While materials design in the context of texture dependent properties is well developed, theoretical tools for microstructure design in the context of grain boundary sensitive properties have not yet been established. In the present work, we present an invertible relationship between texture and grain boundary network structure for the case of spatially uncorrelated two-dimensional textures. By exploiting this connection, we develop mathematical tools that permit the rigorous optimization of grain boundary network structure. Using a specific multi-objective materials design case study involving elastic, plastic and kinetic properties, we illustrate the utility of this texture mediated approach to grain boundary network design. We obtain a microstructure that minimizes grain boundary network diffusivity while simultaneously improving yield strength by an amount equal to half of the theoretically possible range. The theoretical tools developed here could complement experimental grain boundary engineering efforts to help accelerate the discovery of materials with improved performance.

The fracture behavior of a single-crystal Al-nanoplate with an edge crack under tensile loading was simulated using a molecular statics technique to evaluate crack growth resistance in Al. The crack length was determined using a stiffness method. A parabolic function fitted from simulation results was used to predict the crack length from the stiffness value extracted from unloading curves. Based on energy considerations, crack growth resistance was calculated. Crack growth resistance rose sharply in the initial stages of crack growth, and with an additional crack extension, it increased gradually to converge to a constant far exceeding the fracture toughness predicted by the Griffith criterion. This trend in the crack growth resistance curve was closely related to the amorphous zone formed at the crack tip after the onset of crack propagation.

The dislocation movements under the action of electric pulses (athermal effect) at cryogenic conditions were studied by ex situ transmission electron microscopy (TEM) observations and slip trace analysis innovatively. By applying electric pulses directly through aluminum TEM samples in a liquid nitrogen bath, plenty of non-octahedral-like dislocation glides generally forming at high temperatures (e.g., >453 K for aluminum) were observed at cryogenic temperatures (<130 K). Occurrence of the non-octahedral-like dislocation glides indicates a substantial increase in the degrees of freedom for dislocation glides, offering a new/complementary explanation for the acceleration effect of electric pulses on dislocation movements, especially in the sole athermal effect. In comparison, previous theories relied on extra driving force and/or increased dislocation mobility on the octahedral planes in a face-centered cubic metal. The athermal effects of electric pulse were discussed and the selective heating at the dislocation cores was proposed to account for non-octahedral-like dislocation glides.

Powder metallurgy processing of aluminum alloy based metal matrix composites (MMC) is realized to be a promising alternative as expected to advance rapidly compared to other conventional methods. This paper reviews the extensive development in metal–matrix composite research works with particular focus on aluminum alloys 2xxx series as metal–matrix particulates processed by powder metallurgy route. Effect of reinforcement materials such as SiC and Al2O3 on the mechanical properties of the composites manufactured through conventional methods and powder metallurgy route are compared and presented. The influence of percentage of reinforcement material on the overall properties of the MMC's as reported by the researchers are presented. Summary on fundamental aspects of manufacturing MMC's via powder metallurgy route, the effect of mechanical properties, tribological properties, and microstructural properties are presented. Eventually, some advantages of powder metallurgy method are mentioned which may substantiate the claim to consider this as a novel method for near net shape manufacturing.

Dynamic loading of the hat-shaped specimen of 2195-T6 aluminum lithium alloy was carried out with a split Hopkinson pressure bar at ambient temperature. The formation and evolution mechanisms of adiabatic shear band (ASB) in this alloy were investigated and then microstructure was further observed. The microstructure within ASB in 2195 aluminum alloy was characterized by means of optical microscopy and transmission electron microscopy. The width of ASB was about 20–30 um. Nano-grains (50–100 nm) were observed in the middle of shear zone. Experimental results show that the diffusive transformation took place within ASB during high strain rate deformation, namely the precipitates dissolving in the matrix in the process (within about 71 µs). Based on thermodynamics and kinetics analyses, dissolution of precipitates was firstly investigated during adiabatic shearing deformation, and a dissolution model was suggested in the present work. The diffusive transformation and the microstructure evolution within ASB in 2195 alloy were explained.

Al-based composites reinforced with Mg–7.4%Al mechanically alloyed particles have been synthesized by hot pressing followed by hot extrusion. Microstructural characterization of the bulk samples reveals the phase transformation of the reinforced particles (Mg(Al)ss + γ-Al12Mg17) to the stable intermetallic β-Al3Mg2 phase which occurs during consolidation. The phase transformation leads to the increase of effective volume faction of the reinforcement along with strong interfacial bonding, which causes a significant increase of the strength of the composites retaining appreciable plastic deformation. The strengthening can be attributed to the reduction of ligament size and to the interface strengthening due to better interface bonding (load-transfer) between the Al-matrix and the reinforcing particles.

