Ultrahigh Strain Research Articles

Ultrahigh strain in textured BCZT-based lead-free ceramics with CuO sintering agent

• CuO as a sintering agent lowers the sintering temperature of 125 °C, and maintains BCZT-1.0 at a high texture degree of ∼99%. • CuO-based liquid phases eliminate boundaries between templates and matrix powders, release local stress, decrease grain sizes, and increase dielectric dispersion coefficient. • Maximum strain s max of 0.38% and low h s of 5.2% along with homogeneous d 33 ∼780 pC/N and large d 33 * ∼2950 pm/V was obtained in textured BCZT-1.0. Textured BaTiO 3 (BT)-based lead-free ceramics have gained significant attention due to their high piezoelectric coefficient ( d ) and very large field induced strain ( S ). However, costly nano-size raw materials, excessively high sintering temperature and low Curie temperature ( T c ) hinder their device applications. In this work, highly [001] c -oriented (Ba 0.95 Ca 0.05 )(Zr 0.04 Ti 0.96 )O 3 ceramics with x mol% CuO ( x = 0.25, 0.5, 1.0, 2.5) denoted as BCZT- x were synthesized by templated grain growth using micro-sized raw powders. The introduction of CuO sintering agent lowered the sintering temperature by 125 °C to 1450 °C, and the BCZT-1.0 achieved a high texture degree of ∼99%. In addition, the CuO-based liquid phases eliminated boundaries between BT templates and BCZT matrix powders. Such liquid-phase sintering reduced sintering stresses, decreased the average grain size of BCZT-1.0 from 16 μm down to 13 μm, and increased the dielectric dispersion coefficient γ to 1.63. The almost smoothed out T O-T anomaly in the temperature dependence of dielectric permittivity and comparably high T c (> 102 °C) lead to better temperature stability. The narrower grain orientation distribution with full width at half maximum (FWHM) of ∼5.9° and smaller domains with the size of 0.1–0.5 μm in width and 3–8 μm in length were obtained, a high field induced maximum strain S max of 0.38% and low H s of 5.2% have been achieved in BCZT-1.0 textured ceramics together with a high and homogeneous piezoelectric stress coefficient d 33 ∼780 pC/N and very large d 33 * ∼2950 pm/V.

Optimal design of a low-cost high-performance hybrid fiber engineered cementitious composites

Engineered cementitious composites (ECC) is a fiber reinforced high-performance cementitious material with an ultra-high tensile strain capacity (above 3%) and excellent durability. However, such excellent strain capacity far exceeds some engineering requirements and is usually not fully utilized. Meanwhile, its high cost limits it application only in local engineering. In this study, a low-cost high-performance hybrid fiber ECC (HF-ECC) with both polypropylene (PP) fiber and polyethylene (PE) fiber was manufactured. Both macroscopic and microscopic mechanism analyses were conducted to investigate the effect of fiber characteristics and proportions on the performance of HF-ECC. The results show that the ultimate tensile strain of HF-ECC can reach 5% even the volume fraction of PP and PE fibers account for 1%, respectively. Its fiber cost is 43.8% lower than that of pure PE-ECC, which reduces the corresponding total cost by 27.5%. This paper presents an in-depth investigation of the characteristics of HF-ECC, direct tension, compression, fiber-bridging, pore structure, fiber distribution, and fiber dispersion. Finally, the optimal design of the HF-ECC is conducted through pseudo-strain-hardening indices and multi-criteria evaluation.

Microstructure Evolution and Deformation Mechanism of Tantalum-Tungsten Alloy Liner under Ultra-High Strain Rate by Explosive Detonation.

The microstructure evolution and plastic deformation mechanism of a Ta-2.5W liner under the ultra-high-strain-rate conditions generated by the explosive detonation were investigated in this study. For this purpose, a modular soft-recovery apparatus was designed to non-destructively recover the Ta-2.5W explosively formed projectile (EFP) in the ballistic endpoint. The electron backscattered diffraction (EBSD) method was employed to examine the microstructure of the Ta-2.5W liner before and after deformation. The microstructure of the recovered EFP exhibited significant grain refinement with preferred fiber texture. The theoretical computation results showed that the temperature of the EFP was in the range of 0.27–0.65 Tm. The deformation mechanism of the Ta-2.5W liner forming EFP driven by the detonation is the continuous dynamic recrystallization (CDRX) induced by high strain deformation, rather than the conventional dynamic recrystallization of nucleation and growth. The new grain structures evolve when the low-angle grain boundaries are transformed into the high-angle grain boundaries, and the specific grain refinement mechanism is the progressive rotation of subgrains near pre-existing grain boundaries.

