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Plastic deformation of titanium alloys depends on the temperature and the mechanical loading mode. It is accommodated by a complex mixture of slip and twinning systems. It remains nevertheless unclear which deformation modes are activated in the polycrystal during loading, especially with the temperature. To better understand the mechanical behaviour of textured α-Ti, neutron diffraction measurements have been performed to analyse the intergranular strain evolution under tensile tests at different temperatures ranging from ambient up to 300 °C. The material has then been characterized from meso- (grain) to macroscopic scales to obtain relevant information about the deformation mechanisms governing its global behaviour. An elastoplastic self-consistent approach has been used to explain and interpret the experimental observations achieved under thermomechanical loadings. The model has enabled us to successfully predict the measured macroscopic behaviour and lattice strain development. The study has also provided a comprehensive data set and a complete description of temperature influence onto the mechanical state and the plastic anisotropy, especially at the mesoscopic level. The evolutions of the deformation mode hierarchy and the internal stress fields with the temperature have been determined. [ABSTRACT FROM AUTHOR]

Weld residual stress and fracture behavior of 316L electron beam weldments, which are of particular interest in power generation industry, were investigated in this work. Two butt‐weld joints were manufactured in stainless steel 316L plates of 6 mm and 25.4 mm thicknesses. Three complementary methods were used to measure the three orthogonal components of the residual stress in the weld coupons, and fracture tests were conducted on single edge notched bending specimens extracted from different regions of the welds and parent metals. The residual stress measurements showed a maximum value of 450 MPa in longitudinal direction, while it was less than 150 MPa in the other two orthogonal directions, revealing that in our material, and with the chosen weld parameters, the residual stresses were biaxial. The fracture resistance of the weldment and parent material was similar, with material microstructure differences being more significant than the measured residual stresses. The study suggests that 316L electron beam weldments are not susceptible to fracture failure due to their high ductility and ability to relieve residual stresses through gross plasticity. Electron beam welding may therefore be suggested as a reliable manufacturing technology for safety critical 316L components. [ABSTRACT FROM AUTHOR]

After α + β-zirconium has fully transformed into β-phase upon heating, the intensities of all β-Zr Bragg reflections decrease simultaneously as a function of time. It is shown that this effect represents a transition from the kinematic to the dynamic theory of diffraction due to the ever increasing crystal perfection driven by thermal recovery of the system. The best fitting coherent crystallite size of 30 μm and other microstructural features are verified by in situ laser scanning confocal microscopy. This effect of primary extinction in neutron diffraction has been employed to further investigate the crystal perfection kinetics. Upon further heating, crystal recovery is identified as a process of dislocation annihilation, suffering from lattice friction. Upon cooling, precipitating α-Zr induces strain into the perfect β-crystallites, re-establishing the kinematic diffraction intensities. An Avrami analysis leads to the estimations of nucleation time, consumption of nucleation sites and lower-dimensional growth. Such technique bears great value for further investigation on all metal systems annealed close to the melting temperature. [ABSTRACT FROM AUTHOR]

Tantalum-clad tungsten targets are a popular choice for spallation neutron production, due to the combination of high neutron yield and corrosion resistance. Such targets typically use the Hot Isostatic Press (HIP) process to bond the cladding to the core; this produces a strong bond but also introduces large residual stresses in the target and cladding. This is of particular interest at the ISIS neutron source, because cladding breaches are currently believed to limit the lifetime of ISIS TS2 targets. Two different and complementary methods were used to measure the residual strain in a tantalum-clad tungsten strip manufactured using the same HIP process as ISIS targets. The strip was produced with deliberately asymmetric cladding, causing it to deflect in proportion to the residual stress. FEA simulations were used to back-calculate the stress from the measured deflection. The strip was then placed on the ISIS instrument ENGIN-X, which allowed detailed through-thickness strain profiles to be measured via neutron diffraction. The results of both methods confirm the presence of large residual strains, and agree reasonably well with FEA simulations of the cladding process. [ABSTRACT FROM AUTHOR]

