Cr Zr Alloy Research Articles

Enhanced combination properties of Cu-0.8Cr alloy by Fe and P additions

With the goals of exploring the feasibility of replacing Zr with Fe and P in Cu–Cr–Zr alloys and developing Cu–Cr–Fe–P alloys with excellent mechanical and electrical properties, the effects of Fe and P additions on the microstructures and properties of the as-cast, cold-rolled and aged Cu-0.8Cr alloys are investigated. The results indicate that adding Fe and P into the Cu-0.8Cr alloy can promote the precipitation of a large amount of fine, uniformly dispersed Cr and Cr3P particles. From Cu-0.8Cr to Cu-0.8Cr-0.17Fe-0.048P, the area fraction of precipitates increases from 3.1% to 6.3% while their average diameter reduces from 1.6 μm to 1.4 μm. When subjected to 95% cold rolling plus 450 °C aging for 1 h, the Cu-0.8Cr-0.17Fe-0.048P alloy exhibits a Vickers hardness of 140.4 HV and an electrical conductivity of 73.2%IACS, higher than 96.7 HV and 58.4%IACS in the Cu-0.8Cr alloy. Among three different processing routes investigated, the one with initial 50% cold rolling → aging at 500 °C for 1 h → final 95% cold rolling allows the Cu-0.8Cr-0.17Fe-0.048P alloy to gain most in both its tensile strength (569 MPa) and electrical conductivity (64%IACS). The findings in this work provide insights to composition and processing designs for new Cu–Cr alloys with high strength and electrical conductivity.

Comparison of the Microstructure of Machined and Laser Sintered Shaped Charge Liner in the Hydrodynamic Regime

To gain further insight into the mechanisms underlying jet formation and elongation of laser sintered shaped charge liners under high strain rate deformation, Cu–Cr–Zr alloy liners fabricated by selective laser sintering process were deformed by explosive detonation. Their as-manufactured (liner) and resultant (slug) microstructure have been investigated in comparison with those of traditional machined liners employing both optical and scanning electron microscopy. The resultant slug microstructure of both machined and laser sintered liners revealed a smaller refined equiaxed grain size consistent with traditionally fabricated liners, characteristic of dynamic recrystallization. The disappearance of the (originally present) pores in the post-shot/recovered material microstructure was observed for laser-sintered liners. Comparison of the forward and rear region of the slug revealed variations in liner deformation, a result attributed to temperature variation across the slug. In contrast with the machined liner, a unique feature of precipitation, observed in the ending (slug) microstructure of the laser sintered liner is indicative of the associated extreme high strain and strain rate liner deformation which occurred during slug formation. The precipitates are likely compounds of Chromium and Zirconium which are constituents of the laser sintered copper alloy—the first time this observation is reported. This study provides a link between post charge evolution microstructure and liner manufacturing processes, potentially providing a new route to help optimise jet formation and effectiveness.

Nano-Sized Precipitates in a Cast Cu–Cr–Zr Alloy and Their Evolution during Subsequent Heat Treatment

Nano-sized precipitates in centrifugally cast Cu–0.43Cr–0.22Zr alloy and their evolution during subsequent solid-solution treatment and aging were investigated by TEM and HRTEM. They are particles of Cr and Cu–Zr phase, such as Cu51Zr14. Many nano-sized precipitates are found in the cast alloy; they will get smaller or disappear during solid-solution treatment and the dissolved atoms are inhomogeneously distributed in the copper matrix and form aggregations up to generation of very tiny clusters after solution quenching. Furthermore, aging treatment will create many new nano-sized precipitates, and causes the inherited precipitates being recovered and the clusters being grown, resulting in the formation of more and finer precipitates in the aged alloy in comparison with the case of the as-cast alloy. Therefore, it can be inferred that the more the tiny precipitates formed in the as-cast alloy, the more the precipitates in the aged alloy. The treatment combining solid-solution one and aging is beneficial to the formation of more and finer precipitates in a Cu–Cr–Zr alloy.

