Ceramics are strong but brittle. According to the classical theories, ceramics are brittle mainly because dislocations are suppressed by cracks. Here, the authors report the combined elastic and plastic deformation measurements of nanoceramics, in which dislocation-mediated stiff and ductile behaviors were detected at room temperature. In the synchrotron-based deformation experiments, a marked slope change is observed in the stress–strain relationship of MgAl2O4 nanoceramics at high pressures, indicating that a deformation mechanism shift occurs in the compression and that the nanoceramics sample is elastically stiffer than its bulk counterpart. The bulk-sized MgAl2O4 shows no texturing at pressures up to 37 GPa, which is compatible with the brittle behaviors of ceramics. Surprisingly, substantial texturing is seen in nanoceramic MgAl2O4 at pressures above 4 GPa. The observed stiffening and texturing indicate that dislocation-mediated mechanisms, usually suppressed in bulk-sized ceramics at low temperature, become operative in nanoceramics. This makes nanoceramics stiff and ductile.

Theoretical models for the strength and ductility of high-order hierarchically nanotwinned metals are developed, and especially analytical expressions of mechanical parameters with various influencing factors are deduced. Furthermore, the size effect on mechanical properties is analyzed based on these mechanism-based plasticity models, wherein the effects of twin spacing and grain size on the strength and ductility are discussed systemically. Related analysis demonstrates that the twin spacing plays an important role. Through adjusting the twin spacing of the primary layer of twin lamellae and optimizing the combination of twin spacing of the high-order layers, expected mechanical properties with high strength and high ductility could be achieved. Besides, the grain size also has a significant effect, and the reduction in grain size still induces a positive effect on the strength, whereas a negative effect on the ductility. Finally, a material design approach for the optimization of comprehensive mechanical properties is suggested.

Effects of microstructure constituents of α2-Ti3Al/γ-TiAl lamellae, β-Ti grains and γ grains, with various volume fractions on room-temperature ductility of γ-TiAl based alloys have been studied. The ductility of the alloys containing β phase of about 20% in volume increases to more than 1% as the volume fraction of γ phase increases to 80%. However, γ single phase alloys show very limited ductility of less than 0.2%. The present results, thus, confirmed the significant contribution of β phase to enhancement of the room-temperature ductility in multi-component TiAl alloys.

We have examined tensile properties of a novel heat-resistant aluminium (Al)-based alloy (with a composition of Al-5Mg-3.5Zn (at%)) strengthened by the T-Al6Mg11Zn11 (cubic) intermetallic phase at various temperatures. The tested specimens of the present alloy were solution-treated at 450°C for 24 h and subsequently aged at 200 or 300 oC for 1 h. The granular precipitates of the T phase were dispersed rather homogenously in the grain interior in the specimen aged at 300°C. In the specimen aged at 200°C, numerous fine precipitates with a mean size of ∼20 nm were observed in the α-Al matrix. The specimen pre-aged at 200°C for 1 h exhibited a superior strength to the conventional Al alloys at elevated temperatures ranging from 150 to 200°C (corresponding to service temperatures for compressor impellers in turbochargers).

The stability of the Ti50Pd50-xRux alloy was investigated using first-principles density functional theory within the plane-wave pseudopotential method. Firstly, the Ti50Pd50 gave equilibrium lattice parameter and lowest heats of formation in better agreement with experimental data to within 3%. The heat of formation decreases with an increase in Ru concentration, consistent with the trend of the density of states which is lowered at the Fermi level as Ru content is increased which suggests stability. It was also found that from the calculated elastic constants the structures showed positive shear modulus above 20 at. % Ru, condition of stability. Furthermore, the addition of Ru was found to strengthen the Ti50Pd50-xRux system at higher concentrations. The thermal coefficients of linear expansion for the Ti50Pd31.25Ru18. 75 are higher at low temperature, and that the TiPd-Ru system tends to expand more at low content of 18.75 at. % Ru than at higher content. Partial substitution of Pd with Ru was found more effective as a strengthening element and may enhance the martensitic transformation temperature of the Ti50Pd50 alloy.

