Blar i NTNU Open på forfatter "Holmestad, Randi"
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Effects of Germanium, Copper, and Silver Substitutions on Hardness and Microstructure in Lean Al-Mg-Si Alloys
Mørtsell, Eva Anne; Marioara, Calin Daniel; Andersen, Sigmund Jarle; Røyset, Jostein; Reiso, Oddvin; Holmestad, Randi (Journal article; Peer reviewed, 2015)It is shown that strength loss in a 6060 Al-Mg-Si alloy caused by reduction in solute can be compensated by adding back smaller quantities of Ag, Ge, and Cu. Nine alloys were investigated. Ge was found to be the most ... -
Electron Microscopy Characterization of Aluminium-Copper-Titanium-Steel Joint made using the Hybrid Metal Extrusion & Bonding Method
Turgun, Hursanay (Master thesis, 2020)Multimaterielle skjøter er nyttige i produksjon av lette strukturer med høy ytelse og funksjonalitet. Denne avhandlingen undersøker en skjøt sammensveiset ved bruk av den innovative Hybrid Metal Extrusion & Bonding (HYB) ... -
Electron microscopy of intermetallic phases in aluminium-steel joints
Bergh, Tina (Doctoral theses at NTNU;2021:168, Doctoral thesis, 2021)Joints that combine the light weight of aluminium (Al) alloys with the high strength of steels, can be beneficial in structural components. For instance, in automobiles, Al-steel joints can enable improvement of the ... -
Elemental electron energy loss mapping of a precipitate in a multi-component aluminium alloy
Mørtsell, Eva Anne; Wenner, Sigurd; Longo, Paulo; Andersen, Sigmund Jarle; Marioara, Calin Daniel; Holmestad, Randi (Journal article, 2016)The elemental distribution of a precipitate cross section, situated in a lean Al-Mg-Si-Cu-Ag-Ge alloy, has been investigated in detail by electron energy loss spectroscopy (EELS) and aberration corrected high angle annular ... -
Enhanced Mechanical Properties in 6082 Aluminum Alloy Processed by Cyclic Deformation
Chen, Xuanliang; Mørtsell, Eva Anne; Sunde, Jonas Kristoffer; O, Minho; Marioara, Calin Daniel; Holmestad, Randi; Kobayashi, Equo (Peer reviewed; Journal article, 2021)Aging heat treatment is the most commonly used strengthening method for Al–Mg–Si alloys since high-density precipitates will be formed to hinder the movement of dislocations. In the current work, room temperature cyclic ... -
The evolution of precipitates in an Al–Zn–Mg alloy
Thronsen, Elisabeth; Shah, Sohail; Hatzoglou, Constantinos; Marioara, Calin Daniel; Wenner, Sigurd; Andersen, Sigmund Jarle; Holmedal, Bjørn; Holmestad, Randi (Peer reviewed; Journal article, 2023)The precipitation sequence in Al–Zn–Mg alloys has been subject to many revisions over the years as more structural details of the early-stage Guinier-Preston (GP) zones and precipitates have been uncovered. To further ... -
Extra electron diffraction spots caused by fine precipitates formed at the early stage of aging in Al-Mg-X (X=Si, Ge, Zn)-Cu alloys
Matsuda, Kenji; Kawai, Akihiro; Watanabe, Katsumi; Seungwon, Lee; Marioara, Calin Daniel; Wenner, Sigurd; Nishimura, Katsuhiko; Matsuzaki, Teiichiro; Nunomura, Norio; Sato, Tatsuo; Holmestad, Randi; Ikeno, Susumu (Journal article; Peer reviewed, 2017)Age-hardenable Al-Mg-Si, Al-Mg-Ge, and Al-Zn-Mg alloys including Cu were investigated by transmission electron microscopy to understand extra diffraction spots that appear in their selected area electron diffraction patterns. ... -
First principle calculations of pressure dependent yielding in solute strengthened aluminium alloys
Frafjord, Jonas; Ringdalen, Inga Gudem; Hopperstad, Odd Sture; Holmestad, Randi; Friis, Jesper (Journal article; Peer reviewed, 2020)The pressure dependence of the yield stress in solute strengthened aluminium alloys is investigated by first principle calculations. The solute elements studied are magnesium, silicon and copper. A fixed boundary cluster ... -
Fully resolved strain field of the β’’ precipitate calculated by density functional theory
Frafjord, Jonas; Dumoulin, Stephane; Wenner, Sigurd; Ringdalen, Inga Gudem; Holmestad, Randi; Friis, Jesper (Peer reviewed; Journal article, 2020)The β′′ precipitate is the main hardening phase in age hardenable Al-Mg-Si alloys, and it is therefore of major scientific and industrial importance. A full model of the β′′ precipitate cross-section embedded in an aluminium ... -
Grain boundary structures and their correlation with intergranular corrosion in an extruded Al-Mg-Si-Cu alloy
Lervik, Adrian; Wenner, Sigurd; Lunder, Otto; Marioara, Calin Daniel; Holmestad, Randi (Peer reviewed; Journal article, 2020)A detailed analysis of grain boundaries in a highly textured Al-Mg-Si-Cu alloy is presented in this work. Electron backscatter diffraction demonstrates the presence of three main categories of grain boundaries in addition ... -
