Preparation And Properties Of Casting Dispersion-Strengthened Copper Alloys

The heat sink materials(HSMs)for fabrication of the water-cooled divertors of future fusion reactors are required to possess excellent thermal conductivity,high temperature mechanical stability and high resistance to ion and neutron irradiations.The presently known dispersion-strengthened copper alloys(DS-Cu)do not suit the property requirements of the HSMs working at the extreme thermal load and irradiation conditions.Moreover,the DS-Cu alloys are produced through a complex sequence of procedures including inner oxidation,and especially,the massive and effective production of the materials remains a serious problem.In the present work,we propose a simple method of making nanoparticles reinforced DS-Cu alloys,and the main procedures are:preparation of oxygen-bearing copper-based amorphous alloys as the intermediate alloys,followed by vacuum arc-melting of the intermediate alloys with pure Cu and Cr,and by subsequent thermal or thermo-mechanical treatments.The structure,composition and microstructure of the alloys were characterized by X-ray Diffraction(XRD),Electron Probe Microanalysis(EPMA),Scanning Electron Microcopy(SEM)and Transmission Electron Microscopy(TEM),and the microhardness,room-temperature tensile properties and electrical conductivity of the alloys were also measured.The experimental results of the preparation,microstructure characterization,and property measurements are presented in what follows:(1)The preparation of DS-Cu alloys has been realized by vacuum arc-melting the mixture of the oxygen-bearing Cu-Y amorphous alloys,pure Cu and Cr,and the specific procedures are:The Cu-Y intermediate amorphous alloys were first prepared by means of vacuum arc-melting and melt quenching methods,and the oxidation processing was conducted at a temperature determined from the crystallization temperature of the amorphous alloy and under a suitable oxygen partial pressure.Finally,the mixtures of the oxygen-bearing Cu-Y amorphous alloy,pure Cu and Cr of appropriate weight percentages were vacuum arc melted.(2)The electrical conductivity test showed that the conductivity of the as-cast DS-Cu alloys decreased from 95%IACS(0.2 wt.%Y)to 87%IACS(0.6 wt.%Y)with increasing Y content,and was slightly decreased after cold rolling.The mechanical strength of the as-rolled alloys was improved significantly,for instance,the 0.3 wt.%Y alloy exhibited a tensile strength(?_b)as high as 622 MPa,and was plastically fractured.Annealing at 950°C for 1 h resulted in greatly reduced strength and brittle fracture along the crystal of the 0.3 wt.%Y alloys.The as-rolled alloys containing 0.75 wt.%Cr exhibited a tensile strength of 414 MPa and plastic fracture,and after solid solution at 980°C for 1 h and aging at 475°C for 2 h(SA),the strength decreased to 283 MPa,which is about 120 MPa higher than that of the Cr-free alloy,and the brittle fracture mode was unchanged.However,Fracture surface observation revealed the formation of many dimples in the interior of the Cu grains,which indicated that the addition of Cr would help to improve the mechanical properties of the SA alloys but slightly affected the conductivity,reducing it to 82±1%IACS.(3)TEM observation confirmed the dispersive distribution of spherical second-phase nanoparticles with a size of 2-10 nm in the Cu matrix,indicative of the formation of a DS-Cu alloy.Compared with the Cr-free alloy,the precipitates in the grain of the Cr-containing alloy was significantly reduced after SA,the grain boundary precipitates remained existed,but tri-angular joints appeared.The precipitate of grain boundary were determined to be a mixture of face-centered cubic Cu solid solution and nano unknown phase,and intragranular precipitate were determined to be an unknown body-body tetragonal(a=b=0.43 nm,c=0.31 nm)phases.Nanometer-sized FCC-type Cr-rich particles were found to exist in the Cr-containing alloy,showing a coherent orientation relationship with the Cu matrix.This study indicated that a small amount alloying addition of Cr could alter the microstructure and properties of the alloys.The underlying mechanism will be studied in our further work.