Optimization of strength, ductility and electrical conductivity of a Cu–Cr–Zr alloy by cold rolling and aging treatment

To balance the paradox of both high mechanical properties and electrical conductivity of copper alloys, a nominal hot-rolled Cu-0.4 wt.%Cr-0.3 wt.%Zr alloy strips were subjected to different thermo-mechanical process. The microstructures of the alloys are characterized by optical microscopy and transmission electron microscopy and the mechanical properties and the electrical conductivity are evaluated. The results show that a desired combination of strength, ductility and conductivity can be obtained by controlling the sequence of cold rolling and aging. It suggests that the treatment route with an order of aging followed by cold rolling (ACR) is better than that with the order of cold rolling with aging (CRA). The ultimate tensile strength 568 MPa and electrical conductivity 75.3%IACS are obtained after aging at 450 °C for 3 h followed by 80% cold rolling at room temperature. The high electrical conductivity and ductility is attributed to twin lamellar structure.

Microstructural evolution and wear performance of the high-entropy FeMnCoCr alloy/TiC/CaF2 self-lubricating composite coatings on copper prepared by laser cladding for continuous casting mold

Abstract

Investigations on diffusion behaviors in Ti–rich Ti–Nb–Zr–Cr system: Experimental measurement and CALPHAD modeling

Accurate diffusivities are essential for the design and production of biomedical alloys with excellent properties. In the present work, ternary and quaternary interdiffusion behaviors in Ti–rich Ti–Nb–Cr, Ti–Zr–Cr and Ti–Nb–Zr–Cr systems at 1273 K were experimentally investigated via the diffusion couple technique. Ternary interdiffusivities of bcc Ti–Nb–Cr alloys were then determined using the Matano–Kirkaldy method. Subsequently, on the basis of the presently obtained interdiffusivities together with the diffusivity and mobility parameters of Ti–Nb–Zr–Cr sub–binary and sub–ternary systems and the thermodynamic descriptions for bcc Ti–Nb–Zr–Cr system, the atomic mobilities of Ti,Nb, Zr and Cr in bcc Ti–Nb–Zr–Cr alloys were assessed by means of CALPHAD (CALculation of PHAse Diagrams) method. Moreover, the comprehensive comparisons between the experimental diffusion properties of bcc Ti–Nb–Cr, Ti–Zr–Cr and Ti–Nb–Zr–Cr systems (i.e., interdiffusivities, composition profiles, interdiffusion fluxes and diffusion paths) and the calculated/model–predicted data due to the present atomic mobilities were conducted in order to verify the reliability of the mobilities. The present atomic mobilities for bcc Ti–Nb–Zr–Cr system can provide the accurate ternary and quaternary interdiffusivity matrices over a wide composition range.

Interaction of (Ti, Cr)B2-Based Composites with a Nickel Alloy

The paper examines how the Ni–Zr–Cr alloy wets (Ti, Cr)B2, AlN, (Ti, Cr)B2–AlN, and AlN–(TiB2–TiSi2) refractory materials. The wetting of (Ti, Cr)B2 leads to near-zero contact angles. The introduction of AlN additions deteriorates wetting of the refractory materials by the nickel alloy, and the Ni–Zr–Cr alloy does not wet pure aluminum nitride. There is insignificant diffusion of Zr to (Ti, Cr)B2 in contact of the alloy with the refractory materials. There is no interaction in the AlN–(Ni–Zr–Cr) system. The composite materials are promising for use in contact with high-temperature corrosive alloys.

Transient creep behavior and dislocation cell structure development during creep-fatigue deformation of fully annealed Cu–Cr–Zr alloy

Creep-fatigue tests of Cu–0.7Cr–0.09Zr (mass%) alloy, which include stress-holding-type creep and strain-controlled fatigue, were conducted at elevated temperatures. A simple creep test was also carried out in order to compare the results with the results of the creep-fatigue test. The creep strains accumulated during creep deformation in creep-fatigue and simple creep tests were 310% and 12%, respectively. Such a large difference was due to the stacking of normal/inverse-transient creep in the creep-fatigue test. A dislocation cell structure smoothly developed in the simple creep test, whereas the cell intermittently developed in the creep-fatigue test because compressive plastic deformation immediately after creep partly broke apart the cell walls and prevented the cell structure from smoothly developing. Compressive stresses necessary for −1.5% strain were changed as cycling progressed in the creep-fatigue test. A much higher compressive stress would introduce a much higher dislocation density immediately before creep deformation. At the start of creep, these dislocations recovered and their number gradually decreased, which resulted in the appearance of inverse-transient creep.

