Arnab Sarkar

Bio: Arnab Sarkar is an academic researcher from Indian Institutes of Technology. The author has contributed to research in topics: Annealing (metallurgy) & Microstructure. The author has an hindex of 5, co-authored 12 publications receiving 95 citations. Previous affiliations of Arnab Sarkar include Indian Institute of Technology Bombay & Indian Institute of Technology Kharagpur.

Implications of microstructure, Taylor factor distribution and texture on tensile properties in a Ti-added Fe-Mn-Al-Si-C steel

Abstract: Structure-property relationship in a Ti-added medium Mn multicomponent steel has been studied and compared with a Ti-free variant of same composition. Both the steels with initial ferrite-austenite microstructure were subjected to cold rolling, followed by annealing treatment at 1073K for 3 and 50 min. The Ti-modified steel shows good strength-ductility combination after 50 min of annealing. In contrast, a reverse trend is observed in the Ti-free variant where strength-ductility relationship ameliorates after 3 min annealing. The remarkable strength in the Ti-free variant originates from the higher volume fraction of Mn5(Al,Si)C precipitates having larger lattice misfit, higher fraction of deformed grains and finer ferrite grain size. The presence of Ti as a microalloying element in the Ti-modified steel instigates the formation of Ti-rich intermetallic carbide precipitates which refine the ferrite grain size during extended annealing. However, the evolution of such precipitates and refinement of ferrite grains do not significantly improve its tensile strength owing to the coarser size and lower lattice misfit of the precipitates, lesser fraction of deformed grains and predominant presence of cube fibers. The Taylor factor distribution within the range of (~2–5) is also studied to understand its implications on the texture-property relationship of the developed steels. It is observed that the γ-fiber fraction of ferrite phase increases due to higher number of grains within the Taylor factor range of (~3–4) and this, in turn, enhances the elongation in both the Ti-free (3 min annealed) and Ti-added (50 min annealed) steels.

Interfacial Microstructural and Corrosion Characterizations of Friction Stir Welded AA6061-T6 and AISI304 Materials

Abstract: The use of aluminum in conjunction of steel can reduce the weight of structures but dissimilar materials welded structure results in the formation of intermetallic compounds and inhomogeneous distribution of grains. Since aluminum is more active than the steel, the structures made from such dissimilar materials can be affected from corrosion medium which needs to be investigated. In the present work, friction stir welding has been used to join AA6061-T6 and AISI304 in lap configuration, each having a thickness of 1 mm under varied process parameters. The detailed investigations have been made which includes understanding the effect of process variables on microstructures, intermetallic compounds and their phases, and thereby on corrosion of the aluminum-steel welded joint. SEM with integrated EBSD detector and XRD analyses have been carried out to characterize the weld interface that revealed the evolution of grain boundaries and existence of phases such as Fe2Al5 and AlCrFe2. The grain size of the weld zone has been found to be decreasing with increase in weld speed and plunge depth. The temperature profiles have shown a faster rate of heating and cooling with increase in welding speed and plunge depth which led to the refinement of microstructure. The evolution precipitates mainly comprised of Al, Mg and Si as the major elements. The corrosion rate was found to be increasing with decrease in grain size. Samples were corroded by pitting corrosion, inter-granular corrosion, and environmental corrosion. Severity of pits have been found to be non-uniform in the along weld cross-section.

Enhanced strength-ductility relationship in a medium Mn high Al-alloyed multicomponent steel through thermomechanical processing

Abstract: A medium Mn, high Al, multicomponent steel with duplex ferrite-austenite as the starting microstructure has been designed and the influence of thermo-mechanical processing on the microstructure-texture-tensile property relationship has been investigated. The hot forging-annealing followed by hot rolling-annealing treatment showed poor combination of strength and ductility in the studied alloy. However, a subsequent cold rolling-annealing or warm rolling-annealing treatment has resulted in significant improvement in strength-ductility relationship. An excellent combination of strength (1141–1184 MPa) and ductility (18.1–22.2% elongation) has been achieved in both the cold rolled-1073 K annealed and warm rolled-1073 K annealed specimens due to the presence of fine ferrite grains. Higher fraction of fine M 5 (Al,Si)C precipitates have restricted the grain boundary migration thus leading to smaller ferrite grains in this annealing temperature. However, dissolution of the M 5 (Al,Si)C precipitates and the simultaneous increase in the grain size of ferrite at higher annealing temperature (i.e. 1173 K and 1273 K) deteriorates the strength-ductility relationship in both the cold rolled and warm rolled specimens. The cold rolled-annealed specimens have exhibited better ductility as compared to the warm rolled-annealed specimens due to combined effect of smaller grain size as well as larger volume fraction of gamma (γ) fiber of ferrite.

