Imperial College London

ProfessorDavidDye

Faculty of EngineeringDepartment of Materials

Professor of Metallurgy
 
 
 
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Contact

 

+44 (0)20 7594 6811david.dye

 
 
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Location

 

1.09GoldsmithSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

164 results found

Chang Y, Zhang S, Liebscher CH, Dye D, Ponge D, Scheu C, Dehm G, Raabe D, Gault B, Lu Wet al., Could face-centered cubic titanium in cold-rolled commercially-pure titanium only be a Ti-hydride?, Scripta Materialia, ISSN: 1359-6462

Journal article

Zhou G-H, Xu X, Dye D, Rivera-Diaz-del-Castillo PEJet al., Microstructural evolution and strain-hardening in TWIP Ti alloys, Acta Materializa, ISSN: 1359-6454

Journal article

Ackerman A, Knowles A, Gardener HM, Nemeth AAN, Bantounas I, Radecka A, Moody MP, Bagot PAJ, Reed RC, Rugg DR, Dye Det al., The kinetics of primary alpha plate growth in titanium alloys, Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, ISSN: 1073-5623

The kinetics of primary alpha-Ti colony/Widmanstatten plate growth from the beta are examined, comparing model to experiment. The plate growth velocity depends sensitively both on the diffusivity D(T) of the rate-limiting species and on the supersaturation around the growing plate. These result in a maxima in growth velocity around 40 K below the transus, once sufficient supersaturation is available to drive plate growth. In Ti-6246, the plate growth velocity was found to be around 0.32 um min-1 at 850 oC, which was in good agreement with the model prediction of 0.36 um min-1 . The solute field around the growing plates, and the plate thickness, was found to be quite variable, due to the intergrowth of plates and soft impingement. This solute field was found to extend to up to 30 nm, and the interface concentration in the beta was found to be around 6.4 at.% Mo. It was found that increasing O content will have minimal effect on the plate lengths expected during continuous cooling; in contrast, Mo approximately doubles the plate lengths obtained for every 2 wt.% Mo reduction. Alloys using V as the beta stabiliser instead of Mo are expected to have much faster plate growth kinetics at nominally equivalent V contents. These findings will provide a useful tool for the integrated design of alloys and process routes to achieve tailored microstructures.

Journal article

Goodfellow AJ, Kelleher J, Jones NG, Dye D, Hardy MC, Stone HJet al., 2019, The effect of Mo on load partitioning and microstrain evolution during compression of a series of polycrystalline Ni-Based superalloys, Acta Materialia, Vol: 176, Pages: 318-329, ISSN: 1359-6454

Journal article

Knowles A, Gong P, Rahman KM, Rainforth WM, Dye D, Galindo-Nava EIet al., 2019, Development of Ni-free Mn-stabilised maraging steels using Fe2SiTi precipitates, Acta Materialia, Vol: 174, Pages: 260-270, ISSN: 1359-6454

Computational alloy design has been used to develop a new maraging steel system with low cost, using Mn for austenite reversion and Heusler Fe2SiTi nm-scale precipitates to strengthen the martensite, avoiding high cost alloying elements such as Ni and Co. A pronounced ageing response was obtained, of over 100 HV, associated with the formation of 2–30 nm Fe2SiTi precipitates alongside the development of 10% Mn rich austenite, at the martensite boundaries with the Kurdjumov-Sachs orientation relationship. The precipitates took on different orientation relationships, depending on the size scale and ageing time, with fine precipitates possessing an <100>L21//<100>α orientation relationship, compared to larger precipitates with <110>L21//<100>α. Computational alloy design has been used for the development and demonstration of an alloy design concept having multiple constraints. Whilst in this case computational design lacked the fidelity to completely replace experimental optimisation, it identifies the importance of embedding Thermodynamic and kinetic modelling within each experimental iteration, and vice versa, training the model between experimental iterations. In this approach, the model would guide targeted experiments, the experimental results would then be taken into future modelling to greatly accelerate the rate of alloy development.

