Corrosion behavior of Zr–Nb–Cr cladding alloys

Zr-Nb-Cr alloys were used to evaluate the effects of alloying elements Nb and Cr on corrosion behavior of zirconium alloys. The microstructures of both Zr substrates and oxide films formed on zirconium alloys were characterized. Corrosion tests reveal that the corro- sion resistance of ZrxNb0.1Cr （x = 0.2, 0.5, 0.8, 1.1; wt%） alloys is first improved and then decreased with the increase of the Nb content. The best corrosion resistance can be obtained when the Nb concentration in the Zr matrix is nearly at the equilibrium solution, which is closely responsible for the formation of columnar oxide grains with protective characteristics. The Cr addition degrades the corrosion resistance of the Zrl.lNb alloy, which is ascribed to Zr（Cr,Fe,Nb）2 precipitates with a much larger size than β-Nb.     

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.     

Analysis of phases in a Cu–Cr–Zr alloy

Phases of a Cu–0.31%Cr–0.21%Zr alloy were analyzed by scanning electronic microscope and energy dispersive X-ray spectroscopy (EDXS) and transmission electronic microscope (TEM). The EDXS results showed that there are three types of phases in the alloy, Cu-matrix, chromium-rich and zirconium-rich phases; coarse phases mainly consist of zirconium-rich phase. TEM result showed that fine chromium distributed in matrix and Cu₅₁Zr₁₄ phase was found in matrix.     

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.     

Characterization of the Hot Deformation Behavior of Cu–Cr–Zr Alloy by Processing Maps

Hot deformation behavior of the Cu–Cr–Zr alloy was investigated using hot compressive tests in the temperature range of 650–850 °C and strain rate range of 0.001–10 s-1. The constitutive equation of the alloy based on the hyperbolic-sine equation was established to characterize the flow stress as a function of strain rate and deformation temperature. The critical conditions for the occurrence of dynamic recrystallization were determined based on the alloy strain hardening rate curves. Based on the dynamic material model, the processing maps at the strains of 0.3, 0.4 and 0.5were obtained. When the true strain was 0.5, greater power dissipation efficiency was observed at 800–850 °C and under0.001–0.1 s-1, with the peak efficiency of 47%. The evolution of DRX microstructure strongly depends on the deformation temperature and the strain rate. Based on the processing maps and microstructure evolution, the optimal hot working conditions for the Cu–Cr–Zr alloy are in the temperature range of 800–850 °C and the strain rate range of 0.001–0.1 s-1.     

Brazing alloys based on the Ni–Cr–Zr system for brazing creep-resisting nickel alloys

Summary

Offering the advantages of high welding speed and low heat distortion, laser welding is an attractive process for joining thin steel sheet. This paper describes an investigation of the static and fatigue strength of laser-welded lap joints in thin steel sheet with different sheet thicknesses and tensile strengths and compares the results with those obtained for spot-welded joints. To evaluate the static strength of the joints, a method for estimation of the joint strength and fracture mode is established. To evaluate the fatigue strength of the joints, the mixed-mode fracture-mechanics criterion of Erdogan and Sih is used, giving good characterisation of the fatigue strength, including that of the spot-welded joints.     

Structure and properties of ultra-fine grain Cu–Cr–Zr alloy produced by equal-channel angular pressing

The structure, thermal stability and properties are investigated of a Cu–Cr–Zr alloy with ultra fine grains (UFG) of 160 nm diameter produced by severe plastic deformation through equal-channel angular pressing (ECAP). Special attention is paid to optimization of multi-functional thermal, electrical and mechanical properties of this alloy by aging after ECAP. Fatigue life and cyclic response under strain-controlled experiments are investigated aiming at clarification of mechanisms of plastic deformation and fracture in the precipitation hardened ECAP materials. It is shown that the precipitation strengthened UFG structure remains stable both under elevated temperatures as high as 500°C and under cyclic loading at room temperature. Substantial improvement of fatigue life is evidenced in comparison with conventional coarse-grain materials. The appearance of cyclic softening is noticed and its nature is discussed in terms of dislocation–particle interaction and possible dissolution of precipitates during fatigue.     

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.     

Effect of predeformation on globularization of Ti–5Al–2Sn–2Zr–4Mo–4Cr during annealing

The microstructure evolution during annealing of Ti–5Al–2Sn–2Zr–4Mo–4Cr alloy was investigated. The results show that for the alloy compressed at 810 °C and 1.0 s^?1 deformation amount (height reduction) 20% and 50% and annealed at 810 °C, thermal grooving by penetration of β phase is sufficient during the first 20 min annealing, resulting in a sharp increase in globularization fraction. The globularization fraction continuously increases with the increase of annealing time, and a height reduction of 50% leads to a near globular microstructure after annealing for 4 h. For the alloy with deformation amount of 50% by compressing at 810 °C, 0.01 s^?1 and then annealed at 810 °C, thermal grooving is limited during the first 20 min of annealing and large quantities of high-angle grain boundaries (HABs) remain. With long time annealing, the chain-like α grains are developed due to the HABs, termination migration and Ostwald ripening. The present results suggest that a higher strain rate and a larger height reduction are necessary before annealing to achieve a globular microstructure of Ti–5Al–2Sn–2Zr–4Mo–4Cr.     

