Isothermal Cycling Research Articles

Minimizing lithium deactivation during high-rate electroplating via sub-ambient thermal gradient control

The reversibility of Li electrodeposits must be significantly improved for Li metal anodes to be realized for next-generation, high energy density batteries. The most commonly tested thermal condition in the Li metal battery literature is isothermal ~20 °C (ambient). Elevating the cell temperature (40 °C) improves Li metal stability by suppressing dendritic growth at the expense of augmenting solid electrolyte interphase growth. However, at the high current density and areal capacity tested in this work (10 mA cm−2, 3.0 mA h cm−2), dendritic growth is inevitable and Li metal electrodes succumb to extensive degradation due to Li deactivation. To overcome these shortcomings of isothermal cycling, we expand on our concept of an interelectrode thermal gradient, which enhances Li surface diffusion to homogenize Li electroplating. With mean temperatures near ambient, a thermal gradient (ΔTwarm: 22.6 °C negative electrode, 21.4 °C positive electrode) delays failure compared with isothermal control (20 °C). The greatest benefit of the thermal gradient is unlocked at sub-ambient electrode temperatures. By applying the thermal gradient at low temperatures (ΔTcold: 3.7 °C negative electrode, 2.0 °C positive electrode), SEI growth stifles, dendrite propagation suppresses, and Li deactivation minimizes, stabilizing high-rate Li electroplating and stripping. After 100 cycles, ΔTcold reduces voltage hysteresis and electrode resistance by 51% and 77%, respectively, compared with the most promising isothermal condition (40 °C). Operando optical visualization confirms more reversible and dense Li electrodeposition via sub-ambient thermal gradient control with higher first-cycle Coulombic efficiency in an anode-free configuration. By contrast, isothermal 20 °C control exacerbates porous and dendritic Li electrodeposition with low reversibility.

Oxygen Exchange in Dual-Phase La0.65Sr0.35MnO3-CeO2 Composites for Solar Thermochemical Fuel Production.

Increasing the capacity and kinetics of oxygen exchange in solid oxides is important to improve the performance of numerous energy-related materials, especially those for the solar-to-fuel technology. Dual-phase metal oxide composites of La0.65Sr0.35MnO3-x%CeO2, with x = 0, 5, 10, 20, 50, and 100, have been experimentally investigated for oxygen exchange and CO2 splitting via thermochemical redox reactions. The prepared metal oxide powders were tested in a temperature range from 1000 to 1400 °C under isothermal and two-step cycling conditions relevant for solar thermochemical fuel production. We reveal synergetic oxygen exchange of the dual-phase composite La0.65Sr0.35MnO3-CeO2 compared to its individual components. The enhanced oxygen exchange in the composite has a beneficial effect on the rate of oxygen release and the total CO produced by CO2 splitting, while it has an adverse effect on the maximum rate of CO evolution. Ex situ Raman and XRD analyses are used to shed light on the relative oxygen content during thermochemical cycling. Based on the relative oxygen content in both phases, we discuss possible mechanisms that can explain the observed behavior. Overall, the presented findings highlight the beneficial effects of dual-phase composites in enhancing the oxygen exchange capacity of redox materials for renewable fuel production.

Quantification of the Phase Transformation Kinetics in High Chromium Cast Irons Using Dilatometry and Metallographic Techniques

Further development of high chromium cast irons (HCCI) is based on tailoring the microstructure, necessitating an accurate control over the phase transformation and carbide precipitation temperatures and can be achieved by thermal treatments (TT). To understand the underlying mechanisms controlling the transformation kinetics during the different stages of the TT, it is imperative to adjust the TT parameters to have information of the transformations occurring during non-thermal and isothermal heating cycles, since proper selection of the TT parameters ensures the optimum use of the alloying elements. In this work, the boundaries of the phase transformations for a HCCI containing 26 wt pct Cr for different cooling rates (continuous cooling transformation, CCT, diagram) were established by applying dilatometric measurements. Based on the CCT diagram, a temperature-time-transformation (TTT) diagram was constructed by isothermally holding the samples until complete phase transformation. For determining the initiation and finishing of the transformation, the lever rule assisted by derivatives was applied. The phases present after transformation were determined by combining X-ray diffraction (XRD) and metallographic characterization using optical microscopy (OM) and scanning electron microscopy (SEM). Finally, the data obtained from the dilatometer was experimentally verified by isothermally heat treating some samples using laboratory furnaces. The transformed phase fraction from OM and SEM images was then correlated to the fraction obtained from the TTT diagram.

