37,180 research outputs found

    Effects of Impurity Content on the Sintering Characteristics of Plasma-Sprayed Zirconia

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    Yttria-stabilized zirconia powders, containing different levels of SiO2 and Al2O3, have been plasma sprayed onto metallic substrates. The coatings were detached from their substrates and a dilatometer was used to monitor the dimensional changes they exhibited during prolonged heat treatments. It was found that specimens containing higher levels of silica and alumina exhibited higher rates of linear contraction, in both in-plane and through-thickness directions. The in-plane stiffness and the through-thickness thermal conductivity were also measured after different heat treatments and these were found to increase at a greater rate for specimens with higher impurity (silica and alumina) levels. Changes in the pore architecture during heat treatments were studied using Mercury Intrusion Porosimetry (MIP). Fine scale porosity (<_50 nm) was found to be sharply reduced even by relatively short heat treatments. This is correlated with improvements in inter-splat bonding and partial healing of intra-splat microcracks, which are responsible for the observed changes in stiffness and conductivity, as well as the dimensional changes

    Novel method for refinement of retained austenite in micro/nano-structured bainitic steels

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    A comparative study was conducted to assess the effects of two different heat treatments on the amount and morphology of the retained austenite in a micro/nano-structured bainitic steel. The heat treatments used in this work were two-stage bainitic transformation and bainitic-partitioning transformation. Both methods resulted in the generation of a multi-phase microstructure containing nanoscale bainitic ferrite, and/or fresh martensitic phases and much finer retained austenite. Both heat treatments were verified to be effective in refining the retained austenite in micro/nano-structured bainite and increasing the hardness. However, the bainitic transformation followed by partitioning cycle was proved to be a more viable approach than the two-stage bainitic transformation due to much shorter processing time, i.e. ∼2 h compared to ∼4 day, respectively

    Mechanical Properties Improvement of Low Carbon Steel by Combined Heat Treatments

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    The improvement of the Mechanical properties of the low Carbon steel and increasing its strength, was the goal of some heat treatment technologies developed in the last twenty years. One of these technologies is the Rapid Heat Treatment (RHT), by which the strength of steel increases with the crystalline grain size decrease obtained from the rapidity of austenitizing, and more strength increase may be obtained, if the action of austenitizing is followed by rapid cooling or quenching, but in this case, ductility will decrease simultaneously by increasing the cooling rate. Another mechanical properties improving heat treatment, is the Intercritical Heat Treatment (IHT), by which the ferrite-pearlite structure of low Carbon steel transforms to Dual-Phase structure of ferrite and martensite resulting increase in strength, while a great deal of its ductility is restored. Authors in this paper report about their experiments carried out on a low Carbon-steel, trying to get the advantages of the two above mentioned technologies, by subjecting the formerly rapid heat treated steel, to intercritical heat treatment,. Applying this treatment on the steel in different temperatures inside the intercritical zone, remarkable results were obtained and reported

    Structure, morphology and mechanical properties of electrodeposited composite coatings Ni–P/SiC

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    Physical properties of the NiP/SiC deposits are discussed according to the electroplating parameters and heat treatments. The insertion of silicon carbide in the coatings does not modify their rigidity (E = 230 GPa), increases their hardness slightly (50 Vickers) and decreases the residual stresses in the coatings. The phosphorus content has a major effect on the structure and the physical properties. Indeed, the insertion of phosphorus into the deposits generates a grain size reduction or even an amorphisation which results in morphological modifications observed by AFM. In parallel a very important hardening is associated with incorporation of phosphorus: hardness is multiplied by 3 to reach 600 HV0.1. The deposits tend to become crystalline following the heat treatments. With 420 °C, the precipitation of a Ni3P phase which distorts the crystal lattice is observed, increasing the hardness of the deposits

    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

    Effect of mechanical surface and heat treatments on erosion resistance

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    The effects of mechanical surface treatments as well as heat treatments on the erosion resistance of 6061 aluminum alloy and 1045 steel were studied. Mechanical surface treatments were found to have little or no effect on the erosion resistance. This is due to the formation by particle impact of a work hardened surface layer regardless of the initial surface condition. The erosion resistance of Al single crystals is found to be independent of orientation. This is due to destruction of the surface microstructure and formation of a polycrystalline surface layer by the impact of erodant particles as observed by X-ray diffraction. While upon solution treatment of annealed 6061 aluminum the increase in hardness is accompanied by an increase in erosion resistance, precipitation treatment which causes a further increase in hardness results in slightly lower erosion resistance. Using two types of erodant particles, glass beads and crushed glass, the erosion rate is found to be strongly dependent on erodant particle shape, being an order of magnitude higher for erosion with crushed glass as compared to glass beads. While for erosion with glass beads heat treatment of 1045 steel had a profound effect on its erosion resistance, little or no such effect was observed for erosion with crushed glass

    Microstructure and Residual Stress Evolution of Laser Powder Bed Fused Inconel 718 under Heat Treatments

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    The current work aimed to study the influence of various heat treatments on the microstructure, hardness, and residual stresses of Inconel 718 processed by laser powder bed fusion process. The reduction in residual stresses is crucial to avoid the deformation of the component during its removal from the building platform. Among the different heat treatments, 800 °C kept almost unaltered the original microstructure, reducing the residual stresses. Heat treatments at 900, 980, and 1065 °C gradually triggered the melt pool and dendritic structures dissolution, drastically reducing the residual stresses. Heat treatments at 900 and 980 °C involved the formation of δ phases, whereas 1065 °C generated carbides. These heat treatments were also performed on components with narrow internal channels revealing that heat treatments up to 900 °C did not trigger sintering mechanisms allowing to remove the powder from the inner channels

    Microstructure and Residual Stress Evolution of Laser Powder Bed Fused Inconel 718 under Heat Treatments

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    AbstractThe current work aimed to study the influence of various heat treatments on the microstructure, hardness, and residual stresses of Inconel 718 processed by laser powder bed fusion process. The reduction in residual stresses is crucial to avoid the deformation of the component during its removal from the building platform. Among the different heat treatments, 800 °C kept almost unaltered the original microstructure, reducing the residual stresses. Heat treatments at 900, 980, and 1065 °C gradually triggered the melt pool and dendritic structures dissolution, drastically reducing the residual stresses. Heat treatments at 900 and 980 °C involved the formation of δ phases, whereas 1065 °C generated carbides. These heat treatments were also performed on components with narrow internal channels revealing that heat treatments up to 900 °C did not trigger sintering mechanisms allowing to remove the powder from the inner channels
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