Faculty Publications
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Item Material extrusion additive manufacturing of bioactive glass/high density polyethylene composites(Elsevier Ltd, 2021) Jeyachandran, P.; Bontha, S.; Bodhak, S.; Balla, V.K.; Doddamani, M.Bioactive glasses (BAG) are renowned for their unique ability to bond with tissues and therefore are used extensively for bone repair and functional recovery. In this work, high density polyethylene (HDPE) reinforced with BAG is processed using material extrusion additive manufacturing (MEAM) for potential orthopaedic applications. The constituents are melt compounded by varying BAG proportions (5, 10, and 20 wt %) and subsequently extruded into filaments. DSC curves show an insignificant change in the peak melting temperature, increase in crystallization temperature, and a decrease in the crystallinity of HDPE with BAG addition. Warpage analysis confirms that the enhanced temperature parameters and BAG addition result in reduced warpage and improved dimensional stability. Rheological results show that the addition of BAG increases complex viscosity, storage and loss modulus. Melt behavior and print parameters are tailored to improve first layer adhesion and interfacial bonding rendering dimensionally stable prints without any print induced defects. Dynamic mechanical analysis (DMA) of printed samples show an increase in storage (E?), loss (E?) modulus, and a decrease in damping factor (Tan ?) with BAG addition. MEAM of the developed H/BAG composites shows a strong potential for developing customizable scaffolds and implants as bone replacements. © 2021 Elsevier LtdItem Effect of equiaxed grains and secondary phase particles on mechanical properties and corrosion behaviour of CMT- based wire arc additive manufactured AZ31 Mg alloy(Elsevier Ltd, 2023) Manjhi, S.K.; Sekar, P.; Bontha, S.; Balan, A.S.S.Wire arc additive manufacturing (WAAM) has drawn tremendous attention for manufacturing large and complex components of lightweight material at a moderate cost due to its high deposition rate and energy efficiency. Generally, WAAM-Mg alloy comprises columnar and columnar dendrite grains due to high cooling rates and thermal gradients responsible for anisotropic mechanical properties. To overcome this challenge, in this work, CMT-WAAM, which generally uses comparatively low heat input (33% lower than conventional WAAM), was used to deposit AZ31 Mg thin wall. The metallurgical characterization of the deposited thin wall of the top (T), middle (M) and bottom (B) sections reveals equiaxed grains of average sizes ∼ 58, ∼ 63 and ∼ 38 µm, respectively. In addition, TEM results exhibit the formation of secondary phase particles, i.e., β-Mg17Al12 and ɳ-Al8Mn5. Further, the ultimate tensile strength (UTS) and % elongation (% EL) in the travel direction (UTS = 224 MPa, % EL= 23.47%) are superior to that obtained in the build direction (UTS = 217 MPa, % EL = 20.82%). The corrosion resistance of WAAMed AZ31 Mg alloy is higher than wrought (cold rolled) AZ31 Mg alloy in Hank's balanced salt solution (HBSS). The results of this study reveal the potential of CMT-WAAM to deposit different grades of Mg with desired microstructure, mechanical properties and corrosion resistance. © 2023 CIRPItem Evaluation of functionally graded YSZ - IN625 clad without bond coat using laser directed energy deposition(Elsevier B.V., 2023) Likhwar, J.; Thanumoorthy, R.S.; Bontha, S.; Balan, A.S.S.M-CrAlY or M-Cr-based bond coats are used as a buffer layer to apply ceramic thermal barrier coatings (TBCs) to metal turbine blades. However, due to oxygen diffusion, thermally grown oxides grow over the bond coat material, leading to coating failure in the components. Therefore, this study attempts to fabricate a novel TBC-coated IN625 without bond coat material using a Functional grading approach. The findings from this study may pave the way for processing functionally graded ceramic materials using Laser Additive manufacturing techniques. This study also evaluates the performance of functional grading in joining dissimilar materials using small spot-size laser sources. In the present study, samples were fabricated for three sample