| 1. |
- Sreekanth, Suhas, et al.
(author)
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Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718
- 2020
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In: Metals. - : MDPI AG. - 2075-4701. ; 10:1, s. 01-16
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Journal article (peer-reviewed)abstract
- The effect of three important process parameters, namely laser power, scanning speed and laser stand-off distance on the deposit geometry, microstructure and segregation characteristics in direct energy deposited alloy 718 specimens has been studied. Laser power and laser stand-off distance were found to notably affect the width and depth of the deposit, while the scanning speed influenced the deposit height. An increase in specific energy conditions (between 0.5 J/mm2 and 1.0 J/mm2) increased the total area of deposit yielding varied grain morphologies and precipitation behaviors which were comprehensively analyzed. A deposit comprising three distinct zones, namely the top, middle and bottom regions, categorized based on the distinct microstructural features formed on account of variation in local solidification conditions. Nb-rich eutectics preferentially segregated in the top region of the deposit (5.4–9.6% area fraction, Af) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5–5.7% Af) and the bottom regions (2.6–4.5% Af), where columnar dendritic morphology was observed. High scan speed was more effective in reducing the area fraction of Nb-rich phases in the top and middle regions of the deposit. The <100> crystallographic direction was observed to be the preferred growth direction of columnar grains while equiaxed grains had a random orientation.
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| 2. |
- Sreekanth, Suhas, et al.
(author)
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Effect of process parameters and heat treatments on delta-phase precipitation in directed energy deposited alloy 718
- 2022
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In: Welding in the World. - : Springer. - 0043-2288 .- 1878-6669.
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Journal article (peer-reviewed)abstract
- This article outlines a detailed study of solution treatments and delta precipitation treatments carried out on laser-directed energy deposited (DED) alloy 718 specimens. Two different sets of DED process parameters were used in high and low energy conditions that yield different microstructural features to study the effect of process parameters on delta precipitation. These two conditions were subjected to solution treatment at 1010 °C and 1050 °C each for 1 h, which improved homogeneity and altered grain texture with introduction of annealing twins. The as-built and solution-treated specimens served as the initial reference condition for subsequent delta processing treatments (DPT) performed at three temperatures of 850 °C, 900 °C, and 950 °C to study the effect of short- and long-term exposures ranging from 1 to 48 h. When as-built specimens were subjected to DPT, interdendritic delta precipitates were observed at Nb-rich regions. In contrast, solution-treated specimens under short-term exposure to DPT resulted in intergranular delta phase precipitates whereas under long-term exposures to DPT yielded predominantly intragranular delta precipitates, which grew denser and longer with increased time of treatment. For longer exposure times of 24 and 48 h, a continuous film of intergranular delta phase was noticed. The morphology, location, and volume fraction of delta phase precipitates studied in this research are imperative for designing the performance of alloy 718 built by DED process.
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| 3. |
- Sreekanth, Suhas, et al.
(author)
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Influence of laser-directed energy deposition process parameters and thermal post-treatments on Nb-rich secondary phases in single-track Alloy 718 specimens
- 2021
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In: Journal of laser applications. - : Laser Institute of America. - 1042-346X .- 1938-1387. ; 33:2, s. 1-13
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Journal article (peer-reviewed)abstract
- In this article, process parameters such as laser power, deposition speed, and powder feed rate are varied at three levels, and their effect on geometrical characteristics and microstructural features of laser-direct energy deposited single-track Alloy 718 specimens is analyzed. Furthermore, the influence of standard heat treatments recommended for wrought form of Alloy 718 is investigated on as-built deposits. The main aim of the research is to curtail the amount of secondary Nb-rich precipitates such as Laves and NbCs either during the process or by subsequent heat treatments. The volume fraction analysis of Nb-rich phases shows that processing at high laser power conditions is ideal for minimizing segregation. Upon subjecting as-built deposits to (i) solution treatment, (ii) solution treatment and aging, and (iii) direct aging, a difference in volume fraction of Nb-rich phases is noticed compared to the as-built condition. Characterization of size, morphology, phase constitution through volume fraction estimation, and elemental concentrations employing electron dispersive spectroscopy analysis indicates dissolution of Nb-rich phases when subjected to heat treatments. The delta phase precipitation preferentially occurs in the top and bottom regions and sparsely in the middle region of the specimens subjected to solution heat treatment. In case of specimens subjected to direct aging (718 °C/8 h and 621 °C/8 h), delta phase is not discernable, indicating that a higher temperature (>900 °C) treatment may be necessary for delta precipitation and growth
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| 4. |
- Aryal, Pradip, et al.
