μm and small plate Ti2AlN particles with the sizes of 0.4μm. The elliptical and polygonal Ti2AlN particles have no fixed crystallographic orientation relationship with TiAl matrix, the elliptical and polygonal Ti2AlN/TiAl interfaces are incoherent interphase boundaries composed by many atomic-scale microfacets. The hexagonal and small plate Ti2AlN particles have a fixed orientation relationship with TiAl matrix. Both the hexagonal and small plate Ti2AlN particles have a ledge and terrace coherent interface with TiAl matrix.

In-plane magnetic anisotropy of La0.7Ca0.3MnO3 film grown on (0001) sapphire

La0.7Ca0.3MnO3 (LCMO) films were grown on (0001) single-crystal sapphire (α-Al2O3) substrate by pulsed laser deposition. In this work, the growth of (110) oriented LCMO film on sapphire was achieved by controlling the film's deposition conditions, specifically the substrate temperature. The fixed orientation relationship between the film and the substrate [(110)f∥(0001)s, (1—10)f∥(01—10)s, (001)f∥(2—110)s], was measured by high-resolution X-ray diffraction (HRXRD) and grazing incident X-ray diffraction (GIXRD) techniques. The LCMO film showed interesting in-plane magnetic anisotropy along the two mutually perpendicular in-plane directions, corresponding to [001]f as strong and [1—10]f as weak magnetization directions.

Stability of Microstructure and Mechanical Properties of GH984G Alloy during Long-Term Thermal Exposure

A low cost Ni-Fe-based wrought superalloy for 700 advance ultra-supercritical coal-fired power plants was developed. The stability of microstructure and mechanical properties of this alloy during long-term thermal exposure was investigated by SEM,TEM and tensile tests. The experimental results showed that the major precipitates in the alloy were spherical γ, MC and discrete M23C6 distributing along grain boundary after the long-term exposure at 700 and 750 and no harmful phases, such as σ phase and η phase, were found. However, after exposure at 800 up to 3000 h, small amount of lath-like η phase precipitated at grain boundary by consuming the surrounding γ. The η phase exhibited a fixed orientation relationship with the γ matrix. During thermal exposure γ coarsened with increasing the exposure time and exposure temperature. In addition, all major phases and their stability temperature ranges were calculated by JMatPro and these results were confirmed by the experimental results. The 700 tensile tests revealed that the alloy after exposure at 700 and 750 for 3000 h exhibited excellent ductility and strength. Therefore, the GH984G alloy possessed excellent stability of microstructure and mechanical properties between 700 and 750 up to 3000 h, and it is a promising material for 700 advance ultra-supercritical coal-fired power plants.

Effects of Solution Heat Treatment on Carbide of Ni-Cr-W Superalloy

Abstract The microstructure features of a kind of Ni-Cr-W superalloy after solution heat treatment at different temperatures (1230–1300 °C) for various time (10–120 min) were investigated by means of scanning electron microscope (SEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). The results show that the precipitated phases of the alloy after solution heat treatment are identified as W-rich fcc M6C and Cr-rich fcc M23C6 carbides. The volume fraction of carbides decreases with increasing of the solution heat treatment temperature and time. At the temperature above 1270 °C for 120 min, most of carbides are dissolved into the Ni-matrix, and the carbides distributing at twin boundaries may be dissolved into the matrix first. M6C carbide has no any fixed orientation relationship with the Ni-matrix, but the angle of M23C6 (220) to the matrix (1 1) is 30°.

