xZrx Alloys Research Articles

Influence of Dissolving Fe-Nb-B-Dy Alloys in Zirconium on Phase Structure, Microstructure and Magnetic Properties.

This paper refers to the structural and magnetic properties of [(Fe80Nb6B14)0.88Dy0.12]1−xZrx (x = 0; 0.01; 0.02; 0.05; 0.1; 0.2; 0.3; 0.5) alloys obtained by the vacuum mold suction casting method. The analysis of the phase contribution indicated a change in the compositions of the alloys. For x < 0.05, occurrence of the dominant Dy2Fe14B phase was observed, while a further increase in the Zr content led to the increasing contribution of the Fe–Zr compounds and, simultaneously, separation of crystalline Dy. The dilution of (Fe80Nb6B14)0.88Dy0.12 in Zr strongly influenced the magnetization processes of the examined alloys. Generally, with the increasing x parameter, we observed a decrease in coercivity; however, the unexpected increase in magnetic saturation and remanence for x = 0.2 and x = 0.3 was shown and discussed.

Influence of eutectic microstructure on the critical current density of V1−xZrx superconductors

We present here the studies on the effect of annealing on the structural and magnetic properties of V1−xZrx (x = 0.33 and 0.40) superconducting alloys. We show that the γ-ZrV2 phase grows at the expense of (α-Zr)-(γ-ZrV2) eutectic microstructure when V1−xZrx alloys are annealed at 1473 K for one week. The annealed samples predominantly have a γ-ZrV2 phase with small amounts of β-V and α-Zr phases. The irreversibility field, critical current density, and pinning force density of the as-cast samples are found to be significantly higher than those of annealed alloys. These results indicate that eutectic microstructure is important in utilizing these materials for high field applications.

Structural and magnetic properties of the as-cast V1−xZrx alloy superconductors

We report here the structural, electrical, thermal, and magnetic properties of the as-cast V1−xZrx alloys (x=0–0.4) at low temperatures. We observe that all the alloys undergo successive peritectic and eutectic reactions during cooling from the melt, which leads to the formation of five phases, namely, a body centered cubic β-V phase, two phases with slightly different compositions having a face centered cubic ZrV2 structure, a hexagonal closed packed α-Zr phase, and the β-Zr precipitates. The amount of each phase is found to be dependent on the concentration of zirconium in vanadium. The β-V and ZrV2 phases show superconductivity below 5.2 K and 8.5 K, respectively. We show that the critical current density is large for the V-rich V1−xZrx alloys with x&amp;gt;0.1. The grain boundaries generated from the eutectic reaction and the point defects formed due to the variation in the composition are found to be responsible for the pinning of flux lines in low and high magnetic fields, respectively. Our studies reveal that the choice of the composition and the heat treatment, which leads to eutectic reactions are important in improving the critical current density in this alloy system.

Two channel heat conduction in the superconducting state of the as-cast V[formula omitted]Zr[formula omitted] alloys

We present here the temperature dependence of heat capacity ( C (T)) and thermal conductivity (κ (T)) in the superconducting state as well as in the normal state of as-cast V1−xZrx alloys. Distinct jumps in the C (T) of the alloys indicate the presence of three superconducting phases with transition temperatures TC1 = 5.4 K, TC2 = 8.2 K and TC3 = 8.5 K. From the metallography micrographs, these three phases are identified to be β-V, γ-ZrV2, and γ′-ZrV2 respectively. Apart from these phases, α-Zr and β-Zr phases are also detected in these samples. The experimental κ (T) in the superconducting state of these alloys is observed to be significantly higher than that expected theoretically. Our analysis suggests that the above observation is due to the coexistence of multiple superconducting and non superconducting phases which resulted in the two-parallel channels for the conduction of heat.

