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The mixed powders of TiH2, molybdenum, aluminum and graphite with molar ratios of 2/2/n/2.85 (n ranges from 1.0 to 1.4 mol with an interval of 0.1 mol) were used as raw material powders for this work, and a novel porous Mo2Ti2AlC3 was synthesized via reactive synthesis. Through systematic research on the pore structure parameters of porous Mo2Ti2AlC3 prepared with different aluminum content, the results show that there is a clear correlation between the aluminum content and the pore structure parameters. With the aluminum content rising from 1.0 to 1.2 mol, the viscous permeability coefficient and pore size decreased, while the porosity increased; When the aluminum content increased from 1.2 to 1.4 mol, the pore structure parameters of porous Mo2Ti2AlC3 displayed an opposite trend. The reasons for the evolution laws of these pore structure parameters were also discussed in depth. In addition, the pore structure forming mechanism of porous Mo2Ti2AlC3 ceramics during the activation reaction sintering process has been explored. This work can provide an important reference for the subsequent preparation of quaternary porous MAX phase ceramics.

Using the mixed powder of TiH2, graphite, aluminum and vanadium as starting materials, porous TiVAlC ceramics were fabricated by the reactive synthesis technology at 1300 °C. The chemical steadiness of porous TiVAlC along with the effects of sintering temperature on the viscous permeability coefficient, strength, porosity, pore size and volume expansion rate of the porous TiVAlC were explored, and the mechanism of pore formation was also revealed. The preparation process includes five steps as follows: (i) the complete decomposition of stearic acid at 500 °C; (ii) the pyrolysis of TiH2 at 700 °C, converting TiH2 into hydrogen and titanium (iii) The solid-liquid chemical reaction of solid vanadium, titanium and molten aluminum at 700 °C, converting the mixture into V–Al and Ti–Al compounds; (iv) At 900–1100 °C, Surplus V and Ti interact with graphite to synthesize carbides of TiVC2, VC, and TiC; (v) Reactive synthesized carbides (TiVC2, VC, and TiC), Ti2AlC, V–Al and Ti–Al compounds that yield porous TiVAlC at 1300 °C.

Optical metrology is widely used to measure materials’ deformation and mechanical properties but current fundamental research requires more precise measurement of microstructure and deformation in internal materials. Electron backscattered diffraction (EBSD) technique measures crystal orientation in individual grain and high resolution EBSD (HR-EBSD) method provides information about residual strain and GND density. Deformation of two stainless steels Nitronic 60 and Tristelle 5183 with different proportions of ferrite and carbides are characterised. Push-release bend testing was used to provide progressive increasing bending stress in two iron-based material samples. HR-EBSD and high resolution digital image correlation (HR-DIC) methods characterised residual strain, GND density and plastic strain distributions in each sample. Nitronic 60 and Tristelle 5183 were deformed and obtained 3.8% and 0.9% plastic strain Ɛxx. High GND densities distributed neighbouring grain boundaries in Nitronic 60 while high GND densities distributed around carbides, especially intragranular carbides in Tristelle 5183. HR-EBSD and HR-DIC quantitative characterised deformation in two iron-based alloys, grain/twin boundaries and carbides resulted in GND density increase, promoted work hardening and accumulated high residual elastic strain. Heterogeneous grain/carbide size distribution leaded to stress concentration and cause carbide decohesion and brittle fracture of sample.

The porous Ni-Cr-Mo-Cu alloys were fabricated by an activation reaction sintering technique. The effects of Cr content varied from 10 to 30 wt-% on the corrosion performance of porous alloys in 10 ...

In this paper, the fatigue small crack growth rate of selective laser melting (SLM) AlSi10Mg alloy is studied by in-situ SEM experiment. The experimental results show that the small crack growth rate of SLM AlSi10Mg alloy can be described by Paris law, and the crack growth rate increases significantly with the increase in temperature. In addition, the combination of finite element simulation and fracture analysis shows that the pore is one of the main factors affecting the dispersion of small crack growth rate.

