I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[30411]
Open Access
Abstract: Superelastic metastable β-Ti alloys, which undergo a stress-induced β → α″ transformation, have attracted significant attention in the biomedical and aerospace sectors. However, difficulty in predicting and controlling their superelastic properties, which is often linked to the ω phase, has prevented industrial uptake. The ω phase exists in two distinct forms, athermal (ωath) and isothermal (ωiso), yet despite their differences the two are often conflated, leading to conflicting statements surrounding their influence. Using in situ synchrotron diffraction, the mechanical response of two initially identical samples of Ti-24Nb (at.%), one cooled to form ωath and the other aged to form ωiso, was evaluated. The ωath sample exhibited superelasticity, with the ωath consumed by the growing α″ martensite. In contrast, the ωiso sample showed no evidence of a transformation. These data conclusively show that the ωath should not be considered a problem for superelastic alloy development, whilst the evolution of ωiso is highly detrimental.
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Dec 2025
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I12-JEEP: Joint Engineering, Environmental and Processing
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J. R.
Miller
,
H. C.
Cole
,
J. M.
Hogg
,
J.
Pitchforth
,
L. D.
Connor
,
P.
Vacek
,
S.
Neumeier
,
N. L.
Church
,
P. A.
Midgley
,
D. M.
Collins
,
C. M. F.
Rae
,
H. J.
Stone
Diamond Proposal Number(s):
[31966]
Open Access
Abstract: Single crystal Ni-base superalloys, like many materials containing an A1 structured phase, demonstrate additional forbidden reflections in diffraction experiments. These additional reflections are most commonly attributed to the presence of chemical short-range order, or to thin foil effects in transmission electron microscopy. In this study, transmission electron diffraction and synchrotron X-ray diffraction were used to interrogate the deformation mechanics in a single crystal Ni-base superalloy at room temperature. Additional reflections were observed around those from the A1 phase in both diffraction experiments, arising from relrods along . These relrods were linked to the formation of extensive intrinsic stacking faults (ISFs) within the A1 phase, giving rise to local disorder and a relaxation of the Bragg condition. This study represents the first use of single crystal X-ray diffraction to characterise forbidden reflections in A1 structures from bulk specimens, thereby discounting thin foil effects completely.
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Sep 2025
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I12-JEEP: Joint Engineering, Environmental and Processing
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J. F. S.
Markanday
,
N.
D’souza
,
N. L.
Church
,
J. R.
Miller
,
J. J. C.
Pitchforth
,
L. D.
Connor
,
S.
Michalik
,
B.
Roebuck
,
N. G.
Jones
,
K. A.
Christofidou
,
H. J.
Stone
Diamond Proposal Number(s):
[33375]
Abstract: Factors affecting strain-age cracking (SAC) have been quantitatively assessed in a range of Ni-base superalloys with differing γ′ contents. Differences in the amount of γ′ present in the as-built condition of HA282, STAL 15DE, CM247LC, and IN713LC are highlighted. In the as-built condition, γ′ are absent in HA282, but appear as nano-clusters in IN713LC. On heating, γ′ precipitates coherently in the γ phase, increasing the yield strength. The kinetics of precipitation are dependent on the heating rate and precipitation terminates at different temperatures in different alloys. The propensity to SAC is assessed via volume changes accompanying precipitation, increase in elastic modulus accompanying γ′ precipitation, and a loss in ductility/grain boundary cohesive strength with increasing temperature. A marked feature of additively built microstructures is the dramatically low grain boundary cohesive strength at ~800 °C, which is related to the segregation within the terminal liquid film at the grain boundary. The most important factor contributing to SAC is the lack of ductility and reduced grain boundary cohesive strength.
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Aug 2024
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I11-High Resolution Powder Diffraction
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Claire A.
Murray
,
Project M
Scientists
,
Laura
Holland
,
Rebecca
O'Brien
,
Alice
Richards
,
Annabelle
Baker
,
Mark
Basham
,
David
Bond
,
Leigh D.
Connor
,
Sarah J.
Day
,
Jacob
Filik
,
Stuart
Fisher
,
Peter
Holloway
,
Karl
Levik
,
Ronaldo
Mercado
,
Jonathan
Potter
,
Chiu C.
Tang
,
Stephen P.
Thompson
,
Julia E.
Parker
Diamond Proposal Number(s):
[15723]
Open Access
Abstract: Calcite and vaterite crystallisation is strongly influenced by the presence of additives during the reaction process, as demonstrated by organic molecules in biogenic calcium carbonate formation. The effect of additives on the lattice parameters of calcite and vaterite in syntheses are frequently reported, but only as discrete studies discussing a single polymorph. The intertwined nature of these polymorphs, due to their shared reaction pathway, is rarely discussed. In this work we report the results of a large scale citizen science project to explore the influence of amino acids and related additives on both polymorphs, highlighting their differences and commonalities in terms of the effect on the lattice parameters and polymorph selectivity.
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Jan 2024
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[30411]
Open Access
Abstract: Metastable β Ti alloys based on the Ti–Nb system have received increased attention in recent years due to an attractive range of properties. This includes their ability to undergo martensitic phase transformations on application of a stress, or on cooling below a critical temperature. However, the cyclic behaviour of these materials is unstable, which is a significant barrier to widespread industrial use. Recently, both the thermal and mechanical aspects of the transformation have been shown to be highly sensitive to the presence of internal stresses, which include a contribution from the dislocations produced as a necessary product of the transformation to provide geometric continuity at the phase boundary. It has been hypothesised that these dislocations may be responsible for the unstable cyclic behaviour. Redistribution of these dislocations and their associated stresses at elevated temperatures provides a novel mechanism by which unstable cyclic behaviour can be mitigated. Hence, in this work, in situ synchrotron characterisation is used to assess the effect of thermal cycling subsequent to mechanical loading on the superelastic transformation in a commercial Ti–Nb alloy. For the first time, it was shown that unstable cyclic behaviour can be avoided through the use of inter-cycle thermal treatments, which represents a significant breakthrough in our understanding of Ti–Nb superelastic materials.
