Near Net Shape Group

Hyderabad, India

Near Net Shape Group

Hyderabad, India

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Balasundar I.,Near Net Shape Group | Raghu T.,Near Net Shape Group
International Journal of Material Forming | Year: 2013

Though the capability of Repetitive Upsetting- Extrusion (RUE) process to produce ultrafine grains in a bulk aluminium alloy has been established, a detailed description on the material flow, deformation homogeneity and the die design requirements to process bulk materials has never been addressed. To address these issues commercial pure copper (CP Cu) was subjected up to four cycles of RUE using the die design that has been used by various researchers. The RUE processed CP Cu samples when subjected to macrostructure and microstructure evaluation revealed that apart from inhomogeneous deformation, defects such as axial hole/funnel and folds/laps were induced in the processed samples. The formation of these defects during RUE is attributed to the current die design. Based on a recent study carried out on the extrusion defect - axial hole/funnel, a modified RUE die design has been proposed. CP Cu subjected to RUE using the modified die design revealed that the modified die design not only helps in avoiding the defects but also improves the homogeneity. © 2011 Springer-Verlag France.


Satheesh Kumar S.S.,Near Net Shape Group | Raghu T.,Near Net Shape Group
Materials and Design | Year: 2011

In this study commercially pure nickel sheets are severe plastically deformed at room temperature by constrained groove pressing (CGP) technique and the effect of pass number on the room temperature mechanical behaviour is investigated. Increase in strength observed after first pass is much higher than the increase observed during subsequent passes. Mechanical behaviour of constrained groove pressed sheets indicated negligible strain hardening ability during initial passes; gain in strain hardening ability is observed during latter passes resulting in enhanced ductility. The observation of shortened uniform elongation phase during tensile testing of CGP processed sheets could be linked to the lack of strain hardenability and change in deformation mechanism. Constitutive mechanical behaviour in uniform plastic deformation regime of nickel sheets in annealed condition obeys Hollomon relation whereas severely deformed sheets obey Voce relation closely. Strain hardening characteristics of groove pressed sheets analysed by Kocks-Mecking approach revealed stage-III hardening behaviour associated with high initial hardening rate when compared to annealed sheets. The influence of pass number on dislocation density evolution is assessed by Taylor's expression. The synergistic effect of dislocation generation and recovery on the evolution of constitutive mechanical behaviour in the uniform elongation regime is described by applying single parameter based Kocks model. The kinetics of dislocation storage and dislocation annihilation in severely deformed nickel sheets during deformation corroborated with mechanical properties and dislocation density indicates the dominance of dislocation generation during earlier passes. © 2011 Elsevier Ltd.


Satheesh Kumar S.S.,Near Net Shape Group | Raghu T.,Near Net Shape Group
Journal of Materials Processing Technology | Year: 2013

Pure nickel sheets are subjected to severe plastic deformation by constrained groove pressing technique at room temperature thereby imparting an effective plastic strain of 3.48. The evolution of mechanical behaviour with increasing number of passes revealed intensive increase in strength properties after first pass; however marginal increase is observed subsequently. Gain in ductility which is attributed to dislocation recovery is observed after third pass along with marginal drop in strength. Microstructural evolution during groove pressing of sheets is characterized by X-ray diffraction profile analysis using Williamson-Hall method. Besides the observation of strong shear texture in constrained groove pressed sheets, improvement in strain isotropy with increased straining is revealed from Williamson-Hall plots. The sub-grain/cell size estimated by analysing the diffraction profile of deformed sheets is found to be ∼1390 nm after processing up to three passes. Low grain refinement efficiency observed in this process compared to other severe plastic deformation techniques at similar strain conditions is explained by the deformation characteristics and loading behaviour experienced by the sheets during constrained groove pressing. © 2012 Elsevier B.V.


Satheesh Kumar S.S.,Near Net Shape Group | Raghu T.,Near Net Shape Group
Materials Science Forum | Year: 2011

Pure nickel sheets are severe plastically deformed by constrained groove pressing technique at room temperature up to three passes. A total strain magnitude of 3.48 is imparted to the sheets and further processing is limited by initiation of surface microcracks. The grain size evolution studied by optical microscopy reveals significant grain refinement at the end of third pass evidently illustrating the effectiveness of groove pressing technique for grain refinement in sheet materials. Vickers microhardness measured during different stages of groove pressing process clearly describes the deformation behaviour in different segments of slant and flat regions. The change in mechanical properties of constrained groove pressed sheet is evaluated by room temperature tensile and microhardness tests. Results showed considerable increase in strength and hardness during initial passes followed by slight drop during third pass.


