Nanoquasicrystalline phase formation in binary Zr–Pd and Zr–Pt alloys

This paper reports nanoquasicrystalline phase formation in Zr_100−xPd_x (x=30 and 35) and Zr₈₀Pt₂₀ binary alloys and the kinetics of the nanoquasicrystallization process. While the icosahedral phase (i-phase) forms as a metastable phase in the transient stage during the crystallization of Zr–Pd amorphous alloy, it forms directly from the liquid during melt-spinning of Zr–Pt alloy. The isothermal kinetics studies show that i-phase forms from the Zr₇₀Pd₃₀ amorphous alloy by the primary crystallization process with the Avrami exponent in the range of 1.5–2.5. Three-dimensional atom probe analysis results suggest that the i-phase is slightly enriched with Zr with respect to the matrix and its composition is close to Zr₇₅Pd₂₅. The tendency of quasicrystallization of Zr-based alloys appears to have correlation with the enthalpy of mixing of the system.     

Laves phase fields in Cr–Zr–Nb and Cr–Zr–Hf alloy systems

The phase fields of the Laves phase in the Cr–Zr–Nb and Cr–Zr–Hf alloy systems were investigated at 1573 K. The Laves phase formed in the Cr–Zr–Nb alloy system had a broad off-stoichiometric range in the center of ZrCr₂–NbCr₂ pseudo-binary line, while the Laves phase formed in the Cr–Zr–Hf alloy system had a uniform and limited off-stoichiometric range along ZrCr₂–HfCr₂ pseudo-binary line. The results are discussed, in terms of geometric concept of atomic sizes of the constituent atoms.     

Thermal Electrochemical, and Plasma Oxidation of Ti–50Zr, Cu–50Zr, Cu–50Ti, and Cu–33Ti–33Zr Alloys

The three main methods for oxidation of metallic substrates, thermal, anodic and plasma have been applied to a copper, titanium, and zirconium alloy and its corresponding binaries (Cu–33Ti–33Zr, Cu–50Ti, Cu–50Zr and Ti–50Zr). Polished polycrystalline samples of these alloys were examined before treatment, after vacuum thermal annealing at 100°C and heating in 20 mTorr oxygen at 100, 200, and 300°C. ISS depth profiles were taken of selected samples. The least-noble component oxidizes first, but at high temperatures and with plasma oxidation the noble component segregates to the surface. A comparison of the resulting structures on the ternary and binary alloys with different oxidation methods is used to explore the physico-chemical processes during oxidation. Results from these three methods are discussed in terms of physical/chemical parameters that influence the chemical nature and structure of the resulting oxides. The electrochemical processes that occur during the materials reaction with a chosen environment are used to discuss the physical and chemical mechanisms involved. Intrinsic (thermal and plasma oxidation) and extrinsic (electrochemical oxidation) electric fields are shown to influence the chemical and structural nature of the resulting oxide structures. The influence of transport phenomena is discussed.     

Microstructure and properties of aging Cu–Cr–Zr alloy

The crystallography and morphology of precipitate particles in a Cu matrix were studied using an aged Cu–Cr–Zr alloy by transmission electron microscopy(TEM) and high-resolution transmission electron microscopy(HRTEM). The tensile strength and electrical conductivity of this alloy after various aging processes were tested. The results show that two kinds of crystallographic structure associated with chromium-rich phases, fcc and bcc structure, exist in the peak-aging of the alloy. The orientation relationship between bcc Cr precipitate and the matrix exhibits Nishiyama–Wasserman orientation relationship. Two kinds of Zr-rich phases(Cu4Zr and Cu5Zr)can be identified and the habit plane is parallel to {111}Cu plane during the aging. The increase in strength is ascribed to the precipitation of Cr- and Zr-rich phase.     

Microstructures and mechanical properties of homogenization and isothermal aging Mg–Gd–Er–Zn–Zr alloy

The effects of homogenization and isothermal aging treatment on the mechanical properties of Mg–12Gd–2Er–1Zn–0.6Zr(wt%) alloy were investigated. The precipitated long-period stacking order(LPSO) structure and the aging precipitation sequence of the conditioned alloys were observed and analyzed, respectively. The results indicate that the 14H-LPSO structure occurs after the homogenization treatment and the b0 phase forms after the isothermal aging process. These two independent processes could be controlled by the precipitation temperature range. The significant increase in the elongation of the as-cast alloy after homogenization treatment is attributed to the disappearance of the coarse primary Mg5(Gd, Er, Zn) phase and the presence of the 14H-LPSO structure. The precipitation sequence of the investigated alloy is a-Mg(SSS)/b00(D019)/b0(cbco)/b.Furthermore, the yield tensile strength(YTS) and ultimate tensile strength(UTS) values of the isothermal aging alloy have a great improvement, which could be attributed to the high density of the precipitated b0 phase.     

