Preparation And Properties Of Tungsten Dispersion-strengthened Copper Alloys

With the increasing of technology,developing a copper alloy with both high strength and high conductivity has become the focus of researchers' exploration.In recent decades,dispersion-strengthened(DS)copper alloys gains more attractions due to its enhanced mechanical and electrical propertis and thermal stability.The existing dispersion-strengthened copper alloys mainly contain oxides strengthening phase,but the strong electron scattering effect and the lower irradiation stability become the limiting factors to further improvements.Tungsten is an optimal choice for dispersied phase due to its outstanding hardness,high melting point,good electrical and thermal conductivity,and excellent radiation resistance.Recent works are focused on mechanical alloying method.But particles refining is difficult via exogenous methods,which limits the application of tungsten DS copper alloys.Based on the above,a new preparing strategy with the in-situ reaction as the core is successfully developed in this article.Also,the bulk tungsten dispersion-strengthened copper alloy is generated with excellent comprehensive performance.This research would provide a theoretical basis for the further development of high-performance dispersion strengthened copper alloys.In this work,powder metallurgy synthesizing route of tungsten DS alloy and its mechanical and electrical properties are obtained,and the thermal stability and microstructures are also discussed.The difficulty in preparing tungsten as a dispersed phase focuses in the ultrahigh formation enthalpy of the Cu-W binary system,which results in improving the energy barrier for the outer tungsten particle dispersion and refinement.Therefore,it is necessary to design an intermediate process to reduce the formation energy of tungsten particles.For these reasons,a new process via sol-gel method is designed.In this method,composite oxide is generated as the precursor,and the copper alloy is prepared by hydrogen reduction.The nano-sized tungsten particle is reduced by ductile WO3.In the copper alloy,the harmful influence of coarse particle is eliminated,meanwhile the uniformity and the grain refinement is singnificantly better than that of normal mechanical alloying method.On the basis of above results,a new procedure combined with mechanical alloying and hydrogen reduction is developed,and conducting the research on cold-working and thermal stability.The tungsten forming temperature is remarkably reduced by solid-state mass transfer reaction without intermediate.In the copper matrix,the average particle size is about 30 nm.The tensile strength reaches 596 MPa after cold rolling,and the electrical conductivity of about 85 IACS%is also maintained.The tensile strength and yield strength of annealed Cu-W alloy are 402 MPa and 289 MPa,and the average grain size of that is 0.97?m,maintaining the typical cold-worked texture with Goss and rotated cubic orientation.It shows that its enhanced mechanical properties and thermal stability are mainly derived from the second phase strengthening and the grain refinment strengthening mechanism.The grain refinement effect and dislocation pinning effect are brought by the internal high-density tungsten particles.The increase in resistivity is mainly caused by particle resistance effect,particle electron scattering and grain boundary scatteringBy adding a tungsten dispersion phase instead of the metal oxide phase,the conductivity of the copper alloy can be improved without loss of strength.At the same time,the embrittlement effect with higher content of the dispersion phase can also be suppressed by W particles.In this article,a solid phase mechanal-chemical reaction processing(MCP)method is used to prepare the synergistic dispersion-strengthened alloy containing Ti02 and Al2O3 phases.It expressed that particle coarsening was restrained as the results of the interaction effects between W and oxide nanoparticles due to the shorter diffusion path,achieving a better strengthening effect.The minimum size of dispersoid is about 10 nm.The tensile and yield strengths of 800? annealed Cu-Al-WO3 alloy are 442 MPa and 350 MPa,which only 6%lower than that of hot-extruded sample.The elongation of it is 15%,and the electrical conductivity maintains 80 IACS%.The mutual inhibition effect improves the dispersion uniformity of the strengthening phase in the copper matrix,which avoids grain boundary embrittlement caused by larger particles.The microstructure of annealed alloy maintains the fiber texture.The volume of recrystallized grains is still lower in the copper matrix with better thermal stability.Based on the the experimental results,the microstructure evolution at high-temperature and strengthening phase structure of tungsten dispersion strengthened copper alloys are analyzed.Even after 96 h annealing,the strength and hardness of Cu-W alloy still no longer decrease significantly.There are four stages in recrytallization process,including(1)recovery;(2)substructure forming;(3)fusion of neighbor substructure;(4)nucleation inside the recrystallized grains.The stable structure contains equiaxed recrystallized grains and high-density deformed grains.Ostwald ripen mechanism is applied to describe the tungsten particle coarsening,and the equilibrium concentration and diffusion coefficient in the grain and at the grain boundary are deduced.The experimental results show that the structure of Cu-W interfaces is semi-coherent,corresponding to the K-S orientation relationship.The strengthening mechanism is the dislocation bypass mechanism.Molecular dynamics calculation results verify the thermodynamic stability of the above structure.