In situ fabrication and microstructure of Al2O3 particles reinforced aluminum matrix composites

Abstract Al2O3p/Al composites were prepared by direct melt reaction process. The thermodynamics of in situ chemical reactions between molten aluminum and CeO2 powder was studied. The XRD results show that the components of the as-prepared composites consist of Al2O3 and Al phases. For the as-cast composite specimens, SEM, EDX, TEM and SAD were used to analyze the reinforcement phases and interface characters of composites. The results show that the in situ generated Al2O3 particles, whose sizes are 100–200 nm, have various irregular shapes and disperse uniformly in matrix. TEM observation shows that the interface between particle and matrix is clean. Furthermore, there is no fixed orientation relationship between Al2O3 particles and aluminum matrix. Only [ 1 2 ¯ 10 ] / / [ 111 ] orientation parallel relationship with low exponent is found. Therefore, the composites have isotropic properties. Besides characters mentioned above, there are large amount of high density dislocations and the generated extensive fine subgrains around Al2O3 particles. These features are favorable for improving composite performances. As a result, the composites are comprehensively strengthened not only by Al2O3 particles, but also by the high density dislocations and fine subgrains.

Growth of Vertically Aligned ZnO Nanobelt Arrays on GaN Substrate

Uniformly aligned ZnO nanobelt (NB) arrays have been grown on a (0001) GaN substrate without foreign catalyst such as Au. The NBs mainly grew along [0113] at beginning when the temperature was relatively low, then switched to [0110] at high temperature, and finally switched to [0113] when the temperature was lowed. The alignment of the NBs was due to not only the epitaxial orientation relationship with the substrate but more importantly the presence of metallic Zn nanoparticles at the tip of the ZnO NBs, which were produced by reduction of ZnO source material. The Zn nanoparticle has a fixed orientation relationship with the ZnO NB, indicating that the growth follows the self-catalyzed vapor−liquid−solid process.

Epitaxial growth and magnetic properties of La0.7Sr0.3MnO3 films on (0001) sapphire

In this letter the authors report the growth of (110) oriented La0.7Sr0.3MnO3 films on (0001) single-crystal sapphire substrate. Growth of La0.7Sr0.3MnO3 (LSMO) films with a fixed orientation was achieved by carefully controlling the deposition conditions, specifically the substrate temperature. The fixed orientation relationship between the film and the sapphire substrate ((110)f‖(0002)s, (1¯10)f‖(01¯10)s, (002)f‖(2¯110)s), has been explained via domain matching epitaxy, where there is perfect matching in one direction and 19% planar misfit in the perpendicular direction. LSMO films showed interesting magnetic anisotropy along the two mutually perpendicular in-plane directions, corresponding to [002]f as strong and [1¯10]f as weak magnetization directions.

Three-dimensional morphology of ferrite formed in association with inclusions in low-carbon steel

Three-dimensional (3D) morphology and growth behavior of ferrite formed at intragranular inclusions in low-carbon steel were studied by serial sectioning and computer-aided visualization. The specimens taken from the weld deposit were austenitized and isothermally reacted for varying times. The length, width, and thickness of ferrite plates were measured from 3D-reconstructed images. From the length-to-width ratio, the morphology of ferrite is likely to be a lath rather than a plate in this alloy. Multivariant ferrite plates (or laths) were observed to be nucleated at inclusions and grow in the directions close to 〈110〉 γ with habit planes near {111} γ, probably keeping a fixed orientation relationship with austenite.

Epitaxial growth of yttrium-stabilized HfO2 high-k gate dielectric thin films on Si

Epitaxial yttrium-stabilized HfO2 thin films were deposited on p-type (100) Si substrates by pulsed laser deposition at a relatively lower substrate temperature of 550 °C. Transmission electron microscopy observation revealed a fixed orientation relationship between the epitaxial film and Si; that is, (100)Si//(100)HfO2 and [001]Si//[001]HfO2. The film/Si interface is not atomically flat, suggesting possible interfacial reaction and diffusion. X-ray photoelectron spectrum analysis also revealed the interfacial reaction and diffusion evidenced by Hf silicate and Hf–Si bond formation at the interface. The epitaxial growth of the yttrium stabilized HfO2 thin film on bare Si is via a direct growth mechanism without involving the reaction between Hf atoms and SiO2 layer. High-frequency capacitance–voltage measurement on an as-grown 40-Å yttrium-stabilized HfO2 epitaxial film yielded an effective dielectric constant of about 14 and equivalent oxide thickness to SiO2 of 12 Å. The leakage current density is 7.0×10−2 A/cm2 at 1 V gate bias voltage.

