I. Samajdar - Academia.edu (original) (raw)

Papers by I. Samajdar

Journal of Nuclear Materials, 2009

Journal of Nuclear Materials, 2007

Textures and Microstructures

Rolling textures of low-carbon steel predicted by full constraints and relaxed constraints Taylor... more Rolling textures of low-carbon steel predicted by full constraints and relaxed constraints Taylor models, as well by a self-consistent model, are quantitatively compared to experimental results. It appears that none of these models really performs well, the best results being obtained by the Pancake model. Anew model (“Lamel model”) is then proposed as a further development of the Pancake model. It treats a stack of two lamella-shaped grains at a time. The new model is described in detail, after which the results obtained for rolling of low-carbon steel are discussed. The prediction of the overall texture now is quantitatively correct. However, the γ-fibre components are better predicted than the α-fibre ones. Finally it is concluded that further work is necessary, as the same kind of success is not guaranteed for other cases, such as rolling of f.c.c, materials.

Philosophical Magazine, 2015

Materials Science and Technology, 1998

ABSTRACT The aim of the present investigation is to understand particle redistribution and matrix... more ABSTRACT The aim of the present investigation is to understand particle redistribution and matrix microstructure development during hot extrusion of aluminium matrix composites and the influence of process parameters on these two key microstructural features. Cast composite billets have been partially extruded to study the sequence of microstructure development. Strain and strain rate distribution in the partial extrudates have been measured using a ‘visioplasticity’ technique. Results indicate that strain and strain rate distribution are more homogeneous in the composites than in the unreinforced alloy. Extrudate microstructures reveal the presence of particle bands and deformation bands aligned in the extrusion direction. It is noted that shearing of SiC particle clusters leads to particle banding, and an increase in extrusion ratio and/or a decrease in particle size enhances particle band formation. This phenomenon is attributed to increasing strain partitioning between the cluster and the matrix with increasing strain and/or decreasing particle size. The formation of deformation bands is attributed to a grain splitting phenomenon which is found to be more extensive in composites compared with the unreinforced alloys.

Materials Science and Technology, 2001

... higher C concentration in precipi-tate, because of small dwell time about 5 s) 6 Analysis o... more ... higher C concentration in precipi-tate, because of small dwell time about 5 s) 6 Analysis of M23C6 precipitate in hard zone of austenitic stainless steel clad ... 6, 'Welding, brazing and soldering', 3 edn, 822 828; 1995, Materials Park, OH, ASM International. 2. l. karlsson: Weld. ...

Materials Science Forum, 1994

ABSTRACT Commercial purity aluminum was warm plane-strain extruded 83 and 96%, giving recrystalli... more ABSTRACT Commercial purity aluminum was warm plane-strain extruded 83 and 96%, giving recrystallized ODF cube intensities of 50±25 and 200±30 times random. Local orientation studies, including orientation imaging microscopy, showed that grains within 10° and 20° of cube, nucleated much faster than non-cube grains, especially after higher strain. After 83% reduction the cube grains were no larger than the non-cube. At the higher strain, however, the slightly larger cube grain size appeared to come from earlier nucleation. This evidence for oriented nucleation was further supported by TEM evidence of enhanced recovery of near-cube subgrains and from the fall of the spacing of deformed cube bands from 500 to 120μm as the strain increased. The average recrystallized grain thicknesses were 125 and 106 μm respectively. The cube bands rotated towards cube as the reduction increased - matching the decreased mean deviation of the new cube grains.

