Creep strain recovery of Fe-Ni-B amorphous metallic ribbon

Creep strain recovery and structural relaxation of the amorphous metallic glass Fe40Ni41B19 after longtime loading at different annealing temperatures below the glass transition temperature have been studied using anisothermal differential scanning calorimetry (DSC) and dilatometry (TMA). It has been demonstrated that structural relaxation effects depend on the stress-annealing temperature of the amorphous ribbon. The structural relaxation states of the amorphous ribbon annealed at different temperatures under and without applied stress have been compared. The activation energy spectra were calculated from the anisothermal dilatometric measurements using the modern method based on the Fourier transformation technique. The influence of the annealing temperature on the shape of creep strain recovery spectra has been analyzed. (c) Versita Warsaw and Springer-Verlag Berlin Heidelberg. All rights reserved

Microstructure transformation of Αlpha-titanium after mechanical and laser forming

The effects of microstructure transformation during forming processes viz. Mechanical (contact process via tool and die), laser (contactless process via CO2 laser defocused beam) and a combined process consisting of laser forming followed by mechanical forming was analysed before and after each process. Plastic flow during the deformation is strongly influenced by anisotropy and the work hardening rate, which is due to the limited number of slip planes in a hexagonal close-packed material. Commercially pure titanium can exhibit dominant twinning systems during deformation when either tensile or compression is introduced. Electron backscatter diffraction (EBSD) results show multiple dominate pyramidal slip behaviours due to the lattice rotation when comparing the before and after deformation processes. The Schmid factor and twinning parent/daughter ratios for each individual grain after each forming process were also evaluated. Our findings show twin nucleation and twin growth also contribute a major role when observing the nature of the microstructure for each process. contribute a major role when observing the nature of the microstructure for each process

Discontinuities of Plastic Deformation in Metallic Glasses with Different Glass Forming Ability

AbstractThe metallic ribbons Fe40Ni40B20, Cu47Ti35Zr11Ni6Si1 and Zr65Cu17.5Ni10Al7.5 with different microhardness and glass forming ability were studied at different loading rates from 0.05 to 100 mN/s. We describe in details the differences in elemental discontinuities on the loading curves for the studied alloys. It was found that the discontinuities began at a certain local deformation independently on the macroscopic mechanical properties of a ribbon. More developed discontinuities at higher deformations are created for the materials with lower microhardness and so lower strength

Controlling phase separation in thermoelectric Pb1-xGexTe to minimize thermal conductivity

Intensive studies have been carried out over the past decade to identify nanostructured thermoelectric materials that allow the efficient conversion of waste heat to electrical power. However, less attention has been paid to the stability of such materials under operating temperatures, typically 400 degrees C or higher. Conventionally nanostructured ceramics tend to undergo grain growth at high temperature, lowering the density of interfaces and raising the thermal conductivity, which is detrimental to device performance. Therefore it is preferable to identify materials with stable nanostructures, for example systems that undergo spontaneous phase separation. Here we investigate PbTe-GeTe alloys, in which spinodal decomposition occurs on initial cooling from above 580 degrees C, forming complex nanostructures consisting of Ge-rich and Pb-rich domains on different size scales. The resulting dense arrangement of interfaces, combined with mass fluctuation associated with Pb-Ge mixing, enhances phonon scattering and strongly reduces the thermal conductivity. Here we focus on the nominal composition Pb0.49Ge0.51Te and show that by tuning the synthesis procedure, we are able to control the pattern of compositional domains and the density of interfaces between them. This allows low lattice thermal conductivities to be maintained even after thermal cycling over the operating temperature range

STRUCTURAL MODELS OF THE YIELD STRESS ANISOTROPY OF AMORPHOUS-ALLOYS RIBBONS

Two alternative quantitative mathematical descriptions of the yield stress anisotropy in the plane of amorphous alloys ribbons are proposed that are based on two models: model of the plane stress state and model of the oriented anisotropic polyatomic clusters. These descriptions give adequate approximations of the experimental angular dependences of the yield stress for some amorphous alloys