A supersaturated single-phase Cu–26 at.% Co alloy was produced by high-pressure torsion deformation, leading to a nanocrystalline microstructure with a grain size smaller than 100 nm. The nonequilibrium solid solution decomposed during subsequent isothermal annealing. In situ high-energy X-ray diffraction was used to map changes linked to the separating phases, and the development of a nanoscale Cu–Co composite structure was observed. To gain further information about the relationship of the microstructure and the mechanical properties after phase separation, uniaxial tensile tests were conducted on as-deformed and isothermally annealed samples. Based on the in situ diffraction data, different isothermal annealing temperatures were chosen. Miniaturized tensile specimens with a round cross section were tested, and an image-based data evaluation method enabled the evaluation of true stress–strain curves and strain hardening behavior. The main results are as follows: all microstructural states showed high strength and ductility, which was achieved by a combination of strain-hardening and strain-rate hardening.

The powder thixoforming method was used to fabricate 10 vol% silicon carbide particle (SiCp) reinforced 6061 Al matrix composites with high mechanical performances successfully. Here, we demonstrated with proof that proper solution treatment could not only enhance tensile strength of the composite: its ultimate tensile strength and yield strength increased from 230 to 128 MPa in the as-fabricated state to 275 and 212 MPa solutionized at 808 K for 6 h but also improve composite’s tensile elongation significantly with an increment of 161.5% from 2.6% to 6.8%. Corresponding toughening mechanisms are mainly investigated from the perspective of both microstructure examination and total strain to failure calculation through a modified model. The theoretical predictions are in reasonably good agreement with the experimental data. This work may provide a practical way to alleviate the inverse strength–ductility relationship of particulate reinforced metal matrix composites and provide reference for the SF calculation of similar composites subjected to solution treatment.

The shear-band propagation in bulk metallic glasses (BMGs) during deformation plays a key role in determining their macroscopic ductility. In this work, the shear band propagation during plastic deformation was investigated in the Cu46Zr46Al8 BMG and its in situ or ex situ prepared BMG composites. Compared with the brittle BMG, both types of ductile BMG composites show a more stable shear banding behavior as revealed by a larger power-law scaling exponent obtained from statistical analysis of serrations recorded in compressive curves. A higher cut-off elastic energy density (δc) linked with the multiplication of shear bands is observed for the in situ prepared BMG composites. However, the ex situ fabricated BMG composites show an almost equivalent or slightly larger δc since the dominant shear band but not multiple shear bands mainly governs their deformation. Such observations imply that the shear banding stability of BMGs during deformation is enhanced not only by inducing multiple shear bands but also by obstructing the movement of the dominant shear band at its driven path.

In this research, the effect of austenitizing at 900–1100 °C and tempering at 250–650 °C on the microstructure and mechanical properties of 410 and 410 Ni martensitic stainless steels was investigated. The transformation of austenite to ferrite surrounded the austenitizing within the temperature range of 900–1050 °C. The grain size and hardness measurements proved that austenitizing at 1050 °C leads to the partial dissolution of carbides without a considerable growth of austenite grains. The mechanical tests showed two peaks in strength and troughs in ductility by tempering at 450 and 650 °C due to the formation of primary and secondary carbides. The better ductility and fracture toughness in 410 Ni, comparing to 410, were attributed to the effect of Ni on stacking fault energy. Fractured surfaces revealed ductile fracture of the samples tempered at low temperatures, e.g., 250 °C. However, after tempering at 450 and 650 °C, 410 showed a brittle fracture and 410 Ni exhibited a dual intergranular-brittle fracture mechanism.

Topological constraint theory is a convenient theoretical framework to predict structure–property relationships in glasses and identify optimal compositions featuring targeted macroscopic properties. Although introduced for chalcogenide glasses, molecular rigidity concepts have since been applied with great success to new families of materials, such as silicate glasses, phase-change materials, and proteins. Here, we review recent developments in the extension of rigidity theory to concrete, which is by far the most heavily manufactured material in the world. By capturing the important atomic topology while filtering out less relevant structural details of calcium–silicate–hydrate, the binding phase of concrete, topological constraint theory was used to nanoengineer concrete from the atomic scale by predicting the compositional dependence of hardness, toughness, and creep. As such, rigidity concepts represent a promising tool to accelerate the discovery of new materials with tailored properties.