Images from scanning electron microscopes, transmission electron microscopes and atomic force microscopes have been widely used in digital image correlation methods to obtain accurate full-field deformation profiles of tested objects and investigate the object’s deformation mechanism. However, because of the raster-scanning imaging mode used in microscopic observation equipment, the images obtained from these instruments can only be used for quasi-static displacement measurements; otherwise, spurious displacements and strains may be introduced into the deformation results if these scanning microscopic images are used directly in general digital image correlation calculations for moving and temporally deformed surfaces. Realizing kinematic parameter and dynamic deformation measurements on a scanning electron microscope platform. Establishing a scanning imaging model of moving and temporally deformed objects that contains motion and deformation equations, a scanning equation and an intensity invariance assumption for small deformations. Then proposing a scanning-digital image correlation (S-DIC) method based on combing the characteristics of the scanning imaging mode with digital image correlation. Quantitatively investigating the effects of the spurious displacements and strains introduced when using scanning images to represent moving and temporally deformed surfaces in the measurement results. Numerical simulations verify that the accuracy of the S-DIC method is 10−2pix for the displacement, 10−4 for the strain, 10−4pix/s for the velocity and 10−6s−1 for the strain rate. Experiments also show that the proposed S-DIC method is effective. Conclusions: The results of this work demonstrate the utility of S-DIC on the field of microscopic dynamic measurement.

The raster scanning imaging mode is widely used in scanning electron microscopes (SEMs), transmission electron microscopes (TEM), and atomic force microscopes (AFM), and can achieve subatomic resolution. However, only a point on the shallow surface of an object can be imaged at one time using the raster scanning imaging mode, whereas the entire surface of the object can be imaged in the image plane once and instantaneously using the optical imaging mode, which is a parallel imaging mode. Therefore, the image distortion and blur for the scanning imaging mode are different from the optical imaging. In this paper, we propose a theory to describe the mechanism of the scanning imaging process and restore the degraded image (distorted and blurred image) obtained using an SEM. The theory consists of a scanning equation, motion or deformation equations, and an assumption called the intensity-invariant hypothesis. Numerical simulations of the scanning imaging process and restoration of the degraded images are performed using the scanning imaging formulas, spatial non-uniform point spread function, and inverse restoration algorithms, including algebraic, interpolation, and their hybrid methods to verify the feasibility of our theory. In situ experiments on uniform linear motion, uniaxial tensile, and fatigue were also conducted to demonstrate the validity and efficiency of the proposed scanning imaging theory and restoration methods. We anticipate that this imaging and restoration theory will enable the scanning imaging mode to be used in in situ dynamic imaging and for mechanical property measurement of materials.

Rare earth barium copper oxide (REBCO) type materials are widely used in second-generation high-temperature superconductor tapes to carry high current volumes. These tapes can provide high critical currents along with good tolerance to perpendicular magnetic fields. However, REBCO tapes generally use a laminate structure that suffers from low peeling strength among its inner interfaces. Previously, we proposed a bending-peeling (BP) method and applied it to measurement of the interfacial strength of REBCO tapes at room temperature. All samples failed at the REBCO layer at room temperature. In this paper, we used the BP method to perform low-temperature interfacial strength measurements at liquid-nitrogen temperatures. There are two types of failure, where one involves peeling of the REBCO layer and the other involves peeling at the interface between the tape and the epoxy resin. The errors in the BP method were discussed in detail. The superconducting current was monitored during the BP experiment and showed that the effect of out-of-plane tensile stress on the superconducting current was not significant before the breaking of the tape. The degradation in the superconductivity is mainly caused by the structural failure of the REBCO layer.

In-situ high temperature measurement in a scanning electron microscopy (SEM) environment is an important technique for exploring the microstructure evolution and crack propagation within refractory materials and other advanced alloys. In this paper, in-situ tensile fatigue experiments under SEM environment at room temperature and elevated temperature are performed for studying the fatigue performance and crack propagation process of selective laser melting (SLM) additive manufactured Al-Si10-Mg materials. Firstly, in-situ SLM additive manufactured Al-Si10-Mg fatigue tensile samples are prepared, and micro-CT are employed for the characterization of void defects within SLM additive manufactured Al-Si10-Mg with different laser scanning speeds and laser energy; Secondly, in-situ fatigue experiments are carried out under SEM environment at 25 °C, 100 °C, 200 °C, 300 °C, 400 °C, 500 °C and 600 °C, respectively. The fatigue mechanical behaviors, microstructure evolution and crack propagations of as-fabricated Al-Si10-Mg samples are characterized. Finally, micro-CT tomography 3D imaging techniques are employed for exploring the link between SLM defects and fatigue performances.

