The orientation relationship (OR) and the interfacial structure between Nb solid solution (Nbss) precipitates and α-Nb5Si3 intermetallics have been investigated by transmission electron microscopy (TEM). The OR between Nbss and α-Nb5Si3 was determined by selected-area electron diffraction analyses as (222)Nb//(002)α and . High-resolution TEM images of the Nbss/α-Nb5Si3 interface were presented. Steps existed at the interface that acted as centers of stress concentration and released the distortion of lattices to decrease the interfacial energy. In addition, the interfacial models were proposed based on the observed OR to describe the atomic matching of the interface. The distribution of alloying elements at the Nbss/α-Nb5Si3 interface has also been investigated, and Hf was enriched at the interface to strengthen the grain boundary.

A comparison between results of a recently published quasi-exact solution of the temperature integral used for the Avrami model of isochronal phase transformations and an analytical phase-transformation model in relation to exact solutions from numerical integration has been performed. The results for the transformed fraction from the quasi-exact solution are more precise than the corresponding results of the analytical model, whereas the results for the transformation rate from both models are sufficiently precise for the nucleation mode of site saturation or continuous nucleation. It has been further shown that an analytical solution of the transformation rate cannot be obtained using a quasi-exact solution of the temperature integral in case of mixed nucleation, and that the results of the corresponding solution with the analytical model substantially alleviate the influence of the approximated temperature integral. By this method, an analytical approach of modeling, which can substantially alleviate the deviation (of model prediction) arising from approximations to the temperature integral, has been developed. The proposed approach has been successfully applied to experimental data of the crystallization of bulk amorphous Pd-Ni-P-Cu alloys.

The effects of the fatigue deformation on the localized deformation of a ZCAP-3 bulk metallic glass (BMG) were studied using the nanoindentation technique. A localized mechanical hardening was observed in the ZCAP-3 BMG between the shear bands in the fatigue-damaged zone. In contrast to the indentations of the BMG made far away from the fatigue-damaged zone, there was no indentation size effect. Both the reduced contact modulus and the indentation hardness were larger than those corresponding to the indentations of the ZCAP-3 BMG in the undamaged zone. These observations revealed the possible effects of local heating and stress-induced atomic rearrangements (i.e., inelastic deformation) on the reduction of the free volume in the BMG from the propagation of the fatigue crack.

The microstructure and texture evolution in a cold-rolled AZ31 magnesium alloy during electropulsing treatment (EPT) are investigated and correlated with the mechanical properties. The microstructure is effectively refined, and a tilted basal texture develops gradually during EPT. The yield stress in the treated samples is lower than that in the cold-rolled sample, indicating that texture softening is dominant over strengthening because of grain refinement. The phenomenon is primarily the result of the tilted basal texture. EPT improves the tensile ductility of the EPT samples significantly, albeit slightly compromising the tensile strength. The mechanism of the microstructure evolution during electropulsing is discussed from the viewpoint of grain-boundary motion. Moreover, the ductility enhancement is discussed in terms of the deformation mechanism and texture of the Mg alloy.

The phase equilibria at 300, 400, 500, and 600 °C in the Ag–Bi–Ni system and 300, 400, and 500 °C in the Cu–Bi–Ni system were experimentally determined by metallography and electron probe microanalysis on equilibrated alloys and diffusion couples. Differential scanning calorimetry was used to measure the temperatures of phase transformations. All the experimental results show that the solubilities of the ternary elements of the binary intermetallic compounds in the Ag–Bi–Ni system are limited. However, the binary intermetallic compounds have some solubilities of the ternary elements in the Cu–Bi–Ni system. No ternary intermetallic compound was found in the Ag–Bi–Ni and Cu–Bi–Ni systems. On the basis of the determined results, the phase equilibria in the Ag–Bi–Ni and Cu–Bi–Ni systems were thermodynamically assessed, and reasonable agreement between the calculated results and experimental data was obtained.