Correlation of thermal characteristics and microstructure of multilayer electron beam physical vapor deposition thermal barrier coatings

Referring to the expected increasing amount of aviation until the year 2030, energy and fuel efficiency as well as harmful emissions are of prime importance to the technological and ecological advancement of aircraft engines. Minimizing fuel consumption and improving energy efficiency of jet engines can be reached by increased turbine entry temperatures. However, the permitted combustion temperatures are restricted by material-dependent maximum service temperatures. Nowadays, yttria stabilized zirconia (YSZ) is commonly used as thermal barrier coating (TBC), only withstanding a permanent surface temperature of T ≈ 1200°C. In recent years, research projects have shown that multilayer systems might be a solution to withstand higher combustion temperatures. In order to assess this potential of multilayer systems, quadruple TBC consisting of 7 wt.% YSZ and La2Zr2O7 were deposited on INCONEL® 600 by electron beam physical vapor deposition. The quadruple TBC were fundamentally characterized with regard to their microstructure as well as their thermal conductivity λ. Considering the requirements with regard to the application, the long term behavior under isothermal and thermal cycling load is of great importance. To classify this behavior, atmospheric annealing tests were performed at temperatures of T = 1200°C and T = 1300°C for t = 50 h as well as thermal cycling tests were conducted at a temperature of T = 1150°C for N = 1000 cycles. The results of the quadruple layer TBC were compared to the prior investigated single and double layered TBC coatings consisting of YSZ or 7YSZ/La2Zr2O7. The investigations showed no major influence of multilayer architecture regarding the thermal conductivity λ compared to conventional 7YSZ single layer architecture. Moreover, multilayer architecture leads to the increase of porosity inside the TBC. However, no strong correlation between porosity and thermal conductivity can be revealed. The analyses of the thermal cycled TBC show that TBC delamination is mainly caused by accelerated growth of thermally grown oxide and sintering effects. Furthermore, no improvement of the thermal cycling behavior due to quadruple multilayer architecture compared to 7YSZ single layer can be determined. The comparison of thermal cycling behavior regarding single, double and quadruple layer architecture emphasizes increased TBC lifetime of double layer TBC.

Cyclic plastic response and damage mechanisms in superaustenitic steel Sanicro 25 in high temperature cycling – Effect of tensile dwells and thermomechanical cycling

The cyclic plastic response and damage evolution in isothermal high temperature constant strain rate cycling and during in-phase thermomechanical fatigue in superaustenitic Sanicro 25 steel have been studied both with and without introduction of dwells at maximum strain. Fatigue hardening/softening curves and fatigue life curves are reported for all types of fatigue tests. Rapid hardening and a tendency to saturation has been found primarily in isothermal cycling with dwells and in thermomechanical cycling. Study of the surface damage evolution using SEM observations and FIB cutting revealed the preferential oxidation of grain boundaries perpendicular to the stress axis. Introduction of dwells in maximum tension leads to the enlargement of the plastic strain amplitude and to additional creep damage in the form of cavities along grain boundaries and internal cracks. Fatigue hardening rate in thermomechanical cycling is higher than in constant strain rate cycling and fatigue life decreases substantially in in-phase thermomechanical cycling. These findings are discussed in the perspective of effectiveness of dominant damage mechanisms relevant to individual types of cyclic straining.

A hairpin probe-mediated isothermal amplification method to detect target nucleic acid

We herein describe Hairpin probe-mediated Isothermal Amplification (HIAmp), a novel isothermal method to detect a target nucleic acid. This method employs a hairpin probe (HP) designed to be opened through binding to the target nucleic acid. Upon opening of the HP, the primer binds to the free stem of the opened HP followed by its extension by DNA polymerase, consequently displacing and recycling the target nucleic acid to open another HP and producing an intermediate product (IP) containing a nicking site. The IP then continuously produces a trigger probe (TP), which subsequently initiates the isothermal amplification cycles in two separate ways by binding to either the intact HP or the overhang region of the IP. Through the following well-designed interconnected pathways, a large amount of final double-stranded DNA products (FPs) is produced and a high fluorescent signal is generated from the duplex-specific fluorescent dye, SYBR Green I. By employing this isothermal strategy, target DNA was very sensitively detected down to 64 zmol with the capability to discriminate the target DNA against non-specific DNAs. This work would provide remarkable insight into the design of a new DNA network enabling isothermal amplification.

