Browsing by Author "Sreerag, M.P."

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High Velocity Air Fuel Spraying for Metal Additive Manufacturing - A Study on Copper
(Springer, 2024) Sreerag, M.P.; Vijay, V.A.; Varalakshmi, S.; Rajasekaran, B.
Owing to its reflectivity, Copper manufacturing has always been challenging through laser-based additive manufacturing. In this study, we demonstrate additive/bulk manufacturing of copper using high velocity air fuel (HVAF) spray technology, an emerging variant in the thermal spray family. Rapid deposition of millimeter scale copper parts with good mechanical integrity and decent ductility, comparable to that of cold spray, has been shown feasible. The mechanical properties measured along different built directions showed no significance to be considered anisotropic. Electron backscattered diffraction analysis revealed the possibility of developing favorable bimodal grain distribution with a high volume fraction of ultrafine grains (>50%). However, the intersplat porosities and continuous pores were found to be detrimental despite the low overall porosity. HVAF technology demonstrates great potential and appears to be a promising process methodology for bulk/additive manufacturing of metals with a rapid production rate. Graphical Abstract: (Figure presented.). © ASM International 2024.
High Velocity Air Fuel Spraying for Surface Restoration of Worn-out IN718
(Springer, 2025) Sreerag, M.P.; Abhijith Vijay, V.; Babu, N.N.; Ali, S.S.; Cadambi, S.; Rajasekaran, B.
This study explores the efficacy of high velocity air fuel (HVAF) spraying for repairing worn-out IN718 thrust collars used in the chemical industry. We investigated the characteristics and application potential of thick IN718 depositions for surface restoration, focusing on their adhesion. To evaluate microstructure and adhesion, approximately 2-mm-thick IN718 layers were deposited onto IN718 wrought coupons. The HVAF-sprayed layers were notably dense (99.5%) and exhibited excellent hardness, reaching 450 HV0.3, which suggests superior mechanical properties compared to the bulk material. A three-point bending test was conducted to assess the adhesion strength of these thick deposits. The results demonstrated excellent adhesion in both compressive (1281 MPa with > 2% strain) and tensile bending. Trusting in these promising substrate-layer interfacial adhesion characteristics, the investigation was extended to demonstrate the refurbishment of an actual worn-out industrial IN718 thrust collar. A 2-mm-thick IN718 deposition was applied to the entire worn area, and excess material was subsequently machined to achieve the desired surface finish for reuse. Overall, HVAF spray technology shows significant promise for developing thick metallic layers with excellent interfacial adhesion, providing a robust and viable solution for effectively refurbishing heavily worn metallic components and extending their service life. © ASM International 2025.
On the merit of solute segregation and low angle grain boundary for thermal stability and thermal expansion of cold-sprayed CuCrZr
(Elsevier Ltd, 2025) Abhijith Vijay; Sreerag, M.P.; Varalakshmi, S.; Santhy, K.; Singh, R.; Kondás, J.; Makineni, S.K.; Rajasekaran, B.
The precipitation hardenable CuCrZr alloy is a potential alternative to copper for inner liners in rocket thrust engines. Cold spray manufacturing has been seen as a promising processing route to manufacture bulk additive structure of CuCrZr. This work reveals that the cold-sprayed as-deposited Cu-Cr-Zr alloy, in its inherent non-equilibrium state. It is highly stable up to 950 °C and exhibits lower thermal expansion than the equilibrium Cu-Cr-Zr alloy, deduced using HT-XRD and Thermo-Calc. Atomic-scale compositional and diffraction analysis using Atom Probe Tomography (APT) and Electron Backscatter Diffraction (EBSD) support the Zener pinning effect of Cr segregation near the grain boundaries, along with a large fraction of low-angle grain boundaries (LAGBs), that contribute to the high thermal stability and controlled thermal expansion of the deposit. Cold spray deposition naturally yields microstructural features that are conducive to high thermal stability and controlled thermal expansion, features which are comparable to the self-organized microstructures observed in segregation engineering (SE). © 2025 Elsevier B.V.