Mono-crystalline elastic constants of equiatomic quinary Cr-Mn-Fe-Co-Ni high entropy alloy with the fcc structure have experimentally been determined by a resonance ultrasound spectroscopy at room temperature. The values of the bulk modulus of the high entropy alloy experimentally determined are similar to other conventional fcc metals when the values are normalized by the melting points. This indicates that the entropy change at melting is similar to that of conventional metals. The values of Pough’s index and the Cauchy pressure are determined as 1.79 and -11.6 GPa, respectively. When the ductility of the alloy is judged from the indices, the ductility of the high entropy alloy is limited. In order to explain the negative Cauchy pressure of the high entropy alloy, it is required to assume that relatively strong directional interatomic bondings like intermetallic compounds exist in the alloy though the crystal is disordered solid solution.

Two-sided oxidation experiments were recently conducted at 1000-1200°C in flowing steam with samples of sponge-based Zr-1Nb alloy E110. Although the old electrolytic E110 tubing exhibited a high degree of susceptibility to nodular corrosion and experienced breakaway oxidation rates in relatively short time, the new sponge-based E110 has demonstrated steam oxidation behavior comparable to Zircaloy-4. The sponge-based E110 followed the parabolic law, and the derived oxidation rate constant is in good agreement with the Cathcart-Pawel (CP) correlation at 1100-1200°C. For 1000°C oxidation, the weight-gain of sponge-based E110 is much lower than Zircaloy-4. No breakaway oxidation was observed at 1000°C up to 8000 s. Ring compression tests were conducted to evaluate the residual ductility of oxidized samples at room temperature and at 135°C. All sponge-based E110 specimens were still ductile at 135°C after being oxidized up to 20% equivalent cladding reacted at 1000-1200°C. Metallographic examinations were performed on oxidized E110 specimens to correlate material performance with microstructure.

The deformation mechanisms responsible for the strength and ductility of nanostructured Cu and Cu–Al alloys processed by high pressure torsion have been analyzed in frames of a model of elastic–plastic medium and using the available experimental data. The income of the Peierls strength, as well as solid solution hardening, dislocation hardening, twinning hardening, taking into account possible annihilation processes has been estimated. It was shown that in the Cu–5 at.% Al alloy annihilation processes contribute to the maintenance of deformation. The material is hardened by the accumulation of dislocations at the twin boundaries, postponing the moment of reaching the ultimate strength. In the Cu–16 at.% Al alloy processes of the annihilation are limited. As a result, the possibility of further deformation is limited and the degree of homogeneous deformation decreases in comparison with the case of the Cu–5 at.% Al alloy. Significantly increased concentration of deformation vacancies contributes to the destruction of the former alloy as well.

The effect of Ta concentration on the fundamental mechanical properties of W–Ta alloys has been studied from first principles study. The lattice constants, the cell volumes, and the formation energies of the W1−x Ta x (x = 0.0625, 0.125, 0.1875, 0.25, 0.3125, 0.5, 0.5625, 0.625, 0.75) alloys were calculated. It is shown that Ta alloying in bcc W lattice is an infinite solid solution and the W0.5Ta0.5 have the lowest formation energy. With the optimized geometry and lattice, the elastic constants are calculated and then the elastic moduli and other mechanical parameters are derived. Results show that although the mechanical strength of the W–Ta alloys is lower than that of pure W metal, it is much higher than that of pure Ta metal. On the other hand, the B/G ratio and the Poisson's ratio of the W–Ta alloys is much higher than that of pure W, and even higher than that of pure Ta, indicating that Ta alloying can improve the ductility of bcc W substantially.