Microstructure and mechanical properties of novel β-type Ti–Co–Zr alloys with high specific strength

Microstructure and mechanical properties of (Ti0.8Co0.2)100−xZrx (x = 0, 2, 4, 6 and 8 at%) alloys were investigated. The content of Ti2Co phase decreases with the content of Zr and then increases. The Ti–Co–Zr alloys are composed of eutectic structure of Ti2Co and Ti phase, and the Ti75.2Co18.8Zr6 and Ti73.6Co18.4Zr8 alloys with the particle sizes of less than 10 μm are the microcrystalline alloy. The high yield strength of Ti75.2Co18.8Zr6 and Ti73.6Co18.4Zr8 alloys with high Vickers hardness are attributed to the refinement of the β-Ti phase; the Ti78.4Co19.6Zr2 alloy has high specific compression strength; the specific strength of Ti–Co–Zr alloys are more than 300 Pa · m3 · g−1. Based on the nanoindentation, the range of reduced elastic modulus (Er) and hardness (H) are from 89.6 GPa to 114.6 GPa, from 4.39 GPa to 6.28 GPa, respectively. The H/Er values of five Ti–Co–Zr alloys are higher than that of the CP–Ti (0.0238) alloy, suggesting that the novel Ti–Co–Zr alloys show good wear resistance. In addition, the Ti78.4Co19.6Zr2 and Ti73.6Co18.4Zr8 alloys have good elastic recovery (Ue/Ut), however, the Ti80Co20 and Ti75.2Co18.8Zr6 alloys have good intrinsic plasticity (Up/Ut) in the present Ti–Co–Zr alloys.

First-principles study of structural, mechanical, and electronic properties of W alloying with Zr**Project supported by the Beijing Municipal Natural Science Foundation, China (Grant No. 2182042) and the National Natural Science Foundation of China (Grant Nos. 11875004, 11505006, and 11604008).

The structural, mechanical and electronic properties of W1−xZrx (x = 0.0625, 0.125, 0.1875, 0.25, 0.5) are systematically investigated by means of first-principles calculation. The total-energy calculations demonstrate that the W–Zr binary substitutional solid solution remaining bcc structure can be formed at an atom level. In addition, the derived bulk modulus (B), shear modulus (G), Youngʼs modulus (E) for each of W–Zr alloys decrease gradually with the increase of Zr concentration, suggesting that W alloying with higher Zr concentration becomes softer than pure W metal. Based on the mechanical characteristic B/G ratio, Poissonʼs ratio υ and Cauchy pressure , all W1−xZrx alloys are regarded as ductile materials. The ductility for each of those materials is improved with the increase of Zr concentration. The calculated density of states indicates that the ductility of W1−xZrx is due to the fact that the bonding in the alloy becomes more metallic through increasing the Zr concentration in tungsten. These results provide incontrovertible evidence for the fact that Zr has a significant influence on the properties of W.

The relation between density, thermal expansion and glass-forming ability in polycrystalline Cu–Zr alloys

In contrast to the generally accepted practice for searching metallic glassformers by trial-and-error quenching, we propose using density and coefficient of thermal expansion of as-cast polycrystalline alloys as indicators of the glass-forming ability. We study experimentally these characteristics for Cu100−xZrx alloys over the whole concentration range and a wide temperature range from room temperature up to 1120 K. In the concentration range of 35 < x < 55 at% corresponding to high glass-forming ability, strongly non-monotonous behavior of both quantities is observed. We reveal that location of the extrema on concentration dependencies of both the coefficient of thermal expansion and the density deviation from the additive law correlates with those for critical thickness of Cu–Zr amorphous alloys. We argue that correlation between glass-forming ability and anomalous behavior of thermal expansion is because as-cast polycrystalline samples of glass forming alloys possess highly distorted structure, which cause phonon anharmonicity. Our findings propose new express method to search metallic alloys with high glass-forming ability.

Effect of Zr additions on crystal structures and mechanical properties of binary W–Zr alloys: A first-principles study

Abstract

Magnetic Properties and Electronic Structure of Co/Zr Multilayers

We investigate the magnetic and electronic properties of Co/Zr multilayers with an emphasis on the interfacial effects. The saturation magnetization, coercivity, and uniaxial anisotropy depend significantly on Co thickness. Spin-wave resonance modes were observed, and the change of resonant field as a function of mode number (n) obeys the so-called n2 law. The interlayer coupling constant was determined. The electronic properties of the interfacial alloys were studied using the WIEN2k code, employing the density functional theory. Calculations describe satisfactorily the observed magnetic behaviour. The influence of pressure on the magnetic properties of the interfacial Co1−xZrx alloys was investigated in which we demonstrate that the ferromagnetism is altered by pressure.

