Cu-Cr Alloys Research Articles

Effect of Hard Cyclic Viscoplastic Deformation on the Microstructure, Mechanical Properties, and Electrical Conductivity of Cu-Cr Alloy

Effect of Hard Cyclic Viscoplastic Deformation on the Microstructure, Mechanical Properties, and Electrical Conductivity of Cu-Cr Alloy

Effects of Cr content and electromagnetic stirring on the phase separation of Cu-Cr alloy

The Cu-Cr immiscible alloys were prepared by arc melting. The effects of Cr addition and electromagnetic stirring on the phase separation, microstructure were examined. The results show that serious phase segregation occurs at the center of the sample with increasing Cr contents, forming a sandwich like structure. The shape of the primary Cr transforms from fine dendrite to more developed dendrite. Thermodynamic analysis indicates that Cr addition increases the driving force for the liquid phase separation. The electromagnetic stirring can facilitate elative motion between the Cr droplets and the melts, and thus intensify the segregation phenomenon. With Cr additions, the hardness in non-segregated area shows only slight increase, and in Cr segregated area shows a significant increase. While the electrical conductivity shows only slight decrease with increasing Cr content.

Microstructure and properties of Cu-Cr-Ti alloy with high softening resistance

Abstract Cu-Cr alloys with excellent mechanical and electrical properties have been used in many industrial fields. However, the weak heat resistance of Cu-Cr alloys is a considerable shortness. In this work, Cu-Cr-Ti alloy was fabricated by vacuum melting and plastic deformation. Mechanical property and electrical conductivity of Cu-Cr-Ti alloy were investigated after aging treatment. The results show that peak aging occurs when aging at 450 °C for 1 hour. The mechanism of performance changes are discussed. The softening temperature could be identified as 575 °C, according to percentage of hardness changes of peak-aged Cu-Cr-Ti alloy annealed at different temperature and time. The microstructure explained that the addition of Ti, which retards recrystallization, could enhance the softening resistance of Cu-Cr alloy.

Microstructure and softening resistance of Cu-Cr-Ag alloy

Abstract In this paper, Cu-0.5Cr and Cu-0.5Cr-0.1Ag alloys were used as experimental materials to test the softening resistance of the alloys. The results show that the addition of Ag can improve the hardness and softening temperature of the Cu-Cr alloy, and has little effect on the conductivity. The softening resistance temperature of Cu-0.5Cr-0.1Ag alloy is 575 °C, which is 25 °C higher than that of Cu-0.5Cr alloy. The softening process of the alloy is accompanied by grain recovery, recrystallization and coarsening. Ag atom improves the recrystallization activation energy of copper alloy and delays the recrystallization and recrystallization grain growth in the softening process. Recrystallization is the main factor leading to the softening of the alloy.

Nanocompound-induced anti-softening mechanisms: Application to CuCr alloys

A nanocompound-induced anti-softening mechanism is proposed for preparing high strength and high conductivity CuCr alloys with favorable softening resistance. The mechanism is to introduce nanocompound at the Cu/Cr interface to suppress the coarsening of Cr precipitate. To verify the mechanism, Co and Ti are added to the CuCr alloy. CoTi compounds precipitate around the Cr precipitates after aging treatment. The coarsening of Cr and CoTi phases are both suppressed thanks to the low diffusion rates of Co and Ti atoms in Cu. Additionally, Cr and CoTi precipitates also inhibit the recrystallization. As a result, the CuCrCoTi alloy displays a higher softening temperature (>600 °C) than CuCr alloys.

