Faculty Publications
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Item 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 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 Enhancing fatigue performance of AZ31 magnesium alloy components fabricated by cold metal transfer-based wire arc directed energy deposition through LPB(KeAi Communications Co., 2024) Manjhi, S.K.; Bontha, S.; Balan, A.A.S.Cold Metal Transfer-Based Wire Arc Directed Energy Deposition (CMT-WA-DED) presents a promising avenue for the rapid fabrication of components crucial to automotive, shipbuilding, and aerospace industries. However, the susceptibility to fatigue of CMT-WA-DED-produced AZ31 Mg alloy components has impeded their widespread adoption for critical load-bearing applications. In this study, a comprehensive investigation into the fatigue behaviour of WA-DED-fabricated AZ31 Mg alloy has been carried out and compared to commercially available wrought AZ31 alloy. Our findings indicate that the as-deposited parts exhibit a lower fatigue life than wrought Mg alloy, primarily due to poor surface finish, tensile residual stress, porosity, and coarse grain microstructure inherent in the WA-DED process. Low Plasticity Burnishing (LPB) treatment is applied to mitigate these issues, which induce significant plastic deformation on the surface. This treatment resulted in a remarkable improvement of fatigue life by 42%, accompanied by a reduction in surface roughness, grain refinement and enhancement of compressive residual stress levels. Furthermore, during cyclic deformation, WA-DED specimens exhibited higher plasticity and dislocation density compared to both wrought and WA-DED + LPB specimens. A higher fraction of Low Angle Grain Boundaries (LAGBs) in WA-DED specimens contributed to multiple crack initiation sites and convoluted crack paths, ultimately leading to premature failure. In contrast, wrought and WA-DED + LPB specimens displayed a higher percentage of High Angle Grain Boundaries (HAGBs), which hindered dislocation movement and resulted in fewer crack initiation sites and less complex crack paths, thereby extending fatigue life. These findings underscore the effectiveness of LPB as a post-processing technique to enhance the fatigue performance of WA-DED-fabricated AZ31 Mg alloy components. Our study highlights the importance of LPB surface treatment on AZ31 Mg components produced by CMT-WA-DED to remove surface defects, enabling their widespread use in load-bearing applications. © 2024Item Sequential hybridisation of wire and powder-based additive manufacturing of Inconel 718: Mechanical and microstructural characterization(Elsevier Ltd, 2024) Mudakavi, D.; B Sreesha, R.; Thanumoorthy, R.S.; Anar, S.; Krishnan R, A.; Suryakumar, S.; Bontha, S.; M Adinarayanappa, S.The present study combines the Wire-based DED (W-DED) and Powder-based DED (P-DED) to achieve a high deposition rate and higher feature resolution, respectively, within the single component. The research puts forward a novel Wire-Power (WP) Hybrid DED process, which is realized by sequential deposition of feedstock in Wire and then in Powder form. Based on the deposition-extraction combination, three sample configurations, C1 (Y-X), C2 (X-X) and C3 (Y-Z), were fabricated and characterized for the mechanical properties and microstructural aspects. OM images revealed defect-free P-DED and W-DED interface, while the EBSD analysis showed grain size variations owing to differences in the cooling rates. The Ultimate Tensile Strength (UTS) values of C1 and C2 configurations are about 132.2 and 139.7 % higher in comparison to C3. Low cycle fatigue results showed that the C2 sustained a higher number of completely reversed cycles to failure in comparison to the other configurations. The impact energy absorbed by C3 is the highest, affirming the strong W–P interface. © 2024 Elsevier B.V.Item 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.Item Effect of burnishing strategies on surface integrity, microstructure and corrosion performance of wire arc additively manufactured AZ31 Mg alloy(KeAi Publishing Communications Ltd., 2025) Manjhi, S.K.; R, O.; Bontha, S.; Balan, A.S.S.AZ31 Mg alloy is an emerging material that has received considerable attention in aerospace, automotive, and temporary biodegradable implant applications owing to its attractive properties, such as low density, high specific strength, and biodegradability. Nevertheless, some shortcomings in Mg alloys are their low ductility, which is associated with challenging its manufacturing, and poor corrosion resistance associated with unreliable components. Therefore, a cold metal transfer wire arc additive manufacturing (CMT-WAAM) process is used to manufacture AZ31 Mg alloy and achieved 29.4 % ductility by controlling the gas porosity, keyhole porosity, and internal cracks. Further, severe plastic deformation is induced on the surface of deposited parts by low plasticity burnishing (LPB) with parallel and cross-pattern burnishing to modulate their surface to slow down the kinetics of the corrosion damage. The average surface roughness (Sa) of the cross-burnishing pattern is 0.235 ?m, which is 123.6 % lower than the parallel burnished and 261.7 % lower than the milled specimens. The residual stress (RS) of WAAM is 40 MPa with a tensile nature; however, it is drastically reduced and develops compressive RS of 45 MPa under a parallel burnishing pattern and 62 MPa under a cross-burnishing pattern. Moreover, LPB with cross pattern deformed ?395 ?m depth of WAAMed AZ31 workpiece, which is ?45 % higher than deformed depth (?272 ?m) by parallel pattern burnishing. The electrochemical corrosion rate of the WAAM specimen is 9.71 mm/year, and it is reduced to 1.82 mm/year under LPB caused by compressive residual stress and grain refinement. © 2024 The Authors