Pitsch-Schrader Orientation Relationship Research Articles

Microstructures and mechanical properties of Ti-55511 alloy subjected to rolling in the α+β dual-phase region

In this study, dual-phase region rolling was conducted on a Ti-55511 alloy with different initial rolling reductions in the single-phase region. The mechanical properties and microstructural characteristics of the alloy with different deformation conditions were investigated. Microstructure observations show the formation of a heterogeneous structure with a gradient size distribution of the α phase at the recrystallized grain boundaries, induced by the non-uniform stress distribution. The α phase and the β matrix exhibit the Burgers orientation relationship in the recrystallized region with the gradient structure. However, in the unrecrystallized region of the partially recrystallized specimens and in the grain interiors of the fully recrystallized specimens, the α phase and the β phase exhibit Pitsch-Schrader orientation relationship (P–S OR). A large number of the nano-sized α" martensite bands were observed after the dual-phase region rolling. These bands originated from the α/β interfaces and grew towards the interiors of the α phase. As the deformation increased, these nano-bands underwent a transformation into the {10 1‾ 1}α deformation twins, resulting in the fragmentation of the α phase. Mechanical testing results show that the mechanical properties of the alloy can be improved by the dislocation strengthening, the generation of profuse α phase and other microstructures including the heterogeneous distribution of the α phase, the nano-sized α" martensite and the {10 1‾ 1}α deformation twins.

Novel insights on the grain boundary α phase microstructure formation and orientation development in Ti-6Al-4V alloy

The present work aims to understand the formation of microstructural features and their orientation development at the (prior) β grain boundary regions for Ti-6Al-4V alloy. The grain boundary region in the transformed microstructure primarily contains continuous grain boundary (GB) α phase along with GB α free regions at certain locations. Thin β phase generally separates adjacent GB α variants although it remains absent between many of them. The GB α variants usually follow Burgers orientation relationship (OR) with adjacent β grains although a few of them deviates from following Burgers OR and rather maintain near Potter or Pitsch-Schrader OR with the parent β grains on either side. While the GB α free locations possibly form due to the micro-segregation of β stabilizing elements during liquid→β transformation, the GB α variants without following Burgers OR are likely to associate with strong elemental partitioning during β→α transformation.

Formation of the intermetallic phases Al12Mg17 and Al3Mg2 during heating of elemental Al-Mg composites studied by high-energy X-ray diffraction

The purpose of the present study is to track the formation of the intermetallic phases that form in the binary Al-Mg system and investigate their orientation relationships to the parent Al and Mg elements. Therefore, two compositions Al60Mg40 and Al40Mg60 (wt%), which are very suitable for studying the diffusion of Al in Mg and Mg in Al were heated from room temperature up to elevated temperatures below the melting point. Powder metallurgy, including cold extrusion was used to create a large interface between the Al and Mg, which facilitates fast reaction kinetics. In order to observe the phase formation during heating and analyze the crystal structures, X-ray diffraction using synchrotron radiation was used. The use of high energy X-ray was extremely helpful, enabling the detection of small phase fractions and information on the orientation relationships between the Al and Mg and the intermetallic phases that formed. The γ-Al12Mg17phase was the first phase formed in both alloy compositions on annealing. Subsequently, the β-Al3Mg2phase was formed. After annealing at 400 ºC for 2 h, the Al40Mg60 composition consisted of a very high amount of Al12Mg17 and a small amount of Mg phase while the Al60Mg40 composition consisted of mainly Al3Mg2 and a small fraction of Al12Mg17, indicating that thermodynamic equilibrium has been approximated. On further annealing at 400 ºC for 12 h, both compositions formed only one phase, namely the Al12Mg17 phase in the Al40Mg60 composition and the Al3Mg2 phase in the Al60Mg40 composition. In this condition, a Pitsch-Schrader orientation relationship was found between the Mg and the γ-Al12Mg17 phase, the occurrence of which is discussed within the framework of literature models. No orientation relationship between either the Al or the Mg with the Al3Mg2 phase was found.

