Preparation And Properties Of High Performance Dispersion-Strengthened Copper Alloy

The people’s demand for energy consumption and the environmental problems brought by traditional energy need to be solved urgently with the rapid development China’s improvement of economy and the increasing improvement of people’s living standards.Fusion energy is one of the important ways to solve future energy problems due to its abundant deuterium resources,high energy appreciation rate and low nuclear waste output.However,the harsh service environment of the fusion reactor requires that the divertor heat sink material can resist high heat flow and neutron irradiation for a long time to ensure the long-term stable operation of the fusion reactor.Copper alloys are the primary candidate heat sink materials in fusion reactor divertors owing to the advantages of high thermal conductivity,high thermal stability,good strength and resistance to neutron irradiation.Among them,the precipitation-strengthened CuCrZr alloy has become the preferred heat sink material due to its excellent strength and good thermal conductivity at medium and low temperatures.However,the low hightemperature strength of CuCrZr alloy greatly limits its service temperature range,and it is urgent to develop high-performance copper alloys that can be suitable for future fusion reactor heat sink materials.Therefore,in this paper three nano-sized dispersed phases including Y2O3,WC and W particles were selected to prepare high-performance dispersion-strengthened copper alloys which could be applied as candidate heat sink materials for nextgeneration fusion reactors.The mechanical properties,thermal stability and thermal conductivity of dispersion-strengthened copper alloys were studied.The main research contents and results of this paper are as follows:Cu-lwt%Y2O3 alloys were prepared by citric acid sol-gel method and spark plasma sintering(SPS)technology,and the microstructure and properties of the alloys were characterized.The results show that the average grain size and Y2O3 particle size of the sintered bulk samples are 0.42 μm and 16.4 nm,respectively,which remain basically stable(0.45 μm and 17.0 nm,respectively)after annealing at 800℃.The tensile strength of the alloy at room temperature is 572 MPa,which is maintained at about 563 MPa and 532 MPa after annealing at 800℃ and 900℃,respectively.Compared with pure copper,the thermal conductivity of the alloy decreases significantly(308 Wm-1K-1),because of the low thermal conductivity of Y2O3 phase(27 Wm-1K-1).Cu/WC composite powders were prepared by citric acid sol-gel and high-energy ball milling,and WC dispersion-strengthened copper alloys were prepared by SPS.The distribution of WC in different processes and the effect of WC addition on the mechanical properties and microstructure of the alloy were studied.The results show that the strengths of the Cu-5wt%WC and Cu-10wt%WC alloys synthesized by the citric acid sol-gel method are about 238 MPa and 235 MPa,respectively,and both are brittle fractures.The strength and elongation of Cu-5wt%WC alloy prepared by citric acid sol-gel combined with high-energy ball milling are 248 MPa and 14.6%,and the thermal conductivity at room temperature is about 192.3 Wm-1K-1.The lower mechanical properties and thermal conductivity are mainly due to the obvious agglomeration of WC in the WC dispersion strengthened copper alloy prepared by the two methods and the low thermal conductivity of WC(110 Wm-1K-1).W with higher thermal conductivity(173 Wm-1K-1)was selected as the disperse phase to improve the thermal conductivity of the alloy.Nano-W dispersionstrengthened copper alloys with different tungsten contents(0,2at%,5at%and 8at%)were prepared by high-energy ball milling and SPS technology,and the effect of W content on the properties and microstructure of the alloy was investigated.The results show that the addition of nano-W particles makes the grains of the alloy remarkably refined,and thereby increases the strength of the Cu-W alloy.The tensile strengths of Cu-5.5wt%W,Cu-13.2%W and Cu-20wt%W alloys at room temperature are 330 MPa,410 MPa and 495 MPa,respectively.The average grain sizes of the Cu-5.5wt%W,Cu13.2wt%and Cu-20wt%W alloys are 0.84 μm,0.65μm and 0.54 μm,respectively,and the average particle size of W particles is about 43 nm.The thermal conductivity of the alloys is 325 Wm-1K-1,314 Wm-1K-1 and 307 Wm-1K-1,respectively.High-performance Cu-5wt%W alloy was prepared by citric acid sol-gel reduction combined with SPS technology to further improve the thermal conductivity and the mechanical properties of the alloy,and the comprehensive properties of the alloy were studied.The size of W particle in the Cu/W powder prepared by the sol-gel method is only about 5.8 nm,and W particles is evenly distributed in the Cu particles,which is very important for the preparation of high-performance nano-W dispersionstrengthened copper alloys.The results show that the prepared Cu-5wt%W alloy has excellent comprehensive properties:the tensile strength at room temperature is as high as 706 MPa,and the thermal conductivity and electrical conductivity are about 370 Wm-1K-1 and 85.1%IACS,respectively.At 600℃,the strength of the alloy is maintained at about 400 MPa,and the thermal conductivity is about 358 Wm-1K-1;even at a high temperature of 800℃,the tensile strength is still above 200 MPa,and the thermal conductivity is maintained at 350 Wm-1K-1.The excellent properties of the alloy are inseparable from its special microstructure.The average grain size and W particle size in Cu-5wt%W alloy are 0.48 μm and 7.6 nm,respectively,and maitain stable(0.5 μm and 6.9 nm,respectively)after annealing at 800℃,exhibiting extremely high thermal stability.In addition,the formation and growth mechanism of helium bubbles in the abovementioned high-performance Cu-5wt%W alloys under He+in-situ irradiation were also analyzed.The results indicate that helium bubbles preferentially nucleate at defects such as grain boundaries,phase boundaries and dislocations during irradiation.This work will provide reference for improving the comprehensive properties of dispersionstrengthened copper alloys,as well as for the development of divertor heat sink materials.