Changes In Crystallographic Texture Research Articles

Experimental and theoretical studies of intergranular strain in an alpha titanium alloy during plastic deformation

Two complementary methods were used to analyse the deformation mechanisms involved in the plasticity of commercially pure titanium during compressive loading: neutron diffraction and the self-consistent model. The strain response of 15 crystallographic planes was tracked during the measurement, in directions both parallel and transverse to the straining direction, providing new insight into the mechanical behaviour of the polycrystal. The neutron diffraction results show evidence of tensile twins in the titanium alloy studied. The twin volume fraction was determined from the change in crystallographic texture. The influence and the role of plastic anisotropy were also studied and explained in this work. Good agreement was found between the experimental and predicted results.

Effect of Nano-SiC Incorporation on Mechanical Properties of Micro and Nano-Structured Ni–Co Electrodeposits

Ni-Co/SiC nano-composites were electrodeposited from modified Watts bath containing SiC particles with 50 nm average size, SDS as surfactant and saccharin as grain refiner in appropriate amounts. The effect of grain size and nano-particle incorporation on microstructure and mechanical properties of electrodeposits was investigated. The grain size of the deposits was calculated from X-ray diffraction (XRD) patterns using Williamson-Hall equation and surface morphology of the coatings was studied by means of scanning electron microscopy (SEM). The mechanical properties of electrodeposits were investigated by Vickers microhardness and tensile tests. The results indicated that incorporation of SiC nano-particles increased the microhardness and yield strength of micro-grained deposits due to the change in crystallographic texture, decrease in grain size as well as dispersion hardening. But dispersion hardening mechanism could not be confirmed in nano-structured deposits. Moreover, the increase in the concentration of uniformly dispersed SiC particles initially improved and then decreased the elongation to failure of coarse-grained deposits while a continuous increase was observed for nano-structured deposits.

Two-dimensional simulation of the effect of the migration of triple junctions on crystallographic texture evolution through grain coarsening

A simulation program was developed that belonged essentially to the category of MC Potts methods, but the method also employed a cellular-automata-like character. A 2D grain structure was represented by an array of square cells, and a grain boundary migrated by iteration of occupation events between neighboring pairs of cells. Individual cell pairs were sampled by a systematic random method. The triple junction migration process was explicitly defined. A method to express the ratio of the triple junction mobility to the boundary mobility (mtj/mb) with a simulation parameter was determined by considering tricrystalline specimens. The simulated kinetics for triple junction dragged coarsening coincided essentially with the previously reported results obtained by vertex and statistical models. It was concluded that the crystallographic texture changes through grain coarsening, even when the migration rates of the triple junctions alone depend on combinations of three orientations.

Annealing Behavior of RAFM ODS-Eurofer Steel

Oxide-dispersion-strengthened (ODS) ferritic-martensitic steels are candidates for applications in fusion power plants where microstructural long-term stability at temperatures of ˜650°C to 700°C are required. The microstructural stability of 80% cold-rolled reduced-activation ferritic-martensitic 9% Cr ODS-Eurofer steel was investigated within a wide range of temperatures (300°C to 1350°C). Fine oxide dispersion is very effective to prevent recrystallization in the ferritic phase field. The low recrystallized volume fraction (<0.1) found in samples annealed at 800°C is associated with the nuclei found at prior grain boundaries and around coarse M23C6 particles. The combination of retarding effects such as Zener drag and concurrent recovery decrease the local stored energy and impede further growth of the recrystallization nuclei. Above 900°C, martensitic transformation takes place with consequent coarsening. Significant changes in crystallographic texture are also reported.

Texture analysis of low-carbon steel under annealing conditions using non-contact ultrasound

The ability to rapidly and non-destructively detect crystallographic changes in sheet metals under annealing conditions has potential uses in the strip manufacturing industry. Ultrasonic Lamb wave velocity measurements as a function of the in-plane angle were taken on a number of steel sheets and an aluminium sheet of a nominal thickness of I mm. A number of thermal annealing steps in air were performed on all these sheets and subsequent ultrasonic measurements of the same Lamb wave velocities were taken. The first three crystallographic texture orientation distribution coefficients (ODCs) were inferred from the ultrasonic velocity data. These ODCs were used to construct 'simulated pole figures', illustrating crystallographic texture changes that occurred in the steel and aluminium sheets during the annealing processes. The changes (including those relative to the material's melting point) were found to be much more pronounced in the case of the aluminium sheet. The steel sheets showed a gradual shift from fourfold to twofold symmetry under anneals of increasing temperature, whereas the aluminium sheet showed a much more extreme shift, with a reversal of the ultrasonic fast axes implying substantial recrystallisation

