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The 12% Cr heat-resistant steel used for critical components of fossil-fired power plants works in high-temperature and high-pressure steam environments for a long time and inevitably undergoes a certain amount of plastic deformation during service. This plastic deformation will affect the microstructure and hot ductility of the heat-resistant steel and ultimately influence its service life. Therefore, the effect of hot compression deformation on microstructural evolution at 650°C was investigated in this work. As the amount of hot compression deformation increased, the number of subgrains significantly increased, and their sizes gradually decreased. When the amount of deformation reached 50%, dynamic recrystallization occurred, forming a preferred orientation in the rolling direction. <111> and <001> fiber texture appeared in the microstructure when the deformation amount reached 8%, and the intensity of <111> texture was significantly higher than that of <001> texture. Their intensity values further increased with the increase of the amount of deformation. As the amount of hot compression deformation increased, the deviation angle of the Kurdjumov–Sachs (KS) orientation relationship between M23C6 particles and α-Fe gradually increased. Their KS orientation relationship began to be disrupted at the deformation amount of 6% and was completely destroyed at the deformation amount of 20%. With the amount of deformation increasing up to 50%, there were no micropores at the M23C6/matrix interfaces, and no hot cracking occurred. This was mainly attributed to the occurrence of dynamic recrystallization which alleviated stress concentration at the particles /matrix interfaces. The mechanisms of microstructural evolution involving subgrains, grain boundary characteristics, texture evolution, strain distribution, and orientation relationship were discussed in detail. [ABSTRACT FROM AUTHOR]

The well-known problem of determining the maximum possible disorientation angle of two cubes is extended to groups of three to six cubes. This problem is considered here to allow identification of specific arrangements of grains with a cubic structure at triple-line or quadruple junctions in polycrystals. The minimum disorientation angle between cubes in the group is defined as the characteristic disorientation angle θ c d of the group. The maximum values of θ c d and the arrangements of cubes giving the maximum θ c d are determined for groups of three to six cubes. [ABSTRACT FROM AUTHOR]

A new orientation relationship (OR) is found between Widmanstätten cementite precipitates and the austenite matrix in a 1.3C-14Mn steel. The associated habit plane (HP) and the dislocations in the HP have been investigated with transmission electron microscopy. The HP is parallel toin cementite, and it is parallel toin austenite. Three groups of interfacial dislocations are observed in the HP, with limited quantitative experimental data. The line directions, the spacing and the Burgers vectors of two sets of dislocations have been calculated based on a misfit analysis, which combines the CSL/DSC/O-lattice theories, row matching and good matching site (GMS) mappings. The calculated results are in reasonable agreement with the experimental results. The dislocations ‘Coarse 1’ and ‘Fine 1’ are in the same direction as the matching rows, i.e.. ‘Coarse 1’ dislocations are secondary dislocations with a Burgers vector of, and ‘Fine 1’ dislocations are pseudo-primary dislocations with a plausible Burgers vector of. The reason why the fraction of the new OR is much less than that of the dominant Pitsch OR has been discussed in terms of the degree of matching in the HPs. [ABSTRACT FROM PUBLISHER]

Oxide nanoparticles are quintessential for ensuring the extraordinary properties of oxide dispersion strengthened (ODS) steels. In this study, the crystallographic structure of oxide nanoparticles, and their interface with the ferritic steel matrix in an Al-alloyed ODS steel, i.e. PM2000, were systematically investigated by high-resolution transmission electron microscopy. The majority of oxide nanoparticles were identified to be orthorhombic YAlO3. During hot consolidation and extrusion, they develop a coherent interface and a near cuboid-on-cube orientation relationship with the ferrite matrix in the material. After annealing at 1200 °C for 1 h, however, the orientation relationship between the oxide nanoparticles and the matrix becomes arbitrary, and their interface mostly incoherent. Annealing at 1300 °C leads to considerable coarsening of oxide nanoparticles, and a new orientation relationship of pseudo-cube-on-cube between oxide nanoparticles and ferrite matrix develops. The reason for the developing interfaces and orientation relationships between oxide nanoparticles and ferrite matrix under different conditions is discussed. [ABSTRACT FROM AUTHOR]

