Faculty Publications
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Item Development of thick SiC coating on thin wall tube of zircaloy-4 using laser based directed energy deposition technique(Elsevier B.V., 2020) Rai, A.K.; Srinivasulu, B.; Paul, C.P.; Singh, R.; Rai, S.K.; Mishra, G.K.; Bontha, S.; Bindra, K.S.In the present study, optimization of various laser-processing parameters for the deposition of thick SiC coating on zircaloy-4 (Zry-4) tube is studied in view of the development of accident tolerant fuel clad material for current and future nuclear reactors with the enhanced safety. The SiC coatings are deposited using laser directed energy deposition (LDED). It is found to be quite challenging to deposit desired SiC coating on a thin (~400 ?m) substrate of Zry-4 tubes due to either its excessive melting or damage. This is minimized largely by cooling the tube from inside by passing Ar gas (20 l min?1). It is observed that different processing parameters play a vital role on homogeneity, uniformity and defects-free SiC coatings as well as on the melting and oxidation of Zry-4 substrate. A uniform and homogeneous coating of SiC is deposited on Zry-4 at the optimized laser power density of 4.52 kW cm?2, powder feed rate of 2.71 g min?1and scan speed of 325 mm min?1. The interface between SiC coatings and substrate is characterized using different techniques such as optical microscopy, scanning electron microscopy and X-ray diffraction to access the homogeneity, uniformity, defects and to identify the different phases formed in the coated layer. Coated layer is found to be consisting of Zr(?), SiC, ZrSi2, ZrSi and ZrC types of phases and the same is also confirmed by the ThermoCalc(R) based ternary phase diagram. Further, the effect of processing parameters on substrate melting and the nature of SiC coating is explained by simulating the substrate temperature using COMSOL@ multi-physics. To the author's best knowledge, this would be the first study to report the laser directed energy deposition of SiC on Zry-4 alloy. © 2020 Elsevier B.V.Item Study of melt pool geometry and solidification microstructure during laser surface melting of Inconel 625 alloy(Elsevier GmbH, 2021) Chaurasia, J.K.; Jinoop, A.N.; P, P.; Paul, C.P.; Bindra, K.S.; Bontha, S.The present study aims to comprehend thermo-fluid conditions during laser surface melting (LSM) of Inconel 625 (IN625) alloy using experimental and numerical modelling approaches. Nine tracks were melted on an IN625 plate at different laser powers and scan speeds. Melt pool geometry and grain morphology were evaluated using microscopy techniques. A 3-D finite volume model based on heat conduction solidification equation (HCS model) was used to simulate LSM process. Further, HCS model was expanded to include effects of fluid dynamics (HCS-FD model). Both the numerical models were used to predict melt pool geometry, peak temperatures, temperature gradients and cooling rates. The error in predictions of melt pool geometry from the HCS-FD model was lower when compared to the HCS model. The velocity vectors show a strong surface tension driven flow which has resulted in narrow and deeper melt pools in agreement with the cross sectional images of the melted tracks. Further, solidification characteristics were interpreted to obtain inferences about grain size and morphology. © 2021 Elsevier GmbH