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The Journal of Materials Science awards the annual Robert W. Cahn Prize to recognize the best paper published in the journal each year. The winner of the 2023 Cahn Prize is a research paper titled "Molecular modelling of graphene nanoribbons on the effect of porosity and oxidation on the mechanical and thermal properties." The paper presents molecular simulation models of graphene nanoribbons and examines the impact of porosity and oxidation on their mechanical and thermal conductivity properties. The paper is well-written and provides valuable insights for researchers in this field. Two other papers were selected as runners-up for the prize. All the monthly finalists for the Cahn Prize can be downloaded for free on the journal's website. [Extracted from the article]

Twinning is an important deformation mechanism for magnesium alloys, which has a significant impact on the texture evolution and mechanical properties. Pre-twinning deformation has been considered as an effective method for texture regulation. For each twinning mode, there are six crystallographically equivalent variants. Properly identifying the activated twin and understanding its variant selection criteria are essential for the development of high-performance magnesium alloys. As summarized in this paper, the observed twin variant by the commonly employed electron backscatter diffraction technique can be identified by several approaches, including misorientation analysis, trace analysis and matrix method. Schmid factor analysis was commonly performed to explain the selection of twin variants. To broaden the application scope under complex stress state, a generalized Schmid factor was derived by introducing a stress tensor. The efficiency of Schmid criteria to assess twin variant selection was confirmed to be influenced by the type of the applied stress. To consider the local effect on twin activation, in particular twin-twin transfer and slip-induced twinning, displacement gradient tensor calculation and geometrical compatibility factor analysis have been employed. It was demonstrated that local strain accommodation played a critical role in selecting the variants of cross-boundary twins in magnesium alloys. Assisted with crystal plasticity finite element modeling, the resolved shear stress on twinning and a composite Schmid factor combining the global Schmid factor and geometrical compatibility factor were obtained to better explain the activated twin variants in magnesium alloys. All the above-mentioned Schmid law based criteria and some energy based criteria as well are summarized in this paper. Their applications in evaluating twin variant selection in magnesium alloys are critically reviewed and discussed. [ABSTRACT FROM AUTHOR]

Due to the machining-induced residual stress while processing, the machining distortion of thin-walled 7050 aluminum alloy parts occurs easily, which greatly affects the pass rate of the products. Herein, electromagnetic coupling treatment (EMCT) was proposed to relieve the residual stress of 7050 aluminum alloy. It was found that EMCT had a significant effect on residual stress relief (13.3–89.7%). The energy input by EMCT promoted the movement of dislocation, resulting in the uniform distribution of microplastic strain, the release of stored elastic strain energy, and the residual stress relief, ultimately. A numerical simulation method to visualize the evolution of the electromagnetic field, the stress, and the strain in the materials was proposed to explain the causes of microplastic strain. Specimen #5 with the optimal EMCT processing parameter (1.5 T, 1.5 V) was considered to be the most effective for both residual stress relief and mechanical property enhancement, in which the residual stress decreased by 85.1% and the tensile strength increased by 8.3%. In this paper, it is proposed that EMCT can be used as an effective method to reduce the residual stress of 7050 aluminum alloy. Moreover, it has certain technical reference value for the study of residual stress relief of other thin-walled part materials. [ABSTRACT FROM AUTHOR]

In the last years, a large number of new biocompatible materials for 3D printers have emerged. Due to their recent appearance and rapid growth, there is little information about their mechanical properties. The design and manufacturing of oral appliances made with 3D printing technologies require knowledge of the mechanical properties of the biocompatible material used to achieve optimal performance for each application. This paper focuses on analysing the mechanical behaviour of a wide range of biocompatible materials using different additive manufacturing technologies. To this end, tensile and bending tests on different types of recent biocompatible materials used with 3D printers were conducted to evaluate the influence of the material, 3D printing technology, and printing orientation on the fragile/ductile behaviour of the manufactured devices. A test bench was used to perform tensile tests according to ASTM D638 and bending tests according to ISO 178. The specimens were manufactured with nine different materials and five manufacturing technologies. Furthermore, specimens were created with different printing technologies, biocompatible materials, and printing orientations. The maximum allowable stress, rupture stress, flexural modulus, and deformation in each of the tested specimens were recorded. Results suggest that specimens manufactured with Stereolithography (SLA) and milling (polymethyl methacrylate PMMA) achieved high maximum allowable and rupture stress values. It was also observed that Polyjet printing and Selective Laser Sintering technologies led to load–displacement curves with low maximum stress and high deformation values. Specimens manufactured with Digital Light Processing technology showed intermediate and homogeneous performance. Finally, it was observed that the printing direction significantly influences the mechanical properties of the manufactured specimens in some cases. [ABSTRACT FROM AUTHOR]

