Expanding time–temperature-transformation (TTT) diagrams to interfaces: A new approach for grain boundary engineering

Cantwell, Patrick R.; Ma, Shuailei; Bojarski, Stephanie A.; Rohrer, Gregory S.; Harmer, Martin P.

doi:10.1016/j.actamat.2016.01.010

Cited by 79 publications

(54 citation statements)

References 18 publications

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“…Conceptually, the distinct interface structures observed in both alloys are similar to the formation of interface ‘complexions' which have been identified in the case of grain boundaries in several ceramic and metallic systems2728. Complexions are ‘interface-stabilized states'29 that have a structure and composition different from that of the matrix and remain confined in the region where they form.…”

Section: Discussionsupporting

confidence: 53%

Phase transformation strengthening of high-temperature superalloys

et al. 2016

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Decades of research has been focused on improving the high-temperature properties of nickel-based superalloys, an essential class of materials used in the hot section of jet turbine engines, allowing increased engine efficiency and reduced CO2 emissions. Here we introduce a new ‘phase-transformation strengthening' mechanism that resists high-temperature creep deformation in nickel-based superalloys, where specific alloying elements inhibit the deleterious deformation mode of nanotwinning at temperatures above 700 °C. Ultra-high-resolution structure and composition analysis via scanning transmission electron microscopy, combined with density functional theory calculations, reveals that a superalloy with higher concentrations of the elements titanium, tantalum and niobium encourage a shear-induced solid-state transformation from the γ′ to η phase along stacking faults in γ′ precipitates, which would normally be the precursors of deformation twins. This nanoscale η phase creates a low-energy structure that inhibits thickening of stacking faults into twins, leading to significant improvement in creep properties.

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Section: Discussionsupporting

confidence: 53%

Phase transformation strengthening of high-temperature superalloys

et al. 2016

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“…1(b), the a + b microstructure is metastable above T C for short times. Complexion TTT diagrams exhibit analogous regions of metastability [5], suggesting that they undergo nucleation and growth processes similar to those characteristic of bulk phases. One signature of a grain-boundary complexion transition is the appearance of abnormally large grains [3,6], and experiments have shown that the number density of abnormal grains increases exponentially with temperature [7], an observation that is consistent with a nucleation and growth mechanism.…”

Section: Introductionmentioning

confidence: 92%

“…Just as with bulk phase transformations, complexion transitions take time to occur, and therefore their kinetics can be represented on TTT-style diagrams. The first experimental complexion TTT diagrams were recently reported based on grain growth studies of polycrystalline Y 2 O 3 and Al 2 O 3 [5]. These diagrams clearly show the combinations of time and temperature at which grain-boundary complexion transitions occur, unifying and displaying a large data set in a readily understood format.…”

Section: Introductionmentioning

confidence: 98%

“…Complexion transition kinetics can vary from one grain boundary to another because grain boundaries of different character exist in different thermodynamic states owing to difference in interfacial atomic geometry. It has been shown that complexion transitions preferentially occur on higher energy interfaces [9] at shorter annealing times than transitions on lower energy interfaces [5]. Therefore, the grainboundary character distribution (GBCD) and the resultant grainboundary energy anisotropy present in a polycrystalline material may lead to grain-boundary complexion transitions occurring at a variety of different times and temperatures.…”

Section: Introductionmentioning

confidence: 99%

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Complexion time-temperature-transformation (TTT) diagrams: Opportunities and challenges

Schumacher

Marvel

Kelly

et al. 2016

Current Opinion in Solid State and Materials Science

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a b s t r a c tGrain boundaries and other interfaces can undergo complexion transitions from one thermodynamic state to another, resulting in discontinuous changes in interface properties such as diffusivity, mobility, and cohesive strength. The kinetics of such complexion transitions has been largely overlooked until recently. Just as with bulk phase transformations, complexion transition kinetics can be represented on time-temperature-transformation (TTT) diagrams. An experimental complexion TTT diagram is presented here for polycrystalline Eu-doped spinel annealed at 1400-1800°C. This material developed a microstructure with a bimodal grain size distribution, indicating that a complexion transition occurs within this temperature range. The time and temperature dependence of this complexion transition was analyzed and used to produce a grain-boundary complexion TTT diagram for this system. Complexion TTT diagrams have the potential to be remarkably useful tools for manipulating the properties of internal interfaces in polycrystalline metals and ceramics. The development of experimental complexion TTT diagrams is likely to have an important impact on the field of grain-boundary engineering, and hence the development of these experimental diagrams should be an intense area of focus in the coming years.

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“…Interesting attempts have been implemented by researchers (e.g., Cantwell et al, 2016 andGuo et al, 2015), who investigated the grain size variations through electron scanning techniques. Also, studies in steel features under fire conditions presented by Digges et al (1966), Smith et al (1981), Kirby et al (1986) and Tide (1998).…”

Section: Studies On Mechanical Propertiesmentioning

confidence: 99%

Mechanical properties of High and Very High Steel at elevated temperatures and after cooling down

2017

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High-strength steels (HSS) are produced using special chemical composition or/and manufacturing processes. Both aspects affect their mechanical properties at elevated temperatures and after cooling down, and particularly the residual strength and the ductility of the structural members. As HSS equates the design of lighter structural elements, higher temperatures are developed internally compared to the elements designed with conventional carbon steel. Therefore, the low thickness members, along with the severe effect of high temperature on the mechanical properties of the HSS, constitute to the increased vulnerability of such structures in fire. Moreover, the re-use and reinstatement of these structures are more challenging due to the lower residual mechanical properties of HSS after the cooling down period. This paper presents a review of the available experimental studies of the mechanical properties of HSS at elevated temperatures and after cooling down. The experimental results are collected and compared with the proposed material model (reduction factors) of EN1993-1-2. Based on these comparisons, modified equations describing the effect of elevated temperatures on the mechanical properties of HSS are proposed. Also, the post-fire mechanical properties of HSS are examined. A comprehensive discussion on the effect of influencing parameters, such as manufacturing process, microstructure, loading conditions, maximum temperature, and others is further explored.

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Expanding time–temperature-transformation (TTT) diagrams to interfaces: A new approach for grain boundary engineering

Cited by 79 publications

References 18 publications

Phase transformation strengthening of high-temperature superalloys

Phase transformation strengthening of high-temperature superalloys

Complexion time-temperature-transformation (TTT) diagrams: Opportunities and challenges

Mechanical properties of High and Very High Steel at elevated temperatures and after cooling down

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