| 1. |
- Simm, T. H., et al.
(författare)
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The τ-plot, a multicomponent 1-D pole figure plot, to quantify the heterogeneity of plastic deformation
- 2020
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Ingår i: Materials Characterization. - : Elsevier Inc.. - 1044-5803 .- 1873-4189. ; 160
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Tidskriftsartikel (refereegranskat)abstract
- An approach is presented that allows multi-scale characterisations of heterogeneous deformation in crystalline materials by employing a range of characterisation techniques including: electron backscatter diffraction, digital image correlation and neutron diffraction powder measurements. The approach will be used to obtain critical information about the variations in parameters that characterise the deformed state in different crystallographic orientation texture components of a sample in a statistically significant way. These parameters include lattice strains, texture evolution, peak broadening, dislocation density, planar faults, phase changes and surface strain. This approach allows verification of models of plastic deformation to provide a more detailed view of plastic deformation heterogeneity at multiple length scales than obtained by other characterisation approaches. The approach demonstrated here is applied to two stainless steel alloys; an alloy that exhibits phase transformation during deformation and an alloy that remains the same phase all through deformation process.
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| 2. |
- Davies, P., et al.
(författare)
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The hierarchy of microstructure parameters affecting the tensile ductility in centrifugally cast and forged Ti-834 alloy during high temperature exposure in air
- 2016
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Ingår i: Acta Materialia. - 1359-6454 .- 1873-2453. ; 117, s. 51-67
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Tidskriftsartikel (refereegranskat)abstract
- Ductility regression is the main concern in using Ti-834 titanium alloy at temperatures above 500 °C for aerospace applications. The reduction of ductility in titanium alloys at high temperatures is strongly correlated to the exposure time. In the current study the effect of prolonged exposure at 500 °C on the tensile ductility of two differently processed Ti-834 alloys was investigated. In order to simulate actual Ti-834 processing routes, forged and centrifugally cast materials were used. The tensile tests were conducted on various specimens exposed at 500 °C for 100, 200 and 500 h to observe microstructure feature changes. Moreover, the effect of microstructure, microtexture, α-case, α2 and silicide precipitate coarsening during high temperature exposure was studied thoroughly. The cast alloy was found to have a minimum ductility and failed at 1.8% strain after exposure at 500 °C/500 h when the α-case layer was retained during testing, whilst, the ductility of the forged alloy was unaffected. The effects of individual microstructural parameters on the ductility regression in Ti-834 alloy were quantified. The results showed that 7.1% strain differences between the cast and forged alloy are related to microstructural variations including; morphology, lath widths, grain size and shape, grain orientations and microtexture. A total of 9.6% strain loss was observed in centrifugally cast Ti-834 after aging at 500°C/500 h and quantified as follow; 3.6% due to α-case formation during high temperature exposure, 0.2% due to α2-precipitates coarsening, 4.4% due to further silicide formation and coarsening, 1.4% due to additional microstructure changes during high temperature exposure. Furthermore, silicide coarsening on α/β phase boundaries caused large void formation around the precipitates. A theoretical model supported by experimental observations for silicide precipitation in fully colony and duplex microstructures was established. The element partitioning during exposure caused Al and Ti depletion in the vicinity of the β phase in the lamellae, i.e., αs area. This resulted in lowering the strength of the alloy and facilitated the formation of Ti3(SiZr)2 precipitates. The Al depletion and nano-scale partitioning observed at the αs/β boundaries resulted in easy crack initiation and promoted propagation in the centrifugally cast colony microstructure and reduced the basal slip τcrss. Furthermore, silicides were not formed in αp (high Al, Ti and low Zr areas) in the forged duplex microstructure that promoted superior mechanical performance and ductility over the cast alloy.Graphical abstract
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| 3. |
- Steuwer, Axel, et al.
(författare)
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A combined approach to microstructure mapping of an Al-Li AA2199 friction stir weld
- 2011
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Ingår i: Acta Materialia. - : Elsevier BV. - 1873-2453 .- 1359-6454. ; 59:8, s. 3002-3011
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Tidskriftsartikel (refereegranskat)abstract
- A wide range of complementary techniques are used to build up a detailed picture of the microstructural zones found in friction stir welds (FSW) in an advanced AA2199 Al-Li alloy. Neutron and synchrotron X-ray diffraction, transmission electron microscopy, differential scanning calorimetry, small angle X-ray scattering, scanning electron microscopy, electron backscatter diffraction (EBSD) and hardness mapping are brought together to build up a detailed two-dimensional picture of the grain morphology, precipitate type, size, volume fraction and matrix solute content across the weld cross section and to explain the general lack of a W-shaped hardness profile across FSW in third-generation Al-Li-Cu Mg alloys. Dissolution of the age-hardening phases occurred in different regions of the weld, depending on their respective solvus temperatures, with 5' dissolving within the heat-affected zone and T-1 coarsening in the thermo-mechanically affected zone before going into solution in the weld nugget. Changes to the precipitate distribution, and especially to the T1 phase, are linked to a significant reduction in hardness (strength) and unstrained lattice parameter across the weld zone. It was also possible to show that the low recovery of nugget zone hardness is primarily due to its poor natural ageing response. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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