| 1. |
- Chen, Ling, et al.
(författare)
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Analysis of In Situ Mechanical Properties of Phases in High-Alloyed White Iron Measured by Grid Nanoindentation
- 2015
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Ingår i: Journal of Materials Engineering and Performance. - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 24:10, s. 4022-4031
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Tidskriftsartikel (refereegranskat)abstract
- The paper presents an analysis of the in situ mechanical properties (e.g., hardness, elastic modulus, and volume fraction) of phases in high-alloy white iron measured by grid nanoindentation statistically, to reveal the contributions of individual phase properties to the global properties of the material. The in situ mechanical properties of phases measured by grid indentation were validated through targeted indentation. Gaussian and Weibull mixture models were used in analyzing the grid nanoindentation measurements to assess the goodness-of-fit of the indentation data. The nanohardness and indentation modulus measured by grid nanoindentation were directly correlated to the microstructural characteristics of the sample materials. The statistical analysis results were also compared with the mechanical properties and volume fractions obtained using targeted indentation and quantitative metallography based on microstructure analysis to validate the statistical results. The influences of heat treatment on the microstructure, hardness, and elastic modulus of individual phases in the material are also discussed.
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| 2. |
- Chen, Ling, et al.
(författare)
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Characterization of Microstructure and Mechanical Properties of High Chromium Cast Irons Using SEM and Nanoindentation
- 2015
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Ingår i: Journal of Materials Engineering and Performance. - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 24:1, s. 98-105
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Tidskriftsartikel (refereegranskat)abstract
- The effects of composition changes and heat treatment on the microstructure and mechanical properties of high-chromium white cast irons were studied in order to characterize possible improvements in product performance and machinability. Materials characterization was performed using nanoindentation, SEM, and EDS techniques. Present results show that changes in carbon and silicon contents as well as heat treatment strongly affect the mechanical properties and their variation in the material. In the as-cast condition, the sample with relatively lower carbon and silicon contents has an austenite-martensite matrix and is much harder than the sample with relatively higher carbon and silicon contents having more eutectic carbides in a bainite matrix. Annealing leads to softening of the materials relative to the as-cast condition, with the relatively higher carbon-silicon material being marginally harder due to the presence of more eutectic carbides. A similar trend is seen after the hardening treatment, and the presence of primary carbide can restrict the extent of hardening due to the loss of alloying elements from the matrix.
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| 3. |
- Goel, Sneha, 1993-, et al.
(författare)
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Effect of Different Post-treatments on the Microstructure of EBM-Built Alloy 718
- 2019
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Ingår i: Journal of materials engineering and performance (Print). - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 28:2, s. 673-680
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Tidskriftsartikel (refereegranskat)abstract
- Electron beam melting (EBM) of Alloy 718 is of rapidly growing interest as it allows cost-effective production of complex components. However, the inherent flaws in the component in as-built state are of concern in view of the severe working conditions in which Alloy 718 components typically operate. The present work entails an investigation of changes in microstructure that accompany some post-treatments that are being widely considered to address defects in EBM processed Alloy 718. The effect of two different post-treatments, namely hot isostatic pressing (HIP) and a combined HIP + heat treatment (HT) carried out inside the HIP vessel, have been studied and results from as-built and post-treated specimens were compared in terms of porosity/lack-of-fusion, microstructure, phase constitution (NbC content, Ύ-phase) and micro-hardness. Post-treatment resulted in reduction in defect content by more than an order of magnitude. HIPing led to complete dissolution of Ύ phase. In comparison to as-built material, HIPed specimens exhibited significant drop in hardness. However, a sharp ‘recovery’ of hardness to yield values higher than in as-built condition was observed after HIP + HT and can be attributed to precipitation of γ′′ phase. © 2018, The Author(s).
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| 4. |
- He, Junjing, et al.