The aim of this work was to study the deformation behavior of an Armco iron after severe plastic deformation by equal channel angular pressing (ECAP). Particular attention was paid to predict the dislocation density by different approaches like the model proposed by Bergström. Experimental measures of dislocation density by different techniques are used in the discussion. Cylindrical samples of ARMCO iron (8mm of diameter, 60mm of length) were subjected to ECAP deformation using a die with an intersecting channel of Φ=90° and outer arc of curvature of ψ= 37° die. Samples were deformed for up to 16 ECAP passes following route Bc. The mechanical properties of the material were measured after each pass by tensile tests. The original grain size of the annealed iron (70 μm) was drastically reduced after ECAP reaching grain sizes close to 300nm after 16 passes.

Equal channel angular pressing (ECAP) was carried out on extruded ZK60 magnesium alloy until an equivalent strain of ∼4 (corresponding to 4 passes) at 523K following route Bc. The effect of the deformation on both microstructure and texture was investigated by analysis of inverse pole figures and pole figures respectively, determined by EBSD. Additionaly, the mechanical properties were evaluated through tensile tests. The ECAPed processed ZK60 alloy showed the presence of dynamic recrystallization (DRX) process, correlated with a strong basal fiber texture. The presence of pyramidal slip was also observed, which can be correlated with the presence on twin-oriented boundaries in the material. Both the grain size reduction and the existence of texture influenced the ductility of the magnesium alloy processed by ECAP, as the ductility of the ZK60 alloy after four ECAP passes increased two times in comparation with the initial (un-processed) material.

Hot deformation and dynamic recrystallization (DRX) behavior of the Cu–Cr–Zr–Ag alloy were studied by hot compressive tests in the 650–950 °C temperature and 0.001–10 s−1 strain rate ranges using Gleeble-1500D thermomechanical simulator. The activation energy of deformation was determined as Q = 343.23 kJ/mol by the regression analysis. The critical conditions, including the critical strain and stress, for the occurrence of DRX were determined based on the alloy strain hardening rate. The critical strain related to the onset of DRX decreases with temperature. The ratios of the critical to peak stress and critical to peak strain were also identified as 0.91 and 0.49, respectively. The evolution of DRX microstructure strongly depends on the deformation conditions in terms of temperature and strain rate. Dislocation generation and multiplication are the main hot deformation mechanisms for the alloy. The addition of Ag can refine the grain and effectively improve the DRX of the Cu–Cr–Zr alloy. It can also inhibit the growth of the DRX grains at 950 °C deformation temperature, making the microstructure much more stable.

The twinning-induced plasticity effect enables designing austenitic Fe-Mn-C-based steels with >70% elongation with an ultimate tensile strength >1 GPa. These steels are characterized by high strain hardening due to the formation of twins and complex dislocation substructures that dynamically reduce the dislocation mean free path. Both mechanisms are governed by the stacking-fault energy (SFE) that depends on composition. This connection between composition and substructure renders these steels ideal model materials for theory-based alloy design: Ab initio-guided composition adjustment is used to tune the SFE, and thus, the strain-hardening behavior for promoting the onset of twinning at intermediate deformation levels where the strain-hardening capacity provided by the dislocation substructure is exhausted. We present thermodynamic simulations and their use in constitutive models, as well as electron microscopy and combinatorial methods that enable validation of the strain-hardening mechanisms.

Nanotwins require little energy to form in metals, but their impact on strength and ductility is dramatic. New mechanisms of strengthening, strain hardening, ductility, and strain-rate sensitivity have been observed in nanowires, films, and bulk materials containing nanoscale twins as the twin-boundary spacing decreases. These mechanisms can act in concert to produce interface-dominated nanomaterials with extreme tensile strength and plastic deformation without breaking. This article reviews recent theoretical and experimental understanding of the physical mechanisms of plasticity in nanotwin-strengthened metals, with a particular focus on the fundamental roles of coherent, incoherent, and defective twin boundaries in plastic deformation of bulk and small-scale cubic systems, and discusses new experimental methods for controlling these deformation mechanisms in nanotwinned metals and alloys.