Low cycle fatigue life modelling using finite element strain range partitioning for a steam turbine rotor steel

Materials made for modern steam power plants are required to withstand high temperatures and flexible operational schedule. Mainly to achieve high efficiency and longer components life. Nevertheless, materials under such conditions experience crack initiations and propagations. Thus, life prediction must be made using accurate fatigue models to allow flexible operation. In this study, fully reversed isothermal low cycle fatigue tests were performed on a turbine rotor steel called FB2. The tests were done under strain control with different total strain ranges and temperatures (20 °C to 625 °C). Some tests included dwell time to calibrate the short-time creep behaviour of the material. Different fatigue life models were evaluated based on total life approach. The stress-based fatigue life model was found unusable at 600 °C, while the strain-based models in terms of total strain or inelastic strain amplitudes displayed inconsistent behaviour at 500 °C. To construct better life prediction, the inelastic strain amplitudes were separated into plastic and creep components by modelling the deformation behaviour of the material, including creep. Based on strain range partitioning approach, the fatigue life depends on different damage mechanisms at different strain ranges at 500 °C. This allows for the formulation of life curves based on either plasticity-dominated damage or creep-dominated damage. At 600 °C, creep dominated while at 500 °C creep only dominates for higher strain ranges. The deformation mechanisms at different temperatures and total strain ranges were characterised by scanning electron microscopy and by quantifying the amount of low angle grain boundaries. The quantification of low angle grain boundaries was done by electron backscatter diffraction. Microscopy revealed that specimens subjected to 600 °C showed signs of creep damage in the form of voids close to the fracture surface. In addition, the amount of low angle grain boundaries seems to decrease with the increase in temperature even though the inelastic strain amplitude was increased. The study indicates that a significant amount of the inelastic strain comes from creep strain as opposed of being all plastic strain, which need to be taken into consideration when constructing a life prediction model.

Optimal configurations for maximizing generalized output of two-finite-potential-reservoir endoreversible generalized engine cycles

Universal optimization is a primary objective of the study of generalized thermodynamic optimization theory. Previously, research into dynamic optimization of cyclic processes such as heat engines, chemical engines, battery power circuits, and commercial engines was limited to the research objectives of the specific discipline involved; conclusions were unique to the scope of each application, making it impossible to reveal any commonality between the research objectives and conclusions of these different disciplines. Following a review of the existing literature on dynamic optimization of thermodynamic and chemical cycles, and research into the concept of generalized thermodynamic optimization theory, a physical model of an endoreversible generalized engine with two generalized finite potential reservoirs is established, and the corresponding dynamic optimization problem is formulated solving the generalized output maximization of a generalized engine cycle and its corresponding optimal cycle configuration with the constraint of generalized displacement conservation. Subsequently, universal optimization results are derived applying the Euler-Lagrange equation and average optimal control theory, and simplified optimization results are obtained based on the universal results when generalized flow rate and generalized speed satisfy three specific relationships. Application of the above findings to thermodynamic and isothermal chemical cycles, battery power circuits, and commercial engine cycles is discussed and the concept of generalized thermodynamic dynamic optimization for irreversible cycles is proposed. The work in this paper enriches and completes the generalized thermodynamic optimization theory.

Water vapor transport to a semi-infinite material with simultaneous varying surface relative humidity and temperature

The water vapor transfer between the indoor air and hygroscopic finishing materials is of importance for the moisture balance of the room. Most protocols for determining the effect are based on isothermal conditions and cycling relative humidity in the form of square wave or sinusoidal functions. A new analytical solution for a material exposed to a both time varying surface relative humidity and temperature is presented in the paper. The time varying temperature inside the material is assumed to follow the surface temperature throughout the material layer since the reaction time for temperature changes in a reasonable thin surface material is rather short compared with the one for moisture changes. The semi-infinite approach is justified by the fact that the penetration depth for moisture variations are very limited for diurnal variations. The analytical approach and solution are presented in the paper

Thermal behaviour of TIG arc surfacing affecting mechanical properties of AISI 4340 steel substrate under static and dynamic loading

