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The composition-dependent properties and their correlation with the phase stability of Fe75+xPd25-x (-10:0 ≤ x ≤ 10:0) alloys are systematically investigated by using first-principles exact muffin-tin orbitals (EMTO)-coherent potential approximation (CPA) calculations. It is shown that the martensitic transformation (MT) from L12 to body-centered-tetragonal (bct) occurs in the ordered alloys with about -5:0 ≤ x ≤ 10:0. In both the L12 and bct phases, the evaluated a and c/a agree well with the available experimental data; the average magnetic moment per atom increases whereas the local magnetic moments of Fe atoms, dependent on both their positions and the structure of the alloy, decrease with increasing x. The tetragonal shear elastic constant of the L12 phase (C') decreases whereas that of the bct phase (Cs) increases with x. The tetragonality of the martensite (|1 - c/a|) increases whereas its energy relative to the austenite with a negative value decreases with Fe addition. All these effects account for the increase of MT temperature (TM) with x. The MT from L12 to bct is finally confirmed originating from the splitting of Fe 3d Eg and T2g bands upon tetragonal distortion due to the Jahn-Teller effect. [ABSTRACT FROM AUTHOR]

Martensitic phase transition in an aged Fe–Pd–Rh alloy was studied using transmission electron microscopy (TEM) and x-ray diffraction. Both TEM and x-ray diffraction reveal the appearance of an intermediate structure between the fcc→L10 martensitic transformation. The intermediate phase, denoted L1m, has a monoclinic structure with lattice parameters of a=3.193 Å, b=3.684 Å, c=3.141 Å, and β=92.042°, and the normal L10 martensitic phase has an ordered structure with lattice parameters of a=3.876 Å, c=3.684 Å, and c/a=0.950, as confirmed by TEM and x-ray diffraction. [ABSTRACT FROM AUTHOR]

We have investigated the influence of twin boundary properties on the damping behavior of single crystalline Fe-31.2Pd (at%) alloy, which exhibits a weak first-order martensitic transformation. Different static tensile stress was applied by dynamic mechanical analyzer to adjust the twin boundary density and hydrogen was doped to modify the twin boundary mobility. A high damping capacity (tan δ > 0.1) in a wide temperature range from about 140 K to 230 K was observed under a low static stress of about 0.3 MPa. Hydrogen doping further increased the maximum value of the damping capacity by introducing a relaxation tan δ peak. The damping capacity decreased with increasing static stress probably due to the decrease in twin boundary density. [ABSTRACT FROM AUTHOR]

Elastocaloric effects of a Ni50Fe19Ga27Co4 alloy exhibiting a typical first‐order martensitic transformation (MT) and an Fe‐31.2Pd (at.%) alloy exhibiting a weak first‐order MT, respectively, have been compared using their single crystals. A flat region appears in the temperature dependence of elastocaloric effect in the Ni50Fe19Ga27Co4 alloy, while such region is missing in the Fe‐31.2Pd alloy. The elastocaloric effect of the Ni50Fe19Ga27Co4 alloy originates essentially from the latent heat released by the stress‐induced MT, while that in the Fe‐31.2Pd alloy originates essentially from the entropy change caused by elastic deformation of the parent and martensite phases. Although the Young's modulus in the [001] direction at Ms is nearly the same for the two alloys (E ∼ 2 GPa), its slope dE/dT is largely different between the two alloys. It is approximately 0.003 GPa K−1 for the Ni50Fe19Ga27Co4 alloy and 0.2 GPa K−1 for Fe‐31.2Pd alloy. [ABSTRACT FROM AUTHOR]

The elastocaloric effect under tensile stress along the [001] direction has been investigated in an Fe-31.2Pd (at.%) alloy, which exhibits a weak first-order martensitic transformation at 230 K from a face-centered cubic structure to a face-centered tetragonal ( c/a < 1) structure. A stable temperature variation of 1.9 K was observed at room temperature (∼288 K) up to 10000 cycles of sinusoidal tensile stress (200 MPa). The stress-strain curve shows a macroscopic strain of 1.2% under 200 MPa with a negligible stress hysteresis. The macroscopic strain coincides with the lattice strain obtained by in situ X-ray diffraction. A significant extension of the 200 reflection, perpendicular to the tensile direction, was observed. This peak extension could be the way the specimen realizes a high elastic strain, even under tensile stress. [ABSTRACT FROM AUTHOR]

A disordered Fe-31.2Pd (at.%) alloy exhibits a weak first-order martensitic transformation (MT) from a face-centered cubic structure to a face-centered tetragonal structure. We employed a Dynamic Mechanical Analysis (DMA) to understand the transformation behavior. As the temperature decreases, the storage modulus E ′ decreases in the parent phase and increases in the martensite phase. The loss tangent (tan δ ) shows a slight increase when approaching M s (=225 K), suggesting the formation of movable interfaces even above M s . The value of tan δ is nearly proportional to (1 − c/a ) 2 below M s , meaning that highly mobile twinned interfaces are essential for internal friction below M s . The so-called transitory term of tan δ is negligibly small for the MT of this alloy. [ABSTRACT FROM AUTHOR]

The effect of an external magnetic field B on the martensite phase transformation temperature T 0 was studied for single crystalline Fe 72 Pd 28 thin films. From in-plane and out-of-plane aligned magnetic field dependent resistance measurements under various fields up to 9 T, T 0 was determined. The relation between T 0 and B is explained quantitatively by the Clausius–Clapeyron equation. The calculated value of 0.62 K/T is close to the values of the linear fits of 0.79 K/T and 0.76 K/T obtained from measurements with B aligned in-plane and out-of-plane. [ABSTRACT FROM AUTHOR]