Orthorhombic α″ phaseoften forms in Ti alloys through martensite transformation during quenching. Here, we report the formation of orthorhombic α″ phasein a low modulus β-Ti alloy during isothermal ageing. Thecoexists with α and ω phases, and remains stable for 120 h during ageing at 673 K. Thephase is highly coherent with the β matrix, sharing the same basic orientation relationship asphase://[0 0 2]α″, [1 0 0]β//[1 0 0]α″, [0 1 1]β//[0 1 0]α″. But differing from orthorhombicphase, the lattice constants ofphase are determined asa = 0.352 nm,b = 0.494 nm, andc = 0.464 nm. [ABSTRACT FROM AUTHOR]

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),. [ABSTRACT FROM PUBLISHER]

Constituent and dispersoid phases in two Direct Chill-cast 3xxx aluminum alloys after low-temperature annealing, with different silicon content have been studied. The lattice parameters, chemical composition, morphology and orientations relationships of constituent particles with regard to Al matrix have been addressed. Al(Fe,Mn) is found to be the most prominent constituent phase in the alloy with a low Si content. The orientation relationship between aluminum matrix and this phase is determined as,, which is consistent with the orientation relationships of Al(Fe,Mn) dispersoids.–Al(Fe,Mn)Si constituent particles in the Si rich alloy have been found to have various possible orientations. A gradient of Fe content is found in the–Al(Fe,Mn)Si dispersoids due to slow diffusion of Fe into dispersoids during annealing. [ABSTRACT FROM AUTHOR]

We have investigated microstructure and orientation relationship (OR) of the?and?phases in an as-cast ingot and nodular bainite of Cu-14.9 at.% Sn alloy by using transmission electron microscopy. Proeutectoid?grains and surrounding?phase (prior?phase) possess well-defined (1?1?1)?//(1?1?0)?,OR, that is, Kurdjumov–Sach (K–S) OR, while these two phases formed by eutectoid decomposition exhibit some deviation from K–S OR. On the other hand, the?and?phases in nodular bainite exhibit (1?1?1)?//(1?1?0)?,, which is Nishiyama–Wassermann (N–W) OR, as well as K–S OR. The emergence and variations of these ORs between the?and?phases have been interpreted from the viewpoints of (i) matching of interplanar spacing of {1?1?1}?, {1?1?0}?and {6?6?0}?planes, (ii) minimum strain criteria based on the invariant line concept for K–S OR and (iii) correspondence of atomic positions in the relevant phases by employing the structural ledge concept for N–W OR. [ABSTRACT FROM AUTHOR]

A model based on near coincidence of diffraction intensity-weighted reciprocal lattice spots was used to study the orientation relationships between a precipitate and matrix in various alloys. The model was used to calculate the orientation relationship and interface orientations between phases including body-centred cubic, body-centred tetragonal, face-centred cubic and hexagonal close-packed crystals. Comparison of calculated results with those reported from various experimental observations demonstrate that in most cases the model can predict the orientation relationship between two phases with an accuracy of a few degrees or better. Calculation of the interface orientation was found to be very sensitive to the exact orientation relationship and therefore, in some cases, showed significant deviation from experimental observations. [ABSTRACT FROM PUBLISHER]

Precipitating phases in a supersaturated Cu-8.6 at.% Sn alloy annealed at 573 K have been studied by using transmission electron microscopy. Three Hume-Rothery (HR) phases,δ,ζandϵwere identified in theαmatrix, each with distinct morphologies. Theδphase emerges in the form of rhombic precipitates inside grains with an orientation relationship (OR):. Theζphase emerges both inside grains and at grain boundaries. Frequently observed OR is. Intragranularζparticles consistently satisfy this OR; while it is proposed that a cellular morphology, whose details have been reported separately, develops only when this condition is satisfied forζprecipitates at grain boundaries. Theϵphase emerges along {111}αplanes inside grains with a planar morphology. These plates exhibit two types of ORs:. and. The latter is the OR, reported for the same alloy annealed at 593 K. These findings are discussed from the viewpoints of the layer structures of the respective HR phases. It was shown that both the atomic configuration and interlayer spacing of theδandζphases match well with {111}α, while theϵphase cannot satisfy these two conditions simultaneously, resulting in one of the two ORs. [ABSTRACT FROM AUTHOR]

