| 1. |
- Johari, G.P., et al.
(author)
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Effects of pressure-temperature protocols on the properties of crystals and ageing effects : an analogy with glasses
- 2022
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In: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 102:4, s. 299-320
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Journal article (peer-reviewed)abstract
- Properties of a crystal are used to determine the point defects concentration, n, the self diffusion coefficient, D and variation of n and D with tempertaure, T. Also, spontaneous change in the properties of a crystal’s non-equilibrium state is used to determine the decrease in n with time. Both n and D decrease with increase in the pressure, P, until the pressurising-rate dependent, kinetic-freezing pressure for defects disorder, PD-F, is reached. At P > PD-F, a crystal is in a non-equilibrium state. We consider such configurationally-frozen states of a crystal produced by using three unusual P-T protocols: (i) pressurising a crystal to P > PD-F, cooling to a low T and depressurising, (ii) pressurising to P < PD-F, cooling through the defects freezing temperature, TD-F, and depressurising, and (iii) cooling a crystal at 1 bar to T D-F pressurising and maintaining at high P. The non-equilibrium state of the crystal would have defect concentration that kinetically froze at P = PD-F or T = TD-F, but its volume and phonon properties would not correspond to the kinetically-frozen state at P = PD-F or at T = TD-F. On aging, their properties would change differently than those of a non-equilibrium state of a crystal produced by quenching at a fixed P. We relate n, D and the electrical resistivity to thermal conductivity, κ, by the Wiedemann-Franz equation, and discuss how κ would change on aging of a crystal. The above-given effects alter the properties of metallic and non-metallic, metastable materials during their commercial use.
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| 2. |
- Lindgren, Kristina, 1989, et al.
(author)
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Atom probe tomography characterisation of powder forged connecting rods alloyed with vanadium and copper
- 2022
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In: Philosophical Magazine. - : Informa UK Limited. - 1478-6435 .- 1478-6443. ; In Press
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Journal article (peer-reviewed)abstract
- The precipitation of V and Cu in the powder forged connecting rods of Fe-V-Cu-C alloy, were studied by atom probe tomography (APT). The purpose of alloying with V was to further improve the mechanical properties of the existing powder forged materials based on Fe-Cu-C. In this study, materials tested at room temperature and 120 degrees C were investigated. It was found that Cu was unevenly distributed on a micrometer scale. The local Cu content affected the Cu precipitation; a higher Cu content resulted in a higher volume fraction of precipitates. The V was found to form very small nitrides. The N presumably originates from the sintering process. The vanadium nitrides act as nucleation points for the Cu precipitates during cooling of the material during fabrication. APT analysis of the deformed material close to the fracture surface of the tensile test samples showed a similar volume fraction of Cu precipitates, but statistical analysis of the data indicates that both Cu and VN precipitates are more diffuse than in the undeformed material.
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| 3. |
- Safara, Nima, et al.
(author)
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Study of the mean size and fraction of the second-phase particles in a 13% chromium steel at high temperature
- 2020
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In: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 100:2, s. 217-233
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Journal article (peer-reviewed)abstract
- The mean size and fraction of the second-phase particles in a 13% chromium steel are investigated, while no plastic deformation was applied. The results of the measurement are compared with the modelling results from a physicallybased model. The heating sequence is performed on samples using a Gleeble thermo-mechanical simulator over the temperature range of 850–1200°C. Using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS), the size distribution and composition of the carbides were evaluated, respectively. For obtaining particle size distribution (PSD), an image-processing software was employed to analyse the SEM images. Additionally, the relation between the 2D shape factor and size of the particles is also studied at different temperatures and most of the particles turned out to have a shape factor close to two. In order to measure the carbide weight fraction, electrochemical phase isolation was employed. The Ms and fraction of the martensite phase after quenching of samples are calculated and the results were comparable with the measured hardness values at corresponding temperatures. The measured hardness of the samples is found to comply very well with the measured mean size of the precipitates. The calculated mean size of the particles from the model shows very good agreement with both hardness value and experimentally measured mean size, while the calculated volume fraction from simulation follows a slightly different trend.
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| 4. |
- Zohrevand, Milad, et al.
(author)
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An investigation on microstructure and mechanical properties of 316 stainless steel: a comparison between ultrasonic treatment and thermal annealing
- 2022
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In: Philosophical Magazine. - : Taylor & Francis. - 1478-6435 .- 1478-6443. ; 102:14, s. 1321-1343
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Journal article (peer-reviewed)abstract
- The effect of ultrasonic treatment (UST) and thermal annealing (THA) post-processes on the mechanical properties and the related microstructural mechanisms of the tensile pre-strained 316 stainless steel was investigated. It was shown that both processes reduce the microhardness and the yield point as well as increasing the elongation of the pre-deformed alloy. A 10% reduction of the yield point and 28% increase in the elongation was observed after the higher power UST (500 W), while an enhanced ductility of 56% and 41% reduction of the yield point was measured for the high-temperature THA (800°C) treated steel. The increased ductility was related to de-twinning and dislocation annihilation mechanisms, which increase the mean free path distance of dislocations. The de-twinning mechanism was proposed as the boundary migration mechanism and reverse gliding of the partial dislocations by cyclic shear stress for the THA and UST processes, respectively. Unlike the UST process, the high-temperature thermal annealing was associated with the formation of M23C6 precipitates, which causes depletion of alloying elements from the vicinity of grain boundaries and makes the alloy more prone to intergranular corrosion. Compared with THA, the advantages of the UST process are as follows: a rapid and straightforward process, low energy consumption, enhanced ductility without significant reduction in strength, and inhibition of grain boundary precipitation.
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