To investigate the dynamic recrystallization (DRX) behavior of forged 42CrMoA steel during hot deformation, the hot deformation experiments of forged 42CrMoA steel under different deformation conditions (strain rate, temperature, and strain) were carried out in this paper. The hot deformation activation energy of forged 42CrMoA steel was determined to be 413627.2 J · mol - 1 . The constitutive model and DRX kinetic model of the steel were established. Analyzing the reconstructed parent phase grains reveals that when the strain is constant, as the deformation temperature increases and the strain rate decreases, the average size and DRX volume fraction of the parent phase grains gradually increase, and the peak stress gradually decreases. When the deformation temperature and strain rate are constant, as the strain increases, the average size of the parent phase grains gradually decreases, and the volume fraction of DRX gradually increases. Based on the cellular automaton theory model and considering the influence of grain deformation on the DRX process, a cellular automaton dynamic recrystallization (T-DRX-CA) model for forged 42CrMoA steel based on topological deformation technology was established, and the microstructure evolution under different deformation conditions was simulated. The microstructure evolution under different deformation conditions was simulated, which was compared with experimental results. The results showed that the average errors between the simulated and experimental values of the average grain size of the parent phase, the volume fraction of DRX, and peak stress were all less than 8%, and the simulated results were in good agreement with the experimental values, which indicates that the established model can accurately predict the DRX behavior of the forged 42CrMoA steel in the process of hot deformation. The hot deformation behavior of forged 42CrMoA steel under different deformation conditions was investigated by a cellular automaton dynamic recrystallization (T-DRX-CA) model based on topological deformation technique. The results showed that the average errors between the simulated and experimental values of the average grain size of the parent phase, the volume fraction of DRX, and peak stress were all less than 8%, and the simulated results were in good agreement with the experimental values, which indicates that the established model can accurately predict the DRX behavior of the forged 42CrMoA steel in the process of hot deformation. [ABSTRACT FROM AUTHOR]

During high-temperature applications, tensile stability is significantly important and urgent for the security of components. In this paper, the high-temperature tensile tests under different creep strain were performed and analyzed through scanning electron microscope (SEM) and transmission electron microscope (TEM) of TC11 titanium alloy. It is found that the creep strain, dynamic α precipitation and deformation modes have significant influence on the high-temperature tensile behavior of TC11 titanium alloy. An abnormal characteristic of high-temperature tensile stress plateau was observed with the increasing of the creep strain. Moreover, an increment of 100 MPa for yield strength was achieved when the creep strain increased from 0.075 to 0.21%. For low creep strain, sample was controlled by the dislocation slip. While at high creep strain, it promotes the precipitation of nano-sized α particles, and dislocation slip hardly transfers across the α/β interface. Then, dislocation tangles, deformation twins and stacking faults become dominated, which results in an obvious stress plateau in the stress–strain curve. [ABSTRACT FROM AUTHOR]

Some key structural parts made of welding titanium alloys usually serve in hydrogen environment in aerospace, ship building and chemical industries. To investigate the hydrogen embrittlement (HE) behaviors of the welded titanium alloy joints and the impact factors, the TC4 titanium alloy joints welded by laser welding method were first treated by ultrasonic surface rolling process (USRP). Then, slow-rate tensile tests were conducted under electrochemical hydrogen charging condition to compare the mechanical properties of the TC4 laser welded joints before and after USRP. On this basis, the HE behaviors and mechanisms of the USRP-treated TC4 laser welded joint and the USRP-untreated one were discussed in detail. The results show that USRP could significantly improve the anti-hydrogen embrittlement behaviors of the TC4 laser welded joint, which could be attributed to the grain refinement and residual compressive stress in the deformation layer induced by USRP. The results of this paper provide a theoretical basis for the design of anti-hydrogen embrittlement metal materials. [ABSTRACT FROM AUTHOR]