Effect of High Strain-Rate Deformation and Aging Temperature on the Evolution of Structure, Microhardness, and Wear Resistance of Low-Alloyed Cu–Cr–Zr Alloy

The effect of the preliminary high strain-rate deformation, performed via the method of dynamic channel-angular pressing (DCAP), and subsequent annealings on the tribological properties of a dispersionhardened Cu–0.092 wt % Cr–0.086 wt % Zr alloy has been investigated. It has been shown that the surfacelayer material of the alloy with a submicrocrystalline (SMC) structure obtained by the DCAP method can be strengthened using severe plastic deformation by sliding friction at the expense of creating a nanocrystalline structure with crystallites of 15–60 nm in size. It has been shown that the SMC structure obtained by the high strain-rate DCAP deformation decreases the wear rate of the samples upon sliding friction by a factor of 1.4 compared to the initial coarse-grained state. The maximum values of the microhardness and minimum values of the coefficient of friction and shear strength have been obtained in the samples preliminarily subjected to DCAP and aging at 400°С. The attained level of microhardness is 3350 MPa, which exceeds the microhardness of the alloy in the initial coarse-grained state by five times.

Heat treatment effects on the microstructure and properties of Cu–Cr–Zr alloy used for the ITER blanket components

Cu–Cr–Zr bronze is used as a heat sink for enhanced heat flux first wall components and structural material for blanket module connectors of ITER. The solution annealing at 980 °C for 0.5 h, water quench and ageing at 475 °C for 3 h is specified as a reference heat treatment for ITER. The proper heat treatment is provided the better performance taking into account for various structural elements operating under different conditions. However, the actual manufacturing cycle might be different from the recommended one. As the result, heat treatment effects on the properties of Cu–Cr–Zr bronze might be different from that one specified in the ITER documentation. Thus, the effect of various types of heat treatment (in particular the parameters of aging) on the Cu–Cr–Zr alloy's properties is a very important. This paper deals with the investigation of heat treatment effects during aging at a temperature range of 350–750 °C and aging time from 5 to 180 min on the structure and physical-mechanical properties of Cu–Cr–Zr bronze.

Influence of high pressure torsion-induced grain refinement and subsequent aging on tribological properties of Cu-Cr-Zr alloy

Effects of ultrafine grain formation via high pressure torsion (HPT) and precipitation during aging on the microstructure, mechanical and tribological properties of a Cu-Cr-Zr alloy have been investigated systematically. HPT results in the formation of ultrafine-grained (UFG) structure in the alloy with an average grain/subgrain size of 155 nm which leads to remarkable improvement in its hardness and strength along with a reduction in elongation to failure. Aging of UFG alloy brings about further strengthening due to the precipitation. UFG formation by HPT increases substantially the wear resistance of Cu-Cr-Zr alloy and reduces the friction coefficient. The highest wear resistance and the lowest friction coefficient are obtained on the sample processed by HPT and subsequent aging. The dominant wear mechanism of the alloy varies depending on the applied processes. Adhesion with smearing is the predominant wear mechanism for the initial (warm extruded) samples having coarse-grained (CG) structure. UFG samples show less adhesional effect with less smearing, and a higher tendency to the formation of cracks, abrasion and delamination seem to be dominant in those samples. Oxidative wear mechanism is also operative in both CG and UFG alloy samples. It may be concluded from this study that a combined process including UFG formation by HPT and subsequent precipitation by artificial aging provides a simple and effective processing procedure for improving the strength, hardness and wear resistance of Cu–Cr–Zr alloys without modification of the chemical composition.

Structure and orientation relationship of new precipitates in a Cu–Cr–Zr alloy

ABSTRACTThe crystallography and morphology of the nano-sized precipitate particles in a ternary Cu–Cr–Zr alloy were studied by transmission electron microscopy. A new type of face-centred-cubic (f.c.c) Cr-rich precipitate was observed. This precipitate is ordered and solute enriched on alternate {110} f.c.c planes, with an ellipsoid-shaped morphology. The new orientation relationship (OR) between the precipitate and Cu matrix satisfies [211]M//[011]p and [100]M//[111]p, {-111}M//{200}p and {02-2}M//{02-2}p. The difference between this new OR and the Nishiyama–Wasserman OR between body-centred-cubic (b.c.c) Cr and the Cu matrix can be detailed by Δg vectors in the diffraction patterns. Furthermore, the precipitation strengthening effect is increased greatly with the formation of these new precipitate particles when compared to binary Cu–Cr alloys.