Ultrahigh strain rate-activated superplastic forming of aluminum and gold nanometals

Commonly, the increased free surface of nanometals results in completely different mechanical behaviors from their bulk counterparts. At present, studies on the plasticity behavior of nanometals is widely carried out under quasi-static states. Understanding the plasticity mechanism of nanometals during a high-speed forming process is largely unexplored. This study explored the rate dependence of the forming behaviors of Al and Au nanofilms using laser-induced ultrahigh strain rate forming processes. The results showed that the superplastic behavior of the nanofilms can be activated above a critical value of the strain rate (>2.0E8 s−1). The Al nanofilm exhibited a maximum vertical strain of ∼ 567% at a strain rate of 8.1E8 s−1, and that of the Au nanofilm was ∼ 620% at a strain rate of 8.8E8 s−1. The superplastic forming mechanism mediated by interstitials was revealed for the first time. Further, the potential contribution of the interstitial-mediated plasticity mechanism in breaking through grain size limit and constitutive model modification was discussed. The discovery of this particular mechanism supplements the deformation mechanism diagram and constitutive relationship of nanometals, and is thus of great significance to the study of material responses in extreme conditions and manufacturing process analysis and optimization.

Ultrastretchable and wearable conductive multifilament enabled by buckled polypyrrole structure in parallel

AbstractStretchable conductive fibers have attracted much attention due to their potential use in wearable electronics. However, the ultra-high strain insensitive conductivity is hindered by mechanical mismatch in Young’s modulus and failure of stretchable structures under large deformation. This challenge is addressed with a conductive and elastic multifilament made of the polyurethane monofilaments that are surface-coated with buckled polypyrrole (PPy) of which flexibility is improved by sodium sulfosalicylate. Such parallel conductive monofilaments with PPy buckling on surface reduce the influence of cracks in the conductive coating on the overall conductivity, displaying an ultra-high strain insensitive behavior (quality factor Q = 10.9). Remarkably, various complex forms of wearable electronic textiles made by this conductive multifilament maintain the strain-insensitive behavior of the original multifilament, even upon the large deformation of human joint. This multifilament with wrinkled PPy has attractive advantages in the application of super-stretched wearable electronic devices.

Heterogeneous carbon/silicone composite for ultrasensitive anisotropic strain sensor with loading-direction-perception capability

Anisotropic strain sensors are crucial to accurately detecting the complex strain states in wearable devices and robotics. Large directional sensitivity differences are the key for strain sensors to differentiate loading directions. Here, an ultrasensitive anisotropic strain sensor consisting of orthogonal heterogeneous piezo-resistive composite (HePC) and homogenous piezo-resistive composite (HoPC) is demonstrated for loading direction perception. Benefited by a unique stiff-soft-stiff segment structure design, the HePCs with ultrahigh strain sensitivity were fabricated with carbon black (CB)/silicone nanocomposite with a low Young's modulus as the soft segment (SoS) and carbon-fiber-reinforced CB/silicone nanocomposite with a high Young's modulus as the stiff segment (StS). The HePC with a length ratio (LStS/LSoS) of 14:1 offers an average gauge factor of 70 (ε < 1%), which is increased more than 60 times than that of HoPC, due to the strain concentration effect in the SoS of HePC. Moreover, the anisotropic strain sensor fabricated demonstrates significant directional sensitivity differences due to the heterogeneous structure, and their relative resistance changes (RCR) vary considerably from positive to negative upon the change of loading directions. This makes the sensor highly effective to distinguish strain magnitude and direction simultaneously, and succeeding in monitoring complex human body gestures. Meanwhile, the relation between the loading direction and the measured parameter K (RCR in X-direction over that in Y-direction) is proposed to predict the loading angle. Considering its ultrahigh sensitivity and loading-direction-perception capability, the anisotropic strain sensor with the heterogeneous structure of stiff-soft-stiff segments is promising in wearable devices, robotic systems, artificial intelligence, etc.