Haynes 282 is a γ ′ precipitation-strengthened nickel-based superalloy known for its exceptional high-temperature creep resistance and excellent fabricability. Recent advancements in powder-bed fusion-based additive manufacturing (PBF-AM) have enabled the fabrication of Haynes 282 with accurate, site-specific control of the grain orientation and morphology at the microscale. This ability opens up new avenues for microstructure design, to improve the material's fatigue crack resistance and service life. This paper investigates the fatigue crack growth behavior of hybrid microstructure Haynes 282 fabricated via PBF-AM. Previous experiments revealed a higher crack propagation rate in the coarse columnar-grained microstructural regions when compared against fine-grained areas. Here, a strain gradient crystal plasticity model was adapted to study the fracture-related mechanical fields at the crack tip in the two microstructures. The simulation results showed a consistent influence of grain structure and texture on crack propagation, as was seen in the experiment. The model analysis revealed higher crack propagation driving force along crack direction in the coarse-grained sharply textured microstructure and higher driving force for crack kinking in fine-grained more diffusely textured microstructure, which is ascribed to the combined effect of yield stress, hardening rate, texture and grain morphology. The presented modeling approach will facilitate the development of the AM-based accurate microstructure design by deepening the fundamental study in AM-specific microstructure-properties relations. [ABSTRACT FROM AUTHOR]

To obtain ultra-high strength with guaranteed ductility, stable nanolamellar austenite packed with high densities of dislocations and nanotwins is inserted into nanolamellar martensite. An ultra-high yield strengths of 1.6–2.2 GPa at room temperature and 1.94–2.5 GPa at liquid nitrogen temperature were obtained in the steel, which is combined with good uniform elongation of 4–9%. The designed steel is shaped with the combination of solid solution strengthening, lamellar boundary strengthening and dislocation strengthening. The nanostructure is stabilized by C distribution, and in this way the stress–strain carrying capacity of martensite and austenite is increased, thus ensuring ultra-high strength. In addition, the generation of TRIP effect at low temperatures ensures the realization of strain-hardening rate and uniform elongation at ultra-high strength. Therefore, the nanolamellar martenite-austenite microstructure and strong carbon partitioning through martensite and austenite is considered as a fundamental guarantee for the ultra-high strength and toughness. Our results provide an optional strategy for the development of new ultra-strong alloys for low-temperature applications. [ABSTRACT FROM AUTHOR]

The large deformation of difficult-to-deform metal under pulsed currents involves the coupling effect of grain refinement and electroplasticity, making it challenging to capture the flow behavior accurately during severe plastic deformation. To develop a highly accurate constitutive model that accounts for the coupling effect, a current-assisted plane strain compression (CAPSC) test of 30CrMnSiA was carried out, using a peak current density (Jp) range of 0–30 A mm−2 and duty ratio (d) of 0–20%. A microstructural observation was also performed via the EBSD test on the specimens after the CAPSC test. The result indicates that the true stress decreases significantly with increased Jp and d, descending to a stable value of 13% under high Jp and high d regions. Pulsed current accelerates grain refinement, promoting the transition from low-angle grain boundaries to high-angle grain boundaries through the recovery mechanism. Fine grain sizes increased from 31.7 to 45.5% in the pulsed-current condition compared to the non-current condition. Based on the above discovery, a physical-based constitutive model frame was proposed to characterize the independent evolution and transformation of dislocation density at the grain boundary and interior. Besides, the current density is also coupled into the model as an influence term of the material parameters to capture the influence of electroplasticity on grain refinement. Comparing the test stress to the predictive stress reveals that the model accurately predicts the CAPSC stress of 30CrMnSiA with a correlation coefficient of 0.974 and an average relative error of 4.56%. [ABSTRACT FROM AUTHOR]

To conquer the trade-off between strength and ductility, a new strategy for preparing heterostructured (HS) 2024Al alloys with various heterogeneity levels through introducing submicro-Al3Ti particles and adjusting partial remelting duration of powder thixoforming was proposed. The results indicate that the difference in volume fraction between soft and hard domains of the resultant HS alloys gradually decreases from 0.27 to 0.02, while that of microhardness also decreases from 1.58 to 1.17 GPa, i.e., the heterogeneity level gradually decreases with prolonging the remelting time. The excellent strength–ductility synergy is simultaneously achieved by a moderate heterogeneity level (the differences in microhardness of 1.23 GPa and volume fraction of 0.02) in the HS alloy thixoformed at the partial remelting time of 80 min. This is primarily ascribed to the largest strain gradient caused by the accumulation of the highest density dislocations at the boundary during deformation, which produces the highest heterodeformation-induced (HDI) strengthening and hardening. In addition, the dislocations emitted from the submicro-Al3Tip during the later deformation stage also improve the strain strengthening and hardening, further leading to the improvement in strength–ductility synergy. [ABSTRACT FROM AUTHOR]

