144 research outputs found

    The use of custom beam profiles in laser deposition

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    The work presented in this thesis discovers that through the use of shaped laser beam profiles the microstructure of the deposition can be modified. It has been seen that though modifying the beam profile melt pool flow observed during the preposition process has altered. A number of problems have been identified with current laser deposition processes, typically porosity, cracking and undesired deposition profile. The work identifies that thermal profiles are a major factor influencing both the microstructure and deposition. Methods for observing and measuring thermal profiles are explored. A number of beam profiles are used in this study showing a number of effects on the thermal profiles present during the deposition on Inconel 625 onto mild steel substrate. EBSD and ESD analysis is used to examine the properties of the depositions. Further imaging and analysis of melt pool flow during the process is undertaken using high speed camera imaging, motion tracking and novel pyrometry techniques. As was expected the use of modified beam profiles had an influence on the microstructure of the depositions formed, large variations in grain size an orientation were observed along with alloy element segregation. Through the melt pool imaging techniques developed it was observed that the material transport mechanisms were modified by the shaped laser beam dramatically reducing the material transport velocity, indicating a reduced thermal gradient. This work shows that through modifying the laser beam profile factors influencing the quality of a resulting deposition can be changed. Through further work this principle can be expanded to use the laser beam profile as an input factor to allow the used design of deposition profiles

    Residual stress of as-deposited and rolled Wire + Arc Additive Manufacturing Ti–6Al–4V components

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    Wire + arc additive manufacturing components contain significant residual stresses, which manifest in distortion. High-pressure rolling was applied to each layer of a linear Ti–6Al–4V wire + arc additive manufacturing component in between deposition passes. In rolled specimens, out-of-plane distortion was more than halved; a change in the deposits' geometry due to plastic deformation was observed and process repeatability was increased. The Contour method of residual stresses measurements showed that although the specimens still exhibited tensile stresses (up to 500 MPa), their magnitude was reduced by 60%, particularly at the interface between deposit and substrate. The results were validated with neutron diffraction measurements, which were in good agreement away from the baseplate