Magnetic and nonmagnetic shape memory alloys (SMAs) exhibit thermoelastic martensitic transformations (MTs) which are hysteretic due to their first‐order nature. According to the thermodynamic Landau theory of phase transitions, which assumes ideal thermoelastic equilibrium at each point of the MT interval, the hysteresis is explained by the different limits of stability for austenite and martensite in the phase diagram. No interactions on the phase boundaries are taken into account. In the real alloys, the hysteresis of MT is related not only to the stability intervals of two phases but also to the processes of nucleation and growth of the resultant phase inside the parent phase. In turn, the features of these processes are related to the heights of energy barriers caused by the incompatibility of austenitic and martensitic lattices, crystal defects and some other physical factors. However, the defects, normally, play a minor role in the width of MT hysteresis if compared to the thermodynamic and crystallographic factors. A reduction of hysteresis of MT in SMAs, being crucial for technology, presents a challenging problem for science. A decrease of hysteresis width of MT was observed recently for the single crystals of ferromagnetic SMAs such Ni–Fe(Co)–Ga and Fe–Pd on approaching of their transformation paths to the critical point in stress–temperature phase diagram. Moreover, the superelastic and shape memory properties characterized by the nearly‐zero hysteresis width were observed in the postcritical transformational regime. Here we show that both the Landau‐type theory of ferroelastic phase transitions and neutron diffraction experiments carried out under axial compression describe the essential features of these properties. We also interpret the experimentally observed anhysteretic phenomena in Ni–Mn–Ga thin films and nanobeam actuators in terms of their postcritical state. [ABSTRACT FROM AUTHOR]

A time-of-flight (TOF) neutron strain scanner is a white-beam instrument optimized to measure diffractograms at precise locations within bulky specimens, typically along two perpendicular sample orientations. Here, a method is proposed that exploits the spatial resolution (~1 mm) provided by such an instrument to determine in a nondestructive manner the crystallographic texture at selected locations within a macroscopic object. The method is based on defining the orientation distribution function (ODF) of the crystallites from several incomplete pole figures, and it has been implemented on ENGIN-X, a neutron strain scanner at the ISIS facility in the UK. This method has been applied to determine the texture at different locations of Al alloy plates welded along the rolling direction and to study a Zr2.5%Nb pressure tube produced for a CANDU nuclear power plant. For benchmarking, the results obtained with this instrument for samples of ferritic steel, copper, Al alloys and Zr alloys have been compared with measurements performed using conventional X-ray diffractometers and more established neutron techniques. For cases where pole figure coverage is incomplete, the use of TOF neutron transmission measurements simultaneously performed on the specimens is proposed as a simple and powerful test to validate the resulting ODF. [ABSTRACT FROM AUTHOR]

An amendment to this paper has been published and can be accessed via a link at the top of the paper. [ABSTRACT FROM AUTHOR]

The microstructural evolution and deformation mechanisms of 316L stainless steel (SS) have been investigated at 297, 173, 50 and 15 K by in situ neutron diffraction during tensile loading and correlative transmission electron microscopy (TEM). The yield strength and ultimate tensile strength of 316L stainless steel are significantly improved at cryogenic temperatures. In contrast to room temperature, deformation-induced martensitic transformation was observed at all cryogenic temperatures. The γ-austenite (FCC) content decreases and α′-martensite (BCC) increases with increasing strain, a fraction of this γ to α′ transformation is accompanied by the transient appearance of ε-martensite (HCP) as an intermediate phase. The maximum volume fraction of ε-martensite increases with decreasing deformation temperature and reaches 13% for deformation at 15 K. TEM results confirm that γ → ε → α′ and γ → α′ martensitic transformations occur during cryogenic deformation, while mechanical twins were observed only at 173 K. The evolution of lattice strain, phase volume fraction, stacking fault probability (SFP) and stacking fault energy (SFE) were quantified to investigate the correlation between deformation mechanisms and mechanical behaviour of 316L SS as a function of deformation temperature. [ABSTRACT FROM AUTHOR]

In this work we present a preliminary investigation by means of neutron diffraction experiment to determine the residual stress state in three different iron meteorites (Chinga, Sikhote Alin and Nantan). Because of the very peculiar microstructural characteristic of this class of samples, all the systematic effects related to the measuring procedure - such as crystallite size and composition - were taken into account and a clear differentiation in the statistical distribution of residual stress in coarse and fine grained meteorites were highlighted. Moreover, the residual stress state was statistically analysed in three orthogonal directions finding evidence of the existence of both type I and type II residual stress components. Finally, the application of von Mises approach allowed to determine the distribution of type II stress. [ABSTRACT FROM AUTHOR]