The SA508-3 steel has been acknowledged as nuclear-grade steel used to manufacture power plant components owing to its high strength, good toughness, and low sensitivity to irradiation embrittlement. In this study, the dynamic mechanical properties of SA508-3 steel are investigated by the split Hopkinson pressure bar tests with a wide range of strain rates (0.0001–6000 s−1) and elevated temperatures (20–600 °C), and the corresponding flow stress curves are obtained. The results suggested that the dynamic stress–strain response of SA508-3 steel is dependent both on the strain rate and temperature, and the temperature sensitivity (na) is independent of the strain rate. Based on the experimental results, a constitutive model is built by Johnson–Cook (J-C) model to describe the dynamical property of SA508-3 steel, and the flow stresses predicted by the established J-C constitutive model at all the tested strain rates and temperatures are in good agreement with the experimental data. Furthermore, a successful finite element (FE) analysis of the milling process of SA508-3 steel at different cutting parameters is carried out by implementing the established J-C constitutive model into the third-wave-AdvantEdge software, and the predicted cutting forces are agreed well with the experimental results, which provides a strong support for the FE analysis of SA508-3 steel milling process. [ABSTRACT FROM AUTHOR]

Accurate and consistent constitutive model is required to characterize the material behavior in a variety of thermo-mechanical problems. Herein, widely used Johnson–Cook (J–C) model parameters are evaluated for Fe–30Mn–9Al–0.8C low-density steel to predict the flow stress in various forming applications. For this low-density steel prepared in our laboratory, the material compositions are optimally chosen to yield the best ductility (> 70%) with good tensile strength. Tensile tests have been performed at strain rates varying from 10–4 to 10–1 s−1 and at various temperatures such as 150 °C, 300 °C and 450 °C to determine the J–C parameters. Thereafter, genetic algorithm (GA) technique has been used to obtain optimum values of J–C parameters that best fit the experimental stress–strain data. The improved values of the J–C parameter are implemented in ABAQUS explicit software to replicate the experimentally observed tensile test data. It has been observed that the developed constitutive model can produce a fairly accurate and precise estimation of flow stress with a good correlation to experimental data under various strain rates and temperature conditions. [ABSTRACT FROM AUTHOR]

René 65 is a high strength cast & wrought (CW) Ni-base superalloy with thermomechanical performance tailored toward intermediate temperature and stress conditions (677 °C/690 MPa). René 65 Turbine disk rotor forgings are typically subject to a sub-solvus heat treatment utilized to retain a uniform and fine-grained microstructure that confers a high level of fatigue performance and strength at the expense of high-temperature creep resistance. However, the processing of René 65 via laser powder bed fusion (LPBF) can enable this material to exhibit intermediate or coarse-grained microstructures after heat treatment that possess improved creep resistance. The effect of the difference in the processing route in conjunction with heat treatment on the resulting microstructure is presented and correlated to the creep behavior (at 677 °C/690 MPa) and stress relaxation behavior (700 °C). A good correlation of relaxation and creep behaviors was found, with LPBF processed René 65 exhibiting overall improved resistance to high-temperature deformation. The primary factor with regards to microstructural difference toward the stress relaxation/creep behavior of René 65 has been identified to be the size and volume fraction of tertiary γ' present resulting from the chosen processing pathway. [ABSTRACT FROM AUTHOR]