Optimizing the Electrical and Mechanical Properties of Cu-Cr Alloys by Hf Microalloying

Cu-0.4Cr (wt.%) alloys with the microalloying of Hf elements were subjected to a modified rolling–aging process to achieve high strength, high electrical conductivity and high ductility simultaneously. Transmission electron microscopy and X-ray line broadening analysis were conducted to characterize the microstructures of these alloys. Deformation twins and high-density dislocations were introduced into the copper alloys via the modified rolling–aging process and the microalloying of Hf, improving the mechanical properties of copper alloys. The Cu-Cr-Hf alloy with a reduced Hf content performed well in terms of strength, electrical conductivity and ductility. The microalloying of 0.4 wt.% Hf in the Cu-0.4Cr alloy was sufficient to achieve a good combination of high tensile strength (593 MPa), high uniform elongation (~5%) and high electrical conductivity (80.51% IACS).

Interfacial Phenomena and Microstructure of Copper/Steel Bimetal Structure Produced by a New Hybrid Additive Manufacturing Process Combining Selective Laser Melting and Directed Energy Deposition

As a novel exploration, the hybrid additive manufacturing (AM) process combining selective laser melting (SLM) and directed energy deposition (DED) was used to produce a copper/steel bimetal structure in this paper. Stainless steel was deposited on the SLMed Cu-Cr alloy substrate successfully by DED. The interfacial phenomena, microstructure, and forming mechanism were investigated systematically. The Cu element of the substrate flowed up due to the Marangoni flow, and liquid phase separation occurred during the process. This work indicates that the microstructure and morphology between the cladding layer of steel and Cu-Cr substrate are significantly influenced by the laser power.

In-situ observation of damage structure in Cu-Cr-Zr and Cu-Cr alloy during 1.25 MeV electron irradiation

The sink strengths of precipitate/matrix interfaces in Cu alloys, were investigated by performing in-situ observation of electron irradiation in high-voltage electron microscopy (HVEM). Fine black spot defects, which seemed to be dislocation loops were observed at irradiation temperature ranging between RT and 373 K in Cu–Cr–Zr, Cu–Cr and GlidCop Al–60 alloys with low number density. In Cu–Cr, loops formed on a part of precipitates interfaces. Hence, a part of precipitate/matrix interfaces is a sink with interstitial bias. Whereas, most of the interfaces are neutral sinks for point defects. In the case of Cu–Cr–Zr and GlidCop Al–60, black spots formed around dislocation, which were induced during two-step heat treatment. The results showed that the precipitate/matrix interface of Cr-rich precipitates in Cu alloys serve as a strong sink for point defects.

Effects of Y addition on the microstructure, properties and softening resistance of Cu-Cr alloy

The effects of Y content on the microstructure and properties of Cu-0.9Cr and Cu-1.45Cr alloys were investigated systematically in present manuscript. Cu-Cr-(Y) alloys were prepared by vacuum melting and casting, solid solution treatment at 960 °C, (90% cold rolling) and aging treatment at 460 °C. The results indicate that the addition of 0.1 wt% Y refines the eutectic structure of as-cast Cu-0.9Cr and Cu-1.45Cr alloys. Besides, the hardness of Cu-Cr-(Y) alloys after solid solution treatment increases with the increase of the Y content. CRA (cold-rolling and aging) process can enhance the hardness of peak-aged alloys compared with SSA (solid solution and aging), the peak-aged hardness and corresponding conductivity of cold-rolled alloys slightly increase by addition of Y. Especially, when CRA for 300 min, the ultimate tensile strength, hardness of Cu-0.95Cr-0.1Y alloy (433 MPa, 146.8 HV) are superior to those of Cu-0.9Cr alloy (333 MPa, 102 HV), indicating that addition of Y significantly inhibits the over-aging during CRA. The TEM results reveal that Cr precipitates of FCC and BCC structures exist in the Cu-Cr-Y alloy aged for 300 min, and Y element suppresses the coarsening of Cr precipitates and the reduction of dislocation density. Moreover, the softening temperature of peak-aged Cu-Cr-Y alloys is ~70 °C higher than that of Cu-Cr alloys since the addition of Y inhibits the coarsening of Cr precipitates.