Satheesh Kumar S.S.,Near Net Shape Group | Raghu T.,Near Net Shape Group
Materials and Design | Year: 2014

High purity aluminium sheets (~99.9%) are subjected to intense plastic straining by constrained groove pressing method successfully up to 5. passes thereby imparting an effective plastic strain of 5.8. Transmission electron microscopy studies of constrained groove pressed sheets divulged significant grain refinement and the average grain sizes obtained after five pass is estimated to be ~0.9. μm. In addition to that, microstructural evolution of constrained groove pressed sheets is characterized by X-ray diffraction peak profile analysis employing Williamson-Hall method and the results obtained fairly concur with electron microscopy findings. The tensile behaviour evolution with increased straining indicates substantial improvement of yield strength by ~5.3. times from 17. MPa to 90. MPa during first pass corroborated to grain refinement observed. Marginal increase in strengths is noticed during second pass followed by minor drop in strengths attributed to predominance of dislocation recovery is noticed in subsequent passes. Quantitative assessment of degree of deformation homogeneity using microhardness profiles reveal relatively better strain homogeneity at higher number of passes. © 2013 Elsevier Ltd.


Satheesh Kumar S.S.,Near Net Shape Group | Raghu T.,Near Net Shape Group
Materials and Design | Year: 2015

Change in strain path during severe plastic deformation (SPD) of metallic materials has shown significant influence on the microstructural evolution, grain boundary characteristics and mechanical behaviour. In the present work high purity aluminium sheets are severe plastically deformed at room temperature by conventional constrained groove pressing (CGP) technique and cross-CGP technique up to 2,4, and 6 passes thereby imparting total effective plastic strain of 2.32, 4.64 and 6.96 respectively. Change in strain path is imposed during cross-CGP by rotating the sheets by ±. 90° along thickness axis between each pass. Microstructural evolution of processed sheets studied by electron back scattered diffraction (EBSD) analysis revealed ultra-fine grains (~. 1. μm) irrespective of change in strain path. Analysis of grain boundary characteristics showed significant influence of strain path change on the evolution of relative fraction of low angle and high angle boundaries. The grain refinement mechanism during deformation processing in both conventional CGP and cross-CGP is corroborated to the evolution of misorientation distribution. Though considerable improvement in room temperature tensile characteristics is observed in both cases, cross-CGP processed Al sheets exhibited superior tensile properties. © 2015 Elsevier Ltd.


Balasundar I.,Near Net Shape Group | Raghu T.,Near Net Shape Group | Kashyap B.P.,Indian Institute of Technology Bombay
International Journal of Material Forming | Year: 2015

The high temperature deformation behaviour of cast and homogenised near α titanium alloy Titan 29A (M/s MIDHANI, India), equivalent to IMI 834 (M/s TIMET, UK) was studied towards developing a processing map. The processing map is interpreted in terms of the microstructural changes occurring during deformation, based on the values of a dimensionless parameter η which represents the energy dissipation through microstructural evolution processes. An instability criterion (ξ < 0) is applied to demarcate the flow instability regions in the processing map. Both the parameters (η and ξ) were computed from the experimental data generated by hot isothermal compression tests conducted at various temperature (T) and strain rate (έ) combinations T = 850-1100 °C and έ = 3 × 10−4 to 10 0/s. The deterministic domains observed in the investigated temperature and strain rate regime are attributed to continuous dynamic recrystallization of α lamella and dynamic recrystallization of β grains. © 2013, Springer-Verlag France.


Balasundar I.,Near Net Shape Group | Raghu T.,Near Net Shape Group
Materials and Design | Year: 2010

During the last decade or so there has been a tremendous growth in the research and development of equal channel angular pressing (ECAP) process which was originally proposed by Segal et al. Numerical analyses are being used extensively to evaluate the effect of various die design and process parameters in ECAP. Friction is one such important parameter. Coulomb and shear friction models have been used in the numerical analysis of ECAP process and contradicting results have been reported. This study evaluates the effect of coulomb and shear friction models on the deformation pattern, strain distribution and load requirement during ECAP process and suggests which friction model should be used in the numerical analysis of ECAP process. © 2009 Elsevier Ltd. All rights reserved.


Balasundar I.,Near Net Shape Group | Raghu T.,Near Net Shape Group
Materials and Design | Year: 2010

Axial hole or funnel is a common extrusion defect observed during a direct extrusion process. Though a common defect, the parameters that influence the nature and formation of this defect have not been studied and reported. Further, the die design requirement to avoid the defect has also been not yet established. In this regard, finite element analysis has been carried out to investigate the effect of important extrusion parameters such as extrusion ratio (R), extrusion die angle (θ), deformation zone height (h), friction (μ) and constitutive material behaviour on the defect formation and its characteristic. The conditions under which the defect can be avoided have been established. Physical modeling experiments using plasticine were carried out to validate the numerical modeling results. © 2010 Elsevier Ltd. All rights reserved.


Balasundar I.,Near Net Shape Group | Raghu T.,Near Net Shape Group
International Journal of Material Forming | Year: 2010

Repetitive upsetting-extrusion (RUE) that was originally invented to process powder materials for bulk mechanical alloying is currently being used to process bulk materials. Bulk materials are subjected to severe plastic deformation using the same die design that was used to process powder materials. As the deformation behaviour of powder and bulk materials are quite different, it has to be evaluated whether a single die design is suitable to process both these materials. Further, information on the deformation behaviour and strain homogeneity that can be achieved by subjecting bulk materials to RUE process are also currently not available. To address these issues, both numerical analysis and actual experiments on commercial pure copper has been carried out. The results obtained are presented and discussed here © 2010 Springer/ESAFORM.

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