Surface modification of medium carbon AISI 4340 structural steel using TIG arcing process under various heat input (Ω) of varying arcing current (I) and arc travel speed (S) has been studied. Weld isotherm and thermal cycle of the fused zone has been analytically established and validated with experimentally measured results. TIG arcing process has been found to change the microstructural characteristics of the fusion modified matrix by transformation of fine niddle shape martensite, which has significantly enhanced its hardness from 256 ± 10 HV to 745 ± 8 HV and thus its mechanical properties. Formation of residual stresses in the surface modified the substrate is examined by hole drill method up to a depth of 1.3 mm. A residual stress of tensile nature is found to exist up to an appreciable depth from the top modified of the substrate, which has adversely affected its static and dynamic properties by enhancement of resolved stress in the matrix during the bend test. Surface modification improves flexural properties of the substrate with a maximum improvement of flexural yield strength at a relatively slow arc travel speed of 6 cm/min, while the Ω lies in the range of 0.6–1.21 kJ/mm. A favourable to improvement in static and dynamic properties of the substrate were found at relatively higher Ω of TIG arcing at slower S. It has primarily happened due to development of relatively slower cooling rate in the matrix introducing comparatively ductile lath martensite in it.

Isothermal and thermomechanical fatigue behaviour of type 316LN austenitic stainless steel base metal and weld joint

Thermomechanical fatigue (TMF) studies were carried out on type 316 LN austenitic stainless steel (SS) base metal (BM) and its weld joint (WJ) with a temperature interval of 623–873 K under in-phase (IP) and out-of-phase (OP) combinations of mechanical strain and temperature. Tests were performed under mechanical strain control mode using the strain amplitudes in the range, ±0.25% to ±0.6%. Besides, isothermal low cycle fatigue (IF) tests were also conducted on the weld joint at 873 K. TMF cycling resulted in a slightly higher cyclic stress response (CSR) compared to IF loading for the weld joint. The IP TMF cycling yielded a higher plastic strain amplitude in comparison to OP TMF for both the base metal and the weld joint. Cyclic life of the weld joint is found to be inferior to that of the base metal. The fatigue lives exhibited by the base metal and the weld joint varied in the following sequence: IP TMF < IF < OP TMF. Preferential crack initiation in the weld region owing to embrittlement of transformed δ-ferrite was noticed with an increase in the mechanical strain amplitude under both TMF and IF cycling conditions. Crack initiation and propagation generally occurred in transgranular mode under IF and OP TMF and mixed (trans-plus intergranular) mode under IP TMF cycling. Electron back scattered diffraction (EBSD) measurements were employed to investigate the substructural development in terms of local misorientation distribution, inverse pole figure (IPF) maps and boundary dislocation density (ρ) in the weld metal region, under IF and IP TMF cycling. The dislocation density was found to decrease for both IF and IP TMF cycling compared to the as-welded condition, with the decrease being higher for IF cycling. The TMF data generated for the type 316LN SS base metal and weld joint at different strain ranges in the present study clearly demonstrated a lack of conservatism associated with the current design practice which is based on the IF data at the maximum temperature (Tmax) of the service cycle.

Thermal cycling effects on the creep-fatigue interaction in type 316LN austenitic stainless steel weld joint

Thermomechanical fatigue (TMF) tests under in-phase temperature-mechanical strain combination were performed on a type 316 LN austenitic stainless steel weld joint using temperature ranges of 573–823 K, 623–873 K and 673–923 K employing a mechanical strain amplitude (Δεmech/2) of ±0.4%. Isothermal low cycle fatigue (designated as IF) tests were also carried out at the maximum temperatures (Tmax) of TMF cycling. The interaction of creep deformation with IF and TMF cycling was assessed by incorporating hold periods of 1 min and 5 min at the maximum tensile strain. TMF cycling resulted in considerably lower lives compared to IF, with the life reduction being more significant under hold conditions. Further, a clear difference in the cyclic stress response (CSR) was observed between creep-TMF and creep-IF cycling, depending on the hold duration and temperature range. The contribution of creep deformation to the overall damage was found to be higher under TMF compared to IF cycling at the Tmax. The observed variations in the cyclic lives under IF and TMF cycling with and without hold times were explained on the basis of the dominant fracture mechanisms identified through detailed microstructural characterization of the crack initiation and propagation modes. The extent of intergranular damage was seen to increase with an increase in the temperature range and the hold period. The role of oxidation in the development of damage was observed to be different under creep-TMF and creep-IF cycling. Numerous grain boundary microvoids and their inter-linkages caused enhanced crack propagation under creep-TMF, compared to creep-IF cycling. A comparison of the deformation behaviour, cyclic life and damage developed in the material under IF and TMF suggested that the performance of the weld joint under TMF cycling cannot be satisfactorily represented through IF tests at the Tmax.