Study of Hypervelocity Impingement for Cu Nanoparticles on CuCr Alloy Target Electrodes in Initiating Vacuum Breakdown

The metal particles in vacuum gaps with a strong electric field would be accelerated to hypervelocity and impinge on target electrodes, which could trigger electric breakdown in the vacuum gaps. The objective of this article is to study the hypervelocity impingement phenomena between Cu nanoparticles and CuCr alloy target electrodes based on molecular dynamics (MD) method. The impingement phenomena in the cases of Cu nanoparticle and Cu target, Cu nanoparticle and Cr target, Cu nanoparticle and CuCr interface target with the impact velocities 5, 8, and 10 km/s are studied, respectively. Furthermore, the various effects associated with the hypervelocity impingement and their significance on vacuum breakdown are also discussed. The results show that the impingement could cause severe plastic deformation and thermal ionization on the impacting materials, deform a crater on the target, and release a cloud of metal vapor and ejection of secondary particles in the vacuum gap and it would lead to the vacuum breakdown. The impact materials and the impact velocities would have significant influence on the impingement phenomena and even on the vacuum breakdown initiated by the impingement.

Effect of Scanning Speed on Properties of Laser Surface Remelting Layer of CuCr Alloy

Effect of Scanning Speed on Properties of Laser Surface Remelting Layer of CuCr Alloy

Analysis of Micro Arc Plasma Characteristics of the Mixed Metal Vapor in Vacuum Circuit Breaker

For the mechanical vacuum circuit breaker, the particle composition group of the metal vapor arc varies with different operating conditions, which will lead to the discontinuous variation of the electrical conductivity between electrodes. The change of mixed metal vapor arc macroscopic electrical characteristics results from the space-time change of microscopic arc plasma characteristics. For the vacuum circuit breaker, the interruption performance is directly influenced by the composition of the metal vapor arc plasma and the characteristic parameters. For evaluating the electrode characteristics and establishing a database of mixed metal vapor arc characteristic parameters for the vacuum interrupter, this paper presents a study of the copper chromium (CuCr) alloy contacts used in vacuum circuit breakers. The Eindhoven model was used to derive a Local Thermodynamic Equilibrium (LTE) vacuum arc plasma particle composition model. The thermodynamic parameter variation of metal vapor arc plasma is calculated by statistical thermodynamic method, and the electrical conductivity was calculated by Chapman-Enskog method. The mass density, enthalpy, specific heat and electrical conductivity for different alloy proportion (CuCr25, CuCr40, CuCr50, CuCr60 and CuCr75) were compared and quantitatively characterized.

Experimental investigation on the erosion behavior in high-current vacuum arcs and resulting microparticles dynamics

Microparticles are an inevitable component of vacuum arcs. This paper focused on the dynamics of microparticle and erosion behavior in high-current vacuum arcs. The arc was sustained with AC 110 Hz between two butt CuCr alloy contacts with a diameter of 10 mm. An in situ microparticle diagnostic system suitable for vacuum arcs was developed. Three sources of microparticles were observed and the corresponding motion characteristics were obtained by our method. The influence of current and Cr content on erosion characteristics was investigated. The results indicate that the increase of Cr content contributes to inhibiting production of microparticles when the current is small. CuCr30 has the best effect of suppressing microparticle production among the three tested alloy materials under large current. The work of this paper helps with the understanding of microparticle behavior in high-current vacuum arcs and may provide a path for the design of a vacuum electrode.

Effect of Cr@RGO structure on microstructure and properties of RGO/CuCr25 composite

CuCr alloy with high Cr content (20–50 wt.%) is the main contact material for medium voltage and high current vacuum interrupters. However, the influence of network distribution of Cr particles affect the conductivity of CuCr alloy, and its properties strongly depend on the size of Cr particles. In this paper, Cr@RGO (Cr powder coated with reduced GO) was prepared by BSA (bovine serum protein) electrostatic assembly method, and then RGO/CuCr composites with different graphene content were prepared by vacuum hot pressing sintering process. The results show that the size of Cr particles decreases with the increase of graphene content and the network of Cr particles became fractured. When the content of RGO is 3.0 wt.%, the size of Cr phase is 19.9 μm, which is 23.8% less than that of CuCr25 of 26.1 μm. The Brinell hardness and electrical conductivity of 3.0 wt.% RGO/CuCr composite are 102.5 HB and 52.9% IACS, which is increased by 8% and 6% in contrast with that of CuCr25. And the Preparation of RGO/CuCr is simple, feasible, replicable and easy to achieve the goal of the industrial preparation.