Precipitation evolution in Al–Zr and Al–Zr–Ti alloys during aging at 450–600 °C

The transformation of Al₃Zr (L1₂) and Al₃(Zr_1−xTi_x) (L1₂) precipitates to their respective equilibrium D0₂₃ structures is investigated in conventionally solidified Al–0.1Zr and Al–0.1Zr–0.1Ti (at.%) alloys aged isothermally at 500 °C or aged isochronally in the range 300–600 °C. Titanium additions delay neither coarsening of the metastable L1₂ precipitates nor their transformation to the D0₂₃ structure. Both alloys overage at the same rate at or above 500 °C, during which spheroidal L1₂ precipitates transform to disk-shaped D0₂₃ precipitates at ca. 200 nm in diameter and 50 nm in thickness, exhibiting a cube-on-cube orientation relationship with the α-Al matrix. The transformation occurs heterogeneously on dislocations because of a large lattice parameter mismatch of the D0₂₃ phase with α-Al. The transformation is very sluggish and even at 575 °C coherent L1₂ precipitates can remain untransformed. Mechanisms of microstructural coarsening and strengthening are discussed with respect to the micrometer-scale dendritic distribution of precipitates.     

Solidification structure and mechanical properties of Al–Li–Cu–Zr cast alloys

Abstract

The microstructure and properties of three Al–3Li–1Cu ternary alloys have been studied, in particular the effect of Zr additions on the microstructure, precipitation and mechanical properties. The results showed that, for these Al–Li casting alloys, Zr content up to 0.2 wt-% was acceptable, and the Zr additions appeared to refine the grain structure. During aging, the Zr rich phase provided nucleation sites for δ' phase and promoted δ' phase refinement and homogenisation. Under optimised conditions, the tensile strength and elongation to failure of the Al–Li–Cu–Zr casting alloys were 400 MPa and 2.5%, respectively.     

Phase diagram calculation and predication of Au–Pd–Zr ternary system

Au-Pd-Zr ternary alloy phase diagram at 25℃ was calculated by Panda phase calculation software,and the thermodynamic data were based on three binary alloy phase diagrams:Pd-Au,Au-Zr,and Pd-Zr.Five composition points in the ternary phase diagram were selected to predict the precipitation order.One(32Au-32Pd-36Zr) of the five composition points in ternary phase diagram was chosen to verify the correctness of the phase diagram calculation and the precipitation order by scanning electron microscopy(SEM),energy dispersive spectroscopy(EDS),and X-ray diffraction(XRD).The unknown phase in XRD patterns was predicated by EDS and materials studio(MS) software.The experimental results show that there are seven key ternary reactions points and 17 phase regions in all isothermal sections at 25℃.The thermodynamic process and microstructure for the alloy phase can be described in order according to the vertical section in phase diagram.The phase compositions of the chosen one point are consistent with calculation prediction.The unknown phase in XRD patterns should be Zr_2AuPd by the first principle X-ray simulation.     

Surface and electrochemical characterization of Ni–Zr intermetallic compounds

In this paper the Ni–Zr system has been considered with the aim of investigating the role of composition and structure of an early–late transition metals system on the electrocatalytic activity, for the hydrogen evolution reaction. As a matter of fact, pure Ni and Zr show low activity, while their intermetallic compounds generate a higher catalytic efficiency. Five alloys, with increasing Ni content starting from Ni₃₃Zr₆₇ up to Ni₇₅Zr₂₅, have been prepared and characterized. The alloy of composition (Ni_0.55Mn_0.30V_0.10Co_0.05)_2.1Zr has also been considered, in order to investigate the catalytic efficiency related to a Laves structure. The thickness and composition of the surface oxides have been investigated and their effect on reducing the catalytic efficiency of the as-prepared alloys has been discussed. The activity of the samples submitted to a surface activation treatment with hydrofluoric acid, that removes the oxide layer and allows to evidence the properties of the compounds, has been observed to increase significantly. The trend of the electrocatalytic efficiency with the composition of the alloys is discussed considering a synergetic effect between Ni and Zr. The Laves phase appears slightly more active than the binary intermetallic compound.     

