Cr Zr System Research Articles

Study on eutectic-oxidation coupling reaction of Cr-Zr system in high temperature steam environment

The isothermal steam oxidation behavior of Cr-coated Zr-1Nb alloy at 1350 ℃ and 1400 ℃ was investigated. The temperatures are above the Cr-Zr eutectic temperature. The reliability of the experimental setup and methodology was confirmed by conducting isothermal steam oxidation experiments on bare Zr-1Nb specimens at 1100∼1400 ℃, and the corresponding oxidation kinetics correlation was obtained. After the eutectic-oxidation reaction, the surface of the coated specimens exhibited a “crocodile skin” morphology composed of “ridges” and “hollows”, which was attributed to the non-uniform eutectic reaction. Due to the much higher O affinity of Zr compared to Cr, and the higher solubility of Cr in β-Zr compared to α-Zr(O) and ZrO2, the ZrO2 and α-Zr(O) layers initially grew on the Cr-Zr eutectic during oxidation. Cr continuously diffused inward and eventually precipitated as Cr-rich phases within the metallic matrix. Three types of Cr-rich phases were observed, with varying oxygen content and reflecting the oxidation process of the Cr-rich phases. The Cr-rich phases were ultimately oxidized into a mixture of Cr2O3 and ZrO2. The parabolic weight gain rates for the oxidation of Cr-Zr eutectic are compared with the oxidation kinetics correlation derived from the bare Zr-1Nb specimens, and the model applicability of the oxidation kinetics correlations of Zr alloys in the simulations of Cr-Zr eutectic-oxidation reaction is discussed.

Experimental investigation of the phase equilibria, phase stability, and defect structure in the Cr–Zr system by using DSC, XRD, and SEM

The solid-state phase transformations, phase stability, and defect structure in the Cr–Zr system were investigated experimentally by using differential scanning calorimetry (DSC), X-ray diffraction (XRD), and Scanning electron microscope (SEM) along with EDX. Arc melting was used to synthesize all of these alloys. The temperature of the Cr and Zr-rich eutectic L ↔ C36–Cr2Zr + Cr and L ↔ β-Zr + C15–Cr2Zr were determined to be 1861 ± 3 K and 1588 ± 3 K, respectively. The temperature corresponding to the eutectoid transformation β-Zr ↔ α-Zr + C15–Cr2Zr was found to be 1099 ± 2 K. The temperature pertaining to C36–Cr2Zr ↔Cr + C15–Cr2Zr transformation were determined to be 1844 ± 3 K. These values are notably different from previous measurements and are more accurate. The liquidus temperature in the composition range from 60 to 100 at.% Zr was measured for the first time. All the alloy specimens were characterized by X-ray diffraction. The lattice parameters and relative phase fraction of the constituent phases were evaluated by using Rietveld refinement of the XRD data. At ambient temperature, the refined lattice parameter of C15–Cr2Zr increases linearly with Zr concentration from 31 (7.199 Å) to 34 at.% Zr (7.210 Å). The oxygen impurities play an important role in the sluggish transformation of the C14/C36–Cr2Zr ↔ C15–Cr2Zr Laves phase. The density calculated based on lattice parameters determined by XRD and the theoretical model for anti-site type defects makes it is fair to conclude that C15–Cr2Zr Laves phase is a substitutional type solid solution. The experimental data presented here is consistent and reliable, and it supersedes previous findings.