The chemical expansion of ceria (CeO2−δ) and ceria-zirconia (Ce0.8Zr0.2O2−δ, CZO80) thin films is investigated by high-temperature laser Doppler vibrometry (LDV) at temperatures from 600 to 950 °C. The films are deposited on single-crystalline 8 mol-% yttria-stabilized zirconia substrates, which act as pumping cells to adjust oxygen non-stoichiometry in the thin films. Oxygen deficiency causes film expansion, leading to mechanical strain that bends the sample. The total displacement, i.e., the sum of bending and film-thickness change, is determined contact-less by LDV. A differential laser Doppler vibrometer (D-LDV) is realized to enable measurements on a very long time scale, which is necessary due to the long equilibrium times of the ceramic films. These displacements are compared to those acquired with a commercial single-point laser Doppler vibrometer (SP-LDV) for motions above 1 Hz. Here, both devices yield similar results. CZO80 films are found to bend a substrate much more than ceria films under similar experimental conditions. A model describing the displacement of the sample is derived from the Stoney model and applied to calculate deflections using literature data. The displacements at the center of the CZO80 sample measured with the SP-LDV increase from 0.18 nm at 10 Hz and 600 °C to 32.7 nm at 0.1 Hz and 800 °C. For ceria, the displacements range from 1.6 nm (10 Hz, 800 °C) to 79.4 nm (0.1 Hz, 900 °C). The D-LDV enables the detection of quasi-static displacements at very low frequencies. The ceria sample exhibits 218 nm at 0.001 Hz and 800 °C. [ABSTRACT FROM AUTHOR]

Grain boundary engineering (GBE) has shown a promising application in improving resistance to intergranular corrosion (IGC) of polycrystalline metallic materials with low-stacking fault energy, such as austenitic stainless steels. However, the traditionally uniform plastic pre-straining methods, such as cold rolling, in thermomechanical processing are hard to implement on complicated surfaces. Here, we demonstrate a novel approach using gradient plastic strain induced by surface mechanical grinding treatment with a rotary tool and subsequent annealing to optimize grain boundary character distribution (GBCD) in the near-surface layer. The gradient plastic strain followed by long-time annealing (24–96 h) in 304 stainless steels achieved an optimized GBCD with over 75% frequency of coincidence site lattice (CSL) boundaries and disconnected random boundary network in the near-surface layer. The intergranular corrosion tests showed that the resulting 304 stainless steels with the optimized GBCD in the near-surface layer present an excellent resistance to IGC behavior due to a high fraction of Σ 3 n boundaries. During the annealing process, severe plastic strain near the surface results in small size grain clusters via strain recrystallization, while low-level plastic strain in the subsurface promotes the formation of high fraction of CSL boundaries and large size grain clusters via strain-induced boundary migration. After the complete depletion of gradient plastic strain, the directional growth of grain clusters promotes the further extension of surface GBE into interior region. Thus, the thickness of surface GBE region can be regulated by the annealing time. [ABSTRACT FROM AUTHOR]

Flexible low-dielectric constant (low-k, k < 4.0) SiCOH films were deposited onto ITO/PEN flexible substrates by plasma-enhanced chemical vapor deposition of tetrakis(trimethylsilyloxy)silane precursor at room temperature with plasma powers from 20 to 100 W. The pristine SiCOH films had a mechanical strength up to 9.1 GPa and a low k-value down to 2.00, and they were transparent, smooth, and hydrophobic. As the plasma power increased, there were an increase in the suboxide structure, increase in density, and decrease in the methyl group concentration. In the lower plasma power regime of 20–60 W, the k-value decreased as the plasma power increased due to the increased suboxide structure. In the higher plasma power regime of 60–100 W, the k-value increased as the plasma power increased due to the decreased methyl concentration and increased density. The mechanical properties increased as the plasma power increased. Upon repeated mechanical bending tests with bending cycles up to 10,000, the flexible SiCOH films maintained their transparency, smoothness, and hydrophobicity and showed a stable k-value below 4.0. There were no significant changes in the FTIR spectra and no cracks or delamination observed in the films. The SiCOH films showed stable physical, chemical, and electrical properties under the repeated mechanical bending. [ABSTRACT FROM AUTHOR]

The resistance to chloride-induced stress corrosion cracking was investigated on a high-strength CrNiMnMoN austenitic stainless steel in the hot-rolled and in different cold-drawn states. The resistance against chloride-induced stress corrosion cracking was determined by slow strain rate tests in different chloride containing solutions at elevated temperatures. A fracture analysis was carried out using scanning electron microscopy. Improved resistance is obtained by the formation of deformation-induced twins. In addition, synchrotron X-ray diffraction measurements show full austenite stability during all cold-drawing steps. [ABSTRACT FROM AUTHOR]

