Faculty Publications
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Item Influence of wire-electric discharge machining process parameters on surface integrity of Ni-rich Ni-Ti-Hf alloys(Institute of Physics, 2023) Balaji, V.; Narendranath, S.Ni-Ti-Hf Shape memory alloys (SMAs) have shown promising results in high-temperature applications in aviation, space and energy exploration, actuators, etc. In the past decade, extensive work has been carried out to understand the behavior of High-Temperature SMAs (HTSMAs). NiTi-based SMAs are grouped as hard-to-machine materials, and machining these materials through traditional methods leads to high tool wear, dimensional inaccuracy, degradation of Shape Memory properties, etc. Therefore, Non-Conventional machining processes are a better choice for machining these alloys. It is evident from previous studies that Wire Electric Discharge Machining (WEDM) yields better results compared to other processes. The current study investigates the effect of WEDM input variables such as servo gap voltage (SV), spark-ON duration (TON), wire electrode feed rate (WF), and spark-OFF duration (TOFF) on the machining of Ni-Ti-Hf HTMSAs. The surface integrity of the machined samples was analyzed by investigating characteristics like machined surface morphology, machined surface quality, subsurface microhardness, and recast layer thickness. TON emerged as the most critical parameter for surface roughness and Material Removal Rate. Various defects like micro-cracks, micro-pores, craters, and globules were found on the machined surfaces, and approximately 30% harder surface was found near the machined region. The average thickness of the recast layer observed for Hf-15 and Hf-20 samples was around 12 μm and 50 μm for samples with lower and higher discharge energies, respectively. © 2023 IOP Publishing Ltd.Item Microstructural evolution and cyclic oxidation behavior of HVOF-sprayed NiCrSi and NiCrC coatings on T11 steel(Elsevier Inc., 2024) Medabalimi, S.; Hebbale, A.M.; Singh, R.; Desai, V.; Ramesh, M.R.This study analyzes NiCrSi and NiCrC coatings developed on low alloy ferritic stainless steel (grade T11) through the HVOF spraying technique. The coatings were characterized by their phase constitution, microstructure, cyclic oxidation behavior, and hardness. X-ray diffraction (XRD) analysis confirmed the presence of the NiCr solid solution matrix as the primary phase in both coatings. Moreover, the microstructure of the NiCrSi coating included the hard intermetallic compounds like Cr?Si and Ni?Si and the NiCrC coating contained the hard phases like Cr?C? and Ni?C which improved the hardness and the wear resistance of the coatings. Microhardness measurements revealed that the coatings had an average hardness of 300 ± 50 HV, significantly greater than the substrate hardness of 225 ± 25 HV. Cyclic oxidation tests were carried out at 700 °C revealed that both the coatings showed a lower weight gain than the uncoated substrate, suggesting enhanced oxidation resistance. This was because the protective oxide layers like Cr?O? and SiO? in the NiCrSi coating and Cr?O? and NiO in the NiCrC coating were formed. X-ray analysis establish ed. the presence of these oxides, which inhibited oxygen penetration through the coatings and provided additional protection against oxidation. Therefore, the study revealed that both NiCrSi and NiCrC coatings have good mechanical and oxidation resistance properties, which make them suitable for high-temperature applications where there is a need for improved durability, wear resistance, and protection against oxidation. © 2024Item Machining Parameter Optimization of Wire Electrical Discharge Machining for Ni50.3Ti29.7Hf20 Alloy Using TOPSIS and Grey Wolf Optimization Technique(Springer, 2025) Bhaskar, M.; Balaji, V.; Narendranath, S.; Sahu, R.K.Ni50.3Ti29.7Hf20 is an alloy with shape memory characteristics that can withstand high temperatures. It possesses remarkable strength, hardness, and exceptional corrosion resistance. SMAs are well-suited for various applications, including automotive sensors, automobiles, aerospace technologies, robotics, actuators, and MEMS devices. However, its unique properties make it difficult to machine using conventional methods. Wire EDM is an unconventional machining process suited for difficult-to-machine materials like Ni-Ti-Hf alloy, providing high accuracy and precision and minimizing the risk of material damage. This paper focuses on the optimization of machining parameters, namely Discharge time (PON), Pause time (POFF), Gap voltage (GV), and Wire travel speed (WS) during WEDM of Ni-Ti-Hf shape memory alloy utilizing the TOPSIS and GWO techniques. The aim is to obtain optimal machining parameters for improving the machined Ni-Ti-Hf alloy’s material removal rate (MRR) and surface roughness (Ra). The optimal machining parameters from GWO were PON = 123.8 µs, POFF = 50 µs, WS = 2, and GV = 25. The predicted values of material removal rate and surface roughness are 4.22 mm3/min and 3.62 µm, respectively. The experimental verification demonstrates the proposed optimization approach's effectiveness, as the predicted values correlate strongly with the actual values. © ASM International 2023.Item Effect of process variables on heat transfer and the product quality during layer deposition of Al4043 alloy by wire arc additive manufacturing(John Wiley and Sons Inc, 2025) Raghavendra Pai, K.; Vijayan, V.; Samuel, A.; Prabhu, K.N.In the present work, heat transfer dynamics