Arc erosion resistance of CuCrMo films deposited via magnetron sputtering

Copper-chromium (CuCr) alloys are widely used as electrical contact materials, and their arc erosion resistance can be improved by reducing the sizes of the Cu and Cr phases or by adding Mo. In this study, supersaturation solid solutions of CuCr and CuCrMo films were prepared via magnetron sputtering. After annealing at 773 K, the CuCr and CuCrMo films are composed of a small Cu-rich face-centred cubic phase and a Cr-rich body-centred cubic phase. Meanwhile, the addition of Mo reduces the diffusion rate during annealing. The lattice distortion of the CuCrMo thin film exceeds that of the CuCr film, and the elastic modulus and hardness increase. Compared with those of the CuCr film, the erosion area of the CuCrMo film is larger, and the depth of the erosion pit is lower. The arc erosion experiment proved that CuCrMo films exhibit satisfactory arc erosion resistance.

Mechanical alloying of the immiscible Cu-60wt%Cr alloy: Phase transitions, microstructure, and thermodynamic characteristics

Solid state alloying of immiscible alloy systems such as Cu-Cr is an important field of physical metallurgy. Currently, non-equilibrium techniques are successfully applied in the synthesis of Cu-Cr alloys; however, the mechanism of formation of these alloys remains unclear due to the unavailability of data regarding their microstructure evolution and thermodynamic characteristics. In this work, a mechanical alloying (MA) Cu-60wt%Cr alloy is prepared by high-energy milling. The phase transitions, thermodynamic properties, and microstructure of this alloy are analyzed using X-ray diffraction, differential scanning calorimetry, and transmission electron microscope techniques. The obtained results demonstrate that the supersaturated Cr(Cu) solid solution alloy has a supra-nanometer-sized microstructure and is composed of crystalline and amorphous phases. To form the alloy, the localized Cu is first transformed into an amorphous state, then the disordered Cu atoms diffuse into the Cr matrix during the MA process. The diffusivity of Cr atoms in the Cu lattice is significantly hindered, even when the lattice is heavily defected.

Mechanism investigation on high-performance Cu-Cr-Ti alloy via integrated computational materials engineering

In this work, the influence of different Ti additions on microstructure and property in Cu-Cr alloys has been studied and the primary relationship of processing-microstructure-property in Cu-Cr-Ti alloy has been constructed via the CALPHAD-based Integrated Computational Materials Engineering (ICME) approach and experimental validation. The peak-aged Cu-0.5Cr-0.2Ti alloy offers an excellent combination of hardness 192.6 HV, tensile strength 629.3 MPa, yield strength 603.0 MPa, electrical conductivity 51.3 %IACS and elongation 10.9 %. The calculated results suggest that the addition of Ti could promote the nucleation and hinder the growth of Cr precipitate in Cu-Cr-Ti alloys during aging treatment, which may promote the homogeneous formation of small-size precipitate Cr and improve the strength of the Cu-Cr alloy. Microstructural characterization has validated the calculation results and revealed that the exceptional properties of this alloy are mainly attributed to nano-scale Cr precipitates achieved through the optimal thermomechanical processing from present ICME. Thus, the present ICME flowchart is applicable to design alloy composition and optimize the processing for the desired microstructure and property in engineering industries.

