Effect of cerium on microstructure,texture and properties of ultrahigh-purity copper

The effects of Ce addition(310 ppm and 1500 ppm)on the microstructure,texture and properties of ultrahigh-purity copper(99.99999%)were systematically studied using scanning electron microscopy(SEM),transmission electron microscopy(TEM)and electron backscattered diffraction(EBSD)analyses,combined with the microhardness and conductivity tests.Regarding the microstructure of the as-cast and as-extruded samples,the addition of Ce refines the grain size of the ultrahigh-purity copper and the refinement effect of 310Ce alloy is greater than that of 1500Ce alloy.This is due to the stronger compone nt supercooling and the accele rated recrystallization caused by lower Ce co ntent.In addition,Ce can react with Cu to form the Cu-Ce eutectic phases,which are deformable during the hot deformation.Furthermore,the added Ce can weaken the texture,showing a variation of brass recrystallization(BR),rotated cube,copper and S texture components,which depends on the recrystallization,the particle stimulated nucleation(PSN)as well as the stacking fault energy(SFE).Most remarkably,the introduction of Ce enhances the hardness of the ultrahigh-purity copper without obviously reducing its conductivity.The major{111}orientations and the stress distributions are responsible for such a superior conductivity of the Ce-containing alloys.

Triboelectric behaviors of materials under high speeds and large currents

Using special testers,the triboelectric behaviors of several materials were investigated in this paper under the conditions of high speeds and large currents.The obtained results revealed that the tribological behaviors and current-conducting characteristics have complicated interrelationships.Worsening in the servicing conditions can obviously deteriorate the tribological as well as electrical behaviors;high sliding speeds and large electrical currents can worsen the tribological and electrical conductivity properties,while an appropriate contact pressure can benefit the electrical contact properties.Further analyses reveal that the worsening effects of the above factors,such as frictional heat,arc discharge,arc heat,and surface morphology,result in poor triboelectric contact performance.Among these,the electric arc is one of the most serious factors,because the occurrence of an electric arc may cause severe oxidation,melting,and roughening of the contact surface,thereby causing deterioration in the current-conducting quality as well as material loss.

Graphene oxide effects on the properties of Al2O3-Cu/35W5Cr composite

Graphene oxide(GO)nanosheets were dispersed into premixed powders(Cu-0.4 wt%Al/35W5Cr)by wet grinding and vacuum freeze-drying process.The 0.3 wt%GO/Al2O3-Cu/35W5Cr and 0.5 wt%GO/Al2O3-Cu/35W5Cr composites,used for electrical contacts,were fabricated by vacuum hot-pressing sintering.The microstructure was analyzed by field emission scanning electron and transmission electron microscopy.In addition,the Raman spectroscopy and X-ray photoelectron spectroscopy were used to investigate the structural changes of GO before and after sintering.The arc erosion behavior was investigated by the JF04 C electrical contact testing apparatus.Consequently,the Al2O3 nanoparticles were evenly dispersed in the matrix,causing dislocation tangles.GO was converted to reduced graphene oxide after sintering.A group of carbon atoms combined with Cr forming Cr3C2 in situ during sintering,which enhanced the interface bonding.Compared with the Al2O3-Cu/35W5Cr composite,the tensile strength of the two contact materials containing 0.3 wt%GO and 0.5 wt%GO was increased by 45%and 34%,respectively.Finally,pips and craters were present on the anode and cathode surfaces,respectively.Tungsten has undergone re-sintering during arcing and formed needle-like structures.Compared with Al2O3-Cu/35W5Cr,the GO/Al2O3-Cu35W5Cr composites have better welding resistance.The final mass transfer direction of the two composites was from the cathode to anode.

Effects of strain rates on dynamic deformation behavior of Cu-20Ag alloy

Copper alloy is widely used in high-speed railway,aerospace and other fields due to its excellent electrical conductivity and mechanical properties.High speed deformation and dynamic loading under impact load is a complex service condition,which widely exists in the field of national defense,military and industrial application.Therefore,the dynamic deformation behavior of the Cu-20Ag alloy was investigated by Split Hopkinson Pressure Bar(SHPB)with the strain rates of 1000-25000 s^(-1),high-speed hydraulic servo material testing machine with the strain rates of 1-500 s^(-1).The effect of strain rate on flow stress and adiabatic shear sensitivity was analyzed.The results show that the increase of strain rate will increase the flow stress and critical strain,that is to say,the increase of strain rate will reduce the adiabatic shear sensitivity of the Cu-20Ag alloy.The Cu-Ag interface has obvious orientation relationship with;(111)_(Cu)//(111)_(Ag):(^(-)111)_(Cu)//(^(-)111)_(Ag):(^(-)200)_(Cu)//(^(-)200)_(Ag) and [0^(-)11]_(Cu)//[0^(-)11]_(Ag) with the increase of strain rate.The increase of strain rate promotes the precipitation of Ag and increases the number of interfaces in the microstructure,which hinders the movement of dislocations and improves the stress and yield strength of the Cu-20Ag alloy.The concentration and distribution density of dislocations and the precipitation of Ag were the main reasons improve the flow stress and yield strength of the Cu-20Ag alloy.

