Srinivasa R. Bakshi

Bio: Srinivasa R. Bakshi is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Spark plasma sintering & Carbon nanotube. The author has an hindex of 34, co-authored 99 publications receiving 4515 citations. Previous affiliations of Srinivasa R. Bakshi include Naval Postgraduate School & Indian Institutes of Technology.

Microstructural Evolution of Ti–Al–Ni (Cr,Co,Fe)-Based High-Entropy Alloys Processed Through Mechanical Alloying

Abstract: TiAlNiCr, TiAlNiCrCo, TiAlNiCrFe, TiAlNiCrCoFe, TiAlNiCo, TiAlNiFe and TiAlNiCoFe high-entropy alloys were processed through mechanical alloying followed by spark plasma sintering (SPS). All the alloys develop a BCC (Cr-/Cr–Fe-rich) structure after mechanical alloying. Sintering at high temperature promotes the formation of one more BCC phase which is of NiAl type. Phase evolution after mechanical alloying and SPS was studied using X-ray diffraction. Composition of the phases was analysed using energy-dispersive spectroscopy, and microstructural characterisation was done using back-scattered electron images. Characterisation studies done on the alloys confirm the presence of BCC phases. Alloys without Cr develop a single BCC peak after SPS compared to alloys with Cr.

Spark Plasma Sintering Process as a Tool for Achieving Microstructural Integrity

Abstract: The fact that real materials are not perfect crystals, is critical to materials engineering as the presence of crystalline defects is the most important feature of the microstructure which influences the mechanical properties. Exposure of materials to high temperature for long duration would result in structural failure, when a sub-size crack grows into a critical level. This paper concentrates on the novel application of spark plasma sintering (SPS) technique in achieving microstructural integrity of materials by crack closure using the superior capability of SPS for annealing the defects in materials. Due to the presence of applied compressive stress, expansion is restricted and brings about the closure of cracks. The crack surfaces then come in contact with each other, and energization between the crack surfaces causes them to bond. The presentation would bring about the nature of bonding achieved through SPS when two model systems, diffusion bonding of stainless steel discs and stainless steel with ferroboron powder, were considered and highlighted its applicability through systematic optimization.

Microstructure and Mechanical Properties of Ti–Al–Ni–Cr–Co–Fe-Based High-Entropy Alloys

Abstract: Four alloys with nominal compositions of TiAlNiCr, TiAlNiCrCo, TiAlNiCrFe and TiAlNiCrCoFe were synthesized through mechanical alloying followed by spark plasma sintering (SPS). After 8 h of milling, all the alloys developed a major parental BCC phase. SPS done on the alloys revealed that the BCC phase was retained after SPS. Sintering promoted the formation of one more BCC phase thus making the final microstructure comprised of two BCC phases. The phases were characterized using X-ray diffraction and scanning electron microscope. Backscattered electron images of the samples indicated that one BCC phase was rich in Ni and Al, whereas the second BCC phase was rich in Cr, Co and Fe. All the alloys showed good hardness and mechanical strength with values above 2000 MPa except TiAlNiCr.

Effect of Post-Weld Heat Treatment on the Microstructure of Plasma Arc Welded DP600 Steel

Abstract: The effect of isothermal post-weld heat treatment on keyhole plasma arc welded DP600 steel was investigated using optical microscopy, scanning electron microscopy and analytical transmission electron microscopy. The isothermal heat treatment had no effect on the allotriomorphic, Widmanstatten and acicular ferrite in the fusion zone (FZ). The martensite lath structure showed complete recovery in FZ, base metal (BM) and heat-affected zone (HAZ) with the formation of coarse cementite particles of up to 200 nm size in subcritical HAZ. The coarse grain HAZ showed little change in bainite and had tempered martensite and transformed retained austenite. The fine grain HAZ consisted of bainite, tempered martensite and coarsened preexisting cementite. The recovered BM had tempered martensite and reduced dislocation density. Hardness was found to be the lowest in subcritical HAZ, which is attributed to complete tempering of martensite, formation of large cementite particles and disappearance of dislocations.

Fast parallel algorithms for short-range molecular dynamics

Abstract: Three parallel algorithms for classical molecular dynamics are presented. The first assigns each processor a fixed subset of atoms; the second assigns each a fixed subset of inter-atomic forces to compute; the third assigns each a fixed spatial region. The algorithms are suitable for molecular dynamics models which can be difficult to parallelize efficiently—those with short-range forces where the neighbors of each atom change rapidly. They can be implemented on any distributed-memory parallel machine which allows for message-passing of data between independently executing processors. The algorithms are tested on a standard Lennard-Jones benchmark problem for system sizes ranging from 500 to 100,000,000 atoms on several parallel supercomputers--the nCUBE 2, Intel iPSC/860 and Paragon, and Cray T3D. Comparing the results to the fastest reported vectorized Cray Y-MP and C90 algorithm shows that the current generation of parallel machines is competitive with conventional vector supercomputers even for small problems. For large problems, the spatial algorithm achieves parallel efficiencies of 90% and a 1840-node Intel Paragon performs up to 165 faster than a single Cray C9O processor. Trade-offs between the three algorithms and guidelines for adapting them to more complex molecular dynamics simulations are also discussed.

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Carbon Nanotubes: Present and Future Commercial Applications

Abstract: Worldwide commercial interest in carbon nanotubes (CNTs) is reflected in a production capacity that presently exceeds several thousand tons per year. Currently, bulk CNT powders are incorporated in diverse commercial products ranging from rechargeable batteries, automotive parts, and sporting goods to boat hulls and water filters. Advances in CNT synthesis, purification, and chemical modification are enabling integration of CNTs in thin-film electronics and large-area coatings. Although not yet providing compelling mechanical strength or electrical or thermal conductivities for many applications, CNT yarns and sheets already have promising performance for applications including supercapacitors, actuators, and lightweight electromagnetic shields.