| 1. |
- Mahade, Satyapal, 1987-, et al.
(författare)
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Incorporation of graphene nano platelets in suspension plasma sprayed alumina coatings for improved tribological properties
- 2021
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Ingår i: Applied Surface Science. - : Elsevier BV. - 0169-4332 .- 1873-5584. ; 570
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Tidskriftsartikel (refereegranskat)abstract
- Graphene possesses high fracture toughness and excellent lubrication properties, which can be exploited to enhance tribological performance of coating systems utilized to combat wear. In this work, suspension plasma spray (SPS) process was employed to deposit a composite, graphene nano-platelets (GNP) incorporated alumina coating. For comparison, monolithic alumina was also deposited utilizing identical spray conditions. The as-deposited coatings were characterized in detail for their microstructure, porosity content, hardness, fracture toughness and phase composition. Raman analysis of the as-deposited composite coating confirmed retention of GNP. The composite coating also showed good microstructural integrity, comparable porosity, higher fracture toughness and similar alumina phase composition as the monolithic alumina coating. The as-deposited coatings were subjected to dry sliding wear tests. The GNP incorporated composite coating showed lower CoF and lower specific wear rate than the pure alumina coating. Additionally, the counter surface also showed a lower wear rate in case of the composite coating. Post-wear analysis performed by SEM/EDS showed differences in the coating wear track and in the ball wear track of monolithic and composite coatings. Furthermore, Raman analysis in the wear track of composite coating confirmed the presence of GNP. The micro-indentation and wear test results indicate that the presence of GNP in the composite coating aided in improving fracture toughness, lowering CoF and specific wear rate compared to the monolithic coating. Results from this work demonstrated retention of GNP in an SPS processed coating, which can be further exploited to design superior wear-resistant coatings.
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| 2. |
- Goel, Sneha, 1993-, et al.
(författare)
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Effect of post-treatments under hot isostatic pressure on microstructural characteristics of EBM-built Alloy 718
- 2019
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Ingår i: Additive Manufacturing. - : Elsevier BV. - 2214-8604 .- 2214-7810. ; 28, s. 727-737
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam melting (EBM) has emerged as an important additive manufacturing technique. In this study, Alloy 718 produced by EBM was investigated in as-built and post-treated conditions for microstructural characteristics and hardness. The post-treatments investigated were hot isostatic pressing (HIP) and combined HIP + heat treatment (HIP + HT) carried out as a single cycle inside the HIP vessel. Both the post-treatments resulted in significant decrease in defects inevitably present in the as-built material. The columnar grain structure of the as-built material was found to be maintained after post-treatment, with some sporadic localized grain coarsening noted. Although HIP led to complete dissolution of δ and γ′′ phase, stable NbC and TiN (occasionally present) particles were observed in the post-treated specimens. Significant precipitation of γ′′ phase was observed after HIP + HT, which was attributed to the two-step aging heat treatment carried out during HIP + HT. The presence of γ′′ phase or otherwise was correlated to the hardness of the material. While the HIP treatment resulted in drop in hardness, HIP + HT led to ‘recovery’ of the hardness to values exceeding those exhibited by the as-built material.
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| 3. |
- Goel, Sneha, 1993-, et al.
(författare)
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The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718
- 2018
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Ingår i: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives. - Cham : Springer. - 2367-1696 .- 2367-1181. - 9783319894799 - 9783319894805 ; , s. 115-129
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Konferensbidrag (refereegranskat)abstract
- Additive manufacturing (AM) of Ni-based superalloys such as Alloy 718 may obviate the need for difficult machining and welding operations associated with geometrically intricate parts, thus potentially expanding design possibilities and facilitating cost-effective manufacture of complex components. However, processing AM builds completely free from defects, which may impair mechanical properties such as fatigue and ductility, is challenging. Anisotropic properties, microstructural heterogeneities and local formation of undesired phases are additional concerns that have motivated post-treatment of AM builds. This work investigates the microstructural changes associated with post-treatment of Alloy 718 specimens produced by Electron Beam Melting (EBM) for as-built microstructures at 3 build heights: near base plate, in the middle of build and near the top of the build. Two different post-treatment conditions, hot isostatic pressing (HIP) alone and a combined HIP with solutionising and two-step aging were examined and compared to the results for the as-built condition. The influence of various post-treatments on minor phase distributions (δ, γ″, carbides), overall porosity, longitudinal grain widths and Vickers microhardness was considered. The HIP treatment led to significant reduction in overall porosity and dissolution of δ phase, which led to appreciable grain growth for both post-treatment conditions. The variation in hardness noted as a function of build height for the as-built specimens was eliminated after post-treatment. Overall, the hardness was found to decrease after HIP and increase after the full HIP, solutionising and aging treatment, which was attributed to dissolution of γ″ during HIP and its re-precipitation in subsequent heat treatment steps.
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| 4. |
- Ganvir, Ashish, 1991-, et al.