Hydrogen absorption in uranium-based alloys with cubic γ -U structure3

UH3-type hydrides were formed by hydrogenation of splat-cooled U-based alloys upon applying high H2 pressures (>2.5 bar). Hydrogenation of U1−xMox alloys (with x ⩾ 0.12 (12 at.% Mo) containing the cubic γ-U phase leads to a formation of nanocrystalline β-UH3, why those of U1−xZrx alloys (with x ⩾15 at.% Zr) implies a pure α-UH3. The Curie temperature of hydride (UH3)0.85Mo0.15 reaches 200 K; it may be the first U-based ferromagnet with such high TC. The results reflect the dominant U–H interaction.

Magnetocaloric properties, microhardness and corrosion resistance of Gd100-xZrx alloys

With the intention to improve its mechanical properties and corrosion resistance, the magnetocaloric metal Gd was alloyed with Zr by arc melting and heat treatment. All Gd100–xZrx (x=0, 0.5, 1, 1.5, 2) alloys with various Zr dopings showed hexagonal crystal structure. The Curie temperatures (TCs) of Zr doped alloys were lower than that of Gd by ∼2 K. The maximum magnetic entropy changes of Gd99.5Zr0.5 alloy under magnetic field changes of 0–2 T and 0–5 T were 5.27 and 9.41 J/(kg·K), respectively, which were larger than that of pure Gd metal. The addition of a small amount of Zr increased the microhardness of Gd by at least 29.3%. The corrosion resistance of Gd was also improved by Zr doping, demonstrated by increased corrosion potential and reduced corrosion current density in electrochemical polarization curves measurements. These enhanced properties were beneficial to the potential applications of Gd100–xZrx alloys as magnetic refrigerants at room temperature.

The effect of pre-oxidation treatment on the corrosion behavior of amorphous Al1−xZrx solid-solution alloys

The electrochemical behavior of as-deposited and pre-oxidized amorphous Al1−xZrx solid-solution alloys (x=0.25, 0.32, 0.49, 0.65, 0.74) in 1M HCl was investigated by the micro-electrochemical technique. It was found that, for higher Zr alloying contents, x≥0.49, the as-deposited Al1−xZrx alloys exhibit passive corrosion behavior due to the formation of a protective Zr-rich passive film on the Zr-rich alloy surface. The native oxide layer on the as-deposited Al-rich Al1−xZrx alloys (x<0.49) is much less stable, which rapidly results in a total break-down of the protective character of the native Al-rich oxide layer upon anodization in 1M HCl. The pre-oxidized am-Al1−xZrx alloys all exhibited superior corrosion behavior as compared to their as-deposited pendants, attaining passive current densities as low as 3.5×10−2μA/cm2 at 1000mV. The superior corrosion resistance of the pre-oxidized alloys is attributed to a combination of characteristics of the thermally-grown amorphous (Al0.33Zr0.67)O1.83 overlayer: (i) a relatively high Zr fraction, (ii) a structurally and chemically uniform microstructure, (iii) a stable, minimal residual growth defect structure (in the surface region) established by a sufficiently large time of oxidation.

Anomalous electrical conductivity in rapidly crystallized Cu100−xZrx (x = 50–66.6) alloys

Cu100−xZrx (x = 50, 54, 60 and 66.6) polycrystalline alloys were prepared by arc-melting. The crystal structure of the ingots has been examined by X-ray diffraction. Non-equilibrium martensitic phases with monoclinic structure were detected in all the alloys except Cu33.4Zr66.6. Temperature dependencies of electrical resistivity in the temperature range of T = 4–300 K have been experimentally obtained as well as room temperature values of Hall coefficients and thermal conductivity. Electrical resistivity demonstrates anomalous behavior. At the temperatures lower than 20 K, their temperature dependencies are non-monotonous with pronounced minima. At elevated temperatures they have sufficiently non-linear character which cannot be described within framework of the standard Bloch–Grüneisen model. We show that experimental resistivity dependencies may be perfectly fitted by generalized Bloch–Grüneisen model with variable Debye temperature. We found that both the electrical resistivity and the Hall coefficients reveal metallic-type conductivity in the Cu–Zr alloys. The estimated values of both the charge carrier mobility and the phonon contribution to thermal and electric conductivity indicate the strong lattice defects and structure disorder.