    microstructure evolution during heat treatments

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    Funding Information: Authors acknowledge the Portuguese Fundação para a Ciência e a Tecnologia (FCT – MCTES) for its financial support via the project UID/EMS/00667/2019 (UNIDEMI). JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P., in the scope of the projects LA/P/0037/2020 , UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. Funding of CENIMAT/i3N by national funds through the FCT-Fundação para a Ciência e a Tecnologia, I.P., within the scope of Multiannual Financing of R&D Units, reference UIDB/50025/2020–2023 is also acknowledge. FWCF acknowledges Fundação para a Ciência e a Tecnologia ( FCT-MCTES ) for funding the Ph.D. Grant 2022.13870. BD. The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Beamtime was allocated for proposal I-20210986 EC. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. This activity has received funding from the European Institute of Innovation and Technology (EIT) Raw Materials through the project Smart WAAM: Microstructural Engineering and Integrated Non-Destructive Testing. YZ acknowledges the National Natural Science Foundation of China ( 51601091 ), the Natural Science Foundation of Jiangsu Province ( BK 20160826 ), the Six Talent Peaks Project of Jiangsu Province ( 2017-XCL-051 ), the Fundamental Research Funds for the Central Universities ( 30917011106 ), and Key Research and Development Plan of Jiangsu Province ( BE 2020085 ). Funding Information: Authors acknowledge the Portuguese Fundação para a Ciência e a Tecnologia (FCT – MCTES) for its financial support via the project UID/EMS/00667/2019 (UNIDEMI). JPO acknowledges funding by national funds from FCT - Fundação para a Ciência e a Tecnologia, I.P. in the scope of the projects LA/P/0037/2020, UIDP/50025/2020 and UIDB/50025/2020 of the Associate Laboratory Institute of Nanostructures, Nanomodelling and Nanofabrication – i3N. Funding of CENIMAT/i3N by national funds through the FCT-Fundação para a Ciência e a Tecnologia, I.P. within the scope of Multiannual Financing of R&D Units, reference UIDB/50025/2020–2023 is also acknowledge. FWCF acknowledges Fundação para a Ciência e a Tecnologia (FCT-MCTES) for funding the Ph.D. Grant 2022.13870. BD. The authors acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. Beamtime was allocated for proposal I-20210986 EC. The research leading to this result has been supported by the project CALIPSOplus under the Grant Agreement 730872 from the EU Framework Programme for Research and Innovation HORIZON 2020. This activity has received funding from the European Institute of Innovation and Technology (EIT) Raw Materials through the project Smart WAAM: Microstructural Engineering and Integrated Non-Destructive Testing. YZ acknowledges the National Natural Science Foundation of China (51601091), the Natural Science Foundation of Jiangsu Province (BK 20160826), the Six Talent Peaks Project of Jiangsu Province (2017-XCL-051), the Fundamental Research Funds for the Central Universities (30917011106), and Key Research and Development Plan of Jiangsu Province (BE 2020085). Publisher Copyright: © 2023 The Author(s)The study reports that the combined use of in situ interlayer hot forging and post-deposition heat treatment (PDHT) could alter the typical coarse and oriented microstructure of the Ni-based superalloy 625 obtained by arc plasma directed energy deposition (DED) to a fine and non-oriented condition. In situ synchrotron X-ray diffraction and electron backscatter diffraction showed that the high-temperature (1100 °C/ 1 h) PDHT induced significant recrystallization, leading to grain refinement and low texture index, while partially dissolving deleterious Laves and δ phases. Low-temperature (980 °C/ 1 h) PDHT had a limited effect on the grain size refinement and induced the formation of secondary phases. It is shown that conventional heat treatments applied to Ni-based superalloy 625 obtained by arc plasma DED are not conducive to optimized microstructure features. In situ hot forging induced enough crystal defects to promote static recrystallization during PDHT. Besides, high-temperature PDHT met the AMS 5662 grain size requirements.publishersversionpublishe

    Weld Cracking of Precipitation Hardening Ni-based Superalloys - Investigation of repair welding characteristics and susceptibility towards strain age cracking

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    High temperature resistance and strength requirements make nickel-based superalloys the material of choice for the hot section of aero engines. Fabrication in terms of combining wrought and cast parts in the manufacturing of hot structural components enables component optimisation via the use of wrought high-strength parts, where geometrical constraints allow, and cast parts to produce complex geometries. Such an approach requires that the materials involved are weldable. Due to the complex microstructure of precipitation hardening nickel-based superalloys, welding comes with the risk of weld cracking, more specifically solidification cracking, heat affected zone (HAZ) liquation cracking and strain age cracking (SAC). While the first two types require a liquid phase to be present, SAC occurs during heating to post-weld heat treatment, in which age-hardening reactions coincide with the relaxation of weld residual stresses. Increasing engine operating temperatures as well as the intermittent cycling of land-based gas and steam turbines motivates research on the weldability of highly temperature-stable alloys.Hence, the main objective of this work has been the investigation and analysis of microstructural changes and their effect on weldability in terms of susceptibility towards weld cracking of the nickel-based superalloys Haynes\uae\ua0282\uae and ATI 718Plus\uae. This has been addressed by the means of repair-welding studies and a simulative test approach using a Gleeble system. Microstructural changes were found to significantly affect HAZ cracking in cast ATI 718Plus\uae, where high amounts of Laves phase showed an increased resistance towards cracking. Haynes\uae 282\uae shows good weld-cracking resistance, as no HAZ cracks were present after multi-pass weld operations and subsequent post weld heat treatments. A simulative Gleeble test was developed to provide more data on ductility in the SAC temperature range and its dependence on ongoing microstructural changes during thermal exposure. Comparison with Waspaloy showed that the high resistance of Haynes\uae 282\uae towards SAC is correlated with the moderate age-hardening kinetics of the alloy and the rapid formation of a grain boundary strengthening carbide network. Furthermore, grain size was found to be a major factor affecting ductility and hence SAC susceptibility