Journal article

Weekes H, Dye D, Proctor JE, Smith DS, Simionescu C, Prior TJ, Wenman Met al., 2019, The effect of pressure on hydrogen solubility in Zircaloy-4, Journal of Nuclear Materials, Vol: 524, Pages: 256-262, ISSN: 0022-3115

The effect of pressure on the room temperature solubility of hydrogen inZircaloy-4 was examined using synchrotron X-ray diffraction on small groundflake samples in a diamond anvil cell at pressures up to 20.9 GPa. Differentcombinations of hydrogen level/state in the sample and of pressure transmittingmedium were examined; in all three cases examined, it could be concluded thatpressure resulted in the dissolution of d hydrides and that interstitialhydrogen retards the formation of w Zr. A pressure of around 9 GPa was requiredto halve the hydride fraction. These results imply that the effect of pressureis thermodynamically analogous to that of increasing temperature, but that theeffect is small. The results are consistent with the volume per Zr atom of thea, d and w phases, with the bulk moduli of a and d, and with previousmeasurements of the hydrogen site molar volumes in the a and d phases. Theresults are interpreted in terms of their implication for our understanding ofthe driving forces for hydride precipitation at crack tips, which are in aregion of hydrostatic tensile stress on the order of 1.5 GPa.

Journal article

Bantounas I, Gwalani B, Alam T, Banerjee R, Dye Det al., 2019, Elemental partitioning, mechanical and oxidation behaviour of two high-gamma-prime W-free gamma/gamma-prime polycrystalline Co/Ni superalloys, Scripta Materialia, Vol: 163, Pages: 44-50, ISSN: 1359-6462

Cr-containing W-free Co alloys that form strengthening precipitates in an fcc γ matrix are presented to examine the effect of Ta and Nb additions to increase the strength, solvus temperature and gamma prime fraction. The alloys are found to have relatively low density, good oxidation resistance (<0.5 μm scale at 800 °C for 100 h) with coherent Al2O3 and Cr2O3 scales, and reasonable yield strengths, ∼800 MPa. The phase partitioning, measured by atom probe tomography, was found to be similar to W-containing Co/Ni superalloys, with Mo partitioning to the matrix providing solid solution strengthening.

Journal article

Knowles A, Reynolds L, Vorontsov V, Dye Det al., 2019, A nickel based superalloy reinforced by both Ni3Al and Ni3V ordered-fcc precipitates, Scripta Materialia, Vol: 162, Pages: 472-476, ISSN: 1359-6462

A nickel based superalloy has been designed where the fcc γ Ni matrix is reinforced by two different ordered-fcc intermetallic compounds, L12 Ni3Al and D022 Ni3V. Primary ageing at 900–1000 °C precipitated spherical L12 Ni3Al, whose volume fraction and size were controlled by altering the ageing temperature and time. Secondary ageing at 700 °C for 1–1000 h precipitated D022 Ni3V laths. The duplex precipitation increased hardness by up to 85 HV, with ∼ 500 MPa compressive proof strength maintained at 800 °C. Electron microscopy studied the Ni3Al precipitation and confirmed the form of the secondary Ni3V precipitates and their long term stability.

Journal article

Chang Y, Lu W, Guenole J, Stephenson LT, Szczpaniak A, Kontis P, Ackerman AK, Dear FF, Mouton I, Zhong X, Zhang S, Dye D, Liebscher CH, Ponge D, Korte-Kerzel S, Raabe D, Gault Bet al., 2019, Ti and its alloys as examples of cryogenic focused ion beam milling of environmentally-sensitive materials, Nature Communications, Vol: 10, ISSN: 2041-1723

Hydrogen pick-up leading to hydride formation is often observed in commercially pure Ti (CP-Ti) and Ti-based alloys prepared for microscopic observation by conventional methods, such as electro-polishing and room temperature focused ion beam (FIB) milling. Here, we demonstrate that cryogenic FIB milling can effectively prevent undesired hydrogen pick-up. Specimens of CP-Ti and a Ti dual-phase alloy (Ti-6Al-2Sn-4Zr-6Mo, Ti6246, in wt.%) were prepared using a xenon-plasma FIB microscope equipped with a cryogenic stage reaching −135 °C. Transmission electron microscopy (TEM), selected area electron diffraction, and scanning TEM indicated no hydride formation in cryo-milled CP-Ti lamellae. Atom probe tomography further demonstrated that cryo-FIB significantly reduces hydrogen levels within the Ti6246 matrix compared with conventional methods. Supported by molecular dynamics simulations, we show that significantly lowering the thermal activation for H diffusion inhibits undesired environmental hydrogen pick-up during preparation and prevents pre-charged hydrogen from diffusing out of the sample, allowing for hydrogen embrittlement mechanisms of Ti-based alloys to be investigated at the nanoscale.