The true triaxial compression test was performed to further investigate the triaxial mechanical properties of coral concrete. Considering three concrete strength grades and nine stress ratios as variables, 100 mm × 100 mm × 100 mm cubic specimens were tested using a servo-controlled static-dynamic triaxial machine (TAWZ-5000/3000). The failure modes, stress–strain curves, peak stress, and peak deformation of coral concrete were obtained from the tests. The results showed that there are plate splitting and slant-shear in the failure modes of coral concrete. The stress and deformation were influenced by the concrete strength and stress ratio. The triaxial strength of coral concrete was significantly improved compared to the corresponding uniaxial strength. With the quadratic regression analysis, a functional relationship between material parameters and uniaxial compressive strength was established, which can accurately predict the meridian criterion of coral concrete for a certain strength grade. Moreover, comparing theoretical and experimental data, the failure criterion proposed by Wang for lightweight aggregate concrete was further verified to be applicable to coral concrete. [ABSTRACT FROM AUTHOR]

The effect of the evolution of phase transformation strain on the quasi-linear elastic deformation behavior for Nb/Ni50.3Ti49.7 composite was investigated on the basis of the theoretical analysis of martensitic transformation crystallography and in situ synchrotron X-ray diffraction experiment. The calculated and experimental results suggest that during the stress-induced martensitic (SIM) transformation, the B19′ martensitic variants 6 (V6) and 6′ (V6′) survived preferentially among 12 different B19′ martensitic variants due to their maximum phase transformation strains. Additionally, the phase transformation strains for the V6 and V6′ along the < 110 > B2 direction increase nonlinearly as the increase in macroscopic strain during deformation, which is mainly ascribed to the discrepancy in the change rates of the lattice parameters for the B2 parent phase and B19′ martensite. This increase in transformation strains for the V6 and V6′ during deformation is conducive to achieving the high quasi-linear elastic deforming capability (quasi-linear elasticity plus large recoverable strain) in Nb/Ni50.3Ti49.7 composite. [ABSTRACT FROM AUTHOR]

Two B2CO phases (oP8′ with sp2-sp3 hybridization coexist and mP16 with unitary sp3 hybridization) were predicted via structure searching and stability analysis. The study of formation enthalpy reveals that high pressure (HP) technology performed maybe an important method for synthesis. oP8′ and mP16 both have large mechanical modulus and they are typical materials with high hardness. Pressure has a positive correlation with its mechanical modulus. The simulated tensile stress–strain relationship reveals that the maximum stress that oP8′ can bear is 64.7 GPa in the direction [100], and the maximum tensile is 0.24. Among all isoelectronic with diamond (IED) B-C-O phases, oP8′ has the smallest gap and mP16 has the widest gap. With pressure increasing, for B2CO phases with high symmetry and composed of sp3 hybridization, their band gaps all increases monotonically; for B2CO phases composed by sp3-sp2 hybridization coexist or with low symmetry like mP16, their band gaps increased first and then decreased. [ABSTRACT FROM AUTHOR]

The high strain rate dynamic behavior of additively manufactured (AM) 316L stainless steel (SS) is investigated, and a dynamic deformation-induced microstructural evolution is examined in this study. First, the as-built microstructure feature is characterized. The grain morphology is revealed to be location-dependent and driven by the solidification process. A steep rise in the point-to-origin misorientation profile traversing a melt pool boundary is observed, quantitatively describing the influence of process-induced interface on the initial grain orientation state. The static and dynamic mechanical properties are then examined. Compared with conventional wrought 316L SS, AM 316L SS demonstrates an enhanced mechanical strength under quasi-static compression (with a ∼ 95 % increase in yield strength). Under dynamic shearing, strain rate-induced strength enhancement is observed in wrought 316L SS (with a ∼ 47 % increase in dynamic flow stress); AM 316L SS nevertheless demonstrates nearly rate-insensitive responses in its yield stress (with a ∼ 5 % increase in dynamic flow stress). Localized deformation in the form of an adiabatic shear band and the associated structural evolution are analyzed. Radical changes in crystallographic and structural features induced by high strain rate deformation are observed. Grain deformation and rotation lead to a remarkable difference in the grain orientation and spatial direction from the starting state driven by the solidification process. Upon dynamic shearing, the transmission of localized plastic deformation across melt pools is revealed, and the indication in grain rotations is discussed. The change in the geometrically necessary dislocation density is examined, hinting at the competition of the dislocation multiplication and annihilation under localized deformation. The current work enriches the understanding of the dynamic mechanical properties of AM materials at high strain rates. [ABSTRACT FROM AUTHOR]