Experimental Investigation of the Phase Equilibria, Phase Stability and Defect Structure in the Cr-Zr System by Using Dsc, Xrd, and Sem

Experimental Investigation of the Phase Equilibria, Phase Stability and Defect Structure in the Cr-Zr System by Using Dsc, Xrd, and Sem

Вклад механизмов упрочнения при немонотонном изменении свойств в сплаве Cu–0,6Cr–0,1Zr при кручении под высоким давлением

Phase transformations play an important role in the formation of properties in the dispersion-hardened alloys, for example, such as the Cu–Cr–Zr system alloys. It is known that under severe plastic deformation, the diffusion conditions change significantly, which leads to a change in the phase transformation kinetics. In this work, the authors studied the Cu–0.6Cr–0.1Zr alloy in the low concentration solid solution state subjected to high pressure torsion (up to 10 cycles). In this case, due to the solid solution low concentration and the formed ensemble of large particles, the process of solid solution decomposition was excluded at the first stages. The preliminary work on the analysis of such structurally sensitive characteristics as electrical conductivity and lattice parameter made it possible to identify the nonmonotonic nature of a change in the alloying elements concentration in the solid solution during HPT. Nonmonotonicity is related to the significant changes in the characteristics of the second phase particles ensemble under the influence of high voltages. Such significant structural changes are reflected in the nature of the mechanical characteristics change. The authors identified that when increasing the number of HPT revolutions, changes in strength also have a nonmonotonic nature, which corresponds to the nonmonotonic nature of changes in the concentration of alloying elements and electrical conductivity. Various contributions to the Cu–0.6Cr–0.1Zr alloy hardening were analyzed. The analysis identified that the dispersion strengthening contribution plays the main role in the nonmonotonic change in the mechanical characteristics. The calculated data correlate with the obtained experimental results.

Computer simulation of temperature fields in the Cr (film)-Zr (substrate) system during pulsed electron-beam irradiation

The paper presents the results of numerical simulation of the distribution of thermal fields during the formation of Cr-Zr surface alloy using a pulsed low-energy high-current electron beam (LEHCEB). The melting thresholds of the Cr-Zr system for different thicknesses of Cr films were calculated. The melting threshold of the Cr-Zr system increases linearly with increasing Cr film thickness. A linear regression dependency model of the melting threshold on the film thickness is proposed. Evaporation thresholds of the Cr-Zr system for different thicknesses of Cr films were calculated. The evaporation threshold of the Cr-Zr system increases linearly with increasing Cr film thickness. A linear regression dependency model of the evaporation threshold on the film thickness is proposed. The value of the LEHCEB energy density at which the lifetime of the film and substrate are equal is calculated. This value is a maximum value for the effective formation of Cr-Zr. A model of the LEHCEB energy density, at which the lifetime of the film and the substrate are equal, in the form of a third-degree polynomial is proposed.

A systematic study of the oxidation behavior of Cr coatings on Zry4 substrates in high temperature steam environment

Cr coatings have been deposited on the outer surface of zircaloy-4 tube with well control of thickness variations along the tube axis. A series of samples have been oxidized in high temperature steam environment at 1200 °C for different durations. Cr2O3 layers are formed on the surface of the Cr coatings after high temperature oxidation, however, we have found that the thickness of the Cr2O3 layers increases first, and then decreases. The reason is because the Cr2O3 is reduced by the zirconium substrate when the thickness of Cr2O3 reaches its maximum. More detailed study revealed that the entire process can be divided into three stages: initial oxidation stage (I); reduction stage (II); and the oxidation of the sub-coating zirconium at a lower rate than the uncoated Zry4 (III). In addition, precipitation of secondary phases both within the coatings and the zirconium substrate has been studied in detail which plays an important role during the oxidation process. Therefore, the oxidization behavior of the Cr-Zr system is more complex than generally assumed. This study has provided sufficient experimental evidences for the redox reaction between the Cr coating and Zry4 substrate. Diffusion channels of oxygen ions during the reduction reaction have also been studied systematically.