Scripta Metallurgica et Materialia, 1992

Materials Science and Technology, 2010

ABSTRACT

Materials & Design, 2011

The present investigation presents a composite picture of the microstructural developments in a f... more The present investigation presents a composite picture of the microstructural developments in a friction stir welded (FSW) AA5052. Optimized, defect free and chemically homogeneous, FS weld was generalized in four regions-base material (BM), nugget, advancing side (AS) and retreating side (RS), using standard nomenclatures. Each region had its signature of microstructural features. AS had clear indications of shear and of grain fragmentation. The nugget region, on the other hand, had nearly equiaxed grains, with strong in-grain misorientation and presence of grain-interior dislocation structure ruling out contributions from static recrystallization. Equiaxed grains of the nugget region had typical onion ring structure-each ring did approximately correspond to one dominant family of orientation. Microstructural developments, as obtained from relative grain refinement, in-grain misorientation development, relative banding, etc., were most significant in nugget followed by AS and then by RS. Heterogeneous plastic deformation and thermal activation through localized heating/friction were the apparent causes. Most of the friction stir welded specimen fractured away from the nugget and showed ductile mode of failure.

Recrystallization and grain growth were studied in hot extruded B2 Fe-Al by X-ray texture measure... more Recrystallization and grain growth were studied in hot extruded B2 Fe-Al by X-ray texture measurements and Orientation Imaging Microscopy (OIM). Asextruded material contained ultra-fine grains of 0.2-0.4wm. Such grains contained high dislocation densities, but mostly possessed high angle boundaries with the immediate neighbors. Depending on the annealing conditions, a combination of fine equiaxed and/or large columnar grains was observed. The fine equiaxed grains were at least 10 times larger than the as-extruded grain size and contained lower dislocation densities-which points towards primary recrystallization. Large columnar grains were observed in samples with fast heating and/or prolonged annealing at higher temperatures and were possibly formed by grain growth. Samples with predominantly equiaxed grain structure contained a similar texture as in the as-extruded material-a strong [llO] fiber. Formation of the large columnar grains reduced the [110], but increased the [ill] fiber. Possible selection of [ill] grains for grain growth is not due to grain size advantage, as grain size distributions of all three fibers were similar, but can be understood from the consideration of grain boundary character distribution (GBCD) or mesotexture.

Materials Science and Technology, 2006

ABSTRACT A single phase hexagonal close packed Zircaloy 2 was cold deformed to different reductio... more ABSTRACT A single phase hexagonal close packed Zircaloy 2 was cold deformed to different reductions by laboratory rolling. Systematic characterisations of the structural developments were carried out. Bulk texture developments were gradual, strongest developments being noticed at the highest strain. Although formation of well defined deformation fibre(s) could not be identified, overall developments in deformation texture were best captured through Taylor type models incorporating only prismatic slip. Strain localisations were observed as single or double walled dislocation structures at approximately 45 and 60° to the rolling direction. Such strain localisations were always associated with significant lattice reorientations or misorientation developments. Relative softening in lattice strain, observed at the higher reductions, can possibly be explained by the appearance of extensive strain localisations and the associated concurrent local dynamic recovery. The grains or orientations with dominant presence of strain localisations could be indirectly related to negative textural softening.

Materials Science Forum, 2011

Homo-epitaxial (100) single crystal diamond films of different isotopic (13C) composition were sy... more Homo-epitaxial (100) single crystal diamond films of different isotopic (13C) composition were synthesized by micro-wave plasma chemical vapor deposition (MPCVD). Undoped 12C (100) films were also synthesized at different thicknesses. The growth surface of 13C doped showed a sequential morphological change from flat surface to stepped or ledge surface and coarsening of the steps/ledges with the increase of 13C-isotope concentration. As the growth proceeds via surface steps/ledges and coarsening of these steps/ledges, further increase in imperfection of the grown CVD single crystal diamonds observed with the development of non-(100) orientations. In case of undoped 12C samples, as the thickness increased the in-grain misorientation got reduced.

Materials Processing and Texture, 2008

The Journal of Strain Analysis for Engineering Design, 2014

ABSTRACT Interstitial free (IF) and drawing quality (DQ) steel sheets were subjected to conventio... more ABSTRACT Interstitial free (IF) and drawing quality (DQ) steel sheets were subjected to conventional mechanical deep drawing and hydro-mechanical deep drawing operations. Detailed macroscopic strain measurements were made at different cup depths. These were simulated using PAM-STAMP, a commercial finite element–based software. For continuum-based finite element simulations, the required key material properties are strain hardening exponent (n) and anisotropy index (). These were kept either constant or dynamically varied during the simulation. The constant properties were taken from conventional tensile tests of the original material, while the dynamic variation in properties was extrapolated from developments in the crystallographic texture and in-grain misorientation. Considering dynamic properties during simulation provided a superior prediction of macroscopic strains. This study clearly demonstrates the need for considering evolution of critical continuum properties, such as work hardening and anisotropy index, through appropriate microstructural inputs for more realistic macroscopic predictions.