between the substrate and the deposited metal is investigated to assess its effect on the evolution of defects and the quality of the product. A series of experiments involving the deposition of Al4043 wire were conducted on Al4043 aluminum alloy substrate at a voltage range of 13–19 V. A one-dimensional inverse computational model was adopted to estimate the heat flux transients. The metal/substrate interfacial heat flux was correlated with the microstructure evolution during the solidification of the metal. The experimental results clearly indicated that heat transfer plays a dominant role in the final finish and quality of the product and is controlled by variables, such as voltage, gas flow rate (GFR), wire feed rate (WFR), and forward traversal speed. At an integral heat flow (HF) in the range of 3000–5000 kJ/m2 corresponding to voltages between 13.8 and 14.5 V, argon GFR of 12–15 L/min, and a WFR of 4.1 mm/min, the porosity in the additively manufactured component was found to be minimum. The ultimate tensile strength was found to be 65 and 76 MPa, corresponding to the voltage of 13.5 and 14.5 V, respectively, and decreased to 25 MPa for a higher voltage of 19 V. At the GFR range of 8–10 L/min, the HF was in the range of 450–510 kJ/m2 with increased porosity (33%–42%). Porosity was found to decrease (15%–22%) with 12–15 L/min range of GFR and the corresponding HF was in the range of 700–950 kJ/m2. The specimens fabricated under these optimal parameters exhibited superior mechanical properties. © 2024 Wiley Periodicals LLC.Item Process parametric and performance characteristics study of WED machined Ni-Ti-Hf high-temperature shape memory alloys: an experimental and artificial intelligence approach(Institute of Physics, 2025) Balaji, V.; Sahu, R.K.; Narendranath, S.In recent years, to meet the shortcomings of the conventional machining of Ni-Ti-Hf shape memory alloy (SMA), Wire Electric Discharge Machining (WEDM) as one of the unconventional machining methods, has emerged as the preferred method for processing SMAs. Therefore, in this study, according to the Response Surface Methodology-based Central Composite Design layout, WED machining of Ni-Ti-Hf SMA is carried out using the control parameters like spark time (SON), spark pause time (SOFF), gap voltage (Vg), and dielectric flow rate (FDL). A General Regression Neural Network (GRNN) model was used to predict the critical WEDM responses: material removal rate (MRR), surface roughness (Ra), and kerf width (KW). The GRNN model closely agrees with the experimental WEDM responses, resulting in a Mean Absolute Percentage Error below 2%. Field Emission Scanning Electron Microscopy result revealed a recast layer thickness of 10.64 ± 2.06 µm and 38.19 ± 9.55 µm for the samples with the lowest surface roughness (Ra) and highest MRR, respectively. The shape recovery test result shows a less than 4% reduction in recovery ratio post-WEDM. Further, electrochemical corrosion studies revealed that owing to these surface defects, the corrosion rate increased with higher discharge energy. The corrosion rate of the base material, low Ra sample, and high MRR sample were 0.0013 mm yr?1, 0.0128 mm yr?1, and 0.0334 mm yr?1, respectively. © 2025 IOP Publishing Ltd. All rights, including for text and data mining, AI training, and similar technologies, are reserved.Item Microstructure, Mechanical, and Dry Sliding Wear Performance of Equimolar CoCrNiTiMo and CoCrNiTiW High-Entropy Alloy Coatings(Springer, 2025) Addepalli, S.N.; Joladarashi, S.; Ramesh, M.R.In the present investigation, mechanical alloyed CoCrNiTiMo and CoCrNiTiW equimolar HEA powders were employed as feedstock in the development of dense coatings using high-velocity oxy-fuel technique. The dry sliding wear behavior of uncoated substrate and high-entropy alloy (HEA) coatings were extensively investigated at different temperatures and loads using a pin-on-disk tribometer. The microstructures and phases of the mechanical alloyed powders, deposited coatings, and worn surfaces were thoroughly studied. The mechanical alloyed CoCrNiTiMo and CoCrNiTiW HEAs demonstrated the evolution of two BCC solid solutions. However, the deposited coatings reported the formation of additional phases, including Co3Ti intermetallic and NiTiO3 spinel. The microstructural analysis of CoCrNiTiMo and CoCrNiTiW coatings unveiled a compact lamellar structure characterized by robust mechanical interlocking to the substrate. The CoCrNiTiMo and CoCrNiTiW HEA coatings displayed porosities of 1.12 ± 0.05% and 1.39 ± 0.03%, respectively. Additionally, the microhardness assessments revealed superior values for CoCrNiTiMo and CoCrNiTiW HEA coatings, measuring at 927 ± 45 HV0.3 and 951 ± 38 HV0.3, correspondingly. The wear rate of CoCrNiTiMo HEA coating dropped by 70.5%, from 17.34 ± 2.8 × 10?6 mm3/N-m to 5.1 ± 1.6 × 10?6 mm3/N-m with an increment in the wear testing temperature from ambient to 600 °C. Concurrently, the CoCrNiTiW coating experienced a 76.3% drop in the wear rates from 15.8 ± 3.7 × 10?6 mm3/N-m to 3.73 ± 2.1 × 10?6 mm3/N-m. The significant fall in the wear rates at higher temperatures was accredited to the development of oxide tribofilms. CoCrNiTiMo exhibited discernible oxide phases, including CoMoO4, TiO2, and NiO. In contrast, its counterpart, CoCrNiTiW, generated WO3, CoWO4, and TiO2 oxides at a temperature of 600 °C. The adhesive wear at RT transitioned to predominant oxidative wear with slight fatigue and abrasive wear at high temperatures. © ASM International 2025.