In this study, a particular nickel-based superalloy has been studied by transmission electron microscopy and the results are discussed in terms of phase transformations that may have taken place. The alloy has been found to consist of three major phases; a FCCγphase containing a random distribution of nearly sphericalγ′ – Ni3Al(Ti) – precipitates and elongated thin Ni3Ti(Ta) platelets with a hexagonal structure. The orientation relationships between the different phases have been determined; loss of coherency and possible occurrence of misfit-relieving interfacial dislocations are discussed and compared with experimental observations, and possible mechanisms of phase transformations are also addressed. [ABSTRACT FROM PUBLISHER]

Discontinuous precipitation (DP) in Cu–8.6 at% Sn alloy at 573 K has been studied using transmission electron microscopy and electron back scattered diffraction techniques. DP reactions occur only sporadically at grain boundaries after prolonged aging, giving rise to a cellular morphology. The supersaturatedα′phase (face-centred cubic) phase decomposes not into the equilibriumαandεphases as reported to date, but into theαandζ(space groupP63,a = 0.733,c = 0.786 nm) phases, the latter being stable above 835 K. These two phases possess the following orientation relationship (OR):. Well-defined habit planes do not exist. However, broad faces ofζlamellae are often parallel to the {}ζplane. The observed OR and cellular morphology have been interpreted by matching atomic rows across the phase boundaries in two perpendicular directions. Namely, the spacings of (110)αand (0001)ζplanes, which match across the broad faces of theζlamellae, are nearly the same, while, in a perpendicular direction, mismatch between (111)αandspacings amounts to 0.5%. The facing (111)αandplanes form a coincidence site lattice, and atomic configurations in these planes both contain similar triangular atomic networks. It was also found that the orientation of the depletedαphase is often correlated with that of the adjoiningα′grain. This correlation indicated that the OR hold successively uponα′ → ζ → αtransformation. Possible orientations of theαphase have been enumerated, as supervariants to the adjoiningα′grains mediated by theζphase. [ABSTRACT FROM AUTHOR]

The effect of oxide inclusion compositions on microstructure and notch toughness of weld metal for HT780MPa class high-strength steel was investigated. Three different types of weld metals were prepared by varying deoxidant elements. Intragranular bainite microstructure and dispersed oxide inclusions were observed and quantified by an optical microscope and by electron backscattered diffraction analyses to reveal the affectors of notch toughness. It has been found that fracture appearance transition temperature of the weld metal depends on the size of intragranular bainite (acicular ferrite) nucleated on oxide inclusions and that the upper shelf energy is affected by the density of dispersive oxides inclusions. It has also been clarified that all oxide inclusions, which contribute to intragranular transformations, consisted of titanium-rich crystalline phases and manganese-rich amorphous phases. By detailed finite element (FE)-TEM observation, the crystalline phases were identified as MnTi2O4 having Baker–Nutting orientation relationship with the intragranular bainite. It is considered that the reason for the bainite to have the orientation relationships of both MnTi2O4 and austenite is that the MnTi2O4 is generated at the interface between the amorphous phases and austenite previous to the intragranular transformation. [ABSTRACT FROM AUTHOR]

Needle-like precipitates exhibiting Widmanstatten side plate morphology have been observed in Fe-21.7Mn-14.5Al annealed at 1573 K for 2 h followed by furnace cooling. The precipitates were identified to be an L12 (ordered fcc) structure, whereas the matrix had an L21 (ordered bcc) structure. The orientation relationship between the precipitates and matrix was found, by electron diffraction analysis, to be (011)L21//(001)L12, [11 [image omitted]]L21//[ [image omitted]10]L12. Nanoindentation results showed that the hardness of the L12 phase was ∼10.2 GPa, whereas a hardness of ∼15.9 GPa for the L21 matrix was found. [ABSTRACT FROM AUTHOR]

A model based on the near-coincidence of diffraction intensity weighted reciprocal-lattice spots is proposed to determine preferred orientation relationships between two crystalline phases. The preferred orientation is found by minimizing the three-dimensional lattice mismatch, i.e. by maximizing the total overlapping intensity, between the diffraction spots of two crystals. The procedure is biased towards matching reciprocal lattice sites with high structure-factor values, which is physically equivalent to matching planes of high atomic density. In contrast to previous reciprocal-lattice models, including the diffraction intensity in the present method makes it sensitive to the types of atoms in (chemistry of) crystals. The preferred orientation relationship is then used to identify the orientations of low-energy interfaces using a Δg approach. A Voronoi (or Wigner-Seitz) construction based on the Δg values is further used to qualitatively estimate the equilibrium shape of the precipitate in the matrix. The model was tested by performing calculations on hypothetical Au-Cu crystals to investigate the effects of chemistry and fcc truncated-octahedral precipitates in fcc matrices in Al-Ag, Al-Xe and Al-Pb alloys. The present model has the ability to sample the entire orientation space and rationalize and compare alternate orientation relationships in a reasonable timeframe, thereby providing insight into the formation of precipitate orientation relationships and shapes. [ABSTRACT FROM AUTHOR]