A FeCoCrNiMo 0.23 high entropy alloy was processed by powder metallurgy with two conditions: hot extruded and annealed. In situ neutron diffraction, together with electron microscopy, was used to study the deformation mechanisms and concomitant microstructural evolution for both conditions. The as-extruded alloy has a single face-centered-cubic structure with a calculated stacking fault energy of ∼19 mJ/m 2 . When the alloy is tensile deformed, nano-twins and microbands are induced, resulting in an excellent combination of strength and ductility (784 MPa ultimate tensile strength and over 50% elongation). Annealing at 800 °C for 72 h increases the strength of the alloy but decreases its ductility. This is due to the decomposition of the alloy after annealing, causing the formation of Mo-rich intermetallic particles and a decrease of the stacking fault probability. These results highlight that combined mechanisms (i.e. solute strengthening and twin/microband induced plasticity) can effectively improve both the strength and ductility of high entropy alloys. [ABSTRACT FROM AUTHOR]

In-situ neutron diffractometry is performed to study the visco-plasticity in a nickel-base single crystal superalloy during in-situ cooling from high temperatures. It is found that visco-plastic deformation has two contributions from creep and stress relaxation, which are subject to the accumulation of dislocation activity and dislocation annihilation, respectively. Use has been made of the lattice strain evolution of the (200) γ+γ′ peak to confirm this effect. The decrease in lattice strain and macro-stress during in-situ cooling has been observed and confirms that there was softening taking place before thermal strain dominates at lower temperatures. Therefore, in-situ isothermal cyclic loading and relaxation tests under strain control, akin to thermal contraction during casting, have been carried out. A visco-plasticity law was then developed based on macro-strain development during creep and lattice strain evolution during stress relaxation within an appropriate timescale, where transient effects are captured. The constitutive law developed has been used to independently determine the evolution of stress and strain during in-situ cooling. The implementation of these findings into thermo-mechanical modelling during cooling from solidification is also discussed. [ABSTRACT FROM AUTHOR]

High manganese steels are promising candidates for applications in cryogenic environments. In this study, we investigate the mechanical and microstructural responses of a high manganese twinning induced plasticity (TWIP) steel at a low-temperature range (from 373 to 77 K) via in situ neutron diffraction qualification and correlative microscopy characterization. During plastic deformation, stacking fault probability and dislocation density increased at a faster rate at a lower temperature, hence, higher dislocation density and denser mechanical twins were observed, confirmed by microscopic observation. Stacking fault energy was estimated, dropping linearly from 34.8 mJm−2 at 373 K to 17.2 mJm−2 at 77 K. A small amount of austenite transferred to martensite when deforming at 77 K. The contributions to flow stress from solutes, grain boundary, dislocation, and twinning were determined at different temperatures, which shows that the high work strain hardening capacity of the TWIP steel originates from the synergetic strengthening effects of dislocations and twin-twin networks. These findings reveal the relationship among stacking fault energy, microstructure, and deformation mechanisms at the low-temperature range, paving a way in designing TWIP steels with the superb mechanical performance for cryogenic applications. Image, graphical abstract [ABSTRACT FROM AUTHOR]

In situ neutron diffraction and synchrotron X-ray diffraction, combined with image correlation analysis of 2D optical and 3D X-ray tomography datasets, have been used to investigate the relationship between elastic lattice strain and total strain during deformation of Gilsocarbon (IM1-24) polygranular nuclear grade graphite. The specimens were flat-end Brazilian discs under diametral loading, such that a compressive-tensile biaxial stress state was developed in the central region. The X-ray study was at ambient temperature, and the neutron diffraction was conducted at temperatures from ambient to 850 °C. When under compression, there is a temperature-insensitive linear relationship between the total strain and the lattice strain that is measured perpendicular to the graphite basal planes. However, when under tensile stress, the total strain and elastic strain relationship is temperature sensitive: below 600 °C, the lattice tensile strain saturates with increasing total tensile strain; above 600 °C, significantly higher tensile lattice strains are sustained. The saturation in tensile lattice strain is attributed to microcracking in the graphite microstructure. Improved resistance to microcracking and damage tolerance at elevated temperature explains the increase in tensile strength of polygranular graphite. Image 109604 [ABSTRACT FROM AUTHOR]