The formation of friction-induced nanocrystalline structure in submicrocrystalline Cu–Cr–Zr alloy рrocessed by DCAP

The effect of high strain-rate (100000 s-1) deformation by the method of dynamic channel-angular pressing (DCAP), annealing and quasi-static severe plastic deformation (SPD) by sliding friction on the evolution of structure and properties of a low-alloyed dispersion-hardened Cu–Cr–Zr alloys have been investigated. It is shown that the alloying of copper with chromium (0.09–0.14%) and zirconium (0.04–0.08%) microadditions changes the mechanisms of submicrocrystalline (SMC) structure formation and elastic energy relaxation during DCAP: a cyclic character of structure formation due to alternation high-rate processes of fragmentation and dynamic recrystallization, is changed by the processes of fragmentation and partial strain aging with the precipitation of second-phase nanosized particles. The temperature-time annealing (aging) conditions of Cu-Cr-Zr SMC alloys obtained by DCAP for improvement of mechanical properties and electrical conductivity was established. In particular, for the Cu-0.14Cr-0.04Zr SMC alloy, it has been shown that the optimal combination of microhardness (HV=1880 MPa), electrical conductivity (80% IACS) and strength (σ0.2=464 MPa, σu =542 MPa) at retaining satisfactory plasticity was obtained by treatment: DCAP+400°C, 1 h. The increased level of mechanical properties of alloys, compared to copper, is associated with additional strengthening due to precipitation of nanoparticles (5-10 nm) of the Cu5Zr and Cr during DCAP and aging. It has been shown that the low-alloyed Cu–Cr-Zr alloys possess a high ability to strengthen via the methods of DCAP and SPD by sliding friction. It has been determined based on the example of Cu–0.09Cr–0.08Zr alloy that the wear rate of samples with the SMC structure obtained by the DCAP method decreases by a factor of 1.4 compared to coarse-grained state. It was established that the combined treatment DCAP + 400°С + SPD by friction of the alloy gives rise to the friction-induced NC structure with grains 15– 60 nm in size in the surface-layer material, which provides a high level of the microhardness (3350 MPa) and satisfactory tribological properties.

Grain Refinement Kinetics in a Low Alloyed Cu-Cr-Zr Alloy Subjected to Large Strain Deformation.

This paper investigates the microstructural evolution and grain refinement kinetics of a solution-treated Cu–0.1Cr–0.06Zr alloy during equal channel angular pressing (ECAP) at a temperature of 673 K via route BC. The microstructural change during plastic deformation was accompanied by the formation of the microband and an increase in the misorientations of strain-induced subboundaries. We argue that continuous dynamic recrystallization refined the initially coarse grains, and discuss the dynamic recrystallization kinetics in terms of grain/subgrain boundary triple junction evolution. A modified Johnson–Mehl–Avrami–Kolmogorov relationship with a strain exponent of about 1.49 is used to express the strain dependence of the triple junctions of high-angle boundaries. Severe plastic deformation by ECAP led to substantial strengthening of the Cu–0.1Cr–0.06Zr alloy. The yield strength increased from 60 MPa in the initial state to 445 MPa after a total strain level of 12.

Grain Refinement and Mechanical Properties of Cu-Cr-Zr Alloys with Different Nano-Sized TiCp Addition.