HAADF-STEM and DFT investigations of the Zn-containing β'' phase in Al-Mg-Si alloys
Saito, Takeshi; Ehlers, Flemming J H; Lefebvre, Williams; Hernandez-Maldonado, D; Bjørge, Ruben; Marioara, Calin Daniel; Andersen, Sigmund Jarle; Holmestad, Randi (Journal article, 2014)The Zn-containing β″ phase in Al–Mg–Si alloys was investigated by aberration corrected high angle annular dark-field scanning transmission electron microscopy (HAADF-STEM), combined with density functional theory (DFT) ... -
Hardness and Microstructure for Ge-Containing Al-Mg-Si-Cu alloys
Utne, Amund Fredrik (Master thesis, 2012)Four different Al-Mg-Si-Cu-Ge alloys with 0.002--0.037 at.\% germanium were heat treated to the T6 condition and over-aged at 250$^{\circ}$C for up to 100 hours. The hardness was tested during the over-ageing and there ... -
How calcium prevents precipitation hardening in Al–Mg–Si alloys
Wenner, Sigurd; Marioara, Calin Daniel; Andersen, Sigmund Jarle; Holmestad, Randi (Journal article, 2013)We have investigated the effect on precipitate microstructure and hardness upon adding small amounts of Ca to a base Al–Mg–Si alloy. The main investigative techniques were transmission and scanning electron microscopy. We ... -
An improved modelling framework for strength and work hardening of precipitate strengthened Al–Mg–Si alloys
Lu, Feng; Sunde, Jonas Kristoffer; Marioara, Calin Daniel; Holmestad, Randi; Holmedal, Bjørn (Journal article; Peer reviewed, 2022)A modelling framework for the strength and work hardening contributions in age hardened Al–Mg–Si alloys is presented. The modelling work is based on transmission electron microscopy (TEM) measurements of the needle-shaped ... -
In situ DSC investigation into the kinetics and microstructure of dispersoid formation in Al-Mn-Fe-Si(-Mg) alloys
Kemsies, Richard H; Milkereit, Benjamin; Wenner, Sigurd; Holmestad, Randi; Kessler, Olaf (Journal article; Peer reviewed, 2018)Dispersoid strengthening in Al-Mn-Fe-Si(-Mg) aluminum wrought alloys can play an important role in applications at elevated temperatures. Fine and evenly distributed dispersoids are needed to increase alloy strength, which ... -
In situ heating TEM observations of evolving nanoscale Al‐Mg‐Si‐Cu precipitates
Sunde, Jonas Kristoffer; Wenner, Sigurd; Holmestad, Randi (Journal article; Peer reviewed, 2019)This research concerns the precipitation and subsequent dissolution of precipitate phases in an Al–0.86Mg–0.62Si–0.1Cu (at.%) alloy subjected to varying thermal exposure during an in situ heating transmission electron ... -
In-plane structural order of domain engineered La0.7Sr0.3MnO3 thin films
Boschker, Jos Emiel; Monsen, Åsmund Fløystad; Nord, Magnus Kristofer; Mathieu, Roland; Grepstad, Jostein; Holmestad, Randi; Wahlström, Erik; Tybell, Thomas (Journal article, 2013)We present a detailed structural study of tensile-strained La0.7Sr0.3MnO3 thin films. We use the substrate miscut to control the number of rhombohedral variants in the films and study the in-plane order and structural ... -
In-situ studies of multicrystalline silicon nucleation and growth on alpha- and beta-Si3N4 coated substrates
Undheim, Espen; Maeda, Kensaku; Arnberg, Lars; Holmestad, Randi; Fujiwara, Kozo; Di Sabatino Lundberg, Marisa (Journal article; Peer reviewed, 2018)The growth of silicon on various nitride coated quartz substrates were studied using in-situ observation of the solidification process. Three different coating types were used: One consisting entirely of α-Si3N4 particles, ... -
Influence of low Cu addition on quench sensitivity in Al-Mg-Si alloys
Saito, Takeshi; Marioara, Calin Daniel; Røyset, Jostein; Holmestad, Randi (Journal article, 2014)Quench sensitivity in two Al-Mg-Si alloys, one Cu-free and the other with low Cu additions (~0.1 wt%), both having the same amounts of other solutes, has been investigated using transmission electron microscopy (TEM) and ... -
Influence of natural aging and ramping before artificial aging on the microstructure of two different 6xxx alloys
Hell, Christoph Martin; Søreide, Hanne-Sofie Marie Scisly; Bjørge, Ruben; Marioara, Calin Daniel; Li, Yanjun; Holmestad, Randi (Peer reviewed; Journal article, 2022)In this study the effect of a ramp up to artificial aging (AA) temperature in combination with natural aging (NA) was analyzed for two different industrial aluminium alloys. The alloys differ in their Mg/Si ratio as well ...