R. Madhavan

Crystallographic texture and microstructure evolution during hot compression of Ti–6Al–4V–0.1B alloy in the (α + β)-regime

Microstructure and texture are known to undergo drastic modifications due to trace hypoeutectic boron addition (~0.1 wt.%) for various titanium alloys e.g. Ti–6Al–4V. The deformation behaviour of such an alloy Ti–6Al–4V–0.1B is investigated in the (α + β) phase field and compared against that of the base alloy Ti–6Al–4V studied under selfsame conditions. The deformation microstructures for the two alloys display bending and kinking of α lamellae in near α and softening via globularization of α lamella in near β phase regimes, respectively. The transition temperature at which pure slip based deformation changes to softening is lower for the boron added alloy. The presence of TiB particles is largely held attributable for the early softening of Ti–6Al–4V–0.1B alloy. The compression texture of both the alloys carry signature of pure α phase defamation at lower temperature and α→β→α phase transformation near the β transus temperature. Texture is influenced by a complex interplay of the deformation and transformation processes in the intermediate temperature range. The contribution from phase transformation is prominent for Ti–6Al–4V–0.1B alloy at comparatively lower temperature.

Deformation of nanograined Ni–60Co alloy with low stacking fault energy

The evolution of deformation texture in a Ni–60Co alloy with low stacking fault energy and a grain size in the nanometre range has been investigated. The analyses of texture and microstructure suggest different mechanisms of deformation in nanocrystalline as compared to microcrystalline Ni–60Co alloy. In nanocrystalline material, the mechanism responsible for texture formation has been identified as partial slip, whereas in microcrystalline material, a characteristic texture forms due to twinning and shear banding.

Micro-mechanical aspects of texture evolution in nickel and nickel-cobalt alloys: role of stacking fault energy

Abstract The micro-mechanisms associated with the evolution of deformation texture in nickel and nickel–cobalt alloys, with stacking fault energy (SFE) ranging from high to low, has been investigated. Pure nickel and nickel-20 wt.% cobalt alloy, which are high SFE materials, develop a characteristic copper-type texture, which is attributed to dislocation slip. In the medium SFE nickel-40 wt.% cobalt alloy, the texture is copper-type up to 95% reduction; however, subsequent reduction to 98% causes the texture to shift towards brass-type. Microstructural examination suggests that the occurrence of Cu-type shear bands (SBs) preferentially in the Cu {1 1 2}-oriented grains has led to this texture transition. In nickel-60 wt.% cobalt alloy, which is a low SFE material, texture is brass-type from the early stages of rolling. Deformation mechanisms show a gradual transition from deformation twinning to Bs-type SBs, as a function of strain. The strength of the final texture is a synergistic effect of twinning and shear banding. The absence of Cu component during the process of brass-type texture evolution goes against Wassermann’s prediction of texture transition. A modified theory for the formation of brass-type texture is proposed.

Texture Evolution in Nanocrystalline Nickel: Critical Role of Strain Path

The effect of strain path change during rolling on the evolution of deformation texture has been studied for nanocrystalline (nc) nickel. An orthogonal change in strain path, as imparted by alternating rolling and transverse directions, leads to a texture with a strong Bs {110}〈112〉 component. The microstructural features, after large deformation, show distinct grain morphology for the cross-rolled material. Crystal plasticity simulations, based on viscoplastic self-consistent model, indicate that slip involving partial dislocation plays a vital role in accommodating plastic deformation during the initial stages of rolling. The brass-type texture evolved after cross rolling to large strains is attributed to change in strain path.

Study of Texture in Ultra Fine Grained Dual Phase Steel Sheets

Severe cold rolling and short intercritcal annealing is often used to produce ultra-fine grained ferrite and martensite dual phase steels. In this paper, microstructure and texture of Nb-microalloyed steel following cold rolling and short intercritical annealing is investigated. The results show that cold rolling and annealing resulted in ultra-fine grained dual phase steel consisted of polygonal ferrite in the range of ~1-2 μm in size. In cold rolled material, the texture components are γ fiber (//normal direction) and α fiber (//rolling direction). Partial recrystallization texture was observed following intercritical annealing.

