Schaeffler-Type Phase Diagram of Ti-Based Alloys Ishida, K.
Metallurgical and materials transactions. A, Physical metallurgy and materials science,
10/2017, Letnik:
48, Številka:
10
Journal Article
Recenzirano
The α(hcp)/β(bcc) phase equilibria of Ti-based multi-component alloys can be described by a Schaeffler-type diagram, where Al and Mo equivalents (Aleq and Moeq) are used. Aleq is thermodynamically ...defined by the ratio of partial molar free energy changes transfer of one mole of each α forming element and Al from a dilute solution of α to β phases, while Moeq is also deduced by similar thermodynamic quantities of β forming element and Mo. Aleq and Moeq for 40 alloying elements are estimated from the thermodynamic parameters assessed by Kaufman and Murray. It is shown that three types of Ti alloys,
i.e.
, α and near α, α+β, and β alloys, can be exactly classified using Aleq and Moeq. The Ms and β transus temperatures can also be predicted by Aleq and Moeq. The proposed Aleq and Moeq are very useful for alloy design, heat treatment, and microstructural evolution of Ti-based alloys.
Double horn points to an exotic stateThe so-called Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state, a particular kind of superconducting order in which the order parameter oscillates in space, has ...fascinated physicists because it is tricky to stabilize. Kinjo et al. used nuclear magnetic resonance (NMR) measurements to observe a signature of the FFLO state in the material strontium ruthenate (see the Perspective by Pavarini). The modulation in the superconducting order parameter caused a corresponding modulation of spin density, which resulted in a peculiar, double horn–shaped structure of NMR intensity for a certain range of temperatures and applied magnetic field. —JS
Shape-memory alloys, such as Ni-Ti and Cu-Zn-Al, show a large reversible strain of more than several percent due to superelasticity. In particular, the Ni-Ti-based alloy, which exhibits some ...ductility and excellent superelastic strain, is the only superelastic material available for practical applications at present. We herein describe a ferrous polycrystalline, high-strength, shape-memory alloy exhibiting a superelastic strain of more than 13%, with a tensile strength above 1 gigapascal, which is almost twice the maximum superelastic strain obtained in the Ni-Ti alloys. Furthermore, this ferrous alloy has a very large damping capacity and exhibits a large reversible change in magnetization during loading and unloading. This ferrous shape-memory alloy has great potential as a high-damping and sensor material.
Abstract
A fundamental issue concerning iron-based superconductivity is the roles of electronic nematicity and magnetism in realising high transition temperature (
T
c
). To address this issue, FeSe ...is a key material, as it exhibits a unique pressure phase diagram involving non-magnetic nematic and pressure-induced antiferromagnetic ordered phases. However, as these two phases in FeSe have considerable overlap, how each order affects superconductivity remains perplexing. Here we construct the three-dimensional electronic phase diagram, temperature (
T
) against pressure (
P
) and isovalent S-substitution (
x
), for FeSe
1−
x
S
x
. By simultaneously tuning chemical and physical pressures, against which the chalcogen height shows a contrasting variation, we achieve a complete separation of nematic and antiferromagnetic phases. In between, an extended non-magnetic tetragonal phase emerges, where
T
c
shows a striking enhancement. The completed phase diagram uncovers that high-
T
c
superconductivity lies near both ends of the dome-shaped antiferromagnetic phase, whereas
T
c
remains low near the nematic critical point.
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The effects of grain size on the stress–strain characteristics of Cu–Al–Mn-based pseudoelastic (PE) sheet specimens with various relative grain sizes d/t (d=grain size, t=sheet ...thickness) were investigated using cyclic tensile testing. The stress–strain characteristics such as the yield stress σy, work-hardening rate dσPE/dε and stress hysteresis of pseudoelasticity Δσ decreased, and the obtained maximum PE strain εPEMAX increased with increasing d/t. The σy, dσPE/dε, Δσ and εPEMAX plots as a function of d/t were divided into three regions. The critical points dividing the plots into the three regions were located at d/t≈1 and d/t≈2. These results can be explained from the standpoint of constraints between grains, depending on grain structure such as a fine equiaxed grain structure, a columnar-like grain structure and a fully columnar grain structure.
In superelastic alloys, large deformation can revert to a memorized shape after removing the stress. However, the stress increases with increasing temperature, which limits the practical use over a ...wide temperature range. Polycrystalline Fe-Mn-Al-Ni shape memory alloys show a small temperature dependence of the superelastic stress because of a small transformation entropy change brought about by a magnetic contribution to the Gibbs energies. For one alloy composition, the superelastic stress varies by 0.53 megapascal/°C over a temperature range from −196 to 240°C.
Cobalt-Base High-Temperature Alloys Sato, J; Omori, T; Oikawa, K ...
Science (American Association for the Advancement of Science),
04/2006, Letnik:
312, Številka:
5770
Journal Article
Recenzirano
We have identified cobalt-base superalloys showing a high-temperature strength greater than those of conventional nickel-base superalloys. The cobalt-base alloys are strengthened by a ternary ...compound with the L1₂ structure, Formula: see text Co₃(Al,W), which precipitates in the disordered gamma face-centered cubic cobalt matrix with high coherency and with high melting points. We also identified a ternary compound, Formula: see text Ir₃(Al,W), with the L1₂ structure, which suggests that the Co-Ir-Al-W-base systems with Formula: see text (Co,Ir)₃(Al,W) structures offer great promise as candidates for next-generation high-temperature materials.
The physics of the crossover between weak-coupling Bardeen-Cooper-Schrieffer (BCS) and strong-coupling Bose-Einstein condensate (BEC) limits gives a unified framework of quantum-bound (superfluid) ...states of interacting fermions. This crossover has been studied in the ultracold atomic systems, but is extremely difficult to be realized for electrons in solids. Recently, the superconducting semimetal FeSe with a transition temperature T
=8.5 K has been found to be deep inside the BCS-BEC crossover regime. Here we report experimental signatures of preformed Cooper pairing in FeSe, whose energy scale is comparable to the Fermi energies. In stark contrast to usual superconductors, large non-linear diamagnetism by far exceeding the standard Gaussian superconducting fluctuations is observed below T*∼20 K, providing thermodynamic evidence for prevailing phase fluctuations of superconductivity. Nuclear magnetic resonance and transport data give evidence of pseudogap formation at ∼T*. The multiband superconductivity along with electron-hole compensation in FeSe may highlight a novel aspect of the BCS-BEC crossover physics.
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