Journal article

Wang Y, Liu B, Yan K, Wang M, Kabra S, Chiu YL, Dye D, Lee PD, Liu Y, Cai Bet al., 2019, Corrigendum to ‘Probing deformation mechanisms of a FeCoCrNi high-entropy alloy at 293 and 77 K using in situ neutron diffraction’ [Acta Mater. 154C (2018) 79–89], Acta Materialia, Vol: 163, Pages: 240-242, ISSN: 1359-6454

The authors regret that there were errors in Figs. 3 and 4, which in turn meant there were errors in Table 2. In Figs. 3 and 4, the lattice strain ((d-d0)/d0, where d is the lattice spacing) as a function of strain/stress should have plotted. Please find below the corrected versions of the figures and table. The authors would like to apologise for any inconvenience caused. Fig. 3. The evolution of elastic lattice strains along the axial and radial directions in grain families having {111}, {200}, {220}, {311} and {222} crystallographic planes during tensile loading at (a) 77 K and (b) 293 K.[Figure presented] Fig. 4. The (111) first order and (222) second order reflections together with the stacking fault probability as a function of true strain at (a) 77 K, (b) 293 K. [Figure presented] Table 2. Uniaxial materials properties of FeCoCrNi HEA at 77 and 293 K. [Table presented]

Journal article

calvert E, Knowles A, Pope J, Dye D, Jackson Met al., 2019, Novel high strength titanium-titanium composites produced using field-assisted sintering technology (FAST), Scripta Materialia, Vol: 159, Pages: 51-57, ISSN: 1359-6462

To increase the strength of titanium alloys beyond that achievable with α-β microstructures, alternative reinforcing methods are necessary. Here, field-assisted sintering technology (FAST) has been used to produce a novel Ti-5Al-5Mo-5V-3Cr (Ti-5553) metal-matrix-composite (MMC) reinforced with 0-25 wt.% of a ∼2 GPa yield strength TiFeMo alloy strengthened by ordered body-centred cubic intermetallic and ω phases. The interdiffusion region between Ti-5553 and TiFeMo particles was studied by modelling, electron microscopy, and nanoindentation to examine the effect of graded composition on mechanical properties and formation of α, intermetallic, and ω phases, which resulted in a > 200 MPa strengthening benefit over unreinforced Ti-5553.

Journal article

Yang R, Rahman KM, Rakhymberdiyev AN, Dye D, Vorontsov VAet al., 2019, Mechanical behaviour of Ti-Nb-Hf alloys, MATERIALS SCIENCE AND ENGINEERING A-STRUCTURAL MATERIALS PROPERTIES MICROSTRUCTURE AND PROCESSING, Vol: 740, Pages: 398-409, ISSN: 0921-5093

Journal article

Tong VS, Knowles AJ, Dye D, Ben Britton Tet al., 2019, Rapid electron backscatter diffraction mapping: Painting by numbers, Materials Characterization, Vol: 147, Pages: 271-279, ISSN: 1044-5803

Microstructure characterisation has been greatly enhanced through the use of electron backscatter diffraction (EBSD), where rich maps are generated through analysis of the crystal phase and orientation in the scanning electron microscope (SEM). Conventional EBSD analysis involves raster scanning of the electron beam and serial analysis of each diffraction pattern in turn. For grain shape, crystallographic texture, and microstructure analysis this can be inefficient. In this work, we present Rapid EBSD, a data fusion approach combining forescatter electron (FSE) imaging with static sparse sampling of EBSD patterns. We segment the FSE image into regions of similar colour (i.e. phase and crystal orientation) and then collect representative EBSD data for each segmented region. This enables microstructural assessment to be performed at the spatial resolution of the (fast) FSE imaging whilst including orientation and phase information from EBSD analysis of representative points. We demonstrate the Rapid EBSD technique on samples of a cobalt based superalloy and a strained dual phase titanium alloy, comparing the results with conventional analysis. Rapid EBSD is advantageous for assessing grain size distributions in time-limited experiments.