The quench sensitivity of 45vol% SiCp/2024Al composites manufactured by squeezed casting method has been investigated by employing Jominy end quench test which was designed to simulate the one dimension cooling process of the composites. It can be found that the cooling rates decreased with the increase of the distance from the quenched end. The results indicated that the as-quenched and as-aged hardness exhibited a significant decrease with increasing the distance from the quenched end. The depths corresponding to 90% of maximum as-aged hardness were 30 mm. When the quench cooling rate was 23.5 °C/s, the hardness was the maximum. The variation of as-aged hardness with cooling rate was identical with the overall enthalpy involved in the precipitation of all metastable phases (S″ + θ″ + S′ + θ′). The SiCp/2024Al composites exhibited two sensitivity regimes: at slower cooling rates the quench sensitivity had been attributed to the formation of intermediate precipitates during cooling, while it was mildly quench sensitive at higher cooling rates.

In the paper, 2.5 vol% (TiB + TiC)/Ti composite has been fabricated by in situ casting route. 1-D forging and subsequent multistep rolling in (α + β) phase field are conducted on the as-cast composite and, accordingly, the matrix microstructure is significantly refined, and the distribution uniformity of reinforcements is greatly improved. The tensile properties of the composites with different processing states are tested at room temperature (RT), 600 and 700 °C. The results indicate that thermomechanical processing (TMP) can drastically improve strength and elongation of the as-cast composite both at RT and 600 °C. As tensile temperature increases to 700 °C, the UTSs of the composites gradually reduce while the elongations of the composites are enhanced remarkably after TMP. The degradation in UTS can be related to the matrix softening and interfacial debonding at 700 °C.

A new ultrahigh strength hot rolled Ti–Mo-bearing ferritic steel was developed through chemical composition design and rolling processing optimization. To maximize the potential of nanometer-sized (Ti, Mo)C carbide in terms of strengthening ferrite matrix, the optimal chemical composition of 0.1C–0.2Ti–0.4Mo (wt%) was determined through considering the atomic ratio of elements, the solubility temperature of (Ti, Mo)C in austenite, and the excessive growth critical temperature of austenite grain during reheating. The rolling condition in the region through austenite recrystallization region to austenite nonrecrystallization region was adopted to realize a homogenous and fine ferrite grain structure. Results showed that the simulated coiling at 600 °C was found to provide an attractive combination of ferrite grain refinement hardening (360 MPa) and precipitation hardening (324 MPa). An optimal combination of strength and ductility was achieved after coiling at 600 °C (yield strength: 912 MPa; ultimate tensile strength: 971 MPa; total elongation: 16.0%). In addition, the nanometer-sized (Ti, Mo)C carbide was characterized by transmission electron microscopy (TEM) and physical–chemical phase analysis, and its role was discussed in details.

The glass-forming Ti75Zr10Si15 and Ti60Zr10Nb15Si15 alloys composed of nontoxic elements may represent new materials for biomedical applications. For this study, melt-spun alloy samples exhibiting glass–matrix nanocomposite structures were subjected to thermal oxidation treatments in synthetic air to improve their surface characteristics. 550 °C was identified as the most appropriate temperature to carry out oxidative surface modifications while preserving the initial metastable microstructure. The modified surfaces were evaluated considering morphological and structural aspects, and it was found that the oxide films formed at 550 °C are amorphous and consist mainly of TiO2; their thicknesses were estimated to be ∼560 nm for Ti75Zr10Si15 and ∼460 nm for Ti60Zr10Nb15Si15. The thermally treated sample surfaces exhibit not only higher roughnesses and higher hardnesses but also improved wettability compared to the as-spun materials. By immersion of oxidized samples in simulated body fluid Ca- and P-containing coatings exhibiting typical morphologies of apatite are formed.

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 effects of pre-treatments on the precipitate microstructures of an Al–Zn–Mg–Cu alloy are investigated. Meanwhile, the creep-rupture behavior of the under-aged and peak-aged alloys are comparatively analyzed. Additionally, the effects of pre-treatment on the fracture mechanisms are discussed. It is found that the precipitate microstructures are sensitive to pre-treatments. The intragranular precipitates of the peak-aged alloy are larger than those of the under-aged. The precipitate free zone of the peak-aged alloy is wider than that of the under-aged. Some large intergranular precipitates appear on the grain boundaries of the under-aged alloy, and induce the nucleation of microvoids. Eventually, the creep fracture of the under-aged alloy is accelerated. Therefore, the differences in microstructures lead to the shorter creep-rupture life of the under-aged alloy, compared to the peak-aged alloy.

Bi2Sr2Co2Ox (BSC-222) bulk materials have been prepared in air by single hot pressing or partial melting followed by hot pressing. Thermal transport properties of as-prepared samples were compared with BSC-222 samples prepared by single partial melting. Samples prepared through hot pressing have a high bulk density and improved preferential grain orientation. Bulk density and preferential grain orientation are significantly better in samples processed by partial melting followed by hot pressing. In samples prepared by partial melting, the presence of sub-micrometer-sized secondary phases Bi0.75Sr0.25Ox, Sr-based oxide, and CoO, is observed. The lattice contribution to the total thermal conductivity decreases significantly in partially melted BSC-222 samples. By using a classical phonon transport model, this result demonstrates that the decrease in lattice thermal conductivity in partially melted BSC-222 samples may be linked not only to porosity but also to the presence of defects, induced by partial melting process, which may play an important role in phonon scattering.