Strain direction dependency of deformation mechanisms in an HCP-Ti crystalline by molecular dynamics simulations

In this work, effects of uniaxial tensile directions on the deformation mechanisms of a hexagonal close-packed (HCP) titanium crystalline were investigated by molecular dynamics simulations. Three uniaxial tensile directions, namely the [21-1-0], [011-0] and [0001] directions, were studied. When the tensile loading was along the [21-1-0] direction, the parent HCP phase transformed firstly into the body-centered cubic (BCC) phase following the Pitsch-Schrader orientation relationship (OR), and then transformed either into the face-centered cubic (FCC) phase following the Bain path or back to the HCP phase following different variants of the Pitsch-Schrader OR. The new-forming and matrix HCP structures were in a {101-1} twinning relationship with each other. The newly formed FCC phase was in a prismatic-type (P-type) OR with the HCP matrix and in a basal-type (B-type) relationship with the new-forming HCP structure at individual contacting interface. The FCC/HCP interfaces in the P-type OR was immobile while that in the B-type OR propagated by the slip of Shockley partial dislocations. Both FCC/HCP interfaces in the P-type and B-type ORs were observed under high-resolution transmission electron microscope. With the tensile loading along the [011-0] direction, deformation mechanism of the system was dominated by the slip and dissociation of prismatic <a> dislocations. The system stretched along the [0001] direction deformed mainly through the slip and dissociation of pyramidal <c + a> dislocations, as well as through the activation of {101-2} twinning by a pure shuffle mechanism. The present investigation can provide clues in designing titanium alloys with both high strength and good plasticity.

Shape, orientation relationships and interface structure of beta-Nb nano-particles in neutron irradiated zirconium alloy

Under neutron irradiation, radiation enhanced beta-Nb nano-precipitates develop within the α-grains of the Zr-Nb alloys. This radiation enhanced precipitation is of great interest since it may have some influence on the post-irradiation mechanical behavior of the material. In this paper the shape, the orientation relationship and the interface structure of such nano-particles are studied by means of both conventional and high-resolution transmission electron microscopy. The radiation damage was annealed out, thanks to a prior heat treatment and a creep test, in order to easily observe the beta-Nb nano-particles. The nano-particles exhibit a needle-like shape with a short thickness along the c-direction of 1.5 nm on average, a length and a width respectively of 6 nm and 3 nm, on average, in the basal plane. Using high-resolution TEM, a near Pitsch-Schrader orientation relationship is identified for a nano-particle. The interface atomic structure at various locations around the nano-particle has been accurately determined and an atomic model of the interface structure has been proposed.

Interrelationships of defects, nitride modification and excess nitrogen in nitrided Fe-4.75 at.% Al alloy

Abstract In order to investigate the influence of crystal-lattice defects (dislocations) and of a relatively large Al content on the development of different modifications of aluminium nitride in ferrite and on the associated uptake of excess nitrogen, recrystallised and cold rolled specimens of Fe-4.75 at.% Al alloy were subjected to gaseous nitriding treatments at 550 °C employing a nitriding potential of 0.104 atm−1/2. In contrast with earlier results for an alloy of relatively low Al content, in both the nitrided cold rolled and the nitrided recrystallised specimens nanosized AlN precipitates developed, both of the metastable, cubic, NaCl type modification and of the stable, hexagonal, wurtzite type modification, which exhibit with the ferrite matrix a Baker–Nutting orientation relationship and a Pitsch–Schrader orientation relationship, respectively. A high-temperature hydrogen reduction treatment confirmed the stoichiometry of the precipitated nitrides as AlN. The fraction of cubic, NaCl type, AlN is significantly higher in the nitrided cold-rolled specimens because of its preferential development along dislocations. As compared to the nitrided recrystallised specimens, the higher dislocation density and the higher amount of cubic AlN in the nitrided cold-rolled specimens leads to a larger amount of excess nitrogen in the nitrided cold-rolled specimen.

The Process of Tungsten-Nitride Precipitation upon Nitriding Ferritic Fe-0.5 at.% W Alloy

The precipitation of tungsten nitride upon internal nitriding of ferritic Fe-0.5 at.% W alloy was investigated at 610°C in a flowing NH3/H2 gas mixture. Different tungsten nitrides developed successively; the thermodynamically stable hexagonal δ-WN could not be detected. The state of deformation of the surface plays an important role for the development of tungsten nitride at the surface. The morphologies of the tungsten nitrides developed at the surface and those precipitated at some depth in the specimen are different. The nitride particles at the surface exhibit mostly an equiaxed morphology (with the size of the order 0.5 µm) and have a crystal structure which can be described as a superstructure derived from hexagonal δ-WN. These nitride particles show a strong preferred orientation with respect to the specimen frame of reference but have no relation with the crystal orientation of the surrounding ferrite matrix. In the bulk, nanosized and finely dispersed platelet-like precipitates grow preferentially along {100}α-Fe. It is unclear whether these precipitates consist of binary iron nitride α´´-Fe16N2 or of a ternary Fe-W-N. Additionally to the finely dispersed particles, bigger nitrides at ferrite grain boundaries develop exhibiting platelet-type morphology and possessing a crystal structure which can be also described as a superstructure derived from hexagonal δ-WN. Upon prolonged nitriding assumed discontinuous precipitation of the initially precipitated finely dispersed nitrides starts from the ferrite-grain boundaries resulting in lamellas consisting of alternate ferrite and hexagonal nitride lamellas, whereas the nitride lamellas having a Pitsch-Schrader orientation relationship with the surrounding ferrite matrix. The nitrides precipitated upon nitriding in the bulk were found to be unstable during H2 reduction at 470°C. Remarkably, upon such low temperature dissolution of the nitrides took place but only the nitrogen from the nitride particles could diffuse out of the nitride platelets and the specimen, leaving W-rich regions (W-clusters) at the location of the original precipitates.