Conductivity in Fe7Pd3 is characterized by an anomalous increase when traversing the face-centered-cubic (fcc) austenite to face-centered-tetragonal (fct) martensite transition, contrary to most other conventional and ferromagnetic shape memory alloys. Experiments on molecularbeam-epitaxy-grown single crystals indicate a resistivity change of ≈20% during the transformation on top of a quadratic temperature dependence reaching up to room temperature. The physical foundations of residual resistivity changes along the full Bain path are addressed by a Kubo- Greenwood approach within the framework of density functional theory. To do so, a concept to reliably extract the DC conductivities is proposed that yields reproducible results consistent with experiments. Finding that conductivity peaks in the fct phase, we identify a large density of states paired with high velocities at the Fermi level in the majority spin sub-bands in presence of minimum s-d electron scattering as underlying physical origin. [ABSTRACT FROM AUTHOR]

We have examined the transformation strain, Δε, in the [0 0 1] direction of an Fe-31.2Pd (at.%) shape memory alloy under compressive stress applied in the same direction. When the stress is absent, the alloy exhibits a cubic to tetragonal martensitic transformation at 230 K with |Δε| of 1.4%. As the stress increases, the transformation temperature increases linearly and |Δε| decreases linearly and vanishes at 40 MPa (280 K). This point is the critical point of this transformation at which the first-order nature disappears, and the critical exponentβis evaluated to be 0.47 ± 0.04. [ABSTRACT FROM AUTHOR]

In typical shape memory alloys, significant elastocaloric effects appear in association with stress-induced martensitic transformations. However, we report here that in an Fe-31.2Pd (at.%) alloy, a significant elastocaloric effect appears due to lattice softening, which causes a weak first-order martensitic transformation at T 0 (∼230 K). We found that in a wide temperature range of between 175 K (< T 0 ) and 335 K (> T 0 ), the alloy exhibits an adiabatic temperature decrease of more than 1.5 K when a compressive stress of 200 MPa applied in the [0 0 1] direction is removed. The refrigeration capacity calculated in this temperature range is 5 MJ/m 3 . [ABSTRACT FROM AUTHOR]

The methods of scanning electron microscopy, differential scanning calorimetry and x-ray diffraction are used to study the morphological and thermal characteristics of cooling-induced martensite in alloy Fe - 30% Ni - 3% Pd. It is shown that the kinetics of the martensitic transformation is athermal and the morphology is lamellar. The mean values of the parameters of the austenite and martensite lattices are 0.35704 and 0.28614 nm respectively. The thermocycling leaves the points A and A invariable. [ABSTRACT FROM AUTHOR]

Abstract: We discuss the compositional trends in the electronic structure of Fe–Pd alloys in the composition range relevant for martensitic transformations and magnetic shape-memory applications. The results are obtained within the framework of density functional theory based on the Korringa–Kohn–Rostoker Green''s function approach in combination with the coherent potential approximation for the description of disorder. For the body centered cubic structure, we observe with increasing Pd content the gradual disappearance of the pseudogap like structure in the center of the minority spin d-band, while on the face centered cubic side a small peak passes the Fermi level around 80at. % Fe, which has been related previously to a band-Jahn–Teller instability. In addition, we investigate the structural variation of magnetic properties of the magnetic shape-memory composition Fe70Pd30 based on magnetic exchange parameters obtained from our ab initio calculations being mapped onto a classical Heisenberg model. This allows us to estimate the magnetic transition temperature within a mean field approach and Monte Carlo simulations taking into account the induced nature of the Pd atoms, leading to a close, semi-quantitative agreement with experiment in the latter case. [Copyright &y& Elsevier]

Abstract: Freestanding Fe70Pd30 foils with a thickness of about 60μm were fabricated using the splat-quenching technique. A shift of the martensitic transformation temperatures as a function of different annealing treatments (600°C, 700°C, 800°C, 900°C, 1000°C for 15min) was observed by temperature-dependent X-ray diffraction (XRD), resistance and magnetization measurements. The sample annealed at 800°C showed the highest degree of crystallinity for the (200) fcc austenite peak and no secondary phases. Samples annealed below 800°C kept austenite remainders even at −25°C. The transformation temperatures, determined by all three-measurement methods, showed an increase with increasing annealing temperature. [Copyright &y& Elsevier]

Abstract: The effect of Mn addition on the structural and magnetic properties of Fe–Pd ferromagnetic shape memory alloys is investigated. In particular, a complete characterization of the influence of the partial substitution of Fe by Mn has been performed on Fe69.4− x Pd30.6Mn x (x =0, 1, 2.5 and 5) alloys. The substitution of 1% Fe by Mn fully inhibits the undesirable irreversible face-centered tetragonal to body-centered tetragonal transformation without decreasing the face-centered cubic to face-centered tetragonal temperature. In addition, the substitution of 2.5% Fe by Mn gives rise to the highest thermoelastic transformation temperature observed to date in the Fe–Pd system, probably due to an increase in the valence electron concentration. The magnetocaloric effect has been evaluated in this alloy system for the first time. Nevertheless, the low values obtained suggest that the Fe–Pd alloys are not good candidates for magnetic refrigeration applications. [Copyright &y& Elsevier]