Journal article

Joseph S, Lindley T, Dye D, 2018, Dislocation interactions and crack nucleation in a fatigued near-alpha titanium alloy, International Journal of Plasticity, Vol: 110, Pages: 38-56, ISSN: 0749-6419

Dislocation interactions at the crack nucleation site were investigated in near-alpha titanium alloy Ti-6242Si subjected to low cycle fatigue. Cyclic plastic strain in the alloy resulted in dislocation pile-ups in the primary alpha grains, nucleated at the boundaries between the primary alpha and the two-phase regions. These two phase regions provided a barrier to slip transfer between primary alpha grains. We suggest that crack nucleation occurred near the basal plane of primary alpha grains by the subsurface double-ended pile-up mechanism first conceived by Tanaka and Mura. Superjogs on the basal dislocations were observed near the crack nucleation location. The two phase regions showed direct transmission of dislocations between secondary alpha plates, transmitted through the beta ligaments as , which then decompose into dislocation networks in the beta. The beta ligaments themselves do not appear to form an especially impenetrable barrier to slip, in agreement with the micropillar and crystal plasticity investigations of Zhang et al.

Journal article

Wang Y, Liu B, Yan K, Wang M, Kabra S, Chiu Y-L, Dye D, Lee PD, Liu Y, Cai Bet al., 2018, Probing deformation mechanisms of a FeCoCrNi high-entropy alloy at 293 and 77 K using in situ neutron diffraction, Acta Materialia, Vol: 154, Pages: 79-89, ISSN: 1359-6454

The deformation responses at 77 and 293 K of a FeCoNiCr high-entropy alloy, produced by a powder metallurgy route, are investigated using in situ neutron diffraction and correlative transmission electron microscopy. The strength and ductility of the alloy are significant improved at cryogenic temperatures. The true ultimate tensile strength and total elongation increased from 980 MPa to 45% at 293 K to 1725 MPa and 55% at 77 K, respectively. The evolutions of lattice strain, stacking fault probability, and dislocation density were determined via quantifying the in situ neutron diffraction measurements. The results demonstrate that the alloy has a much higher tendency to form stacking faults and mechanical twins as the deformation temperature drops, which is due to the decrease of stacking fault energy (estimated to be 32.5 mJ/m2 and 13 mJ/m2 at 293 and 77 K, respectively). The increased volume faction of nano-twins and twin-twin intersections, formed during cryogenic temperature deformation, has been confirmed by transmission electron microscopy analysis. The enhanced strength and ductility at cryogenic temperatures can be attributed to the increased density of dislocations and nano-twins. The findings provide a fundamental understanding of underlying governing mechanistic mechanisms for the twinning induced plasticity in high entropy alloys, paving the way for the development of new alloys with superb resistance to cryogenic environments.

Journal article

Gao J, Huang Y, Guan D, Knowles AJ, Ma L, Dye D, Rainforth WMet al., 2018, Deformation mechanisms in a metastable beta titanium twinning induced plasticity alloy with high yield strength and high strain hardening rate, Acta Materialia, Vol: 152, Pages: 301-314, ISSN: 1359-6454

Metastable β titanium alloys with both twinning (TWIP) and martensite transformation (TRIP)usually exhibit a low yield strength of between 200 and 500MPa, but high strain hardening rateand large uniform elongation. Alloys that exhibit twinning on a single system provide a higheryield strength, but a lower strain hardening rate. Here, for the first time, we report a new alloy(Ti-7Mo-3Cr wt%) with both high yield strength (695 MPa) and high work hardening rate(~1900 MPa) and a substantial 33.3% uniform elongation. The deformation mechanisms weresystematically investigated using EBSD and TEM for samples strained to 1.3%, 5% and 16%.The high yield strength was achieved through initial deformation mechanisms of two twinsystems, namely both {332}<113> and {112}<111> twinning. Importantly, the martensitetransformation was suppressed at this stage of deformation. The combination of two twinsystems, with approximately the same intensity, resulted in a high strain hardening rate(1600MPa to 1900MPa), much greater compared to alloys that exhibit a single twin system.Moreover, the TRIP effect was observed at strains greater than 5%, which also contributed tothe high strain hardening rate large uniform elongation.