The discovery of Heusler alloys has revolutionized the research field of intermetallics due to the ease with which one can derive potential candidates for multifunctional applications. During recent years, many half Heusler alloys have been investigated for their thermoelectric properties. The f-electron-based rare-earth ternary half Heusler compound DyPdBi has its f energy levels located close to the Fermi energy level. Other research efforts have emphasized that such materials have good thermoelectric capabilities. We have explored using first principles the electronic band structure of DyPdBi by use of different exchange correlation potentials in the density functional theoretical framework. Transport coefficients that arise in the study of thermoelectric properties of DyPdBi have been calculated and have illustrated its potential as an efficient thermoelectric material. Both the theoretically estimated Seebeck coefficient and the power factor agree well with the available experimental results. Our calculations illustrate that it is essential to include spin–orbit coupling in these models of f-electron half Heusler materials.

It is demonstrated that Na doping can significantly improve the hydriding performance of Mg2Ni under an isobaric-isothermal condition of 2 MPa H2 and 350 °C. This is achieved via an increase of the interphase grain boundary area and density of dislocations as compared to the Na-free material. Significant enrichment of Na+ cations on the alloys' surface coupled with the catalytic effect of metallic Ni are suggested to increase the hydrogen–metal bonding strength facilitating hydrogen adsorption/dissociation. The mechanisms of hydrogen absorption are discussed based on a nucleation and growth theory. Additionally, by means of in situ synchrotron powder x-ray diffraction, the transition of Mg2Ni into the stable Mg2NiH0.3 is observed in real-time.

The effect of Co on element segregation and microstructure is investigated in the third generation Ni-based single crystal superalloys with 4, 8.5, and 11.5 wt% Co addition. The results show that the increase of Co content leads to a severe element segregation in as-cast microstructure. After heat treatment, the size of γ′ phase is slightly reduced with Co content increase. During the thermal exposure, the γ′ phase coarsens gradually but its coarsening rate decreases with increasing Co content. In addition, some acicular and blocky topologically close-packed (TCP) phases are precipitated in 4% Co and 8.5% Co alloys. However, no TCP phase can be found in 11.5% Co alloy. Finally, it may be concluded that although a higher Co content is harmful for the element segregation, it is beneficial to maintain the cuboidal morphology of γ′ phase, decrease its coarsening rate, and impede the precipitation of TCP phase.

Cryomilling combined with laser induction hybrid cladding (LIHC) was adopted to produce NiCrAlY coatings on Ni-based superalloy. The characteristics, oxidation resistance, and mechanical properties of the cryomilled NiCrAlY coatings by LIHC were investigated. By increasing the cryomilling time, the as-received spherical powder experienced a transition from flake-shaped to polygonal structure. The particle size increased firstly and then decreased. Moreover, increasing the cryomilling time induced the columnar growth in the NiCrAlY coatings. This in turn improved the oxidation resistance and the mechanical properties of the coatings. Especially, when the cryomilling time was increased to 15 h, the oxidation resistance of the coating at 1423 K was approximately nine times than that of GH4169 superalloy. The tensile strength of the cryomilled (15 h) coating increased to 1085 MPa and the ductility was 20.7%.

The microstructure evolution of a typical nickel-based superalloy was studied in the temperature range of 960–1160 °C with the strain rate of 0.001 s−1 by using electron backscattered diffraction technique. Based on the grain orientation spread method, the dynamic recrystallization (DRX) grains were distinguished from the deformed grains. The results revealed that the volume fraction and the size of DRX grains increased with the increasing deformation temperatures. Most of the original Σ3 boundaries lost their twin characteristics due to crystal rotations during hot deformation. Meanwhile, lots of new Σ3 boundaries were formed in the DRX grains mainly by growth accidents. Moreover, the deformation temperature had a similar effect on the fraction of Σ3 boundary and the Σ3 boundary density in the DRX domains, which increased firstly and then decreased with the increasing deformation temperature. The Σ3 boundary density was analyzed as a function of grain size, and the critical grain size below which no twin forms was calculated to be 2.06 µm. In addition, the coherent Σ3 boundaries were easier to form at the higher deformation temperature due to their lower boundary energy.

Gamma prime (γ′) stability and its influence on tensile behavior of a newly developed wrought superalloy with various Fe contents was studied both experimentally and thermodynamically. The results show that the γ′-solvus temperature is higher and γ–γ′ lattice mismatch is bigger in the alloy with the lower Fe content. During long-term thermal exposure at 650–750 °C, the coarsening behavior of γ′ precipitates follows Ostwald ripening kinetics and the lower Fe content can decrease the coarsening rate of γ′ precipitates due to the increase of the activation energy for γ′ coarsening. Moreover, the lower Fe content can retard the transformation from γ′ to η phase. The tensile properties of the alloys with different Fe contents are almost same after standard heat treatment. However, after thermal exposure, the decrease of tensile strength in the alloy with lower Fe content is less than that of the alloys with higher Fe content due to the improvement of γ′ stability.