WS-19 溶接金属におけるアシキュラーフェライトの 3 次元形態

Three-dimensional (3D) morphology and growth behavior of acicular ferrite formed in low carbon steel weld deposit (0.11%C) was studied by serial sectioning and computer-aided visualization. The specimens taken from the weld deposit were austenitized at 1350℃ and reacted at 570℃ for varying times. The length, width and thickness of individual ferrite plates, measured from 3D-reconstructed images, were ranging from several microns to ∿25μm, less than ∿8μm and from 0.2 to ∿3μm, respectively. The change in the aspect ratio with holding time indicates that the lengthening occurred first and thickening followed after the plate tips impinged mainly on other plates. Multi-variant ferrite plates were observed to be nucleated at inclusions and grow in the specific directions in the matrix, probably keeping a fixed orientation relationship with austenite.

Phase precipitation and phase stability in nimonic 263

Scanning electron microscopy (SEM), transmission electron microscopy (TEM), and thermodynamic calculations were employed to study the phase stability and phase precipitation in the Ni-based superalloy Nimonic 263. The major precipitates at temperatures below 900 °C were gamma-prime and eta (Ni3Ti), with the eta phase starting to precipitate at the expense of the gamma-prime phase after prolonged annealing. The eta precipitates had a thin-plate morphology and formed a regular Widmanstatten pattern. They had a fixed orientation relationship with the fcc matrix. Very fine particles of M23C6 also precipitated intragranularly, and they had a cube-on-cube orientation relationship (OR) with the fcc matrix. Intragranular precipitation of a very fine cylindrical MC carbide was also observed. Grain-boundary (GB) precipitates were mostly M23C6, with a small fraction of MC. Based on the experimental results, a time-temperature-transformation (TTT) diagram was constructed. The experimental results were compared to thermodynamic predictions, and good agreement was observed. The calculations correctly predicted almost all the major phases and their stability temperature ranges. The experimental and calculation results, together, depict a clearer picture of phase stability in the alloy.

Silicate and oxide exsolution in pseudo-spinifex olivine from metaultramafic rocks of the Betic Ophiolitic Association; a TEM study

Transmission electron microscopy (TEM) has been used to study submicroscopic particles in spinifex-like textured olivine from secondary harzburgites collected from the Cerro del Almirez locality in the Mulhacen Complex (Betic Cordillera, SE Spain). Three main types of submicroscopic oxides have been identified: (1) equidimensional Fe-rich spinel (magnetite), with average grain size in the order of 1‐2 μm; (2) elongated Cr-bearing spinels (Fe-chromite to Cr-magnetite) with sizes ranging from 0.2 to 1 μm long and 0.01 to 0.1 μm thick; and (3) equidimensional Ti-rich particles from <0.01 to 0.1 μm and compositions ranging from ilmenite to Fe-Cr-Ti oxide. Chromite and ilmenite particles form parallel, chromite-rich and ilmenite-rich bands, extending along the a-axis of the host olivine. Both phases show a fixed orientation relationship with olivine, with the approximately hexagonal close-packed oxygen planes being parallel in both structures. These textural relationships indicate that both chromite and ilmenite were formed during a common exsolution process. Magnetite particles also are orientated preferentially relative to the olivine, but these particles are homogeneously distributed within the olivine, suggesting either a primary origin or an exsolution process that was not contemporaneous with formation of chromite and ilmenite. Chromite particles commonly are accompanied by lamellae of talc and/or enstatite, both showing a consistent orientation relationship with olivine. Talc lamellae are twice as thick as the associated chromite crystals, whereas enstatite lamellae show a greater thickness and, moreover, form single enstatite particles, which consist of clino- and orthoenstatite intergrowths. Talc formation may be explained by exsolution, together with spinel, from olivine containing OH-groups, probably related to incomplete dehydration of serpentine during olivine formation. On the basis of these results and previously reported petrological data, we have concluded that exsolution of chromite-silicate and ilmenite occurred during the retrograde stage that followed the climax of the eo-Alpine metamorphic event.