Journal article

Gao J, Nutter J, Liu X, Guan D, Huang Y, Dye D, Rainforth WMet al., 2018, Segregation mediated heterogeneous structure in a metastable β titanium alloy with a superior combination of strength and ductility, Scientific Reports, Vol: 8, ISSN: 2045-2322

In β titanium alloys, the β stabilizers segregate easily and considerable effort has been devoted to alleviate/eliminate the segregation. In this work, instead of addressing the segregation problems, the segregation was utilized to develop a novel microstructure consisting of a nanometre-grained duplex (α+β) structure and micrometre scale β phase with superior mechanical properties. An as-cast Ti-9Mo-6W alloy exhibited segregation of Mo and W at the tens of micrometre scale. This was subjected to cold rolling and flash annealing at 820 oC for 2 and 5 mins. The solidification segregation of Mo and W leads to a locally different microstructure after cold rolling (i.e., nanostructured β phase in the regions rich in Mo and W and plate-like martensite and β phase in regions relatively poor in Mo and W), which play a decisive role in the formation of the heterogeneous microstructure. Tensile tests showed that this alloy exhibited a superior combination of high yield strength (692 MPa), high tensile strength (1115 MPa), high work hardening rate and large uniform elongation (33.5%). More importantly, the new technique proposed in this work could be potentially applicable to other alloy systems with segregation problems.

Journal article

Chang Y, Breen AJ, Tarzimoghadam Z, Kürnsteiner P, Gardner H, Ackerman A, Radecka A, Bagot PAJ, Lu W, Li T, Jägle EA, Herbig M, Stephenson LT, Moody MP, Rugg D, Dye D, Ponge D, Raabe D, Gault Bet al., 2018, Characterizing solute hydrogen and hydrides in pure and alloyed titanium at the atomic scale, Acta Materialia, Vol: 150, Pages: 273-280, ISSN: 1359-6454

Ti has a high affinity for hydrogen and are typical hydride formers. Ti-hydride are brittle phases which probably cause premature failure of Ti-alloys. Here, we used atom probe tomography and electron microscopy to investigate the hydrogen distribution in a set of specimens of commercially pure Ti, model and commercial Ti-alloys. Although likely partly introduced during specimen preparation with the focused-ion beam, we show formation of Ti-hydrides along α grain boundaries and α/β phase boundaries in commercial pure Ti and α+β binary model alloys. No hydrides are observed in the αphase in alloys with Al addition or quenched-in Mo supersaturation.

Journal article

Joseph S, Lindley TC, Dye D, Saunders EAet al., 2018, The mechanisms of hot salt stress corrosion cracking in titanium alloy Ti-6Al-2Sn-4Zr-6Mo, Corrosion Science, Vol: 134, Pages: 169-178, ISSN: 0010-938X

Hot salt stress corrosion cracking in Ti 6246 alloy has been investigated to elucidate the chemical mechanisms that occur. Cracking was found to initiate beneath salt particles in the presence of oxidation. The observed transgranular fracture was suspected to be due to hydrogen charging; XRD and high-resolution transmission electron microscopy detected the presence of hydrides that were precipitated on cooling. SEM-EDS showed oxygen enrichment near salt particles, alongside chlorine and sodium. Aluminium and zirconium were also involved in the oxidation reactions. The role of intermediate corrosion products such as Na2TiO3, Al2O3, ZrO2, TiCl2 and TiH are discussed.

Journal article

Coakley J, Radecka AE, Dye D, Bagot PAJ, Martin TL, Prosa TJ, Chen Y, Stone HJ, Seidman DN, Isheim Det al., 2018, Characterizing nanoscale precipitation in a titanium alloy by laser-assisted atom probe tomography., Materials Characterization, Vol: 141, Pages: 129-138, ISSN: 1044-5803

Atom-probe tomography was performed on the metastable β-Ti alloy, Ti-5Al-5Mo-5V-3Cr wt% (Ti-5553), aged at 300 °C for 0 to 8 h, to precipitate the embrittling isothermal ω phase. Accurate precipitate quantification requires monitoring and controlling suitable charge-state ratios in the mass spectrum, which in turn are closely related to the laser pulse energy used. High ultraviolet laser pulse energies result in significant complex molecular ion formation during field-evaporation, causing mass spectral peak overlaps that inherently complicate data analyses. Observations and accurate quantification of the ω-phase under such conditions are difficult. The effect is minimized or eliminated by using smaller laser pulse energies. With a small laser pulse energy, Ti-rich and solute depleted precipitates of the isothermal ω phase with an oxygen enriched interface are observed as early as after 1 h aging time utilizing the LEAP 5000X S (77% detection efficiency). We note that these precipitates were not detected below a 2 h aging time with the LEAP 4000X Si (58% detection efficiency). The results are compared to the archival literature. The Al concentration in the matrix/precipitate interfacial region increases during aging. Nucleation of the α-phase at longer aging times may be facilitated by the O and Al enrichment at the matrix/precipitate interface (both strong α-stabilisers). The kinetics and compositional trajectory of the ω-phase with aging time are quantified, facilitating direct correlation of the APT data to previously published mechanical testing.