An attempt was made to predict the macroscopic plastic flow of a high-performance pipeline steel, consisting of dual constituent phases (soft ferrite and hard bainite), by performing nanoindentation experiments on each microphase with two spherical indenters that have different radii (550 nm and 3.3 μm). The procedure is based on the well known concepts of indentation stress-strain and constraint factor, which make it possible to relate indentation hardness to the plastic flow of the phases. Additional consideration of the indentation size effect for sphere and application of a simple “rule-of-mixture” led us to a reasonably successful estimation of the macroscopic plastic flow of the steel from the microphases properties, which was verified by comparing the predicted stress-strain curve with that directly measured from the conventional tensile test of a bulky sample.

Microstructure evolution, mechanical properties, formability, and texture development were determined for AA6111 samples processed by asymmetric rolling (ASR) with different roll friction, velocity, or diameters, conventional rolling (CR), and equal-channel-angular pressing (ECAP). Highly elongated or sheared grain structures were developed during ASR/CR and ECAP, respectively. ASR led to improved r-values and formability compared with CR primarily as a result of the development of moderate shear-texture components analogous to those developed during ECAP of billet material. ASR based on different roll diameters gave the best combination of strength, ductility, and formability.

The wettability of Pb-free Sn-based solder over the Cu-based Cu60Zr30Ti10 bulk metallic glass surface was investigated. We observed that the as-polished surface was nonwetting for the solder, which was due to the surface oxide layer of ZrOx formed in air. After complete removal of the oxide layer, a thin layer of Ag was deposited on the clean Cu60Zr30Ti10 surface. The Ag-covered Cu60Zr30Ti10 surface showed relatively high resistivity to the reoxidation even in air, and thus the wettability of the Cu60Zr30Ti10 surface for the Sn-based solder was greatly improved.

High-quality SrAl12O19:Pr3+ nanodisks and nanoplates were fabricated via a new processing technique based on a modified polymer steric entrapment method. Serious agglomeration and large particle size distribution of final products, which usually occurred in the conventional method, were eliminated completely. The effects of new synthetic processes on the morphology, crystallization, and yield of products and the relevant mechanisms were discussed. As far as we know, SrAl12O19:Pr3+ nanodisks with mean diameter ∼60 nm and thickness between 5 and 10 nm were successfully synthesized for the first time by this low-cost technique. The new synthetic method may provide a general route to synthesize other refractory mixed-oxide nanocrystals. Photon cascade emission involving transitions 1S0–1I6 followed by 3P0–3H4 in SrAl12O19:1% Pr3+ nanodisks was investigated. Size-effect-induced blue shift of the 4f5d states of Pr3+ was observed in SrAl12O19:1% Pr3+ nanodisks, in which the quantum efficiency was preserved, as in the bulk counterparts.

Directional recrystallization of an Fe–6.5wt%Si alloy was investigated by changing hot zone temperatures and growth rates. Elongated (columnar) grains with an aspect ratio more than 10 can be produced when growth parameters are carefully adjusted. It was found that at a fixed growth rate, the grain length and aspect ratio increase with increased hot zone temperatures. At a fixed hot zone temperature, there is a critical growth rate at which columnar grains have the largest average aspect ratio. Below or above this growth rate, the aspect ratio decreases. Texture and grain orientation analysis showed that the preferentially selective growth to form columnar grains was favored by the formation of low-energy surfaces and grain boundaries.

The Ti-6Al-4V sheet alloys were welded by using a common gas tungsten arc welding process. In this work, we study the correlation of corrosion resistance and oxide layer structure produced after commonly used industrial heat treatments. We also study the oxide scales that were formed as a result of the heat-related treatment/aging process. The results indicate that better corrosion resistance of the Ti-6Al-4V alloy weldment can be obtained and significantly improved by a solution treatment plus an artificial aging (ST+AA) treatment, owing to the enhanced intensity of TiO2, V2O5, and Al2O3 oxides that compacted and grew on the surface of fusion zone. The newly found γ-TiAl and α2-Ti3Al particles that nucleated in the fusion zone due to different heat treatments do affect the composition of the oxide layer. The possible mechanism for this oxide layer formation in the fusion zone is discussed.