Microstructure and corrosion behavior of Zr–1.0Cr–0.4Fe–xMo alloys

Possibility of using Mo as an alloying element in Zr-based alloys was attractive in terms of microstructure refinement and mechanical properties strengthening. In this research, Zr–1.0Cr–0.4Fe–xMo(0, 0.2, 0.4, and 0.6) alloys with different Mo contents were prepared by vacuum arcmelting method, the microstructure and the corrosion resistance of these alloys were investigated. Addition of Mo has a refinement effect on the microstructure; with the increase of Mo content, the a-laths in the as-cast samples and the grain size in the annealed samples decrease. Zr–1.0Cr–0.4Fe–xMo alloys have large numbers of fine second-phase particles(SPPs) in the matrix, the area fraction of the SPPs is more than 10 %. With the increase of Mo content, the population density of the SPPs increases significantly, while the average diameter of the SPPs decreases. Mo addition also affects the texture; the intensity of basal pole texture aligning normal direction decreases with the increase of Mo content in the alloys.Compared with Zr-4 and Zr–1Nb, Zr–1.0Cr–0.4Fe–xMo alloys have excellent corrosion resistance in 500 °C/10.3 MPa steam. The corrosion rates of Mo-containing alloys are higher than that of Mo-free alloy, which is mainly attributed to the solute Mo atoms in the Zr matrix.Change of the SPPs features due to the increase of Mo content alleviates the degradation of corrosion resistance in some degree, but it is not the dominant factor.     

Strong and ductile Al–Zn–Mg–Zr alloy obtained by equal angular pressing and subsequent aging

An ultrafine-grained Al–Zn–Mg–Zr alloy with superior mechanical performance was obtained by high passes of equal angular pressing (ECAP) and subsequent aging. After 8 ECAP passes and aging, the yield strength (YS) and ultimate tensile strength (UTS) of the solid-solutioned alloy are significantly improved from (98±10) and (226±7) MPa to (405±9) and (427±9) MPa, respectively. A large elongation is also maintained ((17.4±2.5)%). The microstructure features including grain refinement, morphology of precipitates, and dislocation density, were revealed with multiscale characterizations, including transmission electron microscopy, electron backscattered diffraction, and X-ray diffraction. After 8 passes of ECAP, the original coarse elongated grains are refined to a unique bimodal grain structure consisting of ultrafine equiaxed and lath-like grains. Additionally, the effects of ECAP and subsequent aging on the strengthening contribution of a variety of strengthening mechanisms, such as dislocation strengthening and precipitation strengthening, were discussed in detail.     

Microstructure and biocorrosion behaviors of solution treated and as-extruded Mg–2.2Nd–xSr–0.3Zr alloys

Mg–2.2Nd–xSr–0.3Zr alloys (x=0, 0.4 and 0.7, mass fraction, %) were prepared by gravity casting. Solution treatment was conducted on the as-cast alloys to homogenize microstructure, and hot extrusion was subsequently conducted. Microstructure was observed using an optical microscope and a scanning electron microscope. Biocorrosion behaviors of the alloy in simulated body fluid were analyzed by mass loss, hydrogen evolution and Tafel polarization experiments. The results show that the amount of residual eutectic phase of the solution treated alloys increases with increasing Sr addition, and the grains are significantly refined after hot extrusion. The corrosion resistance of the solution treated alloys deteriorates apparently with increasing Sr addition, while the corrosion resistance of the as-extruded alloys is improved with Sr addition. Nevertheless, the biocorrosion behavior of the as-extruded alloys obtained by Tafel polarization shows different trends from those obtained by the other two methods.     

Microstructure and mechanical properties of Ti–Nb–Fe–Zr alloys with high strength and low elastic modulus

Zr was added to Ti–Nb–Fe alloys to develop low elastic modulus and high strength β-Ti alloys for biomedical applications. Ingots of Ti–12Nb–2Fe–(2, 4, 6, 8, 10)Zr (at.%) were prepared by arc melting and then subjected to homogenization, cold rolling, and solution treatments. The phases and microstructures of the alloys were analyzed by optical microscopy, X-ray diffraction, and transmission electron microscopy. The mechanical properties were measured by tensile tests. The results indicate that Zr and Fe cause a remarkable solid-solution strengthening effect on the alloys; thus, all the alloys show yield and ultimate tensile strengths higher than 510 MPa and 730 MPa, respectively. Zr plays a weak role in the deformation mechanism. Further, twinning occurs in all the deformed alloys and is beneficial to both strength and plasticity. Ti–12Nb–2Fe–(8, 10)Zr alloys with metastable β phases show low elastic modulus, high tensile strength, and good plasticity and are suitable candidate materials for biomedical implants.     