(author)
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Effect of Substrate Orientation on Melt Pool during Multi-Layer Deposition in V-Groove with Gas Metal Arc
- 2021
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In: Proceedings of the World Congress on Mechanical, Chemical, and Material Engineering. - : Avestia Publishing. - 2369-8136. - 9781927877616
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Conference paper (peer-reviewed)abstract
- Thermo-fluid dynamic and experimental approaches are used to investigate the influence of 20° uphill, downhill and sideway substrate orientation during metal deposition over a previously deposited bead in a V-groove. The computational fluid dynamic model with free surface deformation and metal transfer gives insight into the melt pool flow and causes of defect formation observed on the solidified beads. The experimental metallographs, high-speed images and computational results show good agreement. It is found that the deposition of a second layer on a smooth first layer cooled down to room temperature leads to large changes in melt pool flow pattern at 20° substrate inclination compared to flat condition. It results in undercut and humps with the uphill orientation and undercut with the side inclination. Therefore, lower angle range is necessary for multilayer gas metal arc deposition for these two last configurations.
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| 5. |
- Baghdadchi, Amir, 1994-, et al.
(author)
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Promoting austenite formation in laser welding of duplex stainless steel-impact of shielding gas and laser reheating
- 2021
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In: Welding in the World. - : Springer Science and Business Media LLC. - 0043-2288 .- 1878-6669. ; 65, s. 499-511
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Journal article (peer-reviewed)abstract
- Avoiding low austenite fractions and nitride formation are major challenges in laser welding of duplex stainless steels (DSS). The present research aims at investigating efficient means of promoting austenite formation during autogenous laser welding of DSS without sacrificing productivity. In this study, effects of shielding gas and laser reheating were investigated in welding of 1.5-mm-thick FDX 27 (UNS S82031) DSS. Four conditions were investigated: Ar-shielded welding, N2-shielded welding, Ar-shielded welding followed by Ar-shielded laser reheating, and N2-shielded welding followed by N2-shielded laser reheating. Optical microscopy, thermodynamic calculations, and Gleeble heat treatment were performed to study the evolution of microstructure and chemical composition. The austenite fraction was 22% for Ar-shielded and 39% for N2-shielded as-welded conditions. Interestingly, laser reheating did not significantly affect the austenite fraction for Ar shielding, while the austenite fraction increased to 57% for N2-shielding. The amount of nitrides was lower in N2-shielded samples compared to in Ar-shielded samples. The same trends were also observed in the heat-affected zone. The nitrogen content of weld metals, evaluated from calculated equilibrium phase diagrams and austenite fractions after Gleeble equilibrating heat treatments at 1100 °C, was 0.16% for N2-shielded and 0.11% for Ar-shielded welds, confirming the importance of nitrogen for promoting the austenite formation during welding and especially reheating. Finally, it is recommended that combining welding with pure nitrogen as shielding gas and a laser reheating pass can significantly improve austenite formation and reduce nitride formation in DSS laser welds. © 2020, The Author(s).
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| 6. |
- Christiansson, Anna-Karin, 1947-, et al.
(author)
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Automation of a robotised metal deposition system using laser melting of wire
- 2008
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In: 18th International Conference on<em> </em>Flexible Automation and Intelligent Manufacturing (FAIM 2008). - 9789163327575 ; , s. 122-129
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Conference paper (other academic/artistic)abstract
- This paper presents a system for full automation of free-form-fabrication of fully dense metal structures using robotized laser melting of wire. The structure is built of beads of melted wire laid side by side and layer upon layer governed by synchronized robot motion. By full automation is here meant that the process starts with a product specification of a component, and ends in a geometrically validated dense metal component fulfilling industrial material requirements. Due to the complexity of this flexible manufacturing system, a number of different disciplines are involved. This paper discusses mainly the system design, which includes how off-line programming is used for automatic generation of code and how feedback control is used for on-line adjustment of parameters based on desired building properties. To meet industrial needs, the project is carried out in a close cooperation between research and development activities in academy and industry.
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| 7. |
- Dahat, Shubham, 1996-, et al.