A method is described for the creation of surfaces with cyclically reversible topographical form. Using spherical and cylindrical indenters applied to NiTi shape-memory alloys, an indentation-planarization technique is shown to result in a two-way shape memory effect that can drive flat-to-wavy surface transitions on changing temperature. First, it is shown that deep spherical indents, made in martensitic NiTi, exhibit pronounced two-way cyclic depth changes. After planarization, these two-way cyclic depth changes are converted to reversible surface protrusions, or “exdents.” Both indent depth changes and cyclic exdent amplitudes can be related to the existence of a subsurface deformation zone in which indentation has resulted in plastic strains beyond that which can be accomplished by martensite detwinning reactions. Cylindrical indentation leads to two-way displacements that are about twice as large as that for the spherical case. This is shown to be due to the larger deformation zone under cylindrical indents, as measured by incremental grinding experiments.

We performed density-functional calculations of oxygen incorporation and diffusion in layered Ti2AlC for a range of intrinsic- and impurity-element chemical potentials. In view of the thermal equilibrium coexistence between oxygen-dissolved Ti2AlC and the oxide scale, a thermodynamic scheme is presented that allows the comparison of the relative stability of oxygen defects in different exterior environments. The calculations show that the oxygen atom favors substitution on carbon lattice sites (OC) under oxygen-lean conditions and high temperatures, whereas the occurrence of an oxygen interstitial in the aluminum atomic layer (IO-tri) becomes more preferential in an oxygen-rich atmosphere and low temperatures. Interstitial oxygen (IO-tri) diffusion via a metastable interstitial site (IO-oct) has a comparatively low migration energy. The substitutional oxygen defect (OC) diffuses by exchanging with neighboring carbon vacancy, which needs a relatively high diffusion barrier.

The effect of melt temperature on the structure and mechanical properties of three Zr-based bulk metallic glasses (BMGs)—Zr62Cu17Ni13Al8, Zr55Cu20Ni10Al10Ti5, and Zr52.5Cu17.9Ni14.6Al10Ti5 (Vit105)—has been studied. The results show that the BMGs cast from higher melt temperature exhibit large plastic strains despite their amorphous structure. The samples become macroscopically brittle when the quenched-in crystals form an interconnected microstructure. In contrast to previous studies, there is no notable effect on the Poisson’s ratio (ν) and other elastic constants.

The dynamic mechanical behavior, fracture characteristics, and microstructural evolution of high-strength weldable aluminum-scandium (Al–Sc) alloy were investigated using a compressive split Hopkinson pressure bar at strain rates of 1.3 × 103, 3.6 × 103, and 5.9 × 103 s−1, respectively, and temperatures of −100, 25, and 300 °C. The results showed that the flow stress, work hardening rate, and strain rate sensitivity increase with increasing strain rate but decrease with increasing temperature. Conversely, the activation volume and activation energy increase as the temperature increases or the strain rate decreases. Moreover, the fracture strain decreases with increasing strain rate and decreasing temperature. It was shown that the Zerilli–Armstrong face-centered-cubic (fcc) constitutive equation provides accurate predictions of the mechanical response of the Al–Sc alloy under the considered strain rate and temperature conditions. Scanning electron microscopy observations revealed that the fracture surfaces of the impacted specimens are characterized by transgranular dimpled features, which are indicative of a ductile failure mode. Moreover, transmission electron microscopy observations indicated the presence of both fine and coarse randomly dispersed precipitates within the matrix and at the grain boundaries. It was found that an increasing strain rate reduces the size of the dislocation cells within the impacted Al–Sc microstructure and therefore increases the dislocation density. However, at higher temperatures, the dislocations are annihilated, leading to a reduction in the dislocation density and a corresponding increase in the dislocation cell size. The variations observed in the size and density of the dislocation cells were found to be consistent with the dynamic tendencies noted in the stress–strain response of the Al–Sc alloy.