Beyond Ceria: Theoretical Investigation of Isothermal and Near-Isothermal Redox Cycling of Perovskites for Solar Thermochemical Fuel Production

Thermodynamic data for several LaMnO3-based perovskites indicates that in the high oxygen partial pressure (pO2) range (e.g., 10–7 to 10–3 atm), where isothermal thermochemical redox cycling is via...

An innovative model coupling TGO growth and crack propagation for the failure assessment of lamellar structured thermal barrier coatings

The failure of plasma-sprayed thermal barrier coating (TBC) is often caused by the coating spallation due to crack propagation. In this study, a new model with stacking lamellae is developed based on the cross-section micrograph to explore crack propagation behavior within the ceramic top coat (TC) during isothermal cycling. The dynamic growth process of thermally grown oxide (TGO) is simulated via material properties change step by step. The stress profiles in the lamellar model are first evaluated, and the pore and lamellar interface crack effects on the stress state are further explored. Then, the successive crack growth, linkage, and ultimate coating spallation process is simulated. The results show that the stress intensity in TC enhances with thermal cycling. Large stress concentration always occurs near the pore and lamellar interface crack, which can result in the incipient crack growth. Moreover, the lamellar interface crack also changes the stress distribution within the TC and at the TC/bond coat interface. The multiple crack propagation upon temperature cycling is explored, and the possible coalescence mechanism is proposed. The lamellar crack steadily propagates at the early stage. The crack length sharply increases before the occurrence of coating spallation. The simulated coat spalling path is in line with the experimental result. Therefore, the new lamellar model developed in this work is beneficial to further reveal coating failure mechanism and predict coating lifetime.

Austenite reversion kinetics and stability during tempering of an additively manufactured maraging 300 steel

Reverted austenite is a metastable phase that can be used in maraging steels to increase ductility via transformation-induced plasticity or TRIP effect. In the present study, 18Ni maraging steel samples were built by selective laser melting, homogenized at 820 °C and then subjected to different isothermal tempering cycles aiming for martensite-to-austenite reversion. Thermodynamic simulations were used to estimate the inter-critical austenite + ferrite field and to interpret the results obtained after tempering. In-situ synchrotron X-ray diffraction was performed during the heating, soaking and cooling of the samples to characterize the martensite-to-austenite reversion kinetics and the reverted austenite stability upon cooling to room temperature. The reverted austenite size and distribution were measured by Electron Backscattered Diffraction. Results showed that the selected soaking temperatures of 610 °C and 650 °C promoted significant and gradual martensite-to-austenite reversion with high thermal stability. Tempering at 690 °C caused massive and complete austenitization, resulting in low austenite stability upon cooling due to compositional homogenization.

Effects of Hf, Y, and Zr on Alumina Scale Growth on NiAlCr and NiAlPt Alloys

The effects of Hf, Y, and Zr additions on the growth of a thermally grown alumina scale formed on NiAlCr and NiAlPt alloys were investigated. Isothermal and thermal cycling oxidation experiments were carried out at 1150 °C, and cross sections of the oxidized samples were characterized using scanning electron microscopy. It was observed that single doping as well as co-doping of Hf, Y, and Zr reduces the rate of alumina scale growth on NiAlCr and NiAlPt alloys, with Hf showing a more significant effect than Y or Zr. The following possible contributing factors to these observations were assessed: (1) the ionic size of the minor alloying elements and (2) the bond strength between the doping elements and oxygen in the oxide grain boundaries in terms of formation and melting enthalpies of oxides. It was concluded that the bond strength between the doping elements and oxygen within the oxide grain boundaries plays an important role in retarding the alumina scale growth.

Thermochemical energy storage via isothermal carbonation-calcination cycles of MgO-stabilized SrO in the range of 1000–1100 °C

The reversible gas-solid thermochemical reaction between CO2 and SrO to form SrCO3 is considered for storing high-temperature heat delivered by concentrated solar energy systems. To maintain cycling stability, MgO-stabilized SrO-based materials were synthetized with various precursors and support contents by the co-precipitation, sol–gel, wet-mixing and dry-mixing production methods. Samples were analysed by thermogravimetry over multiple consecutive carbonation-calcination cycles in the range of 1000–1100 °C. The best performance was obtained by using the wet-mixing method with strontium acetate hemihydrate and porous magnesium oxide as precursors: the formulation with 40 wt% SrO featured stable chemical conversion over 100 consecutive carbonation-calcination cycles at 1000 °C and yielded gravimetric energy density of 0.81 MJ/kg.