The Microstructure and High-Strain-Rate Superplasticity of the Al–Mg–Ni–Fe–Mn–Cr–Zr Alloy

The microstructure, superplasticity characteristics at a subsolidus temperature (540°C), and the room-temperature mechanical properties of an alloy of the Al–Mg–Ni–Fe–Mn–Cr–Zr system have been investigated using the methods of scanning and transmission electron microscopy and uniaxial tensile tests. The alloy has a bimodal particle-size distribution; it contains eutectic particles of Al9FeNi with an average size of 0.6 μm; and dispersoids with an average size of 75 nm. The particles of the secondary phases ensure grain size of approximately 4 μm after the recrystallization subsolidus annealing of the cold-rolled sheet. Due to the microsize grain structure, the alloy demonstrates a relative elongation to 500% at a subsolidus temperature in the range of the constant strain rates of 5 × 10–3 to 3 × 10–2 s–1, yield stress 215 MPa, and ultimate strength 330 MPa.

Thermodynamic modeling and experimental study of the Fe–Cr–Zr system

This work developed thermodynamic models for describing phase stability and thermodynamic property of the Fe–Cr–Zr system using the Calphad approach coupled with experimental study. Thermodynamic descriptions of the Fe–Cr and Cr–Zr systems were either directly adopted or slightly modified from literature. The Fe–Zr system has been remodeled to accommodate recent ab-initio calculation of formation enthalpies of various Fe–Zr compounds. Reliable ternary experimental data and thermodynamic models were mainly available in the Zr-rich region. Therefore, selected ternary alloys located in the vicinity of the eutectic valley of β(Fe,Cr,Zr) and (Fe,Cr)2Zr laves phase in the Fe-rich region have been experimentally investigated in this study. Microstructure has been examined by using scanning electron microscope, energy-dispersive X-ray spectroscopy and X-ray diffraction. These experimental results, along with the literature data were then used to develop thermodynamic models for phases in the Fe–Cr–Zr system. Calculated phase equilibria and thermodynamic properties of the ternary system yield satisfactory agreements with available experimental data.

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

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

A new metastable crystalline phase in the Cr–Zr system

A new metastable phase formed during cooling of Zr–Cr alloys with a 36 at% Zr and 64 at% Cr nominal composition has been found during Transmission Electron Microscopy (TEM) studies. The new phase crystallizes in an fcc structure with lattice parameter of 0.817 nm and a chemical composition close to the equiatomic composition.

Stability of Laves phases in the Cr–Zr system

The total energies of Laves phases with various occupations of inequivalent lattice sites in all three structural forms C14, C15 and C36 have been calculated ab initio by a pseudopotential VASP code with a complete relaxation of all structural parameters. The relative stability of Cr 2Zr polytypes is discussed. The calculated values were used in two-sublattice and three-sublattice models for the re-modeling of Gibbs energies of Laves phases and subsequently for the calculation of phase diagram of the Cr–Zr system by the CALPHAD method. A comparison of phase diagrams obtained by our model using first-principles results with previous treatments using an empirical approach as well as with experimental phase equilibrium data is presented. An application of the structural energy differences (lattice stabilities) calculated ab initio provides a similarly good description of the phase diagram of the Cr–Zr system as previous studies, but much fewer adjustable parameters are needed for a thermodynamic description of Laves phases.

Repairing of the defects of the engine vanes of an aeroplane by light beam brazing

The microstructure and hardness distribution of the dispersion strengthened Ni-based alloy ChS88 brazed by light beam in vacuum with the Vpr-42 (Ni–Cr–B–Si system) and PNC-13 (Ni–Cr–Zr system) filler metals were investigated. Because of the diffusion of boron, the brazing filler metal Vpr-42 causes the obvious erosion of the base metal. The analysis of microhardness shows that the hardness distribution of the base metal–transition zone–brazing seam with the Ni–Cr–Zr system filler metal is relatively uniform, and the hardness of the brazing seam with the Ni–Cr–B–Si system filler metal and its transition zone is obviously greater than that of base metal owing to the precipitation of the brittle and hard borides. This shows that when brazed with the Ni–Cr–Zr system filler metal by light beam, the Ni-based alloy joint has better toughness. Under the laboratory conditions, the repair of the surface defects of the vanes by means of light beam vacuum brazing with the Ni–Cr–Zr system filler metal was realized.