Effect of aging and ball milling on the phase transformation of Ni50Mn25Ga17Cu8−xZrx alloys

This study investigated phase transformation of Ni50Mn25Ga17Cu8-xZrx (x = 0, 4, 8) alloys after aging and ball milling. For the Cu4Zr4 and Zr8 dual phase alloys, aging has enhanced magnetic susceptibility and magnetic exchange of the matrix, resulting in an increase of the Curie temperature of austenitic matrix. The decrease of martensitic transformation temperatures for the Cu4Zr4 alloy and the increase of martensitic transformation temperatures for the Zr8 alloy after aging should be related to the dissolution and precipitation of the second phase in the matrix, respectively. Ball milling is effective to smash the Cu4Zr4 and Zr8 alloys to fine particles, but cannot fracture the Cu8 alloy to particles, indicating an inherent high ductility and strength of the Cu8 alloy. Therefore, the macroscopic brittleness of the polycrystalline Cu8 alloy was mainly caused by the weak grain boundaries. For the Cu4Zr4 and Zr8 particles, the martensitic transformation and Curie transition of austenitic matrix disappeared and the Curie transition of second phase remained after ball milling. After post-annealing at 800 °C, the Curie transition of austenite was recovered due to the restoration of atomic order, but the martensitic transformation cannot be retrieved which might be caused by the grain refinement of the austenitic matrix after ball milling.

Effect of Zr addition on the microstructure, phase transformation and mechanical property of Ni50Mn25Ga17Cu8 alloy

This study investigated the microstructure, phase transformation and mechanical property of Ni50Mn25Ga17Cu8−xZrx (x=0, 4 and 8) alloys. The microstructure of alloys changed from a single martensitic phase to a dual phase consisting of martensitic/austenitic matrix and second γ phase after substituting Cu with Zr and the volume fraction of second phase increased with increasing Zr content. The martensitic transformation temperature and transformation enthalpy were reduced after adding Zr, which was related to the introduction of second phase that changed the composition and reduced volume fraction participating in martensitic transformation of the alloy. The decrease of transformation hysteresis after introducing the second phase was thought to be caused by the martenstic structure change of the matrix from tetragonal to orthorhombic that reduced the lattice deformation of austenite→martensite transformation. The mechanical strength of the Cu8 alloy was increased firstly after substituting 4 at% Cu by Zr and then decreased after completely substituting Cu by Zr. The change of mechanical performance was related to the fracture character of the alloys. The intergranular fracture of matrix and second phase dominated in the Cu8 and Zr8 alloys, respectively, but the fracture of Cu4Zr4 alloy was determined by a mixture of intergranular fracture of second phase and transgranular fracture of matrix.

Fracture behavior and structural transition of Ni46Mn33Ga17Cu4−xZrx alloys

This study investigated the fracture behavior and structural transition of Ni46Mn33Ga17Cu4−xZrx (x=0, 2, 4) alloys after undergoing quasi-static compression and ball milling. The introduction of Zr-rich second phase enhanced the compressive strength without improving the mechanical ductility of the alloys. The dispersed second phase formed weak interfacial bonding with the martensitic matrix, which resulted in the low plasticity. After ball milling, the dual phase alloy particles were separated to the second phase particles and the matrix phase particles. The average particle size was reduced with increasing Zr content since the size of the second phase particles was much smaller than that of the matrix particles. Moreover, the structure of the second phase was almost not changed by the ball milling. The martensitic transformation disappears for all the alloys after ball milling because of the disordering of the martensitic matrix. Post-annealing at 800°C can restore the martensitic transformation of the Cu4 and Cu2Zr2 alloys but is not effective to restore that of the Zr4 alloy.