conditions: S1: direct clad, S2: 25% linear grading, and S3: 50% linear grading. The interface between Yttria Stabilized Zirconia (YSZ) and IN625 for the S1 sample showed discontinuous and horizontal cracks along the interface due to steep variations in thermal properties. However, the interface of S2 and S3 samples showed good adhesion and a smooth transition in microstructure between IN625 and YSZ as a result of functional grading. SEM micrographs showed homogeneous YSZ distributions without segregation within the IN625 matrix. This was attributed to strong Marangoni flow as a result of the small spot-size laser beam used in this study. © 2023 Elsevier B.V.Item Hybrid additive manufacturing of ER70S6 steel and Inconel 625: A study on microstructure and mechanical properties(Elsevier Ltd, 2023) Rodrigues, J.P.; Thanumoorthy, R.S.; Manjhi, S.K.; Sekar, P.; Arumuga Perumal, D.A.; Bontha, S.; Balan, A.S.S.Hybrid Additive Manufacturing (HAM) is currently being explored because of its potential to achieve trade-off between build capacity and feature resolution. The present study aims at fabricating ER70S6-Inconel 625 (IN625) bimetallic clad using hybrid Wire Arc Additive Manufacturing (WAAM) and Laser Directed Energy Deposition (LDED) processes. Microstructure evaluation was performed at the cross section of bimetallic clad for distinct materials as well as the interface. WAAM built ER70S6 revealed equiaxed ferritic grains, whereas laser deposited IN625 region showed columnar dendrites with under developed secondary arms. However, the first layer of IN625 exhibited columnar dendrite with secondary arms due to the influence of diffused Fe from the base ER70S6 steel under the action of concentrated laser heat source, which was revealed by energy dispersive spectroscopy (EDS) maps. The measured microhardness across the cross section of the deposit showed values corresponding to inherent material system. The interface did not reveal presence of any intermetallic phases which was confirmed by hardness results and X-Ray diffraction. Shear test revealed superior bond strength between the two materials, maintaining average strength of 452 MPa. The fractography images exhibited fine dimples along with cleavages indicating mixed fracture characteristics. This additive manufacturing method explores a new dimension in multi-material fabrication which, when customized for different materials, serve critical areas in the aerospace and defence sector. © 2023 Elsevier LtdItem Effect of CMT-WAAM Process Parameters on Bead Geometry, Microstructure and Mechanical Properties of AZ31 Mg Alloy(Springer, 2024) Manjhi, S.K.; Sekar, P.; Bontha, S.; Balan, A.A.S.Fabrication of Mg alloys using the additive manufacturing process is quite challenging owing to high oxidation and volatile nature at high temperatures. The present study investigates the effect of wire feed speed (WFS) and travel speed (TS) on single tracks of AZ31 Mg alloy fabricated using the cold metal transfer wire arc additive Manufacturing (CMT-WAAM) process. The WFS and TS of CMT-WAAM are optimized to achieve better deposition quality. An increase in WFS increased the width, height, penetration depth, and heat-affected zone of single tracks. In addition, increasing TS decreased the deposited tracks' contact angle and height. The average grain size at the interface zone, center and top portion of single tracks are 35, 42, and 60 μm. The x-ray diffraction results show only the presence of primary phase α-Mg; interestingly, the β-Mg17Al12 and η-Al8Mn5 secondary phases are identified by SEM + EDS and TEM images. The microhardness increased from the substrate to the top section of single tracks due to the increased volume fraction of secondary-phase particles. Based on the best-chosen process parameters obtained from single-track deposition, a multilayer AZ31 Mg thin wall is deposited. The UTS, YS, and % EL of the deposited thin wall in travel direction (TD) are 222 MPa, 102 MPa, and 18%, while in build direction are 202 MPa, 110 MPa, and 14%, respectively. The tensile strength and elongation % of TD and BD samples exhibited comparable properties and were higher than cast AZ31 Mg alloy. © ASM International 2023.