Modifying La0.6Sr0.4MnO3 Perovskites with Cr Incorporation for Fast Isothermal CO2‐Splitting Kinetics in Solar‐Driven Thermochemical Cycles

AbstractPerovskites are promising oxygen carriers for solar‐driven thermochemical fuel production due to higher oxygen exchange capacity. Despite their higher fuel yield capacity, La0.6Sr0.4MnO3 perovskite materials present slow CO2‐splitting kinetics compared with state‐of‐the‐art CeO2. In order to improve the CO production rates, the incorporation of Cr in La0.6Sr0.4MnO3 is explored based on thermodynamic calculations that suggest an enhanced driving force toward CO2 splitting at high temperatures for La0.6Sr0.4CrxMn1−xO3 perovskites. Here, reported is a threefold faster CO fuel production for La0.6Sr0.4Cr0.85Mn0.15O3 compared to conventional La0.6Sr0.4MnO3, and twofold faster than CeO2 under isothermal redox cycling at 1400 °C, and high stability upon long‐term cycling without any evidence of microstructural degradation. The findings suggest that with the proper design in terms of transition metal ion doping, it is possible to adjust perovskite compositions and reactor conditions for improved solar‐to‐fuel thermochemical production under nonconventional solar‐driven thermochemical cycling schemes such as the here presented near isothermal operation.

Pressure effects on the carbonation of MeO (Me = Co, Mn, Pb, Zn) for thermochemical energy storage

Metal carbonates are attractive materials for combining carbon capture and thermochemical energy storage. Carbonate materials feature high decomposition and formation temperatures and may be considered in applications in combination with concentrating solar power. In the present study in-situ P-XRD carbonation (1–8 bar CO2) and reactor-based experiments (1–55 bar CO2) are combined focusing on the effect of elevated CO2 pressures on carbonation of metal oxides. Carbonation of MnO and PbO at CO2 pressures between 8 and 50 bar in the presence of moisture resulted in reaction with CO2, forming the corresponding carbonates at notably lower temperatures than under dry CO2 atmosphere of 1 bar. This enables the application of metal oxide/metal carbonate reaction couples for energy storage at temperatures between 25 and 500 °C. Based on the reversible carbonation/decarbonation of PbO under varying CO2 pressures, an isothermal storage cycle between PbO/PbCO3·2PbO, triggered by changing the CO2 pressure between 2 and 8 bar, was developed.

Strain controlled isothermal low cycle fatigue life, deformation and fracture characteristics of Superni 263 superalloy

The total axial strain controlled low-cycle fatigue (LCF) behaviour of a wrought nickel-base superalloy Superni 263 has been evaluated at 298 K, 673 K, and 923 K employing the strain amplitudes in the range ± 0.25% to ± 0.80%. All the tests were performed using a triangular wave form at a constant strain rate of 10−3 s−1. The Superni 263 alloy was subjected to a solutionizing treatment at 1373 K/1.5 h followed by water quenching. An ageing treatment of 1073 K/8 h was given to the solutionized samples. The microstructure of the alloy is composed of γʹ in the intragranular regions and discrete M23C6 precipitates on the grain boundaries. Few undissolved (Ti, Mo)C and TiN precipitates were also noticed in the matrix. The strain amplitude and temperature played a significant role in the evolution of macroscopic cyclic stress response and the development of deformation substructure. The alloy displayed serrated flow in the plastic portions of stress-strain hysteresis loops in the tests conducted at 673 K and 923 K, predominantly at strain amplitudes higher than ±0.40%. Several manifestations depicting the occurrence of dynamic strain ageing (DSA) were derived by analysing both the macroscopic and micro-mechanistic information generated. The comparative evaluation of monotonic and cyclic stress-strain curves was conducted and the factors responsible for rapid cyclic hardening during DSA were identified. The fatigue life decreased drastically with increasing temperature, particularly at low strain amplitudes. The strain-life data could be represented well by using Basquin and Coffin-Manson relationships. The slope in Coffin-Manson relationship revealed more negative values under the influence of DSA. The crack initiation and propagation modes at all the test conditions remained transgranular without the indications of interference from creep and oxidation effects. The deformation substructure at elevated temperatures was characterized by the occurrence of co-planar slip, stacking faults, micro twinning and high dislocation density in between the slip bands.