Allotropic hexagonal-close-packed (hcp) → face-centered-cubic (fcc) transformations were reported in Group IVB elements titanium (Ti), zirconium (Zr), and hafnium (Hf) subjected to mechanical milling in a high-energy SPEX shaker mill. Although the transformation was observed in powders milled under regular conditions, no such phase transformation was observed when the powders were milled in an ultrahigh purity environment by placing the powder in a milling container under a high-purity argon atmosphere, which was in turn placed in an argon-filled glove box for milling. From a critical analysis of the results, it was concluded that the hcp → fcc phase transformation was, at least partially, due to pick-up of interstitial impurities by the powder during milling of these powders to the nanocrystalline state.

Nanostructured bulk NiAl materials were prepared at high pressure and temperature (0–5.0 GPa and 600–1500 °C, respectively). The sintered samples were characterized by x-ray diffraction, scanning electron microscope, density, and indentation hardness measurements. The results show that NiAl nanoparticles may have a compressed surface shell, which may be the reason why NiAl nanomaterials were difficult to densify sintering using conventional methods and why high-pressure sintering was an effective approach. We also observed that B2-structured NiAl could undergo a temperature-dependent phase transition and could be transformed into Al0.9Ni4.22 below 1000 °C for the first time. It is interesting to note that Vickers hardness decreased as grain size decreased below ∼30 nm, indicating that the inverse Hall-Petch effect may be observed in nano-polycrystalline NiAl (n-NiAl) samples. Moreover, a tentative interpretation was developed for high-pressure nanosintering, based on the shell-core model of nanoparticles.

New Cu-based bulk glassy alloys (BGAs) with high glass-forming ability (GFA) were synthesized in a Cu-Zr-Al-Ag system. As the compositions of Cu-Zr-Al-Ag alloys with lower Ag and Al content shifted to the Cu-rich range, the supercooled liquid region, reduced glass transition temperature, and γ value increased, leading to the improvement of GFA. The best GFA is located around Cu47Zr45Al5Ag3, which is close to eutectic. Fully glassy samples with diameters up to 15 mm were fabricated by copper mold casting. These Cu-based BGAs exhibit excellent mechanical properties under compression. A large Young's modulus of 104–111 GPa, high fracture strength of 1905–1942 MPa, and distinct plastic strain of 0.002–0.011 were obtained. Additionally, the BGAs also show good corrosion resistance in 1 N H2SO4 solution.

Dense, crystalline mullite (3Al2O3ċ2SiO2) coatings have been deposited by chemical vapor deposition on Si-based substrates using the AlCl3–SiCl4–CO2–H2 system. A graded coating composition has been achieved in the coatings, with the Al/Si ratio being stoichiometric (∼3) at the coating/substrate interface, and increasing monotonically toward the outer coating surface. The highest reported Al-rich mullite has been deposited in the process. At high Al/Si ratios, the mullite structure breaks down and an aluminosilicate phase similar to the metastable δ* Al2O3 is nucleated. Experimental evidence is presented in this study that this phase has some Si-incorporation in it and has been called δ*(Si)Al2O3. Like the other known aluminosilicates, δ*(Si)Al2O3 converts to mullite on heating at elevated temperatures.

The mechanical behavior of electroplated Sn thin films was investigated using thermal-expansion induced strain. For stress above a threshold value, the stress relaxation observed during the thermal cycles is well-described by a power law creep mechanism with exponents similar to those of the bulk material. However, the stress relaxation showed significant thickness dependence so that the relaxation in thicker films is faster than thinner films. The surface oxide was also shown to have a considerable effect on retarding the relaxation by inhibiting diffusion to the surface. The relevance of the stress relaxation to whisker formation in Sn-based coatings is discussed.