Journal article

Bagot PAJ, Radecka A, Magyar AP, Bell DC, Smith GDW, Moody MP, Dye D, Rugg Det al., 2018, The effect of oxidation on the subsurface microstructure of a Ti-6Al-4V alloy, Scripta Materialia, Vol: 148, Pages: 24-28, ISSN: 1359-6462

Atom Probe Tomography (APT) and Transmission Electron Microscopy (TEM) are combined for examining α-case formation in Ti-6Al-4V, generated by air exposure at 800 °C. Below the oxide surface, the microstructure separates into a nanoscale mixture of the α-Ti and α2 Ti3Al phases, of compositions Ti70-O30 and Ti65-O10-Al20-V5 respectively. The α2 phase exists either as bands or as nanoscale spherical precipitates. Nitrogen also penetrates the surface, but to a lesser extent, while vanadium partitions to α2 or in distinctly separate phases. The results demonstrate that oxygen stimulates precipitation of α2, helping to explain embrittlement produced in the O-enriched layer beneath the oxide.

Journal article

Knowles A, Tea-Sung J, Bhowmik A, Jones N, Britton TB, Giuliani F, Stone H, Dye Det al., 2018, Data on a new beta titanium alloy system reinforced with superlattice intermetallic precipitates, Data in Brief, Vol: 17, Pages: 863-869, ISSN: 2352-3409

The data presented in this article are related to the research article entitled “a new beta titanium alloy system reinforced with superlattice intermetallic precipitates” (Knowles et al., 2018) [1]. This includes data from the as-cast alloy obtained using scanning electron microscopy (SEM) and x-ray diffraction (XRD) as well as SEM data in the solution heat treated condition. Transmission electron microscopy (TEM) selected area diffraction patterns (SADPs) are included from the alloy in the solution heat treated condition, as well as the aged condition that contained < 100 nm B2 TiFe precipitates [1], the latter of which was found to exhibit double diffraction owing to the precipitate and matrix channels being of a similar width to the foil thickness (Williams and Carter, 2009) [2]. Further details are provided on the macroscopic compression testing of small scale cylinders. Of the micropillar deformation experiment performed in [1], SEM micrographs of focused ion beam (FIB) prepared 2 µm micropillars are presented alongside those obtained at the end of the in-situ SEM deformation as well as videos of the in-situ deformation. Further, a table is included that lists the Schmidt factors of all the possible slip systems given the crystal orientations and loading axis of the deformed micropillars in the solution heat treated and aged conditions.

Journal article

Joseph S, Bantounas, Lindley, Dye Det al., 2017, Slip Transfer and Deformation Structures Resulting from the Low Cycle Fatigue of Near-alpha Titanium Alloy Ti-6242Si, International Journal of Plasticity, Vol: 100, Pages: 90-103, ISSN: 0749-6419

Near-alpha titanium alloy Ti6242Si, widely used in aero-engine compressor discs, was subjected to low cycle fatigue loading at room temperature. Fracture initiated by facet formation, followed by striated fatigue crack growth prior to final failure. Deformation occurred primarily by planar slip, localized into slip bands in the primary alpha. Within soft-oriented grains in a microtextured region, pile-up of a slip band within one grain resulted in the direct transfer of slip into an adjacent similarly oriented grain. In contrast, pile up of dislocations in a soft grain with a ‘hard’ oriented neighbour resulted in the activation of few non-connected dislocations in the hard grain, with <a>-type dislocations being activated and the observation of cross-slip. Whilst a high density of dislocations was present from precipitation of secondary alpha in the retained beta ligaments, a little dislocation interaction was observed between the transformed beta and the primary alpha grains.