Coordinated grain boundary deformation governed nanograin annihilation in shear cycling

Grain growth and shrinkage are essential to the thermal and mechanical stability of nanocrystalline metals,which are assumed to be governed by the coordinated deformation between neighboring grain boundaries(GBs)in the nanosized grains.However,the dynamics of such coordination has rarely been reported,especially in experiments.In this work,we systematically investigate the atomistic mechanism of coordinated GB deformation during grain shrinkage in an Au nanocrystal film through combined stateof-the-art in situ shear testing and atomistic simulations.We demonstrate that an embedded nanograin experiences shrinkage and eventually annihilation during a typical shear loading cycle.The continuous grain shrinkage is accommodated by the coordinated evolution of the surrounding GB network via dislocation-mediated migration,while the final grain annihilation proceeds through the sequential dislocation-annihilation-induced grain rotation and merging of opposite GBs.Both experiments and simulations show that stress distribution and GB structure play important roles in the coordinated deformation of different GBs and control the grain shrinkage/annihilation under shear loading.Our findings establish a mechanistic relation between coordinated GB deformation and grain shrinkage,which reveals a general deformation phenomenon in nanocrystalline metals and enriches our understanding on the atomistic origin of structural stability in nanocrystalline metals under mechanical loading.

Formation and Relative Stabilities of Core-Shelled L12-Phase Nano-structures in Dilute Al–Sc–Er Alloys

First-principles thermodynamic calculations were carried out at the interface level for understanding the precipitation of coherent L12-phase nano-structures in dilute Al–Sc–Er alloys.All energetics,relevant to bulk substitution,interface formation,interfacial coherent strain and segregation,were calculated and used to evaluate the nucleation and relative stabilities of various possible L12 nano-structures.Only matrix-dissolved solute Er(or Sc)can substitute Sc(or Er)in L12-Al3Sc(or Al3Er).The inter-substitution between L12-Al3Sc and Al3Er is not energy feasible.Ternary L12-Al3(Er x Sc 1.x)precipitates tend to form the Al3Er-core and Al3Sc-shell structure with a sharp core/shell interface.Three possible formation mechanisms were proposed and examined.The eff ects of Er/Sc ratio and aging temperature on the relative stabilities of L12-phase nanostructures in Al were also discussed.

Cu-10Sn-4Ni-3Pb Alloy Prepared by Crystallization Under Pressure: An Experimental Study

The wear-resistant tin bronze （Cu-10Sn-4Ni-3Pb） with tin content above 8 wt.% prepared by traditional melting and casting process usually defects such as low density, poor properties and segregations. The crystallization under pressure processing of Cu-10Sn-4Ni-3Pb alloy was investigated. The microstructures were observed and analyzed and compared with that by traditional melting and casting process. The results show that the dendrite has obviously disappeared and the dendritic segregation alleviated by using the crystallization under 680 MPa pressure process, in comparison with the remarkably dendrite microstructure and severe as-cast defects of alloy prepared by traditional melting and casting technology. Based on the experimental study, the properties and microstructures of Cu-10Sn-4Ni-3Pb tin bronze prepared by crystallization under pressure have been improved significantly.

In situ atomistic observation of the deformation mechanism of Au nanowires with twin–twin intersection

Twin–twin intersections are often observed in face-centered cubic(FCC)metallic nanostructures,which have important contributions to the plastic deformation and strengthening of FCC metals with low stacking fault energies.However,a deep insight into the underlying mechanism involved in the formation and evolution of twin–twin intersections remains largely lacking,especially in experiments.Here,by conducting the in situ straining experiments under high resolution transmission electron microscope(TEM),we directly visualize the dynamic evolution of a twin–twin intersection in Au nanowire at the nanoscale.It shows that dislocations in the incoming twin can either glide onto or transmit across the barrier twin via dislocation interaction with the twin boundary,resulting in the twin–twin intersection.Dynamic twinning and de-twinning of the twin–twin intersection govern the whole deformation of the nanowire.These findings reveal the dynamic behaviors of twin–twin intersection under mechanical loading,which benefits further exploration of FCC metals and engineering alloys with twin–twin intersection structures.

Arc Erosion Behavior of Cu–0.23Be–0.84Co Alloy after Heat Treatment: An Experimental Study

The arc erosion behavior of Cu-0.23Be-0.84Co alloy after heat treatment was investigated experimentally by a JF04C electric contact test system. The arc duration, arc energy, contact resistance and contact pressure of Cu-0.23Be- 0.84Co alloy after solution treatment and aging treatment were analyzed. The arc erosion morphologies were contrastively observed by a three-dimensional measuring system and scanning electron microscopy. For the Cu-0.23Be-0.84Co alloy in solution state and aging state, the maximum values of arc duration are 90 and 110 ms, and the arc energies are 15,000 and 18,000 mJ, respectively. The maximum value of the contact resistance of Cu-0.23Be-0.84Co alloy in different states is about 33 mΩ The contact pressure of Cu-0.23Be-0.84Co alloy in solution state generally changes between 50 and 60 cN during whole make-and-break contacts, while in aging state, it has a larger fluctuation range. Moreover, the quality of moving contact （anode） decreases, while static contact （cathode） increases. The materials transfer from anode to cathode during make-and-break contacts. The total mass losses of Cu-0.23Be-0.84Co alloy in solution state and aging state are 3 and 1.2 mg, respectively. In addition, a number of discrete corrosion pits, molten droplet, porosity and cavity distribute on the surface of moving contact and static contact. The arc erosion model of Cu-0.23Be-0.84Co alloy in make-and-break contact was built. The arc erosion resistance of Cu-0.23Be-0.84Co alloy after heat treatment is closely related to the microstructure and the properties of contact materials. This experimental study is important to evaluate the anode or cathode electrocorrosion fatigue life.