The TiCp/Cu master alloy was prepared via thermal explosion reaction. Afterwards, the nano-sized TiCp/Cu master alloy was dispersed by electromagnetic stirring casting into the melting Cu–Cr–Zr alloys to fabricate the nano-sized TiCp-reinforced Cu–Cr–Zr composites. Results show that nano-sized TiCp can effectively refine the grain size of Cu–Cr–Zr alloys. The morphologies of grain in Cu–Cr–Zr composites changed from dendritic grain to equiaxed crystal because of the addition and dispersion of nano-sized TiCp. The grain size decreased from 82 to 28 μm with the nano-sized TiCp content. Compared with Cu–Cr–Zr alloys, the ultimate compressive strength (σUCS) and yield strength (σ0.2) of 4 wt% TiCp-reinforced Cu–Cr–Zr composites increased by 6.7% and 9.4%, respectively. The wear resistance of the nano-sized TiCp-reinforced Cu–Cr–Zr composites increased with the increasing nano-sized TiCp content. The wear loss of the nano-sized TiCp-reinforced Cu–Cr–Zr composites decreased with the increasing TiCp content under abrasive particles. The eletrical conductivity of Cu–Cr–Zr alloys, 2% and 4% nano-sized TiCp-reinforced Cu–Cr–Zr composites are 64.71% IACS, 56.77% IACS and 52.93% IACS, respectively.

Effect of Fe on microstructures and mechanical properties of an Al–Mg–Si–Cu–Cr–Zr alloy prepared by low frequency electromagnetic casting

The effects of different Fe contents (0.168, 0.356 and 0.601 wt%) on microstructures and mechanical properties of the Al–1.6Mg–1.2Si–1.1Cu–0.15Cr–0.15Zr (all in wt%) alloys prepared by low frequency electromagnetic casting process were investigated in the process of solidification, hot extrusion, solid solution and aging treatments. The results show that the increase of Fe content promotes the formation of feathery grains in the process of solidification and the precipitation of another important strengthening phase Q′ with small size. Additionally, it also results in no recrystallization even after solid solution at a high temperature of 550 °C, which is because of the increase number of elliptical shaped and fine DO22-Al3Zr dispersoids (∼70 nm long and ∼35 nm wide) and the spherical or elliptical shaped Fe-containing phases. When Fe content of the alloy increases to 0.356 wt%, both the ultimate tensile strength and yield strength of the alloy-T6 increase by more than 60 MPa and with little cost of ductility.

Phase transformations in rapidly quenched Al–Cr–Zr alloys during heat treatment

Results from studying the effect zirconium has on solid-phase processes in aluminum–chromium alloys are presented. Rapidly quenched alloys are prepared via melt spinning. The quenching rate is ~106 K/s. By means of physicochemical analysis, it is shown that doping Al–Cr alloys with zirconium improves the thermal stability of supersaturated solid solutions and stabilizes their microcrystalline structure; this hinders the coagulation of intermetallic phases and thus improves the hardness of the alloys. It is found that supersaturated solid solutions of Cr and Zr in aluminum undergo stepwise decomposition; the temperature and time parameters of each step are shown in TTT diagrams.

Physical properties of molten core materials: Zr-Ni and Zr-Cr alloys measured by electrostatic levitation

It is important to understand the behaviors of molten core materials to investigate the progression of a core meltdown accident. In the early stages of bundle degradation, low-melting-temperature liquid phases are expected to form via the eutectic reaction between Zircaloy and stainless steel. The main component of Zircaloy is Zr and those of stainless steel are Fe, Ni, and Cr. Our group has previously reported physical property data such as viscosity, density, and surface tension for Zr-Fe liquid alloys using an electrostatic levitation technique. In this study, we report the viscosity, density, and surface tension of Zr-Ni and Zr-Cr liquid alloys (Zr1-xNix (x = 0.12 and 0.24) and Zr0.77Cr0.23) using the electrostatic levitation technique.

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 0.5 were obtained. When the true strain was 0.5, greater power dissipation efficiency was observed at 800–850 °C and under 0.001–0.1 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.

Damage propagation mechanism in low-cycle creep fatigue of Cu–Cr–Zr alloy

This paper describes a characteristic damage propagation mechanism in low-cycle creep–fatigue of Cu–0.7Cr–0.09Zr (mass%), as investigated by creep–fatigue tests including strain controlled fatigue and stress-holding type creep, and following microstructural observations by scanning electron microscopy (SEM). The total stress-holding time until rupture in the creep–fatigue test was shorter than one-tenth of the rupture life in the simple creep test, and the rupture life of the specimen in the creep–fatigue test was shorter than half of that in the simple fatigue test. The SEM images suggest that the connection between fatigue crack propagating along grain boundaries and intergranular creep voids rapidly accelerates crack propagation.