R. L. Narayan

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Address: TX-103I, Department of Materials Science and Engineering, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016

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Papers by R. L. Narayan

Effect of Sr addition on the high temperature deformation behavior and processing maps of Mg-7Sn alloy

Journal of Alloys and Compounds

Fracture of notched ductile bulk metallic glass bars subjected to tension-torsion: Experiments and simulations

Acta Materialia, 2019

Fracture of notched ductile bulk metallic glass bars subjected to tension-torsion: experiments an... more

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Microstructure-property correlations in as-built and heat-treated compositionally graded stainless steel 316L-Inconel 718 alloy fabricated by laser powder bed fusion

Materials Science and Engineering: A

Mechanical Behavior of Laser Powder Bed Fusion Processed Inconel 625 Alloy

Transactions of the Indian National Academy of Engineering, 2021

$Research paper thumbnail of Temperature-dependence of mode I fracture toughness of a bulk metallic glass$

Temperature-dependence of mode I fracture toughness of a bulk metallic glass

Acta Materialia, 2018

Within the temperature range over which the shear band (SB)-mediated plastic deformation is domin... more Within the temperature range over which the shear band (SB)-mediated plastic deformation is dominant, metallic glasses exhibit an intermediate temperature ductility minimum (ITDM), which occurs at about 65% of the glass transition temperature, T g. This ITDM is associated with a small number of SBs, with each band carrying large amount of plastic strain, which in turn leads to their easy transition to shear cracks, eventually leading to fracture. Some MGs are known to exhibit high room temperature (RT) fracture toughness, which has been associated with SB-mediated crack-tip plasticity. Hence, it is expected that ITDM would also correspond to a minimum in toughness. In order to ascertain this, temperature-dependence of mode I fracture toughness, J c , of a bulk metallic glass (BMG), Vitreloy 105, was investigated by recourse to 4point bend testing of single edge notched specimens within 298-475 K range, which corresponds to ~0.44 and 0.7T g of the tested BMG. Complementary finite element analyses were utilized to convert the critical load for fracture into J c. Results confirm a minimum in J c at ~0.67T g , which is in agreement with the results of unnotched 3-point bend experiments on unnotched bars that show ITDM at 0.65T g. These observations are rationalized with the aid of notch plastic deformation and post mortem fractographic characterizations and in terms of the influence of temperature on factors such as the number of shear bands, the barrier for their conversion into shear cracks, and hydrostatic stress gradients ahead of the notch tip. This study highlights the sensitive nature of BMGs' fracture toughness, even when they are nominally ductile, to temperature.

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Discrete drops in the electrical contact resistance during nanoindentation of a bulk metallic glass

Applied Physics Letters, 2016

Simultaneous measurement of the electrical contact resistance (ECR) during nanoindentation of a P... more Simultaneous measurement of the electrical contact resistance (ECR) during nanoindentation of a Pd-based bulk metallic glass (BMG) shows discontinuities in the current during the loading segment. Through an analysis of the effective change in the contact area that occurs due to the plastic flow via shear banding, we show that the current surges, which are synchronous with the displacement bursts, are associated with shear band nucleation and/or propagation. The potential of nano-ECR measurements for monitoring plastic events in BMGs is discussed. Published by AIP Publishing.

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Statistical nature of the incipient plasticity in amorphous alloys

Scripta Materialia, 2020

An arbitrary probability density function used for fitting Parameter space for () μ Mean of a gau... more

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Twin and dislocation induced grain subdivision and strengthening in laser shock peened Ti

International Journal of Plasticity

Effects of Al addition and cryogenic cyclic treatment on impact toughness of phase-transformable Ti-based bulk metallic glass composites

Journal of Materials Science & Technology

Structural characterization, biocorrosion and in-vitro investigation on Zr62Cu22Al10Fe5Dy1 metallic glass for bio-implant applications

Journal of Non-Crystalline Solids

Investigation of Crystallographic Orientation and Mechanical Behaviour in Laser-Welded Stainless Steel 316L Additive Components

Transactions of the Indian Institute of Metals

Advances in functional and structural ceramics: Development, characterization, and applications

Ceramics International

A Critical Appraisal of the Role of Oxygen in Phase Evolution and Mechanical Properties of Additively Manufactured Bulk Metallic Glasses

Transactions of the Indian Institute of Metals

Oxidation assisted recrystallization and cracking at grain boundaries in Nimonic 80 A during elevated temperature service

Corrosion Science

Additive manufacturing of novel Ti-30Nb-2Zr biomimetic scaffolds for successful limb salvage