A new crystalline approximant of the decagonal phase in Al-Mn alloys

Abstract A new approximant of the decagonal phase has been found in an Al-22 at.% Mn alloy by electron microscopy. The structure is C face-centred orthorhombic with the lattice parameters a=2.41nm, b=3.32nm and c=2.40nm (experimental error: 7plusmn; 2%). Selected-area electron diffraction patterns from regions containing differently oriented grains of this crystalline phase with a common c axis show tenfold symmetry. The phason strain relating the approximant to the quasicrystal is given. Simulated electron diffraction patterns calculated by applying this phason strain to the diffraction the patterns of decagonal Al78Mn22 are in good agreement with the experimental ones. Furthermore, a structural description of the new phase is obtained from the Fourier transformation of the simulated electron diffraction patterns. The new phase is often found to occur together with Al3Mn, with a fixed orientation relationship. The structural relationship of these two phases is discussed.

An electron diffraction study of the tetragonal— monoclinic transformation in 12 mole% ceria-zirconia

The tetragonal (t) ↔ monoclinic (m) transformation occurring in 12 mole% CeO2-ZrO2 is a source of significant transformation plasticity and transformation toughening in this ceramic material. The t↔m transformation is martensitic in nature and a quantitative understanding of the transformation plasticity and transformation toughening requires that the crystallography of this martensitic transformation be understood in detail. Crystallographic characteristics of a martensitic phase transformation are:1. the existence of a unique lattice correspondence between the phases, which specifies the directions in the product crystal lattice into which any given directions in the parent crystal lattice are transformed, 2. a fixed orientation relationship preserved between parent and product phases, and 3. the orientation of the habit plane or interface plane between the parent and product phases.For the t↔m transformation occurring in ceria-zirconia, three possible lattice correspondences are plausible.

Kinetics of alpha precipitation in Ti-6 wt % Cr and Ti-11 wt % Mo

The morphology and kinetics of the precipitation of the alpha phase produced by two different heat treatment routes, namely, (a) direct isothermal decomposition and (b)β-quenching and subsequent ageing, were studied. In isothermally decomposed samples theβ′ (supersaturated) →α + β transformation was seen to occur mainly through the discontinuous growth of the transformed zone consisting of groups of parallel side plates from the grain boundary regions towards the interior of the grain. Unlike for the case of a regular discontinuous precipitation, here the transformed regions are not separated from the untransformed by an incoherent interface and the growingα-plates do obey a fixed orientation relationship with the grain from which they are evolved. The theory of cellular reaction has been applied to explain the growth rate of the duplex (α + β) region. The overall reaction kinetics were analysed on the basis of the Johnson-Mehl formulation and were found to be consistent with that of a discontinuous precipitation reaction, where grain boundary nucleation sites were saturated at an early stage of the transformation. The structure of theβ-quenched samples showed a uniform distribution of athermal omega particles which acted as precursors to theα-precipitates. As a consequence, the reaction rate was greatly enhanced andα-precipitation in the quenched and aged samples was seen to occur continuously in the entire body of the grain.

Orientation of Oxide Films on Metals

IT was suggested by Tammann1 in 1922 that the different rates of oxidation exhibited by iron crystals of different orientations can best be explained by a fixed orientation relationship between the lattice of the iron crystal and the lattice of the oxide film. During the succeeding years, fixed orientation relationships have been demonstrated for reaction products of many kinds, such as recrystallisation structures, products of transformation in the solid state, Widmanstatten figures and others ; in view of the general occurrence of such orientation relationships, it now seems more than likely that oxide (and other) reaction films grown on metal crystals will upon analysis also be found to exhibit fixed orientation relationships. Indeed the results of Finch and Quarrell2, published during the course of our work, seem to prove that films of zinc oxide on zinc, and magnesium oxide on magnesium possess such a relationship, though the analysis does not seem to be complete. We have been successful in demonstrating a fixed orientation relationship for wustite (“FeO”) films grown on iron, and for cuprous oxide films grown on copper.