In the past three decades, we have witnessed the explosive development of micro/nano science and technology, where remarkable research efforts have been made in synthesizing of materials and fabricating of devices at micro- and nano-scale. The unusual mechanical behaviors of materials and devices with reduced their size and dimension pose the open questions to the researchers, which expand the framework of mechanics by advancing the theory, as well as modeling and experimental tools. Researchers in worldwide have been actively involved into this exciting area, making remarkable contributions to measure mechanical parameters and understand the mechanical behaviors of materials and devices at micro- and nano-scale. Micro optical method, as a full field, real-time and non-destructive measurement technique, is one of the earliest techniques used to measure the mechanical properties of materials at micro scale. So far, the optical methods are still an exciting research area in the field of mechanical property measurement of materials and devices at such small scale, even with the further reduction of the size of the research materials and devices, and their experimental platform has been promoted to various scanning microscope platforms, such as scanning electron microscope (SEM), scanning transmission electron microscope (STEM), atomic force microscope (AFM) and so on. This article reviews the research progress of optical techniques developed for the measurement of mechanical properties of materials and devices at micro- and nano-scale, with the aim to clarify the measurement principles and applications of optical methods in small scale, consisting of the experimental equipment, clamping and loading, deformation carriers or marks, optical methods including the holography, speckle and moire, and finally to outline the perspectives in this fast-evolving field.

Cord steel has very strict requirements on the content of impurities. Hydrogen is a harmful gas element in steel and is the cause of hydrogen embrittlement. In this work, the Carrier gas hot extraction method is used to measure the hydrogen content of 77A steel. It was found that the measured value of hydrogen content was related to cooling capability of the mold. It is found that with the increasing of cooling speed of the mold, the hydrogen content increases. The measured hydrogen content can roughly reflect the hydrogen content in the liquid alloy by using the cast iron mold with faster cooling speed.

In situ observation and measurement of high-temperature deformation of hot-section materials in scanning environments is helpful in understanding the microscopic failure and fracture mechanisms of these materials and estimating their safe life cycles. However, in situ high-temperature measurements in a scanning electron microscopy (SEM) environment pose major challenges in high-efficiency heat source design, establishment of stable high-contrast microscopic images, and quantitative measurement of the deformation fields in the high-temperature environment. New methods and approaches must be therefore developed for quantitative measurement of these high-temperature mechanical properties. This article reports use of in situ SEM to measure the high-temperature deformation and fatigue properties of a nickel-based single crystal superalloy (NBSCS) up to 800 °C. A conductive heating source has been constructed based on numerical calculations of the thermal field inside the SEM chamber and analysis of the secondary electron spectrum and thermionic emissions received by the detector. Al2O3 nano-scale particles were coated on the NBSCS surfaces and were used to form speckle patterns to measure the deformation of NBSCS from room temperature up to 800 °C via a digital image correlation technique. The stable spatial geometric configuration and enhanced interfacial strength between the Al2O3 particles and the sample surface with increasing temperature validate the developed high-temperature speckle patterns. Tensile and fatigue experiments are performed for NBSCS samples using the developed system. Full-field displacements are obtained near the notch root and in situ fatigue crack propagation is reported in the temperature range from 600 °C to 800 °C.

Carbon nanotubes (CNTs) are one of the strongest known materials. When assembled into fibres, however, their strength becomes impaired by defects, impurities, random orientations and discontinuous lengths. Fabricating CNT fibres with strength reaching that of a single CNT has been an enduring challenge. Here, we demonstrate the fabrication of CNT bundles (CNTBs) that are centimetres long with tensile strength over 80 GPa using ultralong defect-free CNTs. The tensile strength of CNTBs is controlled by the Daniels effect owing to the non-uniformity of the initial strains in the components. We propose a synchronous tightening and relaxing strategy to release these non-uniform initial strains. The fabricated CNTBs, consisting of a large number of components with parallel alignment, defect-free structures, continuous lengths and uniform initial strains, exhibit a tensile strength of 80 GPa (corresponding to an engineering tensile strength of 43 GPa), which is far higher than that of any other strong fibre.

Modern yttrium barium copper oxide (YBCO) superconductor tape can carry a high critical current under a rather high magnetic field with good strain tolerance. However, the interface between the laminas is quite weak, and the interfacial strength has thus attracted considerable research interests. We designed a new method to analyze the interfacial strength of YBCO tape. A piece of tape was first embedded in a rectangular-section beam of epoxy resin, with the tape plane parallel to the middle cross section of the beam and the tape edge at the beam surface. The epoxy beam height was greater than the tape width. Three-point bending was applied to the beam, with one point on the opposite side of the tape across the beam and the other two points at the two ends. The interface was thus tensed during loading. In this way, the interfacial strength could be directly determined, and the interfacial energy could be calculated from the force–displacement curve. The crack interface was examined using scanning electron microscopy and analyzed using energy-dispersive X-ray spectroscopy. The average interface strength was 5.16 MPa. The experimental data were used to further simulate the crack behavior during the cooling process.