Microstructural analysis of oxide layer formation in ferritic stainless steel interconnects

The oxide layer formation of ferritic stainless steel (Crofer22APU) oxidized in an air furnace at 800°C was analysed by transmission electron microscopy (TEM) and electron back scattered diffraction (EBSD).EBSD analysis revealed that crystallographic orientation affects the oxidation behaviour of Crofer22APU. On {110} grains, most oxide granules had the same orientation but on {111} grains, they had random orientation.TEM analysis revealed that the oxide layer consisted of spinel- chromia-spinel multi layered structure on the {110} matrix grain but no sub spinel oxide layer on the {111} matrix grain. On the {110} closed packed plane of matrix, the chromia oxide formation with the <110> direction of rhombohedral structure on the {001} closed packed plane parallels the <001> direction on the {110} plane of BCC matrix was observed, which is known as Pitsch-Schrader orientation relationship. On the {111} plane grain, there was no specific orientation relationship. Energy dispersive spectroscopy (EDS) analysis in TEM showed that an Mn rich region was developed on the {110} grain beneath chromia oxide and the conversion of this region to (Cr,Mn)3O4 spinel oxide layer causes multi layered oxide structures on the {110} matrix grain.

“Cube-on-hexagon” orientation relationship for Fe onGaN(0001¯): The missing link in bcc/hcp epitaxy

We investigate, experimentally and theoretically, the epitaxy of body-centered-cubic Fe on hexagonal GaN. For growth on the Ga-polar GaN(0001) surface we find the well-known Pitsch-Schrader orientation relationship between Fe and GaN. On the N-polar $\text{GaN}(000\overline{1})$ surface we observe coexistence between the familiar Burgers orientation and a new orientation in which the Fe(001) plane is parallel to $\text{GaN}(000\overline{1})$. This ``cube-on-hexagon'' orientation constitutes the high-symmetry link required for constructing a symmetry diagram for bcc/hcp systems in which all orientation relationships are connected by simple rotations.

Three-dimensional size and orientation of the precipitates in AZ91 magnesium alloys measured by TEM techniques

Knowledge of the microscopic structure, including three-dimensional (3-D) size and orientation of the precipitates, is essential to fully understand the mechanical properties of the magnesium alloys and designing the alloys with better performance. Analytical TEM with high spatial resolution offers the simultaneous measurements of 3-D size, structure, orientation, composition of the precipitates from one typical sample along an established crystallographic axis. Besides popular Burgers orientation relationship (OR), other ORs such as Pitsch–Schrader OR, Crawley OR, Potter OR and a new OR with the form of [0001]α 1.0° from [311]γ and (112̄0)α 2.0°? from (033̄)γ between the magnesium matrix and the precipitate γ-Mg17Al12 are identified by TEM imaging and diffraction techniques. As a case study, the thicknesses of the individual precipitates with Burgers OR are further measured to be 100–200 nm through both electron energy-loss spectroscopy and x-ray energy dispersive spectroscopy combining differential x-ray absorption and extrapolation, which are in agreement with the overall 3-D size statistic distribution results obtained through analysing various samples along various directions. Furthermore, the fabricated wedge-shape structure provides a platform on which to study the dependence of the interfacial strain on the variation of the thickness.

High-resolution electron microscopy observations of continuous precipitates with Pitsch-Schrader orientation relationship in an Mg–Al based alloy and interpretation with the O-lattice theory

High-resolution electron microscopy was applied to analyze the continuous precipitated particles of the γ-Mg 17Al 12 phase with Pitsch-Schrader OR in the heat-treated AZ91 alloy at 473 K for 8 h. The existence of a continuous precipitated particle with the Pitsch-Schrader OR including the selection of the habit plane and the growth direction in Mg–Al system is rationalized by the constrained coincidence site lattice/constrained complete pattern shift lattice (CCSL/CDSCL) model and the O-lattice theory.

The crystallography of continuous precipitates with a newly observed orientation relationship in an Mg–Al-based alloy

A new orientation relationship (OR) between γ-Mg 17 Al 12 precipitate and magnesium matrix is identified by the selected-area electron diffraction technique, together with the convergent beam electron diffraction method. The stereogram for the new orientation relationship has been calculated and discussed along with the stereograms for the Pitsch–Schrader OR, the Burgers OR, the Potter OR, the Crawley OR, the Porter OR and the Gjönnes–Östmoe OR in the Mg–Al-based system.