Deformation and fracture toughness of a bulk amorphous Zr–Ti–Ni–Cu–Be alloy

The flow behavior and fracture toughness of two different plate thicknesses (i.e. 4 and 7 mm) of a bulk amorphous Zr–Ti–Ni–Cu–Be alloy was investigated. It is shown that the flow/fracture stress was independent of superimposed hydrostatic pressure over the range 50–575 MPa, suggesting that the flow behavior follows the von Mises criterion. However, the macroscopic orientation of the fracture plane relative to the stress axis was strongly affected by changes in stress state, suggesting some normal stress dependence to the flow/fracture behavior. The fracture behavior was also studied on both notched and precracked bend bars for both plate thicknesses. The average fracture toughness obtained from seven fatigue precracked specimens taken for both plate thicknesses was 17.9±1.8 MPa√m, while the notched toughness obtained on specimens with notch root radii ranging from 65 to 250 μm taken from both plate thicknesses were in the range of 9l–131 MPa√m.     

Effect of minor Zr and Sc on microstructures and mechanical properties of Al–Mg–Si–Cu–Cr–V alloys

The effects of minor contents of Zr and Sc on the microstructures and mechanical properties of Al–Mg–Si–Cu–Cr–V alloy were studied. The results show that the effects of minor Zr and Sc on the as-cast grain refinement in the ingots, the improvement in the strength of the as-extruded alloys and the restriction of high angle grain boundaries in the aged alloys can be sorted as Al₃Sc>Al₃(Zr,Sc)>Al₃Zr. None of them could stop the nucleation of recrystallization, but Al₃(Zr,Sc) phase is a more effective inhibitor of dislocation movement compared to Al₃Sc in the aged alloys. Compared with the mechanical properties of the aged alloy added only 0.15% Sc, the joint addition of Zr and Sc to the alloy leads to a very slight decrease in strength with even no cost of ductility. Taking both the production cost and the little bad influence on mechanical properties into consideration, an optimal content of Zr and Sc in the Al–Mg–Si–Cu–Cr–V alloy to substitute 0.15% Sc is 0.13% Zr+0.03% Sc.     

Hydrogen permeation and structural features of melt-spun Ni–Nb–Zr amorphous alloys

Amorphous (Ni_0.6Nb_0.4)_100−xZr_x (x = 0, 20, 30, 40 and 50 at.%) alloys were prepared by the melt-spinning technique, and the hydrogen permeation through those alloy membranes was examined. The local atomic structure in these alloys was also investigated by radial distribution function (RDF) analysis. Moreover, hydrogen solubility and diffusivity were also measured in order to discuss the mechanism for hydrogen permeation. The permeability of the Ni–Nb–Zr amorphous alloys increases with Zr content and temperature. The maximum hydrogen permeability is 1.59 × 10⁻⁸ mol m⁻¹ s⁻¹ Pa^−1/2 at 673 K for the (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloy. The (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloy showed larger hydrogen solubility and diffusivity than the (Ni_0.6Nb_0.4)₇₀Zr₃₀ amorphous alloy. As the result, the (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloy showed higher hydrogen permeability than the (Ni_0.6Nb_0.4)₇₀Zr₃₀ amorphous alloy at 673 K. The RDF analysis shows that the atomic distance between the Zr atoms increases by hydrogenation. The chemical ordering such that the number of Zr coordinates is much higher than that of Ni and Nb coordinates was found in the (Ni_0.6Nb_0.4)₇₀Zr₃₀ and (Ni_0.6Nb_0.4)₅₀Zr₅₀ amorphous alloys. The relation between the amorphous local structure and the permeation was discussed in detail.     

Crystallization process and shape memory properties of Ti–Ni–Zr thin films

The crystallization process of as-deposited Ti–Ni–(10.8–29.5)Zr amorphous thin films was investigated. The Ti–Ni–Zr as-deposited films with a low Zr content exhibited a single exothermic peak due to the crystallization of (Ti,Zr)Ni with a B2 structure. In contrast, a two-step crystallization process was observed in the Ti–Ni–Zr thin films with a high Zr content. Shape memory behavior of Ti–Ni–Zr thin films heat treated at 873–1073 K was investigated by thermal cycling tests under various stresses. The martensitic transformation start temperature increased with increasing Zr content until reaching the maximum value, then decreased with further increasing Zr content. The inverse dependence of transformation temperature on Zr content in the thin films with a high Zr content is due to the formation of a NiZr phase during the crystallization heat treatment. The formation of the NiZr phase increased the critical stress for slip but decreased the recovery strain.