(författare)
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Low-Cycle Fatigue Properties of a Nickel-Based Superalloy Haynes 282 for Heavy Components
- 2017
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 26:5, s. 2257-2263
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Tidskriftsartikel (refereegranskat)abstract
- Low-cycle fatigue (LCF) tests of the nickel-based superalloy Haynes 282 from a large forged ingot were conducted at 25 and 750 degrees C with total strain ranges from 0.7 to 1.7%. Compared with other tests on this alloy, it was found that the LCF properties showed similar results at room temperature, but improved number of cycles to failure at high temperatures. The number of cycles at a given total strain range showed no large differences between the core and rim positions. By comparing with two other types of low gamma' volume fraction nickel-based superalloys, Haynes 282 gave the best LCF properties at high temperatures. The reason may be due to the dominating transgranular fracture in the current work. A mixture of intergranular and transgranular fractures had been observed in the other alloys. The results demonstrate that heavy components of Haynes 282 can be produced with good LCF properties.
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| 5. |
- Holmberg, Jonas, et al.
(författare)
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Grit Blasting for Removal of Recast Layer from EDM Process on Inconel 718 Shaft : An Evaluation of Surface Integrity
- 2016
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Ingår i: Journal of materials engineering and performance (Print). - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 25:12, s. 5540-5550
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Tidskriftsartikel (refereegranskat)abstract
- The heat generated during EDM melts the work material and thereby allows large amounts to be removed,but an unfavorable surface of a recast layer (RCL) will also be created. This layer has entirely different properties compared to the bulk. Hence, it is of great interest to efficiently remove this layer and to verify that it has been removed. The main objective of this work has been to study the efficiency of grit blasting forremoval of RCL on an EDM aero space shaft. Additionally, x-ray fluorescence (XRF) has been evaluated asa nondestructive measurement to determine RCL presence. The results show that the grit-blasting processing parameters have strong influence on the ability to remove RCL and at the same time introduce beneficial compressive stresses even after short exposure time. Longer exposure will remove the RCL fromthe surface but also increase the risk that a larger amount of the blasting medium will get stuck into the surface. This investigation shows that a short exposure time in combination with a short grit-blasting nozzle distance is the most preferable process setting. It was further found that handheld XRF equipment can be used as a nondestructive measurement in order to evaluate the amount of RCL present on an EDM surface.This was realized by analyzing the residual elements from the EDM wire.
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| 6. |
- Larsson, Per-Lennart, 1961-
(författare)
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On the Influence of Elastic Deformation for Residual Stress Determination by Sharp Indentation Testing
- 2017
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 26:8, s. 3854-3860
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Tidskriftsartikel (refereegranskat)abstract
- The determination of residual stresses in engineering materials using sharp indentation testing is studied analytically and numerically. The numerical part of the investigation is based on the finite element method. In particular, the effect from elastic deformations on global indentation properties is discussed in detail. This effect is essential when residual stresses are to be determined based on the change of the contact area due to such stresses. However, standard relations for this purpose are founded on the fact that the material hardness is invariant as regards residual (applied) stresses. Presently, this assumption is scrutinized and it is shown that it is only valid at dominating plastic deformation around the contact region. The hardness dependence of residual stresses can, however, be correlated in the same way as in the case of stress-free materials, indicating that the wealth of characterization formulas pertinent to indentation hardness is available also for the purpose of residual field determination. Only cone indentation of elastic-perfectly plastic materials is considered, but the generality of the results is discussed in some detail.
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| 7. |
- Larsson, Per-Lennart, 1961-
(författare)
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On the Variation of Hardness Due to Uniaxial and Equi-Biaxial Residual Surface Stresses at Elastic-Plastic Indentation
- 2018
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Ingår i: Journal of materials engineering and performance (Print). - : SPRINGER. - 1059-9495 .- 1544-1024. ; 27:6, s. 3168-3173
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Tidskriftsartikel (refereegranskat)abstract
- It is established long since that the material hardness is independent of residual stresses at predominantly plastic deformation close to the contact region at indentation. Recently though, it has been shown that when elastic and plastic deformations are of equal magnitude this invariance is lost. For materials such as ceramics and polymers, this will complicate residual stress determination but can also, if properly understood, provide additional important information for performing such a task. Indeed, when the residual stresses are equi-biaxial, the situation is quite well understood, but additional efforts have to be made to understand the mechanical behavior in other loading states. Presently therefore, the variation of hardness, due to residual stresses, is examined at a uniaxial stress state. Correlation with global indentation quantities is analyzed, discussed and compared to corresponding equi-biaxial results. Cone indentation of elastic-perfectly plastic materials is considered.
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| 8. |
- Payandeh, Mostafa, et al.