High entropy alloys – Tunability of deformation mechanisms through integration of compositional and microstructural domains

Abstract: The paradigm shift of alloying approach that led to high entropy alloys (HEAs) is now well established. Although the initial years were dominated by equiatomic approach, recent years have seen expansion in non-equiatomic compositional space that can be termed as complex concentrated alloys (CCAs). These HEAs/CCAs provide opportunities for tunable performance by manipulating deformation mechanisms. Understanding has advanced to the point that certain aspects of core effects (entropy of mixing, lattice distortion, sluggish diffusion, and cocktail effect) can be critically examined. In addition, new aspects of metastability engineering and emergence of a wide range of processing strategies has put this field on an exponential growth path. In this review, we categorize the compositional and microstructural approaches that exhibit potential for a combination of shear induced phase transformation and twinning, thereby expanding beyond the slip based mechanisms. The emerging HEAs give greater flexibility for tailoring transformation-induced plasticity (TRIP) and twinning-induced plasticity (TWIP), which have guided design of next-generation steels over the last 20 years to a new level. For TRIP HEAs, the ductility can be extended to as high as 50% while maintaining a strength exceeding 1 GPa. On the other hand, hierarchical microstructural engineering in AlxCoCrFeNi alloys can lead to over 2 GPa strength and >10% ductility. Observations of evolving c/a ratio in HCP phase of certain HEAs hint at possibility of new micromechanisms. While crack tip twin-bridging has been shown as a key mechanism to extend the toughness, concurrent phase transformation at the crack tip has been shown to push the fatigue endurance limit. Tunability of deformation mechanisms in HEAs is unprecedented as compared to the conventional metallic materials, particularly in compositions that exhibit shear induced transformation. The opportunities can be further enhanced by integrating the compositional and microstructure domains, and these aspects are highlighted in this review. The microstructural tailoring can take advantage of high enthalpy states in metastable HEAs with low stacking fault energy values of

Scalable perovskite coating via anti-solvent-free Lewis acid–base adduct engineering for efficient perovskite solar modules

Abstract: High-quality large-area perovskite films are realized by an anti-solvent-free adduct approach using 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone (DMPU) as a Lewis base additive. Perovskite crystallization kinetics was found to depend on the latent heat of vaporization, associated with vapor pressure, and donor number of the Lewis base under force convection in air-knife-assisted D-bar coating. The conventionally used dimethyl sulfoxide (DMSO) or N-methyl-2-pyrrolidone (NMP) Lewis base is inappropriate for high-quality perovskite films because of rapid co-evaporation with solvents by argon gas blowing generated under 1.5 MPa, while the DMPU-containing precursor solution induces the formation of a stable adduct intermediate in the as-deposited film due to the low vapor pressure and high donor number of DMPU. Upon addition of DMPU into the precursor solution, the concentration of DMPU is found to affect the morphology and photo-excited carrier lifetime of the resulting perovskite film. A piece of the (FAPbI3)0.95(CsPbBr3)0.05 perovskite film coated on a 4.8 × 9.6 cm2-substrate was used for testing the photovoltaic performance, where the power conversion efficiency (PCE) significantly improved from 3.21% to 20.08% (best PCE is 20.56%) when 0.5 M DMPU (with respect to 1 M of perovskite) was added into the precursor solution. A monolithic perovskite solar module with an active area of 19.69 cm2, employing the perovskite film formed from the 0.5 M DMPU-containing solution, demonstrates a PCE of 17.94%.