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Transformation induced plasticity (TRIP) effect in high entropy alloys (HEAs) overcomes the strength–ductility "trade-off" and leads to the synchronous improvement of strength and ductility. In this work, we studied a TRIP Fe60Mn20Co10Cr10 HEA with a dual-phase structure consisting of face-centered cubic matrix and hexagonal close-packed (HCP) martensite. By warm-rolling and subsequent annealing, three samples with different recrystallization conditions and HCP phase volume fractions were obtained. The alloys exhibit a good combination of ultimate tensile strength (∼700–900 MPa) and elongation (∼45%–55%), representing sustainable strain hardening behavior over extended deformation regime. To reveal the deformation mechanism of the present TRIP HEA, the method to determine the stacking fault energy (SFE) via a regular solution model was discussed, and the SFE of Fe60Mn20Co10Cr10 alloys at 300 K was estimated as 15.3 mJ/m2. The low SFE promotes the formation and overlapping of stacking faults via dislocation interaction, which provides nucleation sites of HCP martensite and further contributes to the striking strain hardening capacity upon tension. [ABSTRACT FROM AUTHOR]

For piezoelectric films, the surface/interface energy around the nano-fibers plays an important role in predicting the overall properties. Square nano-fibers are very popular in piezoelectric films. This paper presents the size-dependent dynamic effective elastic modulus of piezoelectric films under anti-plane shear waves. The average electro-elastic field resulting from the randomly distributed nano-fibers is solved by applying the effective field method. To express the coupling fields in the effective field, the mapping method and wave function expansion method are introduced. The closed-form solution of piezoelectrically stiffened shear modulus with respect to the shape and volume fraction of fibers and surface/interface properties is obtained. The interacting effect of surface/interface and square shape of nano-fibers is examined. [ABSTRACT FROM AUTHOR]

Surfaces/interfaces in nanostructures play a significant role in deciding the electro-mechanical coupling properties of piezoelectric nanocomposites. A comprehensive electro-mechanical model of nano-size is developed to predict the effective coupling properties of piezoelectric nanocomposites with coated elliptical nano-fibers. The effects of surfaces/interfaces around the coating layer and the shape of the nano-fibers on the effective elastic modulus and piezoelectric coefficient are considered. Combining the generalized self-consistent method, the electro-elastic surface/interface model, and the mapping method, a closed-form solution of the effective electromechanical coupling properties is given. Through numerical calculations, it is found that the elastic modulus and dielectric constant increase with the semi-major axes, while piezoelectric constant expresses different behaviors. The interface effect on the effective electro-elastic moduli is also examined. [ABSTRACT FROM AUTHOR]

Many nanostructures are assumed to be characterized by couple stress effects. Based on the couple stress theory and surface/interface theory, the anti-plane electro-mechanical behavior of piezoelectric composites with a nano-fiber is studied, and the effect of stress and electric displacement at the interface on the size-dependent behavior is examined. By introducing a decoupling function, the governing equations in piezoelectric materials are simplified into two classical governing equations. The displacement and electric potential are expressed by Bessel functions. By satisfying the boundary conditions around the nano-fiber with surface/interface effect, the expanded coefficients are obtained. Excellent agreement with the previous results validates this model. It can be concluded that the interface around the nano-fiber shows greater effect on the stress than that on the electrical fields, and the interface effect increases greatly due to the existence of couple stress. The effect of material properties of nano-fiber on the stress and electric field under different coupling stresses is also examined. [ABSTRACT FROM AUTHOR]

Propagation of Rayleigh-type surface waves in a piezoelectric-piezomagnetic layered half-space is investigated. The materials are assumed to be transversely isotropic crystals. The dispersion relations have been numerically derived and computed by considering the coupling piezoelectric and piezomagnetic behaviors. The phase velocities are obtained for four kinds of electric-magnetic boundary conditions at the free surface. The variations of mechanical displacements, electric and magnetic potentials along the thickness direction of the layer are obtained. The effects of different electric-magnetic boundary conditions on the phase velocity and mode shapes of displacements, electric and magnetic potentials have been discussed. The results show that the lowest mode is Rayleigh mode and that the phase velocities of the higher modes tend to the shear wave velocity of the piezoelectric layer as the frequency increases. The electric boundary conditions dominate the phase velocity. The magnetic boundary conditions have a significant effect on the mode shapes of the displacements, electric and magnetic potentials of the first mode. It is also found that piezoelectric material properties have an important effect on wave propagation. The result is relevant to the analysis and design of various acoustic surface wave devices constructed from piezoelectric and piezomagnetic materials. [ABSTRACT FROM AUTHOR]

The propagation of Rayleigh-type surface waves in a piezoelectric-piezomagnetic layers half-space is examined. It is shown that piezoelectric material properties have important effect on the wave propagation, which is relevant to the analysis and design of various acoustic surface wave devices constructed from piezoelectric and piezomagnetic materials.