Satyam Suwas

Crystallographic texture in Materials

Many naturally occurring as well as man made materials comprise of large number of crystallites with a preferred orientation. The preferred orientation, popularly known as texture, governs various structural and mechanical properties of these materials. Texture may develop during variety of processes like solidification, plastic deformation, annealing and phase transformation. It is, therefore, possible to tailor texture in materials to enhance a particular property. Traditionally, X-ray and neutron diffraction had been used to study texture in materials. It has been very recently that other techniques based on synchrotron X-rays and SEM based Electron Backscattered Diffraction have been developed for complete characterization of texture in materials. In the present review, the authors discuss the pole figures and more comprehensive orientation distribution function methods for texture analysis. In addition, a brief account of texture evolution in various technologically important materials, ranging from common metals and alloys to intermetallics, ceramics and polymers along with some naturally occurring materials like rocks, ice, bones etc. has been given. The present review is particularly aimed at readers newly initiated in this field rather than the experts.

Role of twinning on texture evolution of silver during equal channel angular extrusion

The role of deformation twinning in the texture evolution of pure polycrystalline silver subjected to equal channel angular extrusion (Route A, three passes) has been examined. Microstructural characterization using electron backscattering diffraction and transmission electron microscopy revealed high twinning activity in every pass, as well as significant grain refinement. Polycrystal modelling combined with experimental analysis shows that texture evolution is a result of slip and deformation twinning that occurs in every pass. It is shown that the primary consequence of twinning is the reorientation of the A1 ideal component into the A2 orientation. This process results in a weak A1 and a strong A2 component. This twinning mechanism is repeated in each pass aided by the strain path changes associated with Route A and an apparent regeneration of the microstructure. As a result, with each pass the A1 and C ideal shear components weaken, whereas the components strengthen, tendencies that are distinct from those of high stacking fault fcc metals like Al, Cu and Ni.

Microstructure and texture evolution during accumulative roll bonding of aluminium alloy AA5086

In the present investigation, a strongly bonded strip of an aluminium–magnesium based alloy AA5086 is successfully produced through accumulative roll bonding (ARB). A maximum of up to eight passes has been used for the purpose. Microstructural characterization using electron backscatter diffraction (EBSD) technique indicates the formation of submicron sized (∼200–300 nm) subgrains inside the layered microstructure. The material is strongly textured where individual layers possess typical FCC rolling texture components. More than three times enhancement in 0.2% proof stress (PS) has been obtained after 8 passes due to grain refinement and strain hardening

Role of strain path change in texture development

This work describes the role of strain path change during cold rolling in texture development of pure Cu and Cu(P) alloys. The unidirectional- and two-step cross-rolled materials exhibit different textures. The detailed analysis of these results in terms of the adequate deformation mechanisms is also presented.

Evolution of Texture and Microstructure in Commercially Pure Titanium with Change in Strain Path During Rolling

The evolution of microstructure and texture in commercially pure titanium has been studied as a function of strain path during rolling using experimental techniques and viscoplastic self-consistent simulations. Four different strain paths, namely unidirectional rolling, two-step cross rolling, multistep cross rolling, and reverse rolling, have been employed to decipher the effect of strain path change on the evolution of deformation texture and microstructure. The cross-rolled samples show higher hardness with lower microstrain and intragranular misorientation compared to the unidirectional rolled sample as determined from X-ray diffraction and electron backscatter diffraction, respectively. The higher hardness of the cross-rolled samples is attributed to orientation hardening due to the near basal texture. Viscoplastic self-consistent simulations are able to successfully predict the texture evolution of the differently rolled samples. Simulation results indicate the higher contribution of basal slip in the formation of near basal texture and as well as lower intragranular misorientation in the cross-rolled samples.

Deformation mechanisms during large strain deformation of nanocrystalline nickel

In this letter, a conclusive evidence of the operation of planar slip along with grain boundary mediated mechanisms has been reported during large strain deformation of nanocrystalline nickel. Dislocation annihilation mechanism such as mechanical recovery has been found to play an important role during the course of deformation. The evidences rely on x-ray based techniques, such as dislocation density determination and crystallographic texture measurement as well as microstructural observation by electron microscopy. The characteristic texture evolution in this case is an indication of normal slip mediated plasticity in nanocrystalline nickel.