In situ observation of ageing process and new morphologies of continuous precipitates in AZ91 magnesium alloy

An in situ observation of the precipitating process of γ-Mg 17Al 12 phase in die-cast AZ91 magnesium alloy, was carried out with a transmission electron microscope equipped with a heating stage maintained at 473 K for 8 h. In addition to the thin plate-shaped continuous precipitates, continuous precipitates with rod-shaped and the Potter orientation relationship were observed and analyzed with transmission electron microscopy including high-resolution transmission electron microscopy techniques. It was also observed firstly that there exist plate-shaped continuous precipitates with the Pitsch–Schrader orientation relationship in the die-cast AZ91 magnesium alloy.

Crystal structure and morphology of AIN precipitating on nitriding of an Fe-2at.% Al alloy

Abstract The crystallography of aluminium nitride precipitating on nitriding of an Fe-2at.% AI alloy has been investigated by electron microscopy and by X-ray diffraction. The precipitation of AIN can be described as a classical nucleation and growth process; no evidence has been obtained for clustering of alloying element atoms or other pre-precipitation phenomena. Two modes of AIN precipitation have been observed depending on the initial deformation state of the specimens: (i) in cold-rolled specimens, precipitation of cubic (rock salt) AIN particles with platelet-type morphology exhibiting a Bain orientation relationship with the α-Fe matrix, and (ii) in recrystallized specimens, precipitation of hexagonal (wurtzite) AIN particles without specific morphology and, for a significant part exhibiting a Pitsch-Schrader orientation relationship with the α-Fe matrix. A small fraction of cubic (rock salt) AIN also occurs in the recrystallized specimens. Although the hexagonal (wurtzite) crystal structure of AI...

Structure of β-Nb 2N and γ-Ta 2N heteroepitaxial layers grown on multi-oriented films on Nb and Ta deposited on copper substrates

Heteroepitaxial β-Nb 2N and γ-Ta 2N layers on multi-oriented Nb and Ta films were obtained using the chemical vapour deposition (CVD) method from NbCl 5 (or TaCl 5) transported using a mixture of H 2, N 2 and Ar. The Nb and Ta films were also deposited using the CVD method by reducing with hydrogen the respective pentachlorides on copper foil substrates. The copper had a (001) [100] recrystallization texture or in some cases also the (001) faces of a copper single crystal were used as substrate. Transmission electron microscopy showed that β-Nb 2N and γ-Ta 2N films contained areas with four azimuthal orientations, where the {0001} basal planes were oriented parallel to the substrate plane. The orientation and structural features of the β-NB 2N and γ-Ta 2N films were interpreted in terms of the Pitsch-Schrader orientation relationship.

An O-lattice interpretation of orientation relationships between M 2C precipitates and ferrite

CSL/DSC and O-lattice calculations have been carried out for the case of M 2C secondary carbides precipitated in ferrite during tempering of high speed steel. The simultaneous occurrence of both the Pitsch-Schrader orientation relationship and another recently identified orientation relationship defined by (0001) M 2C //(021) α (1̄100) M 2C //(012̄) α (112̄0) M 2C //(100) α is explained quantitatively by the O-lattice and reduced O-lattice calculations. Possible secondary dislocation networks which accommodate the mismatch at the interface between the two phases are derived through calculation of the CSL/DSC and the secondary O-lattices. The results suggest that the length of the rod-like precipitates in the optimum tempered condition is determined by the length at which coherency between the two lattices breaks down.

The crystallography of secondary carbide precipitation in high speed steel

Precipitation of secondary carbides in a powder metallurgical high speed steel, ASP 23, has been investigated by transmission electron microscopy. Particular attention has been paid to the crystallographic orientation relationships between the precipitated phases and the ferrite matrix. During the hardening treatment prior to tempering, cementite precipitates on prior-austenite grain boundaries and twin boundaries within the martensite plates. The cementite is oriented with respect to one of the adjacent ferrite lattices according to the Bagaryatskii orientation relationship. During tempering at 560°C the cementite coarsens and fine dispersions of MC and M 2C precipitate within the martensite plates. MC obeys the Baker-Nutting orientation relationship while M 2C obeys both the Pitsch-Schrader orientation relationship and another relationship defined by: (0001) M 2C //(021) x; (11¯20) M 2C //(100) x; (¯1100) M 2C //(01¯2) x. The coexistence of both of these orientation relationships for M 2C precipitated in ferrite is explained in terms of the near-coincident site lattice model.