Thermo-viscoplastic behavior of DP800 steel at quasi-static, intermediate, high and ultra-high strain rates

Using the shear-compression specimen (SCS), thermo-viscoplastic behavior of DP800 steel has been investigated systematically over a wide range of strain rates, including quasi-static (0.001–1 s−1), intermediate (10–100 s−1), high (2000–8000 s−1) and ultra-high (16,000–50,000 s−1) regions. Temperatures between 293 and 1073 K were considered. Experimental results show: (1) DP800 steel exhibits non-linear strain rate sensitivity. For tests at strain rates lower than 4000 s−1, the flow stress increases slightly. However, for tests at strain rates above 8000 s−1, a significant flow stress upturn exists; (2) dynamic strain aging (DSA) occurs within the temperature range of 473–873 K and strain rates below 100 s−1; (3) both strain rate sensitivity and temperature sensitivity of DP800 steel are influenced by DSA, and bell-shaped sensitivity curves form; (4) with increasing strain rates, peaks of the bell-shaped temperature sensitivity curves move to higher temperature regions, and this law is equally valid for the effect of temperature on the strain rate sensitivity curves; (5) strain hardening behavior of DP800 steel is dominated by a competition between strain rate hardening, DSA hardening and thermal softening. With increasing strain rate, single peak or double peaks are observed in average strain hardening rate-strain rate curves. According to experiments, a semi-physical constitutive relation has been established, taking into account both the viscous drag effect and the DSA phenomenon. The established constitutive model can predict flow stress curves of DP800 steel accurately with an average error of 7.12%. Both the enhanced strain rate sensitivity due to viscous drag and the bell-shaped flow stress curves caused by DSA are captured correctly.

Ultrafast severe plastic deformation in high-entropy alloy [formula omitted] via dynamic equal channel angular pressing

An extensively investigated high-entropy alloy (HEA), Al0.1CoCrFeNi, is processed by dynamic equal channel angular pressing (D-ECAP) and subsequent annealing. Severe shear deformation and ultrahigh strain rate give rise to simultaneous activation of the {111}〈112〉 macro deformation twins and kink bands with the 〈110〉 or 〈112〉 rotation axes. Secondary kink bands are also observed in primary kink bands. With increasing annealing temperature, the deformation twins and kink bands both become less or disappear. The yield strength is increased by ∼255% solely by D-ECAP compared to the as-cast HEA. A reasonable combination of high strength and good ductility is achieved through annealing twins in recrystallized grains via annealing the D-ECAP-processed alloy at 900 °C. It is the first observation on kink bands within a face-centered cubic HEA under various loading conditions. The strengthening in these D-ECAP-processed samples before and after annealing is discussed in terms of grain boundary strengthening and dislocation strengthening.

A Bioinspired Ultratough Composite Produced by Integration of Inorganic Ionic Oligomers within Polymer Networks.

The nacre-inspired laminates are promising materials for their excellent mechanics. However, the interfacial defects between organic-inorganic phases commonly lead to the crack propagation and fracture failure of these materials under stress. A natural biomineral, bone, has much higher bending toughness than the nacre. The small size of inorganic building units in bone improves the organic-inorganic interaction, which optimizes the material toughness. Inspired by these biological structures, here, an ultratough nanocomposite laminate is prepared by the integration of ultrasmall calcium phosphate oligomers (CPO, 1 nm in diameter) within poly(vinyl alcohol) (PVA) and sodium alginate (Alg) networks through a simple three-step strategy. Owing to the small size of inorganic building units, strong multiple molecular interactions within integrated organic-inorganic hierarchical structure are built. The resulting laminates exhibit ultrahigh bending strain (>50% without fracture) and toughness (21.5-31.0 MJ m-3), which surpass natural nacre and almost all of the synthetic laminate materials that have been reported so far. Moreover, the mechanics of this laminate is tunable by changing the water content within the bulk structure. This work provides a way for the development of organic-inorganic nanocomposites with ultrahigh bending toughness by using inorganic ionic oligomers, which can be useful in the fields of tough protective materials and energy absorbing materials.

Spallation of polycrystalline tungsten using laser-induced shock at ultrahigh strain rates

Laser-induced shock technology was used to achieve the shock loading of polycrystalline tungsten (W) at an ultrahigh strain rate. The shock response and fracture behavior of W were investigated at different tensile strain rates. Unlike the intergranular fracture mode under quasistatic conditions, the transgranular–intergranular-mixed fracture mode of W was detected at high strain rates and the proportion of transgranular cleavage mode increased. The spall strength of W was positively correlated to the strain rate, reaching 5.86 GPa when the tensile strain rate reached 106 s−1 in the spall plane. The mobility of screw dislocations increased at high strain rates, and the simultaneous emission of screw dislocations improved the spall strength while accelerating the expansion of crack nucleation positions, inducing numerous transgranular fractures.