Role of stacking fault energy on texture evolution revisited

Three materials, pure aluminium, Al-4 wt.% Mg, alpha-brass have been chosen to understand the evolution of texture and microstructure during rolling. Pure Al develops a strong copper-type rolling texture and the deformation is entirely slip dominated. In Al-4Mg alloy, texture is copper-type throughout the deformation. The advent of Cu-type shear bands in the later stages of deformation has a negligible effect on the final texture. alpha-brass shows a characteristic brass-type texture from the early stages of rolling. Extensive twinning in the intermediate stages of deformation (epsilon(t) similar to 0.5) causes significant texture reorientation towards alpha-fiber. Beyond 40% reduction, deformation is dominated by Bs-type shear bands, and the banding coincides with the evolution of parallel to ND components. The crystallites within the bands preferentially show parallel to ND components. The absence of the Cu component throughout the deformation process indicates that, for the evolution of brass-type texture, the presence of Cu component is not a necessary condition. The final rolling texture is a synergistic effect of deformation twinning and shear banding.

Texture evolution during annealing of large-strain deformed nanocrystalline nickel

The recrystallization behaviour of cold-rolled nanocrystalline (nc) nickel has been studied at temperatures between 573 and 1273 K using bulk texture measurements and electron back-scattered diffraction. The texture in nc nickel is different from that of its microcrystalline counterpart, consisting of a strong Goss (G) and rotated Goss (RG) components at 773 K instead of the typical cube component. The texture evolution in nc Ni has been attributed to the prior deformation textures and nucleation advantage of G and RG grains.

Deformation Texture and Microstructure Evolution in Nickel and Nickel-Cobalt Alloys

Rolling texture evolution of pure nickel, and nickel – cobalt alloys containing 20wt.%, 40wt.%, 60wt.% cobalt content has been studied to very large true strain (ε ~ 4). The texture evolution in pure nickel and Ni-20Co was very similar, and resulted in typical Cu-type rolling texture. Microstructural analyses showed that the deformation was mostly slip dominated up to 95% beyond which it shear bands. Deformation twinning was a major deformation mechanism up to 50% reduction, and at higher strains, microstructure showed extensive shear banding. The evolution of final Goss texture in low SFE Ni-Co alloys could be explained based on the twin fraction and shear band volumes which showed grains preferably oriented towards Goss.

Deformation and Recrystallization Texture Evolution in Nanocrystalline Nickel

Deformation and recrystallization textures in nanocrystalline nickel with average grain size of 20 nm were investigated using X-ray diffraction, electron microscopy and differential scanning calorimetry. The deformation behaviour of nanocrystalline nickel is quite complicated due to intervention of other deformation mechanisms like grain boundary sliding and restoration mechanisms like grain growth and grain rotation to dislocation mediated slip. Recrystallization studies carried out on the deformed nanocrystalline nickel showed that the deformation texture was retained during low temperature annealing (300°C), while at higher temperature (1000°C), the texture got randomised. The exact mechanism of texture formation during deformation and recrystallization has been discussed.

Study of the Microstructure, Texture and Tensile Properties in as-Extruded AZ91 and ZM21 Magnesium Alloys

In this paper, the microstructure, texture and tensile properties of the magnesium alloys AZ91 and ZM21 extruded at 350°C to the ratio 25:1 are investigated. After extrusion, the mean grain size reduces from 400 µm to 30 µm in ZM21 alloy and from 350 µm to 40 µm in AZ91 alloy. Bulk texture analysis indicates the formation of characteristic extrusion texture in both the alloys. The occurrence of dynamic recrystallization, as revealed through necklace structure formation, and the precipitation of second phase (Mg17Al12) particles in the AZ91 alloy are observed.