Textures of Materials, Pts 1 and 2, 2012

ABSTRACT Texture of the ARB processed commercial purity aluminium was investigated in order to ex... more ABSTRACT Texture of the ARB processed commercial purity aluminium was investigated in order to explore the stable component in rolling texture more than 95 % of rolling reduction in FCC metal sheets having high stacking fault energy. Weak location dependence along normal direction was observed in the sheet up to ARB 8 cycle, whereas the texture could be regarded to be uniform after ARB 8 cycle. The main orientation was Copper component, whereas the minor orientations were Brass and S orientations in the ARB processed pure aluminium sheets rolled up to around 99.9 % reduction.

Acta Materialia, 2015

ABSTRACT The anisotropic tensile response of fully processed cold-rolled grain-oriented (CRGO) st... more ABSTRACT The anisotropic tensile response of fully processed cold-rolled grain-oriented (CRGO) steel was studied for two crystallographic orientations: (110) 〈001〉 and (110) 〈111〉. They showed remarkably different stress-strain behavior and corresponding developments in deformed microstructures. The (110) 〈001〉 oriented CRGO steel specimens retained their orientation stability until ε (true strain) = 0.07. On the other hand, (110) 〈111〉 oriented specimens underwent significant reorientation and displayed formation of strain localizations by ε = 0.03. Discrete dislocation dynamics (DDD) simulations were carried out - three-dimensional (3-D) for "limited" (∼10-4) plastic strain and two-dimensional (2-D) for the experimentally imposed strain - to investigate the orientation effects on the tensile response of the CRGO steel specimens. 2-D DDD simulations were able to provide qualitative and quantitative estimates of the post-yield tensile behavior of (110) 〈001〉 and (110) 〈111〉 samples. Direct comparison between experimental and simulation results confirmed the orientation effect on the overall macroscopic response of the specimens. It was observed that the response of (110) 〈111〉 specimens showed features of reorientation and textural softening and these were captured by the Taylor type deformation simulations.

Textures and Microstructures, 1998

Alloy AA5182 contains coarse constituent particles and submicron dispersoids. While the former ma... more Alloy AA5182 contains coarse constituent particles and submicron dispersoids. While the former may cause particle stimulated nucleation (PSN) during primary recrystallization, the fine dispersoids may ‘arrest’ grain growth during subsequent annealing. Abnormal grain growth was observed after dissolution/coarsening of the dispersoids. Mainly S [{123}〈634〉] grains, but also some Brass [{011}〈112〉] and Cu [{112}〈111〉] grains, were observed to grow abnormally. Both the grain size and the grain boundary character distribution (GBCD) possibly played a role in the selection of the grains for abnormal grain growth. A dramatic increase in the number fraction of extremely low angle (1−5°) boundaries was observed with annealing, the increase being more at 470°C (when dispersoids were stable and grain growth was arrested more effectively) than at 500°C/530°C (when inhibition to grain growth was less). The nature of the CSL boundaries did not change significantly with annealing time/temperature.

Materials Science Forum, 2005

Scripta Materialia, 2003

Detailed studies of precipitation in type 316L (UNS S31603) austenitic stainless steel were carri... more Detailed studies of precipitation in type 316L (UNS S31603) austenitic stainless steel were carried out by using a combination of differential scanning calorimetry, electrical resistivity measurement and transmission electron microscopy. Four distinct stages of precipitation were identified-coherent precipitation, its coarsening and initiation of grain boundary precipitation, r phase and finally M 23 C 6 precipitation.