Microstructure and mechanical behavior of nanostructured composite Cu60Fe40 alloy

In this study, bulk nanostructured composite Cu₆₀Fe₄₀ alloy is prepared by a combustion synthesis technique. The prepared Cu₆₀Fe₄₀ alloy consists of Cu(Fe) solid solution and Fe(Cu) solid solution phases. The large-scaled compositional segregation in the Cu-rich and Fe-rich phases is not observed, respectively. A few micron-sized dendrite (Fe(Cu) solid solution) is embedded into the nanostructured matrix (Cu(Fe) solid solution). The grain size of the matrix is in the range 50–300?nm. The yield and fracture strength of the Cu₆₀Fe₄₀ alloy are 540 and 1050?MPa, respectively, and the fracture strain obtained from the compression test is about 20.9%. The Cu₆₀Fe₄₀ alloy displays notable work hardening in the compressive deformation.     

Solubility criterion for sequential disordering in metal-metal multilayers upon solid-state reaction

An n-body Ni-Ti potential is derived and applied in a molecular dynamics simulation to study the maximum supersaturated solubility of the terminal solid solutions and solid-state reaction in a Ni/Ti bilayer. It reveals that during interfacial reaction of the Ni/Ti bilayer the Ti lattice reaches its maximum solubility by dissolving Ni earlier than Ni does through dissolution of Ti, which results in a sequential disordering of first Ti and then Ni, although Ti has a higher melting point than Ni. In the Ni-Zr, Ni-Mo and Ni-Ta systems, however, the Ni lattice collapses more rapidly because it reaches a maximum solubility earlier than its partners, which have higher melting points than Ni. A solubility criterion is thus relevant for all the above cases; the lower the maximum solid solubility the less stable is the lattice of the metal upon solid-state reaction.     

Elastic solutions with arbitrary elastic inhomogeneity and anisotropy

An efficient numerical algorithm is proposed to accurately compute the elastic fields in two-dimensional (2D) or three-dimensional (3D) microstructures with arbitrary elastic inhomogeneity and anisotropy. It combines the equivalent inclusion method of Eshelby, the microelasticity theory of Khachaturyan, and the spectral iterative perturbation method of Hu and Chen. Its efficiency is compared with those of existing approaches in the literature. The method can be conveniently implemented in phase-field modeling of stress-dependent microstructure evolution and/or of mass/electrical transport.     

Identification of crystal nucleation and growth in an amorphous FeZr2 alloy by means of electrical resistance measurements

A polymorphous crystallization process in an amorphous FeZr₂ alloy has been investigated by means of accurate electrical resistance measurements (ERMs) at elevated temperatures. It was found that, upon crystallization of the amorphous alloy, the electrical resistance increased with increasing temperature, exhibiting three distinct stages. Quantitative microscopy observations revealed that the three stages originated from crystal nucleation, from subsequent growth of crystal nuclei and from coarsening of the crystallites respectively. The activation energies for the crystal nucleation and growth determined from the ERM data agree satisfactorily with the data in the literature. The success in identification of the crystal nucleation and growth processes by means of ERMs may originate from differences in electrical resistance changes due to the crystal formation and the crystalline-amorphous interface formation processes from the amorphous phase.     

Intermetallic compound identification and Kirkendall void formation in eutectic SnIn/Cu solder joint during solid-state aging

Microstructural investigations were performed on the interfacial reactions between eutectic SnIn solder and Cu substrate during reflowing at 433?K and solid-state aging at 373?K. Cu₂(In,Sn) was identified as the only intermetallic compound (IMC) at the interface, which consists of two sublayers with different morphology, a fine-grained sublayer at the Cu side and a coarse-grained sublayer at the solder side. During solid-state aging, voids were found between these two Cu₂(In,Sn) sublayers but not at the substrate interface, which is also attributed to the Kirkendall effect considering the different diffusion fluxes of Sn or In and Cu atoms in different sublayers.     

Scale-dependent fracture mode in Cu–Ni laminate composites

Fracture behavior of Cu–Ni laminate composites has been investigated by tensile testing. It was found that as the individual layer thickness decreases from 100 to 20 nm, the resultant fracture angle of the Cu–Ni laminate changes from 72° to 50°. Cross-sectional observations reveal that the fracture of the Ni layers transforms from opening to shear mode as the layer thickness decreases while that of the Cu layers keeps shear mode. Competition mechanisms were proposed to understand the variation in fracture mode of the metallic laminate composites associated with length scale.     

Retention and thermal desorption of helium in amorphous and crystalline FeBSi alloys

Helium retention in metals is related to their atomic structure and the type of defects they contain. In order to investigate the dependence of helium retention on structure, amorphous Fe₇₉B₁₆Si₅ and crystalline FeBSi alloys were irradiated by helium ions at room temperature. In the crystalline alloy irradiated with 5 keV He⁺ ions, three types of helium trapping sites were found: surface defects produced by the irradiation, interstitial-type dislocation loops, and voids. Although these defects did not exist in the amorphous FeBSi alloy, we did observe thermal desorption peaks related to all three types. In addition, helium was released during the crystallization of amorphous FeBSi that had been irradiated by He⁺ ions.     

Stair-rod dislocations in perovskite films on LaAlO3 substrates

Two types of stair-rod dislocation formed at junctions of {111} stacking faults in SrTiO₃-SrRuO₃ two-layer films on LaAlO₃ substrates have been studied by high-resolution transmission electron microscopy. The first type, formed by the interaction of two stacking faults situated at the flat SrRuO₃-LaAlO₃ interface without any step, has a Burgers vector (a/3)<110>. The other type, formed by the interaction of two stacking faults, of which one starts from the SrRuO₃-LaAlO₃interface area involving an interface step, has a Burgers vector (a/3)<120>. The formation mechanism of the stair-rod dislocations and the effect of the step are discussed.     

Standing Out From the Crowd: How Comparison to Prototypes Can Decrease Health-Risk Behavior in Young Adults

This research tested whether social comparison can encourage adolescents to make less risky health decisions. Two studies demonstrated that when young adults compare themselves with drinkers, they become less willing to drink if they perceive dissimilarity between themselves and those drinkers. When participants in Study 1 compared with someone who drinks regularly, their perceived similarity to prototypical drinkers was positively related to their willingness to drink. In Study 2, participants identified or contrasted themselves with prototypical drinkers; those encouraged to contrast who also felt less similar to the prototype reported less willingness to drink. These studies support the prototype/willingness model's assumption that prototypes affect willingness to drink through social comparison.