Deformation mechanisms of high entropy alloys (HEAs) at cryogenic temperatures have attracted extensive research interest. We used in situ neutron diffraction to study the tensile behavior of a face-centered-cubic HEA at 77 and 15 K and compared its stacking fault energy (SFE) at ambient and cryogenic temperatures. The SFE dropped from 28 mJm−2 at 293 K to 11 mJm−2 at 15 K, leading to the transition of deformation mechanism from deformation-induced twinning to martensite phase transformation. As a result, excellent balance of strength and ductility was achieved at both temperatures. This finding highlights the importance of SFE for cryogenic alloy design. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Cold spray (CS) is a solid-state additive material deposition technique, which has gained attention in the aerospace industry as a potentially viable technology for structural repair of high-value parts made of high-strength alloys such as Ti-6Al-4V (Ti-64). Residual stresses build up in the substrate and deposited materials resulting from the CS process can influence the integrity of a coating or repair. However, the nature, magnitude and distribution of residual stresses in Ti-64/Ti-64 CS repairs are currently unknown. This study aims to evaluate the effects of geometrical variables (i.e. the number of CS layers, CS layer thickness, and substrate thickness) and track pattern on the magnitude and distribution of residual stresses in CS deposit-substrate assemblies. Through-thickness stress distributions were measured experimentally by neutron diffraction and contour method. Furthermore, a comparison among different residual stress build-up mechanisms induced by CS processes has been discussed for different combinations of substrate and deposit assemblies. An analytical model based on the force and moment equilibrium requirements was used to interpret the experimental stress profiles and to predict the residual stress distribution. It was found that residual stresses are highly tensile near the free surface of the Ti-64 deposits as well as towards the bottom of the substrate, and compressive near the interface region. Although all the specimens showed similar stress distribution, the magnitudes were found to be higher in one or more of the following cases: specimens with a higher number of CS layers, lower substrate thickness, higher layer thickness (i.e. at lower scanning speed), and deposited with a horizontal track pattern. • Residual stresses induced by cold spraying of Ti-6Al-4 V were evaluated using neutron diffraction and contour method. • A parametric study was performed on the influence of geometrical and process variables on residual stresses. • An analytical method was used to interpret the experimental results and to compare different stress build-up mechanisms. [ABSTRACT FROM AUTHOR]

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/m 2 and 13 mJ/m 2 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. [ABSTRACT FROM AUTHOR]

The effects of strain rate on the mechanical behaviour and microstructure evolution of extruded Mg AZ31 alloy are investigated here for strain rates ranging from 0.0001 s −1 to 4000 s −1 . High strain rate compression testing was performed using a split Hopkinson pressure bar apparatus. The microstructure and texture evolution were characterised by using electron backscatter diffraction (EBSD) and neutron diffraction. The results show that the yield strength increases by roughly 55% from the quasi-static to the high strain rate regime while the plateau stress increases by roughly 35%. After compression along the extrusion direction, the deformed textures of both quasi-static and high strain rate loading samples are similar, showing that a large portion of grains have been reoriented through the activation of tensile twinning. However, a detail EBSD analysis suggests that there is a higher fraction of secondary compressive twins in high strain rate deformed specimens at 16% strain. A visco-plastic self-consistent (VPSC) model, which incorporates the composite grain scheme to account for twinning, is employed to model the mechanical response and texture evolution, and to elucidate the collaborative nature of the slip-twinning deformation. Using only a single set of parameters, the VPSC model successfully reproduces the stress-strain curves at all tested strain rates, and more importantly, captures the texture and twin volume fraction evolutions. The simulation results suggest that under quasi-static and high strain rate loadings, the dominant slip systems are different in both untwinned grains and tensile twins. The results also suggest that twins are formed at a lower strain at high strain rates when compared to quasi-static loading. [ABSTRACT FROM AUTHOR]