Recrystallization Textures in Aluminum Alloys: Experimental Study and Modelling

The changes in crystallographic texture are investigated during recrystallization in 5182 and 6016 aluminum alloys, which were subjected to various cold rolling reductions. In the current study, the texture varieties in the recrystallized materials are conditioned by both the material’s chemistry and the applied rolling strain. The presence of large constituent particles produces strain heterogeneities during cold rolling which causes a specific texture development. The development of recrystallization textures is discussed based on experimental data and results of crystal plasticity simulations. A recrystallization model based on nucleation and growth selection is presented. The driving force for nucleation was accounted for by applying continuum mechanics crystal plasticity models. For the modeling of the strain heterogeneities around hard undeformable particle a FE-code was used.

An isoclinic elasto‐plasticity model at finite strains with the notion of plastic spin

AbstractIn forming processes metal sheets undergo large deformations. The crystallographic texture changes and preferred directions in the macroscopic behaviour are introduced as a result. This yields an anisotropic behaviour in plastic deformations and, furthermore, these preferred directions may rotate with evolution of plasticity. A phenomenological model for the description of orthotropic elasto‐plastic solids with the notion of plastic spin is developed. The latter is the spin of the continuum relative to the material substructure. A multiplicative decomposition of the deformation gradient tensor into an elastic and a plastic part serves as the basis for the formulation and computational implementation. The resulting incompatible intermediate manifold is identified in the model as an isoclinic configuration. Moreover, the described rate‐independent constitutive model is capable of modelling isotropic elastic and orthotropic plastic material behaviour. The latter is dominated by pre‐existing preferred orientations in the material and is described by a Hill‐type yield criterion. These orientations are allowed to rotate by introduction of the plastic spin into the model. Finally, numerical simulations demonstrate the performance of the model. (© 2011 Wiley‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Enhanced compressive response of hybrid Mg–CNT nano-composites

Uniaxial compressive properties of hybrid Mg/Al–CNT nano-composites are studied in the present paper. Hybrid nano-composites were fabricated using powder metallurgy route followed by microwave assisted rapid sintering technique and hot extrusion. The hybrid Mg/Al–CNT nano-composites exhibited slightly smaller grain sizes compared to monolithic Mg and reasonable hybrid Al–CNT nano-particle distribution up to Al content of 1.00 wt%. Compared to pure Mg, the Mg/Al–CNT nano-composites exhibited higher compressive yield strength (0.2% CYS), ultimate compressive strength (UCS) and work of fracture (WOF) (up to +36%, +76%, +36%) compared to pure Mg but failure strain was compromised. Inclusive of crystallographic texture changes, the effect of hybrid Al–CNT nano-particle integration on the enhancement of compressive properties of Mg is investigated in this paper.

Modeling the crystallographic texture changes in aluminum alloys during recrystallization

The evolution of crystallographic texture during recrystallization annealing is affected by the hot and cold rolling parameters. A 6016 Al alloy with various hot band textures was subjected to conventional rolling and short time annealing at elevated temperature. Asymmetric rolling with differential circumferential velocities of the top and bottom rolls was applied to the aluminum alloy under investigation to modify the hot rolling texture. The presence of large constituent particles enforces strain heterogeneities during cold rolling. The influence of particles on the development of recrystallization textures is discussed based on the experimental data and the results of crystal plasticity simulations. A recrystallization model based on nucleation and growth selection is presented. The driving force for nucleation was accounted for by applying continuum mechanics crystal plasticity models, which allow calculation of the stored energy of plastic strain for specific orientations of the polycrystalline aggregate and for the strain mode under consideration. Crystal misorientations of type 〈1 1 1〉 40° were attributed to enhanced mobility during the growth stage of recrystallization.

A Theoretical Study on Forming Limit Diagram Predictions Using Viscoplastic Polycrystalline Plasticity Models