Interfacial characteristics and mechanical properties of additive manufacturing martensite stainless steel on the Cu-Cr alloy substrate by directed energy deposition

Copper/steel is a typical bimetal functional material, combining the excellent electrical and thermal conductivity of copper alloy and the high strength and hardness of stainless steel. There has been recent interest in manufacturing copper/steel bimetal by directed energy deposition (DED) due to its layer-by-layer method. However, cracks tend to form on the copper/steel interface because of the great difference in thermal expansion coefficient and crystal structure between copper and steel. In this work, interfacial characteristics and mechanical properties of the copper/steel bimetal were studied from one layer to multilayers. The laser power has a great influence on the Cu element distribution of the molten pool, affecting the crack formation dramatically on the solidification stage. Cracks tend to form along columnar grain boundaries because of the Cu-rich liquid films and spherical particles in the cracks. Crack-free and good metallurgical bonding copper/steel interface is formed at a scanning velocity of 800 mm/min and the laser power of 3000 W. The ultimate tensile strength (UTS) and the break elongation (EL) of the vertically combined crack-free copper/steel bimetal are 238.2 ± 4.4 MPa and 20.6 ± 0.7%, respectively. The fracture occurs on the copper side instead of the copper/steel interface, indicating that the bonding strength is higher than that of the Cu-Cr alloy. The UTS of the horizontally combined crack-free copper/steel bimetal is 746.7 ± 22.6 MPa, which is 200% higher than that of the Cu-Cr alloy substrate. The microhardness is 398.6 ± 5.4 HV at the steel side and is 235.3 ± 64.1 HV at the interface, which is 400% higher than that of the Cu-Cr alloy substrate. This paper advances the understanding of the interfacial characteristics of heterogeneous materials and provides guidance and reference for the fabrication of multi-material components by DED.

Improving the mechanical performance of Cu[sbnd]Cr alloy by dissolving Cu in the Cr second phase

The strengthening effects of Cr on CuCr alloys are severely limited due to the relatively low solid solubility of Cr in Cu phase. Apart from the dissolved Cr, it should be noted that a high proportion of Cr in Cu matrix work as the second phase dispersion strengthening. To effectively improve the strengthening effect of Cr in CuCr alloys, it is important to enhance the dispersion strengthening effect of the second phase Cr. In this work, the Cr phase could be strengthened by dissolving Cu atoms through the levitation melting method (LM), without additional alloying element was introduced. The results show that a maximum of Cu (0.46-0.54 wt%) is dissolved into Cr phase in Cu2Cr98 and Cu5Cr95 alloys. The corresponding hardness is 38% and 56% higher for Cu2Cr98 and Cu5Cr95 alloys compared with pure Cr, respectively. This novel strengthening mechanism of the enhanced Cr second phase is further applied in CuCr25 alloys. It is confirmed that the hardness is 57% higher for CuCr25 with enhanced Cr phase than that prepared using conventional methods. Furthermore, the significant strengthening effect is confirmed in the tribological properties. This strategy can be utilized to effectively enhance the mechanical performance of CuCr alloys with high Cr content.

Tailoring the thermal and mechanical properties of diamond/Cu composites by interface regulation of Cr alloying

Copper matrix composites reinforced with 60 vol% diamond particles were prepared by pressure infiltration using Cu-Cr alloy with 0.3–1.0 wt% Cr. The x-ray diffraction, scanning electron microscopy, and transmission electron microscopy were conducted to characterize the Diamond/Cu composites interface. The interface structure evolves from the discontinuous point contact to continuous strip carbides depending on the availability of Cr source. With Cr content increasing, the thermal conductivity of the Diamond/Cu-Cr composites increases first and then decreases. The highest thermal conductivity of 696 W/mK was achieved at 0.5 wt% Cr addition, while the highest tensile strength and bending strength of 252 MPa and 523 MPa were achieved at 0.7 wt% Cr addition. By optimizing the interface thermal resistance and interface bonding strength, Diamond/Cu composites with excellent comprehensive properties can be obtained.