Manufacturing austenitic stainless steels (ASSs) using additive manufacturing is of great interest for cryogenic applications. Here, the mechanical and microstructural responses of a 316L ASS built by laser powder bed fusion were revealed by performing in situ neutron diffraction tensile tests at the low-temperature range (from 373 to 10 K). The stacking fault energy almost linearly decreased from 29.2 ± 3.1 mJm−2 at 373 K to 7.5 ± 1.7 mJm−2 at 10 K, with a slope of 0.06 mJm−2K−1, leading to the transition of the dominant deformation mechanism from strain-induced twinning to martensite formation. As a result, excellent combinations of strength and ductility were achieved at the low-temperature range. [Display omitted] [ABSTRACT FROM AUTHOR]

The intergranular lattice strains in the near-β titanium alloy Ti-β21S have been measured in the longitudinal and transverse directions during tensile loading using neutron diffraction. The obtained results have been modelled and explained using a two-phase elasto-plastic self-consistent model. We first identified the best set of the main model parameters (single crystal elastic constants, critical resolved shear stresses) and investigated the influence of these parameters on the behaviour of both the polycrystal and the diffracting volume. Good agreement between the experimental results and those predicted by the model was found for the macroscopic stress-strain dependencies and lattice strain developments of Ti-β21S. [ABSTRACT FROM AUTHOR]

High manganese steels are emerging as promising structural materials for cryogenic applications due to their low production cost and great potential in achieving excellent strength-ductility combinations. Micro-alloying serves as a desirable method in tailoring stacking fault energy (SFE) of the steels and thus tailoring the mechanical performance. In this study, we investigated the dedicate role of Cu addition played on the mechanical and microstructural responses of high manganese steels at the low-temperature range (293, 173, and 77 K) via in situ neutron diffraction and microscope characterizations. The addition of 1 wt%Cu to the steel not only effectively improved the yield strength (YS) and elongation but also increased the SFE thus postponing the martensite formation. For both high Mn steels, as deformation temperature decreased, the tensile strength was increased linearly, the formation of stacking faults and dislocation was promoted, and the SFE almost linearly decreased with a slope of about 0.06 mJm−2·K−1. The contributions to YS and flow stress from lattice friction, grain boundary, dislocation, deformation twins, and phase transformation were determined based on neutron diffraction results and previously validated models. The work revealed the critical roles of Cu micro-alloying in tailoring the SFE of TWIP steels and the resulting deformation mechanisms, paving the way in adapting new high manganese steels for cryogenic applications. • Cryogenic mechanical properties of two TWIP steels were measured. • Stacking fault energy (SFE) was determined theoretically and experimentally. • Deforming mechanisms were studied at cryogenic temperatures. • Adding Cu can enhance yield strength, tailor SFE, and change deformation behaviors. • Strengthening effects from a variety of hardening mechanisms were determined. [ABSTRACT FROM AUTHOR]

Abstract: In-situ neutron diffraction was employed to monitor the evolution of nano-bainitic ferrite during low temperature isothermal heat treatment of austenite. The first 10 peaks (austenite, γ and ferrite, α) were monitored during austenization, homogenisation, rapid cooling and isothermal holding at 573K. Changes in the α-110 and γ-111 peaks were analysed to determine the volume fraction changes and hence the kinetics of the phase transformation. Asymmetry and broadening in the α-200 and γ-200 peaks were quantified to lattice parameter changes due to carbon redistribution as well as the effects of size and dislocation density. Atom Probe Tomography was then used to confirm that, despite the presence of 1.5 mass% Si, carbide formation was evident. This carbide formation is the cause of poor ductility, which is lower than expected in such steels. [Copyright &y& Elsevier]

Neutron and high-energy X-ray diffraction methods have been used to investigate deformation mechanisms (slip and twinning activities) during uniaxial tensile tests of Grade 1 commercially pure titanium (Ti-α). These two diffraction techniques have provided valuable and complementary information. The predictions made by an Elasto-Plastic Self-Consistent (EPSC) model, taking into account grain reorientation and stress relaxation induced by twinning activity, have been compared with the experimental data. Results clearly demonstrate that there is a good agreement between simulations and diffraction measurements. The EPSC model enables accurate predictions of: (i) the lattice strains developed in variously oriented {hk.l} grain families within the bulk material, (ii) the grain reorientation induced by twinning activity and (iii) the macroscopic stress-strain response. Two different textured products were studied in order to evaluate the influence of texture on the mesoscopic and macroscopic responses of Ti-α alloy. [ABSTRACT FROM AUTHOR]