This paper presents the progress in phase transformation crystallography of the fcc/bcc system based on the O-line model. In contrast to previous numerical methods, closed-form expressions have been derived to describe the orientation relationship (OR), habit plane (HP) normal, dislocation direction and spacing as functions of the lattice parameter ratio (λ) and the angle between the Burgers vectors of the dislocations. Possible directions of the dislocation and the HP normal are presented as elliptical curves in stereographic projections and explicit expressions for the curves are provided. In the 3-D space defined by the OR, the O-line criterion only restricts two degrees of freedom in the OR, while various constraints have been applied to the remaining degree of freedom. A comparison of the calculations with those from existing models indicates the general applicability of the method. Furthermore, the property that the HP normal lays on the surface of an elliptic cone can be readily extended to other systems. [ABSTRACT FROM AUTHOR]

A simple 2-D analytical method has been developed for calculating the crystallographic features, including the orientation relationship (OR), habit plane (HP) and the direction and spacing of dislocations in the HP, under the condition that a pair of Burgers vectors from both phases are parallel to each other lying in the HP. In contrast to previous 2-D models for the OR and HP, which are on the plane normal to the parallel Burgers vectors, the present 2-D model is based on vector analysis in the HP. Closed-form expressions for the crystallographic features have been derived as functions of lattice parameter ratios. While the results are in agreement with those from a 2-D method based on the O-line model, the present method is simpler and improves our understanding of crystallographic features. [ABSTRACT FROM AUTHOR]

EBSD measurements were carried out on four different martensitic steels (T91, P92, EM10 and Eurofer) in various metallurgical conditions (nine different microstructural states). The usual orientation relationships (ORs) between the parent austenitic phase and the resulting martensite in martensitic steels are those of Nishiyama-Wassermann (NW) and Kurjumov-Sachs (KS). The present study first proposes a methodology based on the combined analysis of the misorientation distribution, the pole figures (PFs) and the angle/axis pairs. This methodology leads to the conclusion that neither NW nor KS relationships are able to account for all the features observed whatever the material under study. A third OR proposed by Greninger and Troiano (GT) proves to describe the relationship between austenite and ferrite in all four different martensitic steels much more accurately. [ABSTRACT FROM AUTHOR]

A new Nb-silicide, δ-Nb11Si4, identified as a second phase precipitated from a Nb-Si solid solution, was characterized by combining crystallographic analysis with first-principles calculations. The crystal structure was determined as a body-centered orthorhombic system with space group Immm using transmission electron microscope (TEM). Based on the crystallographic relationship between the δ and Nb phases, [image omitted] // {200}Nb and [image omitted] // 〈001〉Nb, eight possible unit cells were proposed, which were optimized by first-principles calculations. By analyzing the experimental and calculated data, we obtained the final unit cell of the δ phase, which was confirmed by high-resolution TEM images. In addition, density of states and electron density difference of δ-Nb11Si4 revealed that the δ structure was in a metastable state at low temperature because not all the bonding states were filled. [ABSTRACT FROM AUTHOR]

The influence of an applied stress on discontinuous precipitation (DP) in a Cu-2.1 wt % Be alloy aged at 300°C was examined. A compressive stress accelerates the growth of DP cells, which consist of lamellae of the precipitated γ phase and the solute-depleted α phase, but a tensile stress does not essentially change it. The cell growth rates along the loading direction under the compressive and tensile stress are identical to those along the direction perpendicular to the loading direction under the same stress. Both the compressive and tensile stresses have no influence on the incubation time to initiate DP. From measurements of the specimen length change and investigations of the distribution of γ variants in cells in a particular case, specific γ variants among crystallographically equivalent ones are found to be formed, depending on the sense of the applied stress. This result, together with the dependence of the cell growth rate on the sense of the applied stress, can be well understood through the interaction energy between the external stress and the misfit strains of discontinuous γ precipitates. [ABSTRACT FROM AUTHOR]