The Cr-Ni-Zr (Chromium-Nickel-Zirconium) System

The Cr-Ni-Zr system was reviewed by [2000Gup]. In developing high temperature resistant brazing material, the Cr-Ni-Zr system has been studied at the Ni-corner. The results are given here. In order to discuss the new results on Cr-Ni-Zr system, it is necessary to recapitulate the binary systems. The Cr-Ni system [1991Nas] (Fig. 1) is a simple eutectic system, the eutectic reaction L M a + c occurring at 1345 C, where a and c are the terminal solid solutions of body centered (bcc) Cr and face centered cubic (fcc) Ni, respectively. At the eutectic reaction temperature, the c phase extends to 50 at.% Cr and the a phase extends to 32 at.% Ni. Solubility of Ni in Cr decreases with decrease in temperature reasonably fast down to 1100 C. A Ni2Cr ordered phase forms in the c phase region below 600 C. The Cr-Zr system [Massalski2, 1993Oka] shows (Fig. 2) the presence of only one intermediate phase Cr2Zr which occurs in three polymorphic forms, the aCr2Zr(w1) exists below 1592 C, the bCr2Zr(b1) exists between 1592 and 1622 C, and the cCr2Zr(c1) exists between 1622 and 1673 C. Two eutectics, L M a + b1 and L M w1 + a¢ occur at 1592 and 1332 C, respectively. The a¢ phase is the terminal solid solution of bZr. A eutectoid reaction a¢ M x + w1 occurs at 831 C with x representing the aZr phase. The solubility of Zr in Cr is negligible at room temperature and is 1.5 at.% Zr at the eutectic temperature 1592 C. The Ni-Zr system [1991Nas] (Fig. 3) has eight intermediate phases Ni5Zr(e), Ni7Zr2(p), Ni3Zr(k), Ni21Zr8(h), Ni10Zr7(b), Ni11Zr9(m), NiZr(/), and NiZr2(n). The p, /, and n phases melt congruently at 1440, 1260, and 1120 C, respectively. All the other intermediate phases form through peritectic or peritectoid reactions: L + p M e, L + p M h, p + h M k, L + / M m1, and L + m M b occurring at 1300, 1180, 920, 1170, and 1160 C, respectively. Five eutectic or eutectoid reactions: L M c + e, L M h + b, L M / + n, L M n + a¢, and a¢ M n + x occur at 1170, 1070, 1010, 960, and 845 C, respectively. The m phase undergoes eutectoid transformation m M b + / at 978 C. The phases and their structure data are given in the review paper [2000Gup]. [1999Kho] reinvestigated the Cr-Ni-Zr system at the Ni-rich corner, up to 40 at.% Cr and up to 30 at.% Zr. The alloys were melted in a water cooled copper hearth, tungsten electrode arc furnace under argon atmosphere. The component elements were Ni of 99.95 mass% purity, Cr of 99.98 mass% purity, and Zr of 99.95 mass% purity. The alloys in cast condition were used for this investigation.

A theoretical study of the phase equilibria in the CuCrZr system

Small additions of chromium to CuZr alloys or zirconium to CuCr alloys are widely used to improve the mechanical properties of the alloys at high temperatures. There are conflicting opinions in the literature on the question of the existence of the pseudobinary system CuCr 2Zr. From calculation of the CuCrZr phase diagram using the CALPHAD method, the possibility of the existence of this pseudobinary has been ruled out. A number of isothermal and vertical sections have been calculated together with the liquidus surface. The reaction scheme for the whole system is also presented.

