Investigation On The Tailoring Of Nano-sized Phase In Oxide Dispersion Strengthened Copper Alloys

In fusion reactors,the heat sink material in the divertor will be subjected to high neutron irradiation（>6 dpa/fpy）and high heat flux（up to 20 MW/m²）.This means that the requirements for heat sink materials are more stringent.Oxide dispersion strengthened copper alloy is a potential candidate material for heat sink applications.Commercial Glidcop Al25 has been studied for many years,but there are still some problems,and the research of new dispersion-reinforced copper alloys is therefore needed.Firstly,the reasons of coarsening and agglomeration of oxide particles in oxide dispersion strengthened copper alloy were investigated by Rhines-pack internal oxidation experiments.By SEM and TEM analyses,it is found that oxides tend to segregate at grain boundaries,and their particle size increases with the increase of diffusion distance and Al content.When there is water vapor in the internal oxidation environment,the agglomeration and growth of alumina particles will be intensified,and the doping of Ti element can effectively refine the oxide particles.Secondly,based on the experience in the exploration of Rhines-pack internal oxidation experiments,oxide dispersion strengthened copper alloy was prepared by powder method.The powder of Cu-0.2 wt.%Al-0.1 wt.%Ti alloy was prepared by vacuum air atomization,internal oxidation treatment and vacuum hot pressing sintering.The microstructures were characterized by TEM,XRD and APT,and their mechanical properties were tested.The results show that the doping of Ti elements refines the size of the second phase to 3.2±0.5 nm and increases the number density of the second phase to 2.076×10²³ m^-3.The nano-strengthened phase is Al-Ti composite oxide,rather than a mixture of two oxide phases or a"core-shell"structure.The mechanical properties of Cu-0.2 wt.%Al-0.1 wt.%Ti alloy after internal oxidation exceed those of commercial Glidcop Al25 in equivalent state.Finally,the internal oxidation preparation of oxide dispersion strengthened copper alloy with high oxide content was explored.The influence of Al content and Ti content on oxide particles in the oxide layer and the oxidation front was analyzed by a controlled experiment,and the hardness of the inner oxide layer of some samples was analyzed,The following conclusions were obtained:There is a competition between the nucleation and growth of oxides,and O diffusion plays the main role in the early stage and then the Al migration.Under the action of these two mechanisms,the particles in the oxide layer present a gradient distribution.The closer the oxide is to the sample surface,the smaller the particle size,the higher the number density,and the higher the hardness.When the element content of oxide phase is too high,the precipitation and growth of oxide at the grain boundary will inhibit the advance of oxidation front,resulting in a“peak”shape of oxidation front.Ti can still refine oxide particles in oxide dispersion strengthened copper alloy with high oxide content.The study on growth characteristics of oxides as well as tailoring methods,will shed light on the development of high oxide content oxide dispersion strengthened copper alloy in the future.In summary,based on the application background of heat sink materials used in fusion reactor,the microscopic mechanism of oxide growth and segregation during internal oxidation was investigated in this paper.By setting Glidcop Al25 as a reference,a new oxide dispersion strengthened copper alloy was designed and prepared.And the microstructure characteristics and macroscopic properties of nano-oxide phase were effectively tailored.