Bio-inspired fluorescence color-tunable soft actuators with a self-healing and reconfigurable nature

The adaptive behaviors of organisms in response to different environments can inspire the development of smart materials. These biomimetic color-changing actuating materials (BCCAMs) with complex shape memory (SM), self-healing, shape reconfigurable and reprocessing properties may be exactly what the flexible actuators/robots/electronic skins need. Here, we prepared an ultra-high strain (∼1600%) soft actuation material with fluorescence changes, self-healing, and SM performance under a single stimulus by a simple method. At the same time, we developed a simple strategy based on welding to achieve actuators that have a reconfiguring three-dimensional (3D) deformation and medium temperature reprocessing. The resulting 3D soft actuators can achieve effective coordination of these functions. Flexible actuators with multiple functions that can be triggered by a single switch are expected to have value in soft robots, flexible electronic skins, and so on.

Dynamic Hardening of AISI 304 Steel at a Wide Range of Strain Rates and Its Application to Shot Peening Simulation

The hardening behavior of AISI 304 steel is investigated at various strain rates, from the quasi-static state to ultra-high strain rates, because it is necessary for numerical simulation of high-speed deformation problems. This kind of testing at a wide range of strain rates has not been yet reported in the literature although it is indispensable for accurate numerical analyses where deformation takes place with a wide spectrum of strain rates. AISI 304 steel is a kind of austenitic stainless steel used in various engineering fields, which does not harden by heat treatment, but by cold working such as shot peening. In order to obtain hardening properties at each strain rate, tensile tests were carried out using a universal testing machine of the INSTRON 5583 for the quasi-static state, a high speed material testing machine of a servo-hydraulic type for intermediate strain rates, and a tensile split-Hopkinson bar for high strain rates with a digital image correlation method. The hardening properties at the ultra-high strain-rate region were obtained from Taylor impact test results by calibration with an experimental–numerical hybrid inverse optimization for reliable extrapolation results. Finally, the hardening flow stress curves were obtained at various strain rates from the quasi-static state to ultra-high strain rates by interpolating the data with the extended Lim–Huh model. The result shows that the yield stress of 759 MPa at the quasi-static state increased to 1429 MPa at a strain rate of 106 s−1, which is about 1.9 times of the quasi-static yield stress. As a demonstration example, the dynamic hardening properties obtained were applied to a shot peening simulation that required hardening curves at a wide range of strain rates from the static state to 106 s−1. The simulation result with the dynamic hardening properties is compared to that with the quasi-static properties. The comparison shows a notable difference in the maximum compressive residual stress by 32%, demonstrating that it is important to consider the dynamic hardening properties in such high strain rate simulation as shot peening for accurate simulation results.

Hugoniot elastic limit of single-crystal tantalum at normal and elevated temperatures subjected to extreme strain rates

Large-scale nonequilibrium molecular dynamic simulations of impact-induced shock propagation in defect-free single-crystal Ta along the [001] direction is presented, paying particular attention to the formation of elastic-plastic two-wave structures. Plastic deformation and elastic limits of Ta single crystals for various crystal orientations were investigated in a recent paper [R. Ravelo et al., Phys. Rev. B 88, 134101 (2013)]. In the present paper, a comprehensive study on the Hugoniot elastic limit (HEL) and its dependence on associated physical parameters is reported. The observed attenuation of an elastic precursor in a stress-wave profile led to proposing wide-range scaling relations for HEL decay applicable for ultrahigh strain rates. The influence of a lateral dimension on the spatial profile of a stress wave and time profile of free surface velocity (FSV) in the distinct appearance of a spike-valley feature and its consequence on scaling relations is investigated. Further, it is shown that the commonly used method of calculating HEL from a FSV profile is inadequate for submicron-thick samples at high strain rates. The necessary modifications are incorporated that resulted in comparable HEL values by two complimentary approaches of stress and FSV profiles. Simulations carried out for increasing impact strength revealed a power law dependence of HEL with strain rate. A methodology based on extrapolation of stress decay law and strain rate scaling constructed by us is proposed here for prediction of HEL pertaining to larger length samples. Very good agreement between the predicted values and available experimental results makes the modeling robust and applicable for a wide range of strain rates and length scales. Finally, the study is extended for elevated sample temperatures up to melting. Interestingly, yield strength is shown to follow an increasing trend up to a certain temperature, beyond which it decreases. An empirical relation is proposed here for expressing temperature dependence of HEL that explains the observed yield strength anomaly. Results are justified through thermal analysis of shear stress and evolution of dislocation density.