Constitution, Microstructure, and Hardness of Water Atomised and Hot Isostatically Consolidated Copper Alloy Powders

Copper based alloys within the Cu–Cr–Zr system produced in powder form by water atomisation were consolidated to full density by hot isostatic pressing (hipping) at temperatures below 0·5T m. After hipping, materials of a mean grain size between 2 and 10 μm were obtained. The increased capacity for solid solubility of chromium and zirconium in copper, produced on atomisation, resulted in enhanced strengthening by the precipitation of coherent chromium particles during hipping. This approach allowed heat treatment after processing as was the case for the extrusion-heat treatment route. The peak hardnesses obtained were either equal to (Cu–Cr–Zr alloys) or slightly lower than (Cu–Cr alloys) the respective values obtained after extrusion followed by heat treatment. PM/0618

Thermodynamic modeling of the laves phases in the CrZr system

Thermodynamic modeling of the laves phases in the CrZr system

A Thermodynamic Assessment of the Cr-Zr System

An optimized set of thermodynamic functions of the Cr-Zr system has been obtained using phase diagram data from the literature. The excess free energies of the solution phases, liquid and three terminal solid solutions, were described by the Redlich-Kister formula. The Laves phases, αCr 2 Zr, βCr 2 Zr, and γCr 2 Zr, were described by the Wagner-Schottky model: αCr 2 Zr was treated with a two-sublattice model assuming antiestructure atoms on both sublattices; βCr 2 Zr and γCr 2 Zr were described with three sublattices after the formula (Cr, Zr) 6 (Zr, Cr) 4 (Cr) 2 , where the second atoms on the first two brackets are antistructure atoms

Effect of consolidation route on structure and property control in rapidly solidified Al–Cr–Zr–Mn povvder alloy for high temperature service

In this paper the authors describe a new rapidly solidified alloy which is capable of meeting the projected requirements of the aerospace industry. Initial studies using splat quenched particulates were carried out on the Al–Cr–Zr system. Microhardness tests indicated that these alloys age–hardened between 350 and 400°C and showed excellent thermal stability. Further alloy development and studies of fabrication behaviour were carried out using air atomized powder. Powders were consolidated by either conventional or hydrostatic extrusion. Microstructural changes during fabrication were identified and correlated with mechanical property data. The alloy can achieve the requirements of the aerospace industry provided microstructural development is controlled during fabrication.MST/233

Effect of consolidation route on structure and property control in rapidly solidified Al–Cr–Zr–Mn povvder alloy for high temperature service

In this paper the authors describe a new rapidly solidified alloy which is capable of meeting the projected requirements of the aerospace industry. Initial studies using splat quenched particulates were carried out on the Al–Cr–Zr system. Microhardness tests indicated that these alloys age–hardened between 350 and 400°C and showed excellent thermal stability. Further alloy development and studies of fabrication behaviour were carried out using air atomized powder. Powders were consolidated by either conventional or hydrostatic extrusion. Microstructural changes during fabrication were identified and correlated with mechanical property data. The alloy can achieve the requirements of the aerospace industry provided microstructural development is controlled during fabrication.MST/233

Electron probe and X-ray diffraction measurements of intermediate phases in Zr diffused with Cr, Fe, Ni, Cu and Mo

Intermediate phases intended for superconductivity measurements were prepared by diffusing Zr with each of the following elements: Cr, Fe, Ni, Cu and Mo. Composition of the phases was estimated from electron probe measurements and in some cases confirmed by X-ray diffraction. The results indicated these phases to be present: In the Cr-Zr system Cr 2Zr was observed in agreement with the phase diagram in Hansen 1). In the Fe-Zr system FeZr 3, FeZr 2 and Fe 2Zr were observed whereas Hansen shows only Fe 2Zr. In the Ni-Zr system NiZr 2, NiZr, Ni 10Zr 7 and Ni 5Zr were observed but three additional phases reported by Kirkpatrick 2) did not appear in the diffusion couple. In the Cu-Zr system only CuZr 2 and CuZr phases were observed because the parent copper was depleted before the end of the diffusion period. In the Mo-Zr system MoZr was observed but the equilibrium phase Mo 2Zr listed by Hansen was not found at the temperature used here.