(author)
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A Methodology to Parameterize Wire + Arc Additive Manufacturing : A Case Study for Wall Quality Analysis
- 2020
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In: Journal of Manufacturing and Materials Processing. - : MDPI. - 2504-4494. ; 4:1
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Journal article (peer-reviewed)abstract
- The objective of this work was the development of a methodology to parametrize wire + arc additive manufacturing (WAAM), aiming dimension repeatability, and tolerances. Parametrization of WAAM is a difficult task, because multiple parameters are involved and parameters are inter-dependent on each other, making overall process complex. An approach to study WAAM would be through operational maps. The choice of current (Im) and travel speed (TS) for the desirable layer width (LW) determines a parametrization that leads to either more material or less material to be removed in post-operations, which is case study chosen for this work. The work development had four stages. First stage, named ‘mock design’, had the objective of visualizing the expected map and reduce further number of experiments. At the second stage, ‘pre-requisite for realistic operational map’, the objective was to determine the operating limits of TS and Im with the chosen consumables and equipment. Within the ‘realistic operational map’ stage, a design for the experiments was applied to cover a parametric area (working envelope) already defined in the previous stage and long and tall walls were additively manufactured. Actual values of LW (external and effective layer width) were measured and an actual operating envelope was reached. According to the geometry-oriented case study, a surface waviness index (SWindex) was defined, determined, and overlapped in the envelope. It was observed that the walls with parameters near the travel speed limits presented higher SWindex. This operational map was further validated (fourth stage) by selecting a target LW and finding corresponding three parametric set (covering the whole range of operational map) to produce walls on which geometry characterization was carried out. After geometry characterization, obtained LW was compared with the target LW (the maximum values were very tied, with deviations from +0.3 to 0.5 mm), with a SWindex deviation at the order of 0.05. Both results evidence high reproductivity of the process, validating the proposed methodology to parametrize WAAM.
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| 8. |
- Devotta, Ashwin Moris, 1984-, et al.
(author)
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A modified Johnson-Cook model for ferritic-pearlitic steel in dynamic strain aging regime
- 2019
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In: Metals. - : MDPI. - 2075-4701. ; 9:5
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Journal article (peer-reviewed)abstract
- In this study, the flow stress behavior of ferritic-pearlitic steel (C45E steel) is investigated through isothermal compression testing at different strain rates (1 s-1, 5 s-1, and 60 s-1) and temperatures ranging from 200 to 700 °C. The stress-strain curves obtained from experimental testing were post-processed to obtain true stress-true plastic strain curves. To fit the experimental data to well-known material models, Johnson-Cook (J-C) model was investigated and found to have a poor fit. Analysis of the flow stress as a function of temperature and strain rate showed that among other deformation mechanisms dynamic strain aging mechanism was active between the temperature range 200 and 400 °C for varying strain rates and J-C model is unable to capture this phenomenon. This lead to the need to modify the J-C model for the material under investigation. Therefore, the original J-C model parameters A, B and n are modified using the polynomial equation to capture its dependence on temperature and strain rate. The results show the ability of the modified J-C model to describe the flow behavior satisfactorily while dynamic strain aging was operative. © 2019 by the authors. Licensee MDPI, Basel, Switzerland.
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| 9. |
- Hanning, Fabian, et al.
(author)
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Measurement of the thermal cycle in the base metal heat affected zone of cast ATI ® 718Plus TM during manual multi-pass TIG welding
- 2018
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In: Procedia Manufacturing. - : Elsevier BV. - 2351-9789. ; 25, s. 443-449
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Journal article (peer-reviewed)abstract
- This paper presents a method to acquire thermal data in the base metal heat affected zone (HAZ) during manual multi-pass TIG welding of ATI ® 718Plus TM , representing conditions close to an actual repair welding operation. Thermocouples were mounted in different locations along side walls of linear grooves to record temperature data. The thermal cycling was found to be largely independent of location within the HAZ. The recorded temperatures were below the incipient laves melting temperature, indicating that the current test setup requires optimisation to study HAZ liquation. Based on the results of this study, a modified thermocouple mounting technique is proposed. © 2018 Elsevier B.V. All rights reserved.
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| 10. |
- Harati, Ebrahim, 1986-, et al.
(author)
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Effect of HFMI treatment procedure on weld toe geometry and fatigue properties of high strength steel welds
- 2016
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In: Procedia Structural Integrity. - : Elsevier. - 2452-3216. ; 2, s. 3483-3490
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Journal article (peer-reviewed)abstract
- The effects of high frequency mechanical impact (HFMI) treatment procedure on the weld toe geometry and fatigue strength in 1300 MPa yield strength steel welds were investigated. In this regard first the effect of three or six run treatments on the weld toe geometry was evaluated. The fatigue strength and weld toe geometry of as-welded and HFMI treated samples was then compared. Fatigue testing was done under fully reversed, constant amplitude bending load. When increasing the number of treatment runs from three to six, the weld toe radius and width of treatment remained almost constant. However, a slightly smaller depth of treatment in the base metal and a somewhat larger depth of treatment in the weld metal was observed. HFMI treatment increased the fatigue strength by 26%. The treatment did not increase the weld toe radius significantly, but resulted in a more uniform weld toe geometry along the weld. A depth of treatment in the base metal in the range of 0.15-0.19 mm and a width of treatment in the range of 2.5-3 mm, were achieved. It is concluded that the three run treatment would be a more economical option than the six run treatment providing a similar or even more favourable geometry modification.
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