Materials Today: Proceedings

Osteosarcoma is a type of bone cancer mainly observed in children and young adults affecting 3.4 ... more Osteosarcoma is a type of bone cancer mainly observed in children and young adults affecting 3.4 million people per year. In the present study, Ti-30Nb-2Zr, a promising next-generation biomedical implant material was fabricated in the form of a porous scaffold using the selective laser melting (SLM) additive manufacturing route. Here, we quantitatively evaluated the bio-functionality, Young&#39;s modulus, and metal oxidative stress induced by the implant to delineate the tumor ablation ability of Ti-30Nb-2Zr scaffold. The results indicated that Ti-30Nb-2Zr scaffolds have superior osteointegration with L929 murine cells through activation of the AKT and b-catenin protein pathways. Results of fluorescent microscopy delineate the superior cell motility, protein binding ability, and adhesion of fibroblasts owing to the porous nature of the scaffold. Moreover, it demonstrated excellent capabilities in impeding post-surgical tumor recurrence, and more interestingly printed scaffolds almost matched Young&#39;s modulus of human bones. Therefore, this novel 3-D printed scaffold material may have high clinical translational potential for successful limb salvage in tumor-induced bone defect management.

Fracture and deformation in bulk metallic glasses and composites

A generalised hot cracking criterion for nickel-based superalloys additively manufactured by electron beam melting

Additive Manufacturing, 2021

Abstract The influences of microstructure and solidification parameters on the hot cracking behav... more Abstract The influences of microstructure and solidification parameters on the hot cracking behaviour of an additively manufactured Ni-based superalloy via selective electron beam melting (SEBM) have been investigated. Severe intergranular hot cracking is found to occur at grain boundaries (GBs) in the SEBM-built superalloy. A generalised cracking criterion that considers various process parameters along with the GB inclination is developed on the basis of a prevailing hot cracking criterion for columnar-grained microstructure. A parametric evaluation of influencing factors is quantitatively conducted to predict the optimal conditions that could prevent hot cracking while maintaining the desirable fine microstructure. With the aid of numerical simulations, it is determined that while micro-segregation occurs at all types of GBs, its occurrence at the divergent ones tend to promote cracking. Using the results of this work, hot cracking in additively manufactured Ni-based superalloy single crystals can be potentially mitigated.

On simultaneous enhancement in local yield strength and plasticity of short-term annealed bulk metallic glasses

Journal of Alloys and Compounds, 2021

The variations in local yield strength and plasticity of a Zr-based bulk metallic glass at differ... more The variations in local yield strength and plasticity of a Zr-based bulk metallic glass at different fictive temperatures (T f) are studied. To probe the size and distribution of microscopic carriers of plasticity, spherical-tip nanoindentation and microindentation are employed. With nanoindentation, events signifying the departure from Hertzian elastic contact, which manifest as pop-ins in the load-displacement response and correspond to incipient plasticity, are recorded and analyzed. Results indicate that with increasing T f , the incipient plastic event and the number of subsequent pop-ins increases. Using statistical analysis of the scatter in strength, the activation parameters for shear transformation zones (STZs) in all specimens are determined. By considering the linear accumulation of STZs to form a shear band, the increase in shear yield strength along with plasticity, with increasing T f , is explained.

Nanometer-scale precipitations in a selective electron beam melted nickel-based superalloy

Scripta Materialia, 2021

The nanometer-scale (nano-scale) microstructural evolution in an additively manufactured Refree N... more The nanometer-scale (nano-scale) microstructural evolution in an additively manufactured Refree Ni-based superalloy, with single crystal compositions, is investigated through field emission scanning electron microscopy, transmission electron microscopy, and atom probe tomography. We find that nano-scale primary  precipitation occurs in the fine as-built microstructure, leading to an exceptional microhardness of 480.0 ± 6.7 HV at room temperature. Presence of ultra-fine  precipitates, ~ 20 nm in size, is observed in the bottom few layers of the as-built samples, which is hitherto undocumented and contrary to the widespread consensus regarding hierarchical  phase evolution in additively manufactured Ni-based superalloys. Moreover, considerable precipitation of tantalum-rich C14 Laves phase at the grain boundaries and interdendritic regions in the as-built samples emphasizes the need for additive manufacturing specific alloy design.

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Influence of simultaneous alloying with Ca and Sc on the high temperature deformation mechanism, texture, and recrystallization behavior of Mg-Ca-Sc alloys

Materials Characterization, 2021

Abstract The effect of simultaneous addition of non-rare-earth (Ca) and rare-earth (Sc) elements ... more Abstract The effect of simultaneous addition of non-rare-earth (Ca) and rare-earth (Sc) elements on the hot rolled deformation behavior, recrystallization and texture evolution of Mg alloys is evaluated. For this purpose, the microstructures of as rolled and recrystallized ternary alloys, Mg-0.6Ca-0.5Sc and Mg-0.6Ca-1.0Sc were compared with those of binary Mg-0.6Ca and Mg-1.0Sc alloys. Results show that for all the alloys studied, 10 1 ¯ 1 - 10 1 ¯ 2 double twins were the dominant deformation mechanism and 10 1 ¯ 2 extension twinning was suppressed in the presence of Sc in binary as well as ternary systems. Although the grain refinement prowess of Ca and Sc were enhanced on simultaneous addition, their texture weakening capability deteriorated significantly.

R. L. Narayan

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