Fabrication of porous Ni-Cr-Mo-Cu alloys is available through Ni, Cr, Mo and Cu elemental powder reactive synthesis at the sintering temperature of 1150 °C. The pore structures, including swelling behavior, open porosity, pore size and viscous permeability of the porous Ni-Cr-Mo-Cu alloys are systematically investigated. The results revealed that the parameters of pore structure firstly increased, and then decreased with the increase of the sintering temperature. When the sintering temperature rose to 1000 °C, the volume expansion, open porosity and viscous permeability of porous Ni-Cr-Mo-Cu alloys reached the peak value of 8.0%, 41.6% and 17.2 μm2, respectively. In addition, it was confirmed that the pore structure evolution was based on three stages, that is, in the low temperature section before stearic acid decomposition, the formation of pores was initiated by the volatilization of pore-forming agent and the interstitial pores of green compact; when the temperature was lower than 1083 °C, the increase of open porosity was mainly due to the Kirkendall effect caused by solid partial diffusion; while, when the temperature is within the range of 1083 ∼ 1150 °C, the shrinkage behavior at high temperature and a small amount of metal solution formed by the unreacted Cu led to decrease in pore structure parameters.

Porous Ni–Cr–Mo–Cu alloys were prepared via reaction synthesis of mixed powders. Electrochemical performance test and weight-loss method were used to evaluate the effects of chromium content in the range of 10 ∼ 30 wt% on the alloys corrosion performance in 30 wt% H3PO4 solution. The microstructure, element valence and phase composition of the porous Ni–Cr–Mo–Cu alloys were characterized via scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS) and x-ray diffraction analysis (XRD), respectively. And the results show that the alloys exhibited serviceable corrosion performance and the corrosion behavior was better than that of pure Ni and Cu. Incremental changes in the chromium contents within a certain range enhanced the corrosion resistance of the alloys. These alloys with 30 wt% chromium exhibited excellent anti-corrosion ability in the H3PO4 solution. The electrochemical test displayed that the double capacitive loops of the alloys in the H3PO4 solution increased with the chromium content; at chromium content of 30 wt%, the charge transfer resistance and activation energy were 1123 Ω and 74.10 kJ mol−1, respectively. The possible corrosion-inhibition mechanism was examined by XPS, which may be owing to the formation of MoO x (x = 1, 2, 3) and Cr2O3 passivation layers in the H3PO4 solution, which prevent further corrosion in acid environments.

In situ microscopic observation and measurement of deformations for advanced hot-section materials at high-temperature is helpful in understanding their failure mechanisms. Scanning electron microscopy (SEM) and a digital image correlation (DIC) method are combined to capture the failure process. This article reports an in situ high-temperature testing system which can heat the specimen up to 1000 °C and provide clear images simultaneously. The Al2O3 nanoscale particles are developed as high-temperature deformation carriers in SEM–DIC, which are suitable for high-temperature samples with significant advantages of stability, high image contrast and without shedding or melting up to 1000 °C. High-temperature tensile and creep properties of a nickel-based single crystal superalloy (NBSCS) at 750 °C were investigated using this system. In addition, a scanning–DIC (S–DIC) method, which avoids errors introduced by conventional DIC methods, was used to calculate full-field dynamic displacement and strain of high-temperature NBSCS samples. Analysis of the strain fields show that the strain concentrations are generally at the positions of crack initiation or propagation, and the creep cracks interact with each other through the strain field. Finally, the crack opening displacement is obtained using the virtual extensometer.

Nb 3 Sn, a widely adopted superconducting material, suffers from fragility and sensitivity to strain. Many studies have anticipated these drawbacks to be greatly influenced by thermal expansion mismatch between the Nb 3 Sn superconducting phase and matrix. We conducted X-ray diffraction (XRD) stress analysis on a heat treated bronze strand at room temperature and found that its average axial residual stress was -135.7 MPa with fluctuation of about 300 MPa. We developed an elastic analytical model and explained the overall compression. The considerable stress fluctuation phenomenon may originate from diffusion, which was supported by electron probe microanalysis results. This work highlights the importance of volume transmutation and component distribution on the stress status of a superconducting strand and can supplement the thermal mismatch model.