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.     

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 研究了连铸结晶器用Cr Zr Cu合金高温抗氧化性能的变化规律，通过氧化动力学曲线的测定，确定了该合金抗氧化级别的温度区间。运用金相及X射线衍射等分析手段将自行研制的Cr Zr Cu合金与进口同类材料的氧化产物结构进行了对比分析。阐述了Cr、Zr、Mg元素提高合金抗氧化性能作用的机理。结果证明：自行研制的Cr Zr Cu合金具有更好的高温抗氧化性能。     

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.     

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.     

The influence of Cr alloying on microstructures of Fe–Al–Mn–Cr alloys

The effects of increasing chromium content on the phase transformations in Fe–Al–Mn–Cr alloys have been investigated by means of transmission electron microscopy and energy-dispersive X-ray spectrometry. The experimental results revealed that increasing the chromium addition would expand both the A12α-Mn and DO₃ phase-field regions.     

On the formation of faceted Al3Zr (β′) precipitates in Al–Li–Cu–Mg–Zr alloys

Trace additions of Zr to Al alloys inhibit recrystallization through the formation of spherical and coherent Al₃Zr (β′) precipitates. Recently, observations have been made of faceted β′ precipitates in several hot deformed Al alloys, although no systematic experimental study of either the causes of the formation of such precipitates or their orientation relationships with the Al matrix has so far been reported. A detailed examination of the orientation relationships shows that the cube-on-cube orientation relationship existing between spherical, coherent β′ precipitates and the Al matrix does not hold good for the faceted β′ particles and that the faceted β′ particles are twin-related with the matrix. It is shown that the twin-related β′ particles are not incoherent, but bound by large facets fully coherent with the matrix, and that such particles are associated with fairly significant coherency strains. A probable shape of the faceted β′ is also described.     

On the ω phase formation in Cr–Al and Ti–Al–Cr alloys

The interaction between Al and the transition metals Ti and Cr on the stability of the ω phase in metastable β-based structures was studied. Alloys were quenched from the melt to retain at room temperature a metastable β phase (B2 structure), which is stable at high temperatures. The structural study of the ω phase was carried out by correlating the deviation of ω structure from the ideal ω phase to the compositions of the parent β phase. Deviation of ω structures from the ideal one was related to the electron concentration of the parent β phase. A diffuse ω structure is reported in the Cr₂Al phase (C11_b structure) for the first time. The results are consistent with our previous suggestions that Al stabilises the ω phase in transition metals by lowering the spatial conduction electron concentration in the parent β phase and by enhancing p–d hybridisation of valence electrons. In the ternary Ti–Al–Cr alloys, prolonged annealing of the Ti–30Al–10Cr and Ti–20Al–10Cr alloys at 450°C led to the formation of two types of ordered crystalline ω structure.     

Machining of a Zr–Ti–Al–Cu–Ni metallic glass

Zr_52.5Ti₅Cu_17.9Ni_14.6Al₁₀ metallic glass machining chips were characterized using SEM, X-ray diffraction and nano-indentation. Above a threshold cutting speed, oxidation of the Zr produces high flash temperatures and causes crystallization. The chip morphology was unique and showed the presence of shear bands, void formation and viscous flow.     

Fatigue behavior of Zr–Ti–Ni–Cu–Be bulk-metallic glasses

The high-cycle fatigue (HCF) behavior of the Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 (in at.%) bulk-metallic glass (BMG) was studied. Two batches of samples that are from different lots (Batches 59 and 94) are employed in present experiments. The HCF experiments were conducted, using an electrohydraulic machine at a frequency of 10 Hz with a R ratio of 0.1 in air at room temperature and under tension-tension loading, where R=σ_min./σ_max.. (σ_min. and σ_max. are the applied minimum and maximum stresses, respectively). A high-speed and high-sensitivity thermographic-infrared (IR) imaging system was employed for the nondestructive evaluation of temperature evolutions during fatigue testing. No distinct sparking phenomenon was observed at the final fracture moment for this alloy. The fatigue lifetime of Batch 59 is longer than that of Batch 94 at high stress levels (maximum stresses >864 MPa). Moreover, the fatigue-endurance limit of Batch 59 (703 MPa) is somewhat greater than that of Batch 94 (615 MPa). The vein pattern and liquid droplets were observed in the apparent-melting region along the edge of the fractured surfaces. The fracture morphology suggests that fatigue cracks initiated from casting defects, such as porosities and inclusions, which have an important effect on the fatigue behavior of BMGs.