    A comparative study of additive manufacturing techniques: Residual stress and microstructural analysis of CLAD and WAAM printed Ti-6Al-4V components

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    Nowadays, there is a great manufacturing trend in producing higher quality net-shape components of challenging geometries. One of the major challenges faced by additive manufacturing (AM) is the residual stresses generated during AM part fabrication often leading to unacceptable distortions and degradation of mechanical properties. Therefore, gaining insight into residual strain/stress distribution is essential for ensuring acceptable quality and performance of high-tech AM parts. This research is aimed at comparing microstructure and residual stress built-up in Ti–6Al–4V AM components produced by Wire + Arc Additive Manufacturing (WAAM) and by laser cladding process (CLAD)

    The high deposition rate additive manufacture of nickel superalloys and metal matrix composites

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    The deposition rate of Additive Manufacture (AM) processes are a significant factor for the economic production of metallic materials by AM. Higher deposition rates must be achieved if the technology as a whole and nickel alloys in particular are to be more widely adopted within industry. This thesis investigates the potential of two techniques, high power (>1kW) laser beams within a powder bed laser melting (LM) configuration and Plasma Transferred Arc Welding (PTAW) using a wire fed approach for the deposition of Inconel 625, a widely used nickel superalloy. The processing parameters required for stable deposition of material in both single welds and multiple layers was determined, and the deposited material characterised. High deposition rate powder bed LM using 500μm layer thicknesses was conducted and a process stability map for single welds was characterised. Multi-layer multi-weld samples achieved an acceptable relative material density of 99.8%, using a reduction in laser power with increasing height as a thermal control strategy to achieve a deposition rate of 0.023cc/s, an order of magnitude increase in productivity over existing low deposition rate powder bed LM (0.0036cc/s). Deposition at 500μm layers was found to impart a secondary alignment to the microstructure due to a lower ratio of beam diameter vs. layer thickness, thus conductive cooling into previously deposited weld tracks within the same layer becomes significant. PTAW deposition of Inconel 625 was investigated and a process map characterising single bead on plate experiments has been compiled and presented. Deposition strategies for multi-layer, multi-weld features have also been investigated and the importance of thermal control due to thermal isolation from the substrate shown. PTAW deposited material has been characterised by tensile testing at elevated temperatures using both conventional tensile tests and by electrical resistance heating of specimens using a Gleeble thermo-mechanical simulator, validating the novel use of infra-red thermography to measure the thermal gauge length. In addition to a need for increased deposition rate, the limits of material performance in AM with respect to nickel alloys are currently constrained by superalloy related weldability and cracking problems. The work presented in this thesis examines the potential for production of an Inconel 625 based Metal Matrix Composite, which may offer benefits to material properties. Candidate ceramic reinforcement materials were identified and a feasibility study was conducted, identifying TiC as the most promising candidate. Feedstock powders were mixed and assessed, mixing TiC directly with Inconel 625 and mixing pure Ti and carbon in the form of graphite with Inconel 625 to investigate an in-situ reactive processing route. The process parameter windows were characterised for both MMC feedstocks at both 100μm and 500μm layer thickness and with the use of pre-heating to establish the relationships present. Process stability maps were created and significantly the presence of TiC affected the ability of the laser to penetrate the powder bed, not due to its high melting point, but due to its high absorptivity which results in greater melting within the powder bed which hinders penetration and wetting with the substrate. The in-situ forming of TiC was partially successful, but unwanted Mo2C carbides were formed and the matrix structure affected due to the homogenous presence of carbon during processing. The power density of the laser beam was identified as the critical factor in determining the dissolution and re-precipitation behaviour of TiC within the matrix, as opposed to the commonly used energy density metric