Finding the source of their durability Many high-strength materials can fail after repeated exposure to subcritical loading; therefore, understanding the causes of fatigue is key to extending the longevity of the material in use. Bai et al. used chemical vapor deposition to produce centimeter-long carbon nanotubes. They then decorated these nanotubes with titanium dioxide nanoparticles for optical visualization and studied them using noncontact acoustic resonance tests. The authors determined that fatigue lifetime is dependent on the formation of the first defects on straining and is higher at lower temperatures. Science , this issue p. 1104

In extreme environments, such as at ultrahigh or ultralow temperatures, the amount of tape used should be minimal so as to reduce system contamination and unwanted residues. However, tapes made from conventional materials typically lose their adhesiveness or leave residues difficult to remove under such conditions. Thus, the development of more versatile, lightweight, and easily removable tapes for applications in such extreme environments has received considerable attention. Here, we report that horizontally superaligned carbon nanotube (SACNT) tapes can be used to provide perfect van der Waals (vdW) interface contacts over a wide range of temperatures (from -196 to 1000 °C), yielding outstanding adhesiveness with specific adhesion strengths up to ∼1.1 N/μg. With a surface density of only 0.5-5 μg/cm2, hundreds of times lighter than the vertically aligned CNT adhesives, the SACNT tapes can be cost-effectively provided in hundreds of meters. They have multipurpose adhesive abilities for versatile materials and are also easily separated from samples even after exposure to extreme temperature regimes. First-principles calculations confirm the mechanism of vdW adhesion and reveal that ultraflat and nanometer-thick SACNT tapes may yield far greater adhesive abilities. These SACNT tapes show great potential for use in mechanical bonding, electrical bonding, and thermal dissipation in electronic devices.

Microfibers formed by Bacillus subtilis ( B. subtilis ) have attracted interest because of their potential for use as biodegradable fibers. In this work, an efficient method based on the micro-liquid bridge method (LBM) is proposed to investigate the mechanical properties and the deformation evolution in individual fibers. For the first time, tensile testing of fibers of this type containing several cells is conducted in a scanning electron microscope (SEM) chamber and the in situ deformation evolution of the fibers and the septa is observed. Experimental results show that these fibers are almost broken at the positions of the septa at low humidity, but also show that their fracture morphologies are different. At high humidity, local necking deformation occurs at the septum position. To explore the deformation mechanism of an individual bacterial fiber with a diameter of several hundred nanometers under different humidity conditions, we use the finite element method (FEM) to analyze the tensile deformation behavior of these fibers when their septa are at various separation levels. The numerical results indicate that weak interactions among the septa lead to the dispersion of both the fibrous tensile strength and the modulus. These results may be helpful in understanding the deformation mechanism, thus leading to further improvements in the mechanical performance of these fibers.

Creep-fatigue interaction behavior of nickel-based single crystal superalloy was studied in an in-situ SEM platform at 900 °C. Dwell times of 15, 30, 60, 90, 120 s were introduced at the tensile peak stress of each cycle. Experimental results showed that the life cycles firstly decreased rapidly then slightly increased with the increasing dwell time, which was explained by the accumulated inelastic strain. Dislocation microstructure and inelastic strain were correlated for different dwell time by TEM analysis. Crack propagation mode transition was analyzed. Comparing with the stress intensity factor amplitude, crack tip opening displacement was more suitable for characterizing the creep-fatigue small crack growth rate.

Ultralow inter-wall interaction is realized in centimeter-long double-walled carbon nanotube (DWCNT) (Zhang, R. et al. Nat. Nanotech. 8, 912-916 (2013)). To further illustrate the mechanism of this special phenomenon, theoretical analysis combining with the experimental test is conducted, where study of the inter-tube interaction in the carbon nanotube bundles (CNTBs) is also included in this paper. In experiment, nanomanipulation difficulties of the ultra-long carbon nanotube (CNT)/CNTB is overcome by establishing a micro/nanoscale mechanical testing system (m/n-MTS), based on which the inter-wall/inter-tube interaction is firstly in-situ measured under optical microscope (OM). In theory, according to the bottom-up approach, a multi-scale model is developed specially, by which results obtained can be directly compared with the experimental data. The pull-out force consists of three parts: the boundary effect, the configuration force and the dynamic friction. The boundary effect can account for more than 70% when the pull-out velocity equals to 1 μm/s. The configuration force is greatly enhanced for the CNTB because of the commensurate configuration in the circumferential direction. The dynamic friction shows linear dependence on the pull-out velocity and relates to the overlapped area, which can be manifested when the pull-out velocity reaches to a dozen μm/s for the ultra-long DWCNT. The dynamic friction coefficient is proved to be 0.29 multiple of critical value based on the experiment data. The pull-out force in the CNTB is found far less than that in the DWCNT due to the greatly reduced contact area. Moreover, it can be deduced that the dynamic friction will show the same order of magnitude as the contribution from the boundary when the pull-out velocity equals to 10 μm/s or the length is 10 mm. This research reveals the underlying mechanism of the interaction, especially for the dynamic friction force exhibited in the ultra-long CNT/CNTB, and can provide help for designing devices with ultralow friction on macroscale.