Compact Tri-FFPI sensor for measurement of ultrahigh temperature, vibration acceleration, and strain.

As a high-precision fiber optic sensor, a single optical fiber Fabry Pérot interferometer (FFPI) sensor is often used to measure parameters such as temperature or strain. However, the use of combined FFPIs to measure multiple parameters simultaneously has rarely been reported. In this paper, a compact Tri-FFPI sensor consisting of three series-connected FFPIs is proposed to measure high temperature, high acceleration, and large strain. The total length and diameter of the sensing part are only 2558.9 µm and 250 µm, respectively. One of the FFPIs, FFPI-1, contains a cantilever beam structure to measure vibration acceleration. FFPI-2 is used to measure temperature and the temperature compensation of the strain measurement. FFPI-3 is used to measure strain. To ensure that the sensor has high measurement sensitivity, two demodulation methods are used: the light intensity demodulation method for vibration acceleration and the wavelength demodulation method for temperature and strain. The sensor is capable of withstanding ultrahigh temperatures up to 1000°C.

Explosion/impact response of pure molybdenum at ultra-high strain rate and large strains

In order to study the dynamic mechanical properties of molybdenum under high strain rates, experiments are conducted using Hopkinson dynamic compression testing of a small-sized sample and explosion impact dynamic X-ray study of a flat shaped-charge liner. Experimental data agrees well with theoretical calculations and numerical simulations. Results demonstrate that strain hardening, thermal softening, and strain rate strengthening effects during the impact response process of the molybdenum material vary significantly with different impact conditions in a temperature range of 297–1273 K and a strain rate range of 0.0001–48,000 s−1. Strain rate strengthening and thermal softening effects are particularly apparent in the molybdenum material under impact at medium and high strain rates. At extremely high strain rates and large deformations, the dynamic mechanical response provides evidence of thermal softening and strain hardening effects. Stresses that result in damage to the molybdenum material are primarily attributed to the latter.

Simultaneous enhancement of mechanical and shape memory properties by heat-treatment homogenization of Ti2Ni precipitates in TiNi shape memory alloy fabricated by selective laser melting

• The simultaneous enhancement of mechanical and shape memory properties are obtained by homogenizing Ti 2 Ni precipitates in Ti 50.6 Ni 49.4 SMAs by SLM. • The Ti 50.6 Ni 49.4 SMAs with homogeneous Ti 2 Ni precipitates possesses ultimate tensile strength 880 ± 13 MPa and large fracture strain 22.4 ± 0.4%, circumventing the strength-ductility trade-off of TiNi SMAs by additive manufacturing. • The Ti 50.6 Ni 49.4 SMAs with homogeneous Ti 2 Ni precipitates also displays 5.32% recoverable strain and above 98% recovery rate, far superior to those in most of TiNi SMAs by additive manufacturing reported so far. The excellent shape memory and mechanical properties of TiNi shape memory alloys (SMAs) fabricated using selective laser melting (SLM) are highly desirable for a wide range of critical applications. In this study, we examined the simultaneous enhancement of mechanical and shape memory properties using heat-treatment homogenization of Ti 2 Ni precipitates in a Ti 50.6 Ni 49.4 SMA fabricated using SLM. Specifically, because of the complete solution treatment, nanoscale spherical Ti 2 Ni precipitates were homogeneously dispersed throughout the grain interior. Interestingly, the resultant SMA exhibited an ultrahigh tensile strength of 880 ± 13 MPa, a large elongation of 22.4 ± 0.4%, and an excellent shape memory effect, with a recovery rate of > 98% and ultrahigh recoverable strain of 5.32% after ten loading–unloading cycles. These simultaneously enhanced properties are considerably superior than those of most previously reported TiNi SMAs fabricated using additive manufacturing. Fundamentally, the enhancement in tensile strength is ascribed to precipitation strengthening and work hardening, and the large plasticity is mainly attributed to the homogeneous nanoscale globular Ti 2 Ni precipitates, which effectively impeded the rapid propagation of microcracks. Furthermore, the enhanced shape memory properties are derived from the suppression of dislocation movement and formation of retained stabilized martensite by the presence of high-density dislocations, nanoscale Ti 2 Ni precipitates, and abundant interfaces. The obtained results provide insight into the enhancement of the two types of properties in TiNi SMAs and will accelerate the wider application of SMAs.