    Development of weld repair methods for Rene 80 nickel based superalloy

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    Nickel based superalloys are an integral material for gas turbines, where their excellent high temperature mechanical properties and corrosion resistance are utilised. Due to the increasing costs of raw materials, manufacturers are interested in repairing in-service and manufacturing defects in components. Unfortunately, superalloys such as Rene 80 are highly susceptible to welding defects such as liquation cracking and post-weld heat treatment cracking, which make repair welding highly difficult. The aim of the research in this thesis was to develop an improved understanding of welding defect production in nickel-based superalloys. In particular, the effect of repair process and its parameters were examined, with the ultimate aim to produce crack-free repair welds. The main theme of the work involved a large parametric study of the process parameter effects on welding defects in Rene 80 using a high power fibre laser. This work determined an optimised range of parameters which reduced the incidence of cracking. Furthermore, this work also identified a key relationship between the weld bead geometry aspect ratio and the incidence of cracking. This relationship was studied using neutron diffraction to determine the differences in strain and residual stresses between two welds with identical heat input but different geometry. An in-depth investigation of the cracks within the material, identified that as-welded cracks formed via liquation of secondary phases such as carbides, γ/γ’ eutectics, and secondary gamma prime. The post weld heat treatment cracks formed by the strain-age mechanism in Rene 80. From this work, a novel repair procedure avoiding the complications associated with using lower strength filler metal was developed, based on the optimised welding parameters. Finally, a number of advanced low heat input welding processes were also investigated for repair of superalloys

    Powder-based laser hybrid additive manufacturing of metals:a review

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    Recent advances in additive manufacturing (AM) have attracted significant industrial interest. Initially, AM was mainly associated with the fabrication of prototypes, but the AM advances together with the broadening range of available materials, especially for producing metallic parts, have broaden the application areas and now the technology can be used for manufacturing functional parts, too. Especially, the AM technologies enable the creation of complex and topologically optimised geometries with internal cavities that were impossible to produce with traditional manufacturing processes. However, the tight geometrical tolerances along with the strict surface integrity requirements in aerospace, biomedical and automotive industries are not achievable in most cases with standalone AM technologies. Therefore, AM parts need extensive post-processing to ensure that their surface and dimensional requirements together with their respective mechanical properties are met. In this context, it is not surprising that the integration of AM with post-processing technologies into single and multi set-up processing solutions, commonly referred to as hybrid AM, has emerged as a very attractive proposition for industry while attracting a significant R&D interest. This paper reviews the current research and technology advances associated with the hybrid AM solutions. The special focus is on hybrid AM solutions that combine the capabilities of laser-based AM for processing powders with the necessary post-process technologies for producing metal parts with required accuracy, surface integrity and material properties. Commercially available hybrid AM systems that integrate laser-based AM with post-processing technologies are also reviewed together with their key application areas. Finally, the main challenges and open issues in broadening the industrial use of hybrid AM solutions are discussed. 2021, The Author(s).The authors would acknowledge the support received from the ESIF/ERDF Smart Factory Hub (SmartFub) programme in West Midlands. The authors also acknowledge the support received from Yamazaki Mazak, DMG MORI, LASEA and Systems 3R for establishing the hybrid AM facilities at the University of Birmingham.Scopu

    Materials technology for Stirling space power converters

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    This program was conducted in support of the NASA LeRC development of the Stirling power converter (SPC) for space power applications. The objectives of this contract were: (1) to perform a technology review and analyses to support the evaluation of materials issues for the SPC; (2) to evaluate liquid metal compatibility issues of the SPC; (3) to evaluate and define a transient liquid phase diffusion bonding (TLPDB) process for the SPC joints to the Udimet 720 heater head; and (4) to evaluate alternative (to the TLPDB) joining techniques. In the technology review, several aspects of the current Stirling design were examined including the power converter assembly process, materials joining, gas bearings, and heat exchangers. The supporting analyses included GLIMPS power converter simulation in support of the materials studies, and system level analysis in support of the technology review. The liquid metal compatibility study evaluated process parameters for use in the Stirling power converter. The alternative joining techniques study looked at the applicability of various joining techniques to the Stirling power converter requirements

    NASA Contributions to Metals Joining

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    Survey of NASA supported metals joining research having industrial application
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