The Forming Limit Diagrams (FLDs) of textured polycrystalline sheet metals were investigated using micro-macro averaging and two types of grain-interaction models: Full-Constraint (FC) and Self-consistent (SC) schemes, in conjunction with the Marciniak–Kuczynski (MK) approach. By referring to previous FLD studies based on the FC-Taylor model ─ Wu and coworkers [Effect of an initial cube texture on sheet metal formability, Materials Science and Engineering A, 364:182–7, 2004] and Inal and coworkers [Forming Limit comparison for FCC and BCC sheets, International Journal of Plasticity, 21:1255-1266, 2005] ─ we found that the MK-FC strategy leads to unrealistic results. In the former case, the researchers found that an increasing spread about the cube texture produces unexpectedly high limit strains. In the latter work, Inal et al. predicted a remarkably low forming-limit curve for a FCC material and an extremely high forming-limit curve for a BCC material, in the biaxial-stretching range. Our investigations show that simulations performed with the MK-VPSC approach successfully predict more reliable results. For the BCC structure, the MK-VPSC predictions do not give the extreme values predicted when calculations are carried out with the MK-FC approach. In the FCC case, with decreasing textural intensity ─ from the ideal cube texture, through dispersions around the cube texture with increasing cut-off angles, to a random texture ─ a smooth transition in increasing limit strains was obtained. Furthermore, these results suggest that the selected constitutive model is critical for predicting the behavior of materials that exhibit a qualitative change in crystallographic texture, and hence, evolve anisotropically during mechanical deformation.

Defect Morphology and Texture in Sn, Sn–Cu, and Sn–Cu–Pb Electroplated Films

In this paper, the concept of a defect phase diagram is introduced which quantifies the effects of Cu and Pb additions to electrodeposited Sn films on surface defect formation, including but not limited to the formation of Sn whiskers. Transitions were observed in both the defect densities and the morphologies of hillocks and whiskers as Cu and Pb film compositions were systematically varied. Changes in crystallographic texture were also reported for a subset of the Sn-Cu-Pb alloys examined. The transitions between different defect types and the coexistence of certain defect types help to interpret the role of grain boundary pinning in hillock and whisker formation.

IN-SITU X-RAY DIFFRACTION STUDY OF FERROELECTRIC DOMAIN SWITCHING IN ORTHORHOMBIC NKN CERAMICS

The family of perovskite ferroelectrics based on sodium potassium niobate (NKN) ceramics exhibit useful piezoelectric properties and show potential for the replacement of conventional lead based piezoceramics. In the present study, iron-doped NKN ceramics were prepared by a solid state reaction method. Ferroelectric hysteresis measurements indicated that a remanent polarization value approaching 0.4Cm-2 could be obtained by poling under a continuous AC electric field with amplitude of 3 MV m-1. X-ray diffraction (XRD) patterns of these materials were recorded in transmission during poling, using high energy synchrotron X-rays with a wavelength of 1.55 × 10-11m. Changes in crystallographic texture were observed during poling as a result of 90° and 60°/120° domain switching. The strain due to ferroelectric domain switching in orthorhombic NKN is described in terms of the differences in transformation strain between different domain variants, with reference to the high temperature cubic lattice.

Simultaneous Enhancement of Tensile/Compressive Strength and Ductility of Magnesium Alloy AZ31 Using Carbon Nanotubes

AZ31 nanocomposite containing carbon nanotube (CNT) reinforcement was fabricated using solidification processing followed by hot extrusion. The CNT reinforcement was integrated with AZ31 using an Al foil method. The AZ31 nanocomposite exhibited slightly smaller grain and intermetallic particle sizes than monolithic AZ31, reasonable CNT distribution, dominant (10 - 11) texture in the transverse and longitudinal directions unlike monolithic AZ31, and 48% higher hardness than monolithic AZ31. Compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%TYS, UTS, tensile failure strain and tensile work of fracture (WOF) (+10%, +17%, +68% and +92%, respectively). Similarly, compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%CYS, UCS, average compressive failure strain and compressive WOF (+58%, +3%, +5% and +17%, respectively). Inclusive of crystallographic texture changes, the effect of CNT integration on the enhancement of tensile and compressive properties of AZ31 is investigated in this paper.

Enhancing tensile/compressive response of magnesium alloy AZ31 by integrating with Al 2O 3 nanoparticles

AZ31 nanocomposite containing Al 2O 3 nanoparticle reinforcement was fabricated using solidification processing followed by hot extrusion. The Al 2O 3 nanoparticle reinforcement was isolated prior to melting by wrapping in Al foil of minimal weight (<0.50 wt% with respect to AZ31 matrix weight). The AZ31 nanocomposite exhibited slightly smaller grain and intermetallic particle sizes than monolithic AZ31, reasonable Al 2O 3 nanoparticle distribution, non-dominant (0 0 0 2) texture in the longitudinal direction unlike monolithic AZ31, and 30% higher hardness than monolithic AZ31. Compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%TYS, UTS, failure strain and work of fracture (WOF) (+19%, +21%, +113% and +162%, respectively). Also, compared to monolithic AZ31, the AZ31 nanocomposite exhibited higher 0.2%CYS and UCS, similar failure strain, and higher WOF (+5%, +5%, −4% and +11%, respectively). Inclusive of crystallographic texture changes, the effect of Al 2O 3 nanoparticle integration on the enhancement of tensile and compressive properties of AZ31 is investigated in this paper.