Spallation damage of 90W–Ni–Fe alloy under laser-induced plasma shock wave

Laser shock loading is a more promising technology for investigating spallation damage in materials under shock-wave loading. In this paper, shock-induced spallation in a 90W–Ni–Fe alloy at an ultrahigh tensile strain rate of 106 s−1 is investigated using a superintense ultrafast laser facility. The spallation of the 90W–Ni–Fe alloy was dominated by a transgranular fracture of tungsten(W) particles with a high spall strength of 6.46 GPa. Here, we found an interesting phenomenon that the formation of nanograins inside W particles leads to a new mode of transcrystalline fracture of W particles during the laser shock loading. Futhermore, most voids were nucleated inside the W particles rather than at the W/γ-(Ni, Fe) matrix-phase interface. This result contradicts the fracture theory under quasi-static loading, which posits that the W/γ-(Ni, Fe) matrix-phase interface is not the preferred site for the initial failure under shock loading.

Outstanding unipolar strain of textured Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 piezoelectric ceramics manufactured by particle size distribution control of the plate-like BaTiO3 template

High-strain piezoelectric ceramics are required to miniaturize actuators for use in machinery and electronic systems. This paper reports an ultra-high strain of textured Pb(Mg1/3Nb2/3)O3–PbZrO3–PbTiO3 (PMN–PZ–PT) ceramics prepared using a plate-like BaTiO3 (BT) template. Small BT particles (<5 µm), which are difficult to orient as desired during tape casting, were removed from the as-synthesized BT (as-BT) template via a simple sedimentation method. Then, the residual BT (rs-BT) was used to prepare textured PMN–PZ–PT ceramics, which were compared with the textured ceramics prepared using the as-BT. Results show that the textured 0.4PMN–0.22PZ–0.38PT ceramics prepared with 5 vol% of rs-BT yield a significantly enhanced unipolar strain of 0.26% at 2 kV mm−1, when compared to the strain of 0.21% obtained from the textured 0.4PMN–0.22PZ–0.38PT ceramics prepared with the same amount of as-BT.

Distributed Brillouin fiber laser sensor

Brillouin fiber sensors can provide distributed strain and temperature measurements over long distances in standard off-the-shelf fiber by measuring the Brillouin frequency shift as a function of position along a fiber. The primary drawback of these systems is their limited sensitivity, which results from the challenge in identifying the Brillouin frequency shift to within a small fraction of the Brillouin linewidth. In this work, we introduce a technique that overcomes this fundamental limitation by establishing a series of lasing modes that experience Brillouin amplification at discrete spatial locations in the test fiber. The linewidth narrowing and high intensity associated with the lasing transition enable precise measurements of this lasing frequency. As an initial demonstration, we present a sensor that simultaneously excites 40 lasing modes in a 400 m fiber, providing a measurement of the strain at 40 discrete locations with a spatial resolution of 4 m. Each sensor exhibits a minimum detectable strain as low as 4 n ε / H z 1 / 2 with a dynamic range of &gt; 5 m ε and a bandwidth of ∼ 10 k H z . As the first demonstration that Brillouin lasing can be used for distributed fiber sensing, this work establishes an approach that could enable ultrahigh strain sensitivity using off-the-shelf fiber.

Ultra-high temperature flexure and strain driven amorphization in polycrystalline boron carbide bulks

The temperature dependence of the flexural strength of sintered boron carbide was studied. At temperatures above 2000 °C, B 4 C showed an ultrahigh flexural strength exceeding 1 GPa which was accompanied by a change in the deformation mechanism from brittle fracture to plastic deformation . Scanning transmission electron microscopy (STEM) observations revealed that the amorphization can be of microstructural origin for the observed plasticity in B 4 C at temperatures above 2000 °C and a strain rate of 3•10 −3 s −1 . The amorphization occurs inside of the severely deformed grains. Flexural tests below 2000 °C provided evidence for the formation of stacking faults or dislocations, which are ordinary defects after the flexural tests. The results at 2000 °C suggest that the magnitude of the tensile stresses imposed on the B 4 C grains during deformation in flexure and the total strain transferred to a ceramic during the deformation process play the dominant role in the crystalline-amorphous transformation.