• FCC retained phase can be transformed under mechanical loading. • FCC to HCP phase transformation is activated by plasticity. • Temperature delayed the activation of the strain-induced phase transformation. Thermal and mechanical effects on the phase transformation of polycrystalline two-phase HCP/FCC cobalt have been studied in coupled and decoupled ways. This experimental work has involved in situ X-ray and neutron diffraction analysis to determine phase proportions under various thermomechanical conditions, those which are not referenced in the litterature. A quantitative analysis is proposed to better understand phase transformation in a cobalt rolled sheet. New experimental results show that the metastable FCC retained phase can be transformed into HCP phase by a mechanical loading. In accordance with the theory and the literature, the prominent phase (HCP) can subsequently be transformed with an increase of temperature above 743 K. [ABSTRACT FROM AUTHOR]

Primary creep regeneration (PCR) is observed during cyclic creep deformation in many engineering alloys. PCR is a phenomenon in which reverse inelastic strain fully, or partially, resets the early creep strain hardening memory of the material. The current understanding regarding the origin of the PCR behaviour in engineering alloys is limited to the phenomenological observations from the changes in dislocation structures whereas a good mechanistic understanding of the PCR behaviour is crucial for developing robust plasticity-creep predictive models. In this study, we investigated the micromechanical origin of PCR behaviour in type 316H stainless steel at 650 °C using high-temperature mechanical testing and neutron diffraction. A cyclic creep experiment was conducted in-situ at a neutron diffraction beamline, during which various degrees of unloading and reverse loading were applied to the specimen, followed by creep deformation under a load above the material's yield strength. Partial PCR was observed after reverse plastic loading for all the creep dwells, which is contrary to current high-temperature lifetime assessment's procedures advice which is to account for full recovery of primary creep after any reverse plastic loading. The extent of PCR is observed to be proportional to the magnitude of reverse plastic strain up to a level of 0.5% reverse plastic strain. From the measured neutron diffraction data, a strong correlation was observed between the changes in magnitude of the accumulated intergranular residual lattice strains and the macroscopic primary creep strain. Moreover, the increases of lattice strain to saturation and transition from primary creep to secondary regime occur at the same time. Based on these correlations it can be postulated that the PCR behaviour observed due to cyclic loading in type 316H stainless steel at elevated temperature originates from the accumulation of intergranular residual lattice strains during the reverse plastic loading and those time-dependent changes during the creep dwells. [ABSTRACT FROM AUTHOR]

We successfully prepared an Fe 22 Co 20 Ni 19 Cr 20 Mn 12 Al 7 alloy consisting of a face-center cubic (fcc) phase and body-center cubic (bcc) phase that exhibits an outstanding combination of true strength of 1430 MPa and ductility of 19.9% at room temperature (RT). The micromechanical behavior at RT and 77 K for the studied alloy during tensile deformation was investigated using in situ time-of-flight (TOF) neutron diffraction in combination with synchrotron-based high-energy X-ray diffraction (HE-XRD). Here, the striking finding of a large elastic strain of 7.0% and 5.6% is reported for the {200} bcc crystal plane, which was achieved at RT and 77 K, respectively. Such a large lattice distortion observed in the bcc phase was attributed to a new type of stress-induced confined martensitic transformation. We attributed the physical origin of this specific martensitic transformation to the intrinsic microstructural feature of a nano-scale continuous distribution of an ordered-to-disordered crystal structure within the bcc phase, i.e., the disordered A2-structure was distributed continuously in the ordered B2-structure matrix. The stress-induced martensitic transformation from the metastable nano-sized disordered A2-phase was confined by the stable B2-ordered matrix. The new findings in this study provide additional understanding of the deformation mechanisms of high-entropy alloys and insights into alloy design for further enhancement of the mechanical properties of high-performance structural materials used at cryogenic temperatures. [ABSTRACT FROM AUTHOR]