Microstructure and phase transformation of Ni46Mn33Ga17Cu4−xZrx alloys

This study investigated microstructure and phase transformation of Ni46Mn33Ga17Cu4−xZrx (x=0, 2, and 4) alloys. The substitution of Cu by Zr changed the alloy from a single martensite to a dual phase consisting of martensitic matrix and Zr-rich second γ phase at room temperature. The volume fraction of γ phase increased with the increase of Zr content, which resulted in the change of martensitic transformation temperature and transformation enthalpy of the alloys. After aging the dual phase alloys at 400°C and 600°C for 10h, the martensitic transformation temperature was increased and transformation enthalpy was decreased.

The structure, anisotropy and coercivity of rapidly quenched TbCu7-type SmCo7−xZrx alloys and the effects of post-treatments

The effects of wheel speed, Zr content, post-ball milling process and heat treatment on the structure, anisotropy, magnetic properties and phase transition of the melt-spun SmCo7−xZrx alloys were investigated. The crystallographic c-axis is parallel to the ribbon plane for the ribbons prepared at low speeds of 5 and 15m/s, and this orientation is reduced at higher speeds. The out-of-plane coercivity of SmCo6.8Zr0.2 ribbon increases from 123kA/m for 5m/s to 1076kA/m for 60m/s. Zr doping improves the hard magnetic properties and the in-plane coercivity of SmCo7−xZrx alloys increases with the Zr content from 592kA/m for x=0.1 to 1376kA/m for x=0.4. The Rietveld refinements and theoretical analysis reveal that Zr atoms occupy the 2e site. The coercivity mechanisms are different for the alloys with various Zr contents. The ball milling process could enhance the coercivity and remanence of the ribbons due to the grain refinement and the precipitation of Co phase. Heat treatment can further modify the magnetic properties of the alloys. SmCo6.7Zr0.3 alloy heat treated at 400°C has the high maximum energy product (BH)max of 64.5kJ/m3, where the coercivity was enhanced to 1560kA/m by 650°C heat treatment. In addition, the SmCo7−xZrx alloys exhibit excellent hard magnetic properties at elevated temperatures.

Glass-formation and atomic structures of Cux(Zr0.22Hf0.78)1−x and (Cu0.61Hf0.39)1−xZrx alloys investigated by Monte Carlo simulation

Based on a realistic Cu–Zr–Hf n-body potential, Monte Carlo simulations were conducted to investigate effect of constituent elements on the forming ability, energetic state and atomic configuration of metallic glasses in two pseudo-binary systems, i.e. the Cux(Zr0.22Hf0.78)1−x and (Cu0.61Hf0.39)1−xZrx (0<x<1). The simulation results first determined the glass-forming ranges of each system, within which amorphous phase was energetically favored compared to its crystalline counterpart and the maximum driving forces for crystalline-to-amorphous transition of the two systems locating almost at the same composition. Voronoi tessellation analysis revealed that the atomic structures of the two systems were obviously affected by the concentration of Cu and Zr, respectively, and the coordination number distribution could be a clear indication pinpointing the respective glass-forming ranges. Moreover, the calculated microchemical inhomogeneity showed a negative tendency upon amorphization, suggesting that there exhibits short-range chemical ordering in the two pseudo-systems and in the amorphous phase, an atom would prefer to have the dissimilar atoms to be its neighbors.

Temperature dependence of the electrical resistivity and electronic structure of amorphous Fe100−xZrx films and multilayers

The electrical resistivity of amorphous Fe100−xZrx metal alloy films and multilayers has been investigated in a wide temperature and composition range. The overall behavior of the resistivity is consistent with bulk measurements, exhibiting prominent semiconductor-like changes at low temperatures. The transition from positive (metallic) to negative temperature coefficient of resistivity behavior is accompanied by minute changes in magnetoresistance and we can therefore rule out magnetic phase changes as being the cause for the observed changes in the resistivity. Using x-ray absorption and emission spectroscopies we are able to probe the unoccupied and occupied electronic densities of states. The corresponding spectra are found to significantly overlap, as expected for a metallic-like electronic structure and the absence of a band gap. Besides a broadening of the x-ray emission lines expected from an amorphous material, remarkably small differences are observed in the electronic structures when changing the amount of Zr. The resistivity data were modeled and agreement with the Mott variable range hopping model was found, indicating localized electronic states due the disordered structure of the Fe100−xZrx alloys.