Journal article

Knowles A, Bhowmik A, Purkayastha S, Jones NG, Giuliani F, Clegg WJ, Dye D, Stone HJet al., 2017, Data on a Laves phase intermetallic matrix composite in situ toughened by ductile precipitates, Data in Brief, Vol: 14, Pages: 489-493, ISSN: 2352-3409

The data presented in this article are related to the research article entitled “Laves phase intermetallic matrix composite in situ toughened by ductile precipitates” (Knowles et al.) [1]. The composite comprised a Fe2(Mo, Ti) matrix with bcc (Mo, Ti) precipitated laths produced in situ by an aging heat treatment, which was shown to confer a toughening effect (Knowles et al.) [1]. Here, details are given on a focused ion beam (FIB) slice and view experiment performed on the composite so as to determine that the 3D morphology of the bcc (Mo, Ti) precipitates were laths rather than needles. Scanning transmission electron microscopy (S(TEM)) micrographs of the microstructure as well as energy dispersive X-ray spectroscopy (EDX) maps are presented that identify the elemental partitioning between the C14 Laves matrix and the bcc laths, with Mo rejected from the matrix into laths. A TEM selected area diffraction pattern (SADP) and key is provided that was used to validate the orientation relation between the matrix and laths identified in (Knowles et al.) [1] along with details of the transformation matrix determined.

Journal article

Knowles AJ, Jun T-S, Bhowmik A, Jones NG, Giuliani F, Britton TB, Stone HJ, Dye Det al., 2017, A new beta titanium alloy system reinforced with superlattice intermetallic precipitates, Scripta Materialia, Vol: 140, Pages: 71-75, ISSN: 1872-8456

Titanium alloys traditionally lack a nm-scale intermetallic precipitate that can be exploited for age-hardening from solid solution. Here such a strengthening concept is developed in the Ti-Fe-Mo system, with it being found that a high temperature β (bcc A2) single-phase field for homogenisation can be obtained, which following ageing (750 °C/80 h) precipitated B2 TiFe <100 nm in size. The orientation relationship was found to be ⟨100⟩A2//⟨100⟩B2, {100}A2//{100}B2, with a misfit of −6.1%. The alloy was found to be very hard (HV0.5 = 6.4 GPa) and strong (σy, 0.2 = 1.9 GPa) with a density of 6.68 g cm−3. TEM observation and micropillar deformation showed that the precipitates resist dislocation cutting.

Journal article

Knowles AJ, Bhowmik, Purkayastha S, Jones NG, Giuliani F, Clegg WJ, Dye D, Stone HJet al., 2017, Laves phase intermetallic matrix composite in situ toughened by ductile precipitates, Scripta Materialia, Vol: 140, Pages: 59-62, ISSN: 1872-8456

Laves phase based materials are of interest for elevated temperature applications for their high melting points and strengths but are critically limited by their low fracture toughness. Here, a Laves phase intermetallic matrix composite toughened by ductile precipitates has been studied. This microstructure was produced in situ by heat treating a Fe2(Mo,Ti) based alloy to precipitate ∼ 12% volume fraction of fine ∼ 250 nm bcc, A2 (Mo,Ti), phase, with an orientation relationship of . The precipitated A2 phase increased the indentation fracture toughness from 1.1 to 2.2 MPa m1/2 while maintaining a high hardness of HV0.5 = 8.9 GPa similar to monolithic Laves phases.

Journal article

Coakley J, Ma D, Frost M, Dye D, Seidman DN, Dunand DC, Stone HJet al., 2017, Lattice strain evolution and load partitioning during creep of a Ni-base superalloy single crystal with rafted gamma prime microstructure, Acta Materialia, Vol: 135, Pages: 77-87, ISSN: 1359-6454

In-situ neutron diffraction measurements were performed on monocrystalline samples of the Ni-based superalloy CMSX-4 during N-type γ′ raft formation under the tensile creep conditions of 1150 °C/100 MPa, and subsequently on a rafted sample under the low temperature/high stress creep conditions of 715 °C/825 MPa. During 1150 °C/100 MPa creep, the γ′ volume fraction decreased from ∼70% to ∼50%, the lattice parameter misfit was partly relieved, and the load was transferred from the creeping γ matrix to the γ′ precipitates. On cooling back to room temperature, a fine distribution of γ′ precipitates formed in the γ channels, and these precipitates were present in the 715 °C/825 MPa creep regime. Under low temperature/high stress creep, the alloy with rafted γ′ microstructure exhibited superior creep strength to the cuboidal γ′ microstructure produced following a standard heat-treatment. A lengthy creep incubation period was observed, believed to be associated with {111} dislocations hindering propagation of {111} dislocations. Following the creep incubation period, extensive macroscopic creep strain accumulated during primary creep as the γ phase yielded. Finally, the diffraction data suggest a loss of precipitate/matrix coherency in the (0k0) interfaces as creep strain accumulated.