(författare)
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Effect of Material Inhomogeneity on Thermal Performance of a Rheocast Aluminum Heatsink for Electronics Cooling
- 2016
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 25:6, s. 2116-2127
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Tidskriftsartikel (refereegranskat)abstract
- The relation between microstructural inhomogeneity and thermal conductivity of a rheocast componentmanufactured from two different aluminum alloys was investigated. The formation of two different primarya-Al particles was observed and related to multistage solidification process during slurry preparationand die cavity filling process. The microstructural inhomogeneity of the component was quantified as thefraction of a1-Al particles in the primary Al phase. A high fraction of coarse solute-lean a1-Al particles inthe primary Al phase caused a higher thermal conductivity of the component in the near-to-gate region. Avariation in thermal conductivity through the rheocast component of 10% was discovered. The effect of aninhomogeneous temperature-dependent thermal conductivity on the thermal performance of a largerheocast heatsink for electronics cooling in an operation environment was studied by means of simulation.Design guidelines were developed to account for the thermal performance of heatsinks with inhomogeneousthermal conductivity, as caused by the rheocasting process. Under the modeling assumptions, the simulationresults showed over 2.5% improvement in heatsink thermal resistance when the higher conductivity nearto-gate region was located at the top of the heatsink. Assuming homogeneous thermo-physical properties ina rheocast heatsink may lead to greater than 3.5% error in the estimation of maximum thermal resistanceof the heatsink. The variation in thermal conductivity within a large rheocast heatsink was found to beimportant for obtaining of a robust component design.
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| 9. |
- Roos, Stefan, 1983-, et al.
(författare)
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Macro- and Micromechanical Behavior of 316LN Lattice Structures Manufactured by Electron Beam Melting
- 2019
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Ingår i: Journal of materials engineering and performance (Print). - : Springer Science and Business Media LLC. - 1059-9495 .- 1544-1024. ; 28:12, s. 7290-7301
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Tidskriftsartikel (refereegranskat)abstract
- This work focuses on the possibility of processing stainless steel 316LN powder into lightweight structures using electron beam melting and investigates mechanical and microstructural properties in the material of processed components. Lattice structures conforming to ISO13314:2011 were manufactured using varying process parameters. Microstructure was examined using a scanning electron microscope. Compression testing was used to understand the effect of process parameters on the lattice mechanical properties, and nanoindentation was used to determine the material hardness. Lattices manufactured from 316L using EBM show smooth compression characteristics without collapsing layers and shear planes. The material has uniform hardness in strut shear planes, a microstructure resembling that of solid 316LN material but with significantly finer grain size, although slightly coarser sub-grain size. Grains appear to be growing along the lattice struts (e.g., along the heat transfer direction) and not in the build direction. Energy-dispersive x-ray spectroscopy analysis reveals boundary precipitates with increased levels of chromium, molybdenum and silicon. Studies clearly show that the 316LN grains in the material microstructure are elongated along the dominating heat transfer paths, which may or may not coincide with the build direction. Lattices made from a relatively ductile material, like 316LN, are much less susceptible to catastrophic collapse and show an extended range of elastic and plastic deformation. Tests indicate that EBM process for 316LN is stable allowing for both solid and lightweight (lattice) structures.
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| 10. |
- Sieber, Maximilian, et al.
(författare)
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Formation of a Spinel Coating on AZ31 Magnesium Alloy by Plasma Electrolytic Oxidation
- 2016
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Ingår i: Journal of materials engineering and performance (Print). - : Springer. - 1059-9495 .- 1544-1024. ; 25:3, s. 1157-1162
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Tidskriftsartikel (refereegranskat)abstract
- Plasma electrolytic oxidation (PEO) is a common means for the surface modification of light metals. However, PEO of magnesium substrates in dilute electrolytes generally leads to the formation of coatings consisting of unfavorable MgO magnesium oxide. By incorporation of electrolyte components, the phase constitution of the oxide coatings can be modified. Coatings consisting exclusively of MgAl2O4 magnesium-aluminum spinel are produced by PEO in an electrolyte containing hydroxide, aluminate, and phosphate anions. The hardness of the coatings is 3.5 GPa on Martens scale on average. Compared to the bare substrate, the coatings reduce the corrosion current density in dilute sodium chloride solution by approx. one order of magnitude and slightly shift the corrosion potential toward more noble values.
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