Both TEM and SEM/EBSD orientation measurements are carried out on a Eurofer97 martensitic steel. The influence of the prior austenitic grain size is studied using dedicated heat treatments. The intra laths misorientation is estimated by TEM. SEM/EBSD orientation mapping enable to study the actual orientation relationship (OR) between the parent austenitic phase and the martensitic phase. Neither the Nishiyama-Wasserman nor the Kurdjumov-Sachs OR is able to account for both the misorientation angle distributions, the pole figure and the misorientation axes measured. The mixed OR recently proposed by Gourgues et al. (Electron backscattering diffraction study of acicular ferrite, bainite, and martensite steel microstructures, Mater. Sci. Tech. 16 (2000), pp. 26-40.) and Sonderegger et al. (Martensite laths in creep resistant martensitic 9-12%Cr steels - Calculation and measurement of misorientations, Mater. Characterization (2006), in Press.) seems to be able to account for most of these results. Based on this OR, a new angular criterion is proposed to detect blocks of laths. [ABSTRACT FROM AUTHOR]

The orientation relationship (OR) and the interfacial structure of the eutectic α-Nb5Si3 and Nb solid solution (Nbss) lamellar microstructure were investigated by transmission electron microscopy (TEM). The OR between α-Nb5Si3 and Nbss was determined as [image omitted] and [image omitted]. In spite of the significant difference in crystal structure between α-Nb5Si3 and Nbss, the interface was found to be semi-coherent with good matching. High-resolution TEM images of the α-Nb5Si3/Nbss interface are presented to describe the chemistry of the terminating plane of α-Nb5Si3. The results revealed that a pure Nb layer not Si or mixed (Nb + Si) layer of the α-Nb5Si3 phase was bonded to the Nb phase at the interface. A periodic array of edge-type misfit dislocations, with line direction [image omitted] and Burgers vector [image omitted], was observed at the interface. [ABSTRACT FROM AUTHOR]

Multilayers of Cu-Nb have been grown on a Nb seed layer on a Si (100) substrate using a magnetron sputtering technique. The bilayer period (Λ) was varied from 10 to 2.4 nm. Cross-sectional transmission electron microscopy (XTEM) and high-resolution TEM (HRTEM) were used to study the detailed structure as a function of the bilayer period. Although the majority of the structures conformed to a Kurdjumov-Sachs (K-S) orientation relationship between the Cu and Nb layers, the structures exhibit considerable spatial variation. In some local regions, a Nishiyama-Wasserman (N-W) orientation relationship was found. In addition, considerable distortions were observed in both the Cu and Nb regions close to the interface. Using both HRTEM imaging and fast Fourier transform (FFT) of HRTEM images, early stage of the fcc to bcc transition in Cu was detected. The results suggest that, in multilayer structures, the detailed structure of the interface and large local distortions may play an important role in interface-controlled plasticity. [ABSTRACT FROM AUTHOR]

Control of the crystallography of Ni3Al(γ′) precipitates along grain boundaries of NiAl(β) was systematically studied using β bicrystals with controlled orientations. γ′ phase preferentially precipitated along β grain boundaries showing a film-like shape. The variants of γ′ precipitates were uniquely selected, which satisfies the Kurdjumov-Sachs (K-S) relation with a neighboring β grain and deviates from the relation with another adjacent β grain. In the course of tensile deformation, fracture occurred preferentially at the (β/γ′-film) interface deviating from the K-S relation and the fracture stress decreased with increasing deviation angle from the K-S relation. For improvement of the coherency at the irrational (β/γ′-film) boundaries, the control of microstructure and crystal orientation distribution in (β/γ′) two-phase polycrystals was next attempted by thermomechanical processing. After hot-compression in β phase region and subsequently annealing in (β/γ′) two-phase region, γ′ phase transformed from β phase with 111β fiber texture satisfying the K-S relation, resulting in the formation of 110γ′ fiber texture. In particular, a large number of (β/γ′-film) boundaries became partially coherent. This thermomechanical processing was effective in controlling the crystallography of γ′-film along β grain boundaries and leads to the harmonic design of strength and ductility for (β/γ′) two-phase alloys. [ABSTRACT FROM AUTHOR]