Journal article

Chapman TP, Dye D, Rugg D, 2017, Hydrogen in Ti and Zr alloys: industrial perspective, failure modes and mechanistic understanding, Philosophical transactions. Physical sciences and engineering, Vol: 375, ISSN: 0962-8428

Titanium is widely used in demanding applications, such as in aerospace. Its strength-to-weight ratio andcorrosion resistance make it well suited to highly stressed rotating components. Zirconium has a no lesscritical application where its low neutron capture cross section and good corrosion resistance in hot water andsteam make it well suited to reactor core use, including fuel cladding and structures. The similar metallurgicalbehaviour of these alloy systems make it alluring to compare and contrast their behaviour. This is rarelyundertaken, mostly because the industrial and academic communities studying these alloys have littleoverlap. The similarities with respect to hydrogen are remarkable, albeit potentially unsurprising, and so thispaper aims to provide an overview of the role hydrogen has to play through the material life cycle. Thisincludes the relationship between alloy design and manufacturing process windows, the role of hydrogen indegradation and failure mechanisms and some of the underpinning metallurgy. The potential role ofsome advanced experimental and modelling techniques will also be explored to give a tentative view ofpotential for advances in this field in the next decade or so.

Journal article

Tong VS, Joseph S, Ackerman A, Dye, Brittonet al., 2017, Using transmission Kikuchi diffraction to characterise α variants in an α+β titanium alloy, Journal of Microscopy, Vol: 267, Pages: 318-329, ISSN: 1365-2818

Two phase titanium alloys are important for high-performance engineering components, such as aeroengine discs. The microstructures of these alloys are tailored during thermomechanical processing to precisely control phase fractions, morphology and crystallographic orientations. In bimodal two phase (α + β) Ti-6Al-2Sn-4Zr-2Mo (Ti-6242) alloys there are often three microstructural lengthscales to consider: large (∼10 μm) equiaxed primary α; >200 nm thick plate α with a basketweave morphology; and very fine scaled (<50 nm plate thickness) secondary α that grows between the larger α plates surrounded by retained β. In this work, we utilise high spatial resolution transmission Kikuchi diffraction (TKD, also known as transmission-based electron backscatter diffraction, t-EBSD) and scanning electron microscopy (SEM)-based forward scattering electron imaging to resolve the structures and orientations of basketweave and secondary α in Ti-6242. We analyse the α variants formed within one prior β grain, and test whether existing theories of habit planes of the phase transformation are upheld. Our analysis is important in understanding both the thermomechanical processing strategy of new bimodal two-phase titanium alloys, as well as the ultimate performance of these alloys in complex loading regimes such as dwell fatigue. Our paper champions the significant increase in spatial resolution afforded using transmission techniques, combined with the ease of SEM-based analysis using conventional electron backscatter diffraction (EBSD) systems and forescatter detector (FSD) imaging, to study the nanostructure of real-world engineering alloys.

Journal article

Rahman KM, Vorontsov VA, Flitcroft SM, Dye Det al., 2017, A high strength Ti-SiC metal matrix composite, Advanced Engineering Materials, Vol: 19, ISSN: 1527-2648

A SiC reinforced Ti-5Al-5Mo-5V-3Cr matrix metal matrix composite is developed. Monolithic blocks of alloy are hot rolled via pack rolling to produce foils for MMC panel fabrication. These are consolidated using hot isostatic pressing and solution treated and aged for optimum strength. The panels exhibited a strength of 2 GPa in tension and 3.5 GPa in compression, compared to the aerospace steel 300M, which has a tensile strength of 1.69 GPa. The fatigue performance of the material exceeded that of MMCs developed using Ti-21S or Ti-6Al-4V matrices. Finally, the reaction zone between the SiC and matrix is examined, revealing the presence of TiC.

Journal article

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