(författare)
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Novel utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings
- 2021
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Ingår i: Journal of Materials Processing Technology. - : Elsevier BV. - 0924-0136 .- 1873-4774. ; 295
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Tidskriftsartikel (refereegranskat)abstract
- The ability to axially inject liquid feedstock has encouraged the thermal spray research community to explore this concept to deposit coatings for various next generation functional applications. The current study explores the utilization of liquid feedstock in high velocity air fuel (HVAF) spraying to deposit solid lubricant reinforced wear resistant coatings for the first time. The study successfully demonstrates the use of a powder-suspension hybrid processing approach to incorporate a solid lubricant Boron Nitride (as suspension) in a wear resistant Cr3C2–NiCr (as powder) cermet matrix. Coatings were characterized using Scanning Electron Microscopy and Raman Spectroscopy to analyze their microstructure and phase constitution. The results show that the tribological performance of the hexagonal boron nitride (hBN)-incorporated composite coating was significantly better than the traditional powder-derived Cr3C2–NiCr coating. Such hBN-incorporated composite coatings are needed to improve the mechanical properties and enhance the overall tribological performance of metallic components used in various applications, especially at high temperature such as cylinder bore, pistons, deformation tools, etc. The limitations of liquid based lubricants at high temperature motivates the use of hBN reinforced composite coatings as it can form a protective solid lubrication tribo-film. The study concludes that the emerging HVAF technology can accommodate liquid feedstock and be successfully utilized to deposit hybrid powder-suspension composite coatings to create multi length scale microstructures which can be attractive for combining different tribological attributes in the same coatings system.
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| 5. |
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| 6. |
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| 7. |
- Bhardwaj, Sanjay, et al.
(författare)
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Technology Commercialization by Micro, Small and Medium Enterprises (MSMEs) in Indian Context : Challenges and Governmental Support Systems
- 2013
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Ingår i: Indian Journal of Economics and Business. - 0972-5784. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- Post-liberalization, level of protection imparted by Indian government to Micro, Small and Medium Enterprises (MSMEs) is gradually reducing. In the changed scenario, MSMEs need to complete with large companies, both Indian and foreign, with cost-competitive and good quality products. Due to limited resources available with MSMEs, they find it difficult to develop internal technologies and hence need to access technologies developed elsewhere. Technologies developed by public funded Research and Technology Organizations (RTOs) can support MSMEs. However, MSMEs should develop competence to commercialize technologies procured from public-funded RTOs, and also utilize available governmental support to meet the emerging challenges. This paper discusses the challenges and governmental support systems for technology commercialization, with relevant examples, from Indian MSMEs’ perspective.
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| 8. |
- Goel, Sneha, 1993-, et al.
(författare)
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Residual stress determination by neutron diffraction in powder bed fusion-built Alloy 718: Influence of process parameters and post-treatment
- 2020
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Ingår i: Materials and Design. - : Elsevier BV. - 1873-4197 .- 0264-1275. ; 195
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Tidskriftsartikel (refereegranskat)abstract
- Alloy 718 is a nickel-based superalloy that is widely used as a structural material for high-temperature applications. One concern that arises when Alloy 718 is manufactured using powder bed fusion (PBF) is that residual stresses appear due to the high thermal gradients. These residual stresses can be detrimental as they can degrade mechanical properties and distort components. In this work, residual stresses in PBF built Alloy 718, using both electron and laser energy sources, were measured by neutron diffraction. The effects of process parameters and thermal post-treatments were studied. The results show that thermal post-treatments effectively reduce the residual stresses present in the material. Moreover, the material built with laser based PBF showed a higher residual stress compared to the material built with electron-beam based PBF. The scanning strategy with the lower amount of residual stresses in case of laser based PBF was the chessboard strategy compared to the bi-directional raster strategy. In addition, the influence of measured and calculated lattice spacing (d0) on the evaluated residual stresses was investigated.
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| 9. |
- Goel, Sneha, 1993-, et al.
(författare)
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Can Appropriate Thermal Post-Treatment Make Defect Content in as-Built Electron Beam Additively Manufactured Alloy 718 Irrelevant?
- 2020
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Ingår i: Materials. - : MDPI AG. - 1996-1944. ; 13:3
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam melting (EBM) is gaining rapid popularity for production of complex customized parts. For strategic applications involving materials like superalloys (e.g., Alloy 718), post-treatments including hot isostatic pressing (HIPing) to eliminate defects, and solutionizing and aging to achieve the desired phase constitution are often practiced. The present study specifically explores the ability of the combination of the above post-treatments to render the as-built defect content in EBM Alloy 718 irrelevant. Results show that HIPing can reduce defect content from as high as 17% in as-built samples (intentionally generated employing increased processing speeds in this illustrative proof-of-concept study) to <0.3%, with the small amount of remnant defects being mainly associated with oxide inclusions. The subsequent solution and aging treatments are also found to yield virtually identical phase distribution and hardness values in samples with vastly varying as-built defect contents. This can have considerable implications in contributing to minimizing elaborate process optimization efforts as well as slightly enhancing production speeds to promote industrialization of EBM for applications that demand the above post-treatments.
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| 10. |
- Kumara, Chamara, et al.
(författare)
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Microstructure modelling of laser metal powder directed energy deposition of alloy 718
- 2019
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Ingår i: Additive Manufacturing. - : Elsevier. - 2214-8604 .- 2214-7810. ; 25, s. 357-364
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Tidskriftsartikel (refereegranskat)abstract
- A multi-component and multi-phase-field modelling approach, combined with transformation kinetics modelling, was used to model microstructure evolution during laser metal powder directed energy deposition of Alloy 718 and subsequent heat treatments. Experimental temperature measurements were utilised to predict microstructural evolution during successive addition of layers. Segregation of alloying elements as well as formation of Laves and δ phase was specifically modelled. The predicted elemental concentrations were then used in transformation kinetics to estimate changes in Continuous Cooling Transformation (CCT) and Time Temperature Transformation (TTT) diagrams for Alloy 718. Modelling results showed good agreement with experimentally observed phase evolution within the microstructure. The results indicate that the approach can be a valuable tool, both for improving process understanding and for process development including subsequent heat treatment.
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