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Oct 2023
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Open Access
Abstract: Metastable β-Ti alloys based on the binary Ti-Nb system can exhibit a stress induced transformation to the α″ phase allowing superelasticity and shape memory behaviours but they are also susceptible to the formation of the hexagonal ω phase. The presence of ω is widely reported to prevent the α″ transformation, and in certain forms embrittles the material. Most studies characterise the ω phase ex situ and only observation of the ω phase is used to predict its stability. This approach ignores different potential formation mechanisms and results in an ambiguous picture of its true stability. Here, through the use of in situ synchrotron X-ray diffraction we establish the true nature of the α″ and athermal ω phase transformations with respect to both temperature and composition in a series of cold rolled Ti-Nb alloys which initially contained both α″ and ω. Across the range of studied alloys, the α″ start temperature was always found to be above the ω start temperature but both phases were observed to grow simultaneously contradicting previous reports. In addition, the ω start temperature in all alloys was found to be ≤ 10˚C indicating that the ω present in the initial microstructures was metastable. These observations contradict a vast swathe of the conclusions drawn from ex situ data regarding the stability of the ω phase and categorically show that observation of this phase alone cannot be used to establish its stability and the relevant thermodynamic temperature, ωs.
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Oct 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[30411]
Open Access
Abstract: Within the literature significant variations in martensite start temperature (Ms) can be observed for samples of identical composition. However, the factors affecting Ms are not well understood, limiting industrial uptake. Recently, claims that the isothermal variant of the ω phase (ωiso) may be driving many changes in Ms have been called into question due to the absence of any compositionally distinct ωiso following thermal cycling. In the present study, in situ synchrotron X-ray diffraction has been employed to conclusively show that dramatic changes in Ms can be replicated without any formation of ωiso. Dislocations have been shown to be mobile at the temperatures reached and, as such, an alternative mechanism based on the total stress model has been proposed. This added understanding can rationalise many of the discrepancies observed in the literature, and ultimately improve industrial uptake of this class of material.
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Jun 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[20699, 31965]
Abstract: Metastable β-Ti alloys have attracted significant industrial interest due to their exceptionally high specific strength and intrinsic corrosion resistance. Their metastability also leads to the potential for numerous phase transformations, such as the martensitic β → α" which can lead to superelastic behaviour. However, the β phase is also inherently susceptible to the formation of the isothermal ω phase (ωiso) during ageing at low to intermediate temperatures. This Ti-rich hexagonal phase is widely reported to have a detrimental effect on mechanical properties and subsequent phase transformations. However, there are conflicting views as ωiso has also been reported to produce nanoscale microstructures with exceptional strength and improve some superelastic properties. Using in situ synchrotron X-ray diffraction the evolution of ωiso in a commercial superelastic alloy, Ti-24Nb-4Zr-8Sn (wt %), has been evaluated. Heat treatments were subsequently selected to provide a systematic variation in ωiso volume fraction. Samples were then subjected to ex situ and in situ mechanical loading allowing the effect of ωiso precipitation on the mechanical properties and superelasticity to be systematically studied.
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Jun 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[30411]
Abstract: Ti-Nb based metastable β Ti alloys have potential utility across a range of sectors due to their ability to show reversible superelastic behaviour during mechanical cycling. This behaviour results in mechanical hysteresis, whereby energy is absorbed on cycling, giving rise to vibration damping capabilities. However, these alloys typically suffer from changes in the loading response which can often be observed even within the first few cycles. Despite this, the degradation mechanisms are not well characterised or understood. Often, superelastic materials are only studied ex situ, highlighting trends without providing a complete mechanistic understanding of the transformation behaviour. Consequently, there are inconsistencies in reported results, such as a fully recovered single phase β when cycled to low applied stresses, and the observation of retained α” following cycling to higher loads. Therefore, in situ techniques are needed to provide direct information as to any changes within these materials whilst the transformation occurs. Here, in situ synchrotron X-ray diffraction (sXRD) has been used to characterise the evolution of the αʺ phase in Ti2448 (Ti-24Nb-4Zr-8Sn, wt%) during mechanical cycling. These data, provide direct rationale for many discrepancies observed in the literature, and pave the way towards a more complete understanding of the behaviour of these alloys.
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Jun 2023
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I12-JEEP: Joint Engineering, Environmental and Processing
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Diamond Proposal Number(s):
[30411]
Abstract: Alloys based on the Ti-Nb system display a wide range of attractive properties to several industrial sectors, due to their ability to undergo a fully reversible diffusionless phase transformation between the parent bcc β phase and the orthorhombic α" martensite. However, a wide variability in the reported transformation parameters exists, independent of alloy composition. In many cases this variability can be linked to prior processing conditions, such as cooling rate, which promotes a martensitic microstructure when cooled more rapidly, and results in lower measured values of δSIM. Historically it has been suggested that the ω phase precipitates preferentially to the α" when cooled slowly, and acts to suppress Ms. However, recent studies have suggested that ω may not be able to form isothermally within the timeframes necessary to prevent the transformation to α". Consequently, in situ synchrotron X-ray diffraction has been used to monitor the evolution of ω, during thermal cycling a β+α" microstructure to different temperatures. These data will be used alongside complementary ex situ TEM to provide a mechanistic understanding of how temperature affects both the thermal and mechanical transformation from β to α". Further to this we will also show how these effects, coupled with this new understanding, can be manipulated to address other long-term issues associated with these alloys.
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Jun 2023
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