Effect of Texture and Grain Size on Bio-Corrosion Response of Ultrafine-Grained Titanium

The bio-corrosion response of ultrafine-grained commercially pure titanium processed by different routes of equal-channel angular pressing has been studied in simulated body fluid. The results indicate that the samples processed through route Bc that involved rotation of the workpiece by 90 deg in the same sense between each pass exhibited higher corrosion resistance compared to the ones processed by other routes of equal-channel angular pressing, as well as the coarse-grained sample. For a similar grain size, the higher corrosion resistance of the samples exhibiting off-basal texture compared to shear texture indicates the major role of texture in corrosion behavior. It is postulated that an optimum combination of microstructure and crystallographic texture can lead to high strength and excellent corrosion resistance.

Microstructure and texture evolution during accumulative roll bonding of aluminium alloys AA2219/AA5086 composite laminates

Accumulative roll bonding of two aluminium alloys, AA2219 and AA5086 was carried out up to 8 passes. During the course of ARB, the deformation inhomogeneity between the two alloy layers results in interfacial instability after the 4th pass, necking of the AA5086 layers after the 6th pass and fracture along the necked regions after the 7th and 8th pass. The EBSD analysis shows deformation bands along the interfaces after 8 passes of ARB. The ARB-processed materials predominantly show characteristic deformation texture components. The weak texture after the 2nd pass results from the combination of a weakly-textured starting AA2219 layer and a strongly-textured starting AA5086 layer. A strong deformation texture forms due to the high imposed strain after a higher number of ARB passes. Subgrain formation and related shear banding induces copper/S components in the case of the small elongated grains, while planar slip leads to the formation of brass component in the large elongated grains.

Polyvinylidene fluoride based lightweight and corrosion resistant electromagnetic shielding materials

Various NixCo1−x alloys (with x varying from 0–60 wt%, Ni: nickel, Co: cobalt) were prepared by vacuum arc melting and mixed with polyvinylidene fluoride (PVDF) to design lightweight, flexible and corrosion resistant materials that can attenuate electromagnetic radiation. The saturation magnetization scaled with the fraction of Co in the alloy. Two key properties such as high-magnetic permeability and high-electrical conductivity were targeted. While the former was achieved using a Ni–Co alloy, multiwalled carbon nanotubes (CNTs) in the composites accomplished the latter. A unique approach was adopted to prepare the composites wherein PVDF powder along with CNTs and Ni–Co flakes were made into a paste, using a solvent, followed by hot pressing. Interestingly, CNTs facilitated in uniform dispersion of the Ni–Co alloy in PVDF, as manifested from synergistic improvement in the electrical conductivity. A significant improvement in the shielding effectiveness (41 dB, >99.99% attenuation) was achieved with the addition of 50 wt% of Ni40Co60 alloy and 3 wt% CNTs. Intriguingly, due to the unique processing technique adopted here, the flexibility of the composites was retained and more interestingly, the composites were resistant to corrosion as compared to only Ni–Co alloy.

The importance of crystallographic texture in the use of titanium as an orthopedic biomaterial

Crystallographic texture is perceived to play an important role in controlling material properties. However, the influence of texture in modulating the properties of biomedical materials has not been well investigated. In this work, commercially pure titanium (cp-Ti) was processed through six different routes to generate a variety of textures. The effect of texture on mechanical properties, corrosion behavior, cell proliferation and osteogenesis was characterized for potential use in orthopedic applications. The presence of closely packed, low-energy crystallographic planes at the material surface was influenced by the volume fraction of the components in the overall texture, thereby influencing surface energy and corrosion behavior. Texture modulated osteoblast proliferation through variations in surface water wettability. It also affected mineralization by possibly influencing the coherency between the substrate and calcium phosphate deposits. This study demonstrates that crystallographic texture can be an important tool in improving the properties of biomaterials to achieve the enhanced performance of biomedical implants.