The Effect of Copper Content on the Dynamic Grain Growth in AL-Cu-Zr Systems

The effect of copper content on dynamic grain growth in Al-Cu-Zr system was investigated by studying the microstructural development and texture evolution during uniaxial tensile deformation of Al-2wt%Cu-0.3wt.%Zr and Al-4wt%Cu-0.4wt.%Zr alloys at 450°C with a strain rate of 10-3s-1, with a similar initial microstructure in both materials. The initial microstructure consisted of layers of different orientations, the layers being separated by high-angle grain boundaries with low-angle boundaries separating grains within the layers. The initial grain spacing was about 5m and the texture was typical of rolled aluminium alloys. The 4wt.%Cu alloy gave a higher strain rate sensitivity index, m, and a greater ductility compared to the low copper content alloy. An increase in grain size occurred in both materials due to deformation, but this dynamic grain growth (DGG) was much greater in the material with the higher copper content. This was associated with a more rapid conversion of low-angle boundaries to high angle ones in the 4wt%Cu material which is consistent with changes in crystallographic texture occurring during deformation.

Evolution of the Microstructure in Electrochemically Deposited Copper Films at Room Temperature

The room temperature evolution of the microstructure in copper electrodeposits (self-annealing) was investigated by means of X-ray diffraction analysis and simultaneous measurement of the electrical resistivity as a function of time with an unprecedented time resolution. Independent of the copper film thickness, the as-deposited microstructure consisted of nanocrystalline grains with orientation dependent crystallite sizes. A drastic decrease of the electrical resistivity occurs as a function of time associated with orientation dependent grain growth. Simulatenously with grain growth the crystallographic texture changes by a multiple twinning mechanism. The kinetics of self-annealing is strongly affected by the thickness of the deposit. Storage of the copper films at sub-zero temperatures effectively hinders self-annealing and does not affect the kinetics of self-annealing upon reheating to room temperature.

Crystallographic Texture Change of Pilgered Zirconium Alloy Tubes with Heat Treatment

Crystallographic texture of pilgered zirconium alloy tubes was analyzed by neutron diffraction, electron backscatter diffraction (EBSD) and X-ray techniques to study bulk and local texture change with pilgering and heat treatment above re-crystallization temperature. Pilgering resulted in slightly inclining (001) planes to sample normal direction, and aligning effectively (100) planes to the normal of radial direction, respectively. (001) planes of the zirconium tube uniformly exist in radial and tangential directions, however, the (001) planes moved from tangential to radial directions after pilgering followed by heat treatment for 20 hours at 540°C. Some of (001) and (100) planes of pilgered tube were paralleled to longitudinal direction by re-crystallization.

In situ investigation of the microstructure evolution in nanocrystalline copper electrodeposits at room temperature

The microstructure evolution in copper electrodeposits at room temperature (self-annealing) was investigated by means of x-ray diffraction analysis and simultaneous measurements of the electrical resistivity as a function of time. In situ studies were started immediately after deposition of the various thick layers and continued with a unique time resolution until stabilization of the recorded data occurred. Independent of the copper layer thickness, the as-deposited microstructure consisted of nanocrystalline grains with orientation dependent crystallite sizes. Orientation dependent grain growth, crystallographic texture changes by multiple twinning, and a decrease of the electrical resistivity occurred as a function of time at room temperature. The kinetics of self-annealing is strongly affected by the layer thickness: the thinner the layer, the slower the microstructure evolution is, and self-annealing is suppressed completely for a thin layer with 0.4μm. The preferred crystallographic orientation of the as-deposited crystallites is suggested to cause the observed thickness dependence of the self-annealing kinetics.

Effect of laser fluence on surface microstructure of alumina ceramic

The present study discusses the microstructure development during surface modifications of alumina ceramic using high power continuous wave Nd:YAG laser. Laser fluence influenced the microstructure in terms of changes in morphology and (1 1 0) crystallographic texture of the surface grains. The microstructural observations can be used to establish the guidelines for optimising the laser fluence to achieve the desired morphology of the surface grains and extent of texture in the surface modified alumina ceramic.

X-ray diffraction investigation of self-annealing in nanocrystalline copper electrodeposits

X-ray diffraction analysis and electrical resistivity measurements were conducted simultaneously for in-situ examination of self-annealing in copper electrodeposits. Considerable growth of the as-deposited nano-sized crystallites occurs with time and the crystallographic texture changes by multiple twinning during self-annealing. The kinetics of self-annealing depends on the layer thickness as well as on the orientation and/or the size of the as-deposited crystallites.