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Papers by SHUBHAM CHANDRA

International Materials Reviews

Social Science Research Network, 2012

Lecture Notes in Mechanical Engineering, 2022

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.

2018 IEEE SENSORS, 2018

Hygiene in public toilets is generally monitored by manual inspection. Data from many cities reve... more Hygiene in public toilets is generally monitored by manual inspection. Data from many cities reveal that manual inspection regime has systemic biases and enforcement is not uniform. Alternatively, hygiene may be monitored by using sensors to measure concentration of gases produced as byproducts. However, sensor calibration must be done for each installation separately which increases the cost of such a system. We propose a hybrid hygiene monitoring system that combines user ratings to auto-calibrate the gas sensors to produce reliable results. Our algorithm combine both these inputs into a community benchmark hygiene rating. A user App is also developed along with back-end database to handle the reporting and follow-ups by the civic nuthor-ifies.

Single crystal (SX) nickel-based superalloy blade forms a key element of hightemperature gas turb... more Single crystal (SX) nickel-based superalloy blade forms a key element of hightemperature gas turbines that are vital to aviation and power industries, owing to its excellent creep properties at elevated temperatures. Conventional manufacturing of SX Ni-based superalloy components is a tedious and expensive process due to stringent tolerance on part geometry and SX quality. Additive manufacturing (AM) provides unique features such as economic sustainability, automated manufacturing process and capability of printing identical parts. Moreover, the future of AM technologies shows significant promise towards achieving complete layer-wise control, in terms of varying process parameters. This study employs selective electron beam melting (SEBM), a powder-bed metal AM technique, to additively manufacture a first-generation Nickel-based SX superalloy. High vacuum environment and nearly unidirectional thermal gradient, inherent with SEBM, make it the most promising AM technique for SX supera...

Additive manufacturing techniques, specifically those currently employed in metalbased manufactur... more Additive manufacturing techniques, specifically those currently employed in metalbased manufacturing; involve heat transfer and fluid flow physics which are far too complex to be covered in an analytical form. This limits the control over material microstructure thus obtained in a deposited alloy component. To this need, a multi-scale numerical study is carried out combining a three-dimensional finite element (FE) based macro-scale and a cellular automaton (CA) based meso-scale model in order to simulate the dendritic grain growth in the selective laser melting (SLM) technique. The macro-scale model successfully simulates the heat transfer and fluid flow physics associated with a moving melt pool. The CA model deals with the phenomena of solutediffusion on a meso-scale during solidification. The thermal coupling between the two length scales results in a reasonably accurate model capable of accounting for steep thermal gradients, large cooling rates and complex thermal cycles associated with the solidification phenomena occurring during laser-based manufacturing process.

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.

SSRN Electronic Journal, 2019

Materials Science and Engineering: A, 2019

Anisotropic microstructure and mechanical properties of additively manufactured Co-Cr-Mo alloy us... more Anisotropic microstructure and mechanical properties of additively manufactured Co-Cr-Mo alloy using selective electron beam melting for orthopedic implants. Materials

Materialia, 2019

Revealing competitive columnar grain growth behavior and periodic microstructural banding in addi... more Revealing competitive columnar grain growth behavior and periodic microstructural banding in additively manufactured Ti-6Al-4V parts by selective electron beam melting, Materialia (2019), doi:

Journal of Materials Processing Technology, 2019

This work presents a comparative study on the in-situ alloying of NiTi shape memory alloys (SMAs)... more This work presents a comparative study on the in-situ alloying of NiTi shape memory alloys (SMAs) by directed energy deposition (DED), selective laser melting (SLM) and selective electron beam melting (SEBM) processes using pre-mixed Ni-Ti powders. The influence of process parameters on the 2 microstructural homogeneity, phase formation and thermomechanical properties of NiTi alloy has been systematically studied. DED could build solid NiTi alloys with good interlayer fusion and phase transformation characteristics. However, a substantial amount of uniformly dispersed Ti 2 Ni intermetallics can embrittle this material. SLM-built NiTi parts show a tradeoff between microstructural inhomogeneity and keyhole defects when the energy densities are varied. In addition, the strong exothermic reaction in Ni-Ti powder mixtures during printing can disturb the melt pool, making it challenging to elaborate this material and obtain desired phase by using SLM. Moreover, SEBM is found to be unsuitable to in-situ synthesize this highly reactive material due to the lack-of-fusion vs. powder-ignition dilemma in the mandatory preheating step. It is suggested to adopt DED to in-situ alloy NiTi parts when using the elementally blended powders as feedstocks.

Journal of Physics D: Applied Physics, 2017

The process of laser engineered net shaping (LENSTM) is an additive manufacturing technique that ... more The process of laser engineered net shaping (LENSTM) is an additive manufacturing technique that employs the coaxial flow of metallic powders with a high-power laser to form a melt pool and the subsequent deposition of the specimen on a substrate. Although research done over the past decade on the LENSTM processing of alloys of steel, titanium, nickel and other metallic materials typically reports superior mechanical properties in as-deposited specimens, when compared to the bulk material, there is anisotropy in the mechanical properties of the melt deposit. The current study involves the development of a numerical model of the LENSTM process, using the principles of computational fluid dynamics (CFD), and the subsequent prediction of the volume fraction of equiaxed grains to predict process parameters required for the deposition of workpieces with isotropy in their properties. The numerical simulation is carried out on ANSYS-Fluent, whose data on thermal gradient are used to determine the volume fraction of the equiaxed grains present in the deposited specimen. This study has been validated against earlier efforts on the experimental studies of LENSTM for alloys of nickel. Besides being applicable to the wider family of metals and alloys, the results of this study will also facilitate effective process design to improve both product quality and productivity.

Information and Knowledge Management, 2014

Libraries are key ingredients for institutional successes as they enhance the quality of human re... more Libraries are key ingredients for institutional successes as they enhance the quality of human resources for development. The need for preservation of stock through control measures has become imperative particularly for the third world. Thus, this article explores the existence of library security policies, common breaches and prevention measures in Ghanaian polytechnics. The study employed questionnaire survey and in-depth interviews in 5 polytechnics selected through simple random sampling. Data was analysed using frequency tables and interpretative techniques. The study revealed a male-dominated library staff mostly aged between 18 and 40 years, majority of whom had first degrees and above. None had any form of written security policies and common breaches included theft, book non-return, mutilation, mis-shelving and impersonation. Periodic searches, not allowing entry with lethal materials as well as inventory and weeding were some of the preventive measures. However, major setbacks to these efforts included lack of electronic surveillance, inadequate management support, staff lackadaisical attitudes and no proper procedures upon lending.