The effect of the grain size on the mechanical properties of metallic materials has been a topic of significant interest for researchers and industry. For many decades, a relationship defining the mechanical strength proportional to the inverse of the square root of the grain size has been widely accepted despite some reports of deviations from this behavior. Nevertheless, the initial explanations for this relationship, based mainly on the activation of slip systems by dislocation pileups at grain boundaries, have provided essentially no predictive capability. Here, we show that a physically based model for grain boundary sliding predicts, in excellent agreement with experimental data, the flow stress for plastic deformation for a broad range of materials using the fundamental properties of each material over a wide range of grain sizes and testing conditions. This mechanism also successfully predicts the reported enhanced strain rate sensitivity in ultrafine and nanocrystalline materials at different temperatures. [ABSTRACT FROM AUTHOR]

This work proposes a structure which allows characterization of graphene monolayers under combined electric field and mechanical strain modulation. Our approach is based on a cantilever integrated into a two-dimensional graphene-based Field effect transistor (FET). This allows us to change graphene properties either separately or together via two methods. The first way involves electric field induced by the gate. The second is induction of mechanical strain caused by external force pushing the cantilever up or down. We fabricated devices using silicon-on-insulator wafer with practically zero value of residual stress and a high-quality dielectric layer which allowed us to precisely characterize structures using both mentioned stimuli. We used the electric field/strain interplay to control resistivity and position of the charge neutrality point often described as the Dirac point of graphene. Furthermore, values of mechanical stress can be obtained during the preparation of thin films, which enables the cantilever to bend after the structure is released. Our device demonstrates a novel method of tuning the physical properties of graphene in silicon and/or complementary metal-oxide-semiconductor technology and is thus promising for tunable physical or chemical sensors. [ABSTRACT FROM AUTHOR]

In this study, we investigate the temperature-dependent dielectric response of dabcoHBF4 molecular switchable dielectric materials. This compound made of polycrystals has been shaped into pellets under different controlled applied pressures [0.2–1 GPa]. The dielectric analysis carried out on these samples showed that the mechanical stresses induced by this shaping pressure had a significant effect on the value of the dielectric constant in both the ferroelectric and the paraelectric phase. However, the impact of this pressure remains secondary in the AC electrical conductivity, determined for the first time in these compounds. Thus, conductivity values around 2 × 10–7 S/cm in the ferroelectric phase and 2 × 10–6 S/cm in the paraelectric phase were found. The behavior of these compounds over wide frequency ranges [1–1 MHz] and temperature ramps [0.5–10 K/min] revealed that the frequency had no effect on the transition temperature at the difference of temperature rate as expected in most ferroelectric materials. When decreasing the frequency, the dielectric constant gains in value and can reach values higher than 50 in the ferroelectric phase and 1000 in the paraelectric phase with a frequency solicitation at 10 Hz. At lower frequencies, the Curie–Weiss law is lost in the paraelectric regime and an enhanced rise of the dielectric constant with increasing temperature probably reflects an interfacial polarization mechanism. Finally, this dielectric analysis in frequency, temperature (323–403 K) and along temperature ramps allowed to extract analytical laws of behavior associating some of these parameters. For example, one of these equations will be useful in the choice of the temperature ramp to be applied to optimize the switching time between a ferroelectric and a paraelectric state according to a condition on the value of the desired dielectric constant at the low and high states in the implementation of memories. [ABSTRACT FROM AUTHOR]

Bismuth has been proved a promising lead-free element that can mitigate whisker growth on Sn coatings. It is generally believed that the formation of the equiaxed crystal structure of Sn–Bi coating helps to relax the compressive stress uniformly. In this study, the Sn–xBi coatings with the columnar structure were prepared on the Al substrate. The addition of Bi promoted the whisker nucleation on the coatings but effectively mitigated the growth of whiskers. The density of geometrically necessary dislocations increased with the increase in Bi content, resulting in a high whisker density on the coatings. The reason why Bi inhibited whisker growth was proposed from the perspective of creep properties of the Sn–xBi coatings. The solution strengthening of Bi in Sn improved the creep resistance of the coatings. The creep stress exponent measured by nanoindentation indicated that the creep mechanism of the Sn–xBi coatings is dislocation climbing. The improvement of creep resistance led to insufficient dislocations in the coating leading to the limitation of Sn atomic diffusion for whisker growth. [ABSTRACT FROM AUTHOR]