| Beryllium-copper(Be-Cu)alloy is widely used in the fields of instrument engineering,lead frame and equipment manufacturing because of its excellent properties such as high strength,high conductivity,high thermal conductivity and high elasticity.However,due to its scarcity and toxicity,it is necessary to develop a new type of green copper alloy to replace Be-Cu.Cu-Ti alloy is a typical aging-strengthened alloy.When the content of Ti is 1%～6%(mass fraction),a singleα-phase can be spinodal decomposition into two phases:rich solute region and poor solute region,the strength and hardness of Cu-Ti alloy are obviously enhanced,and it has excellent wear resistance,fatigue resistance,corrosion resistance,processing and molding properties,which is comparable to Be-Cu alloy and even more than Be-Cu alloy.However,due to the large difference in atomic radius between Cu and Ti,the electrical conductivity of the alloy decreases.In order to solve these problems,a new method of in-situ generation of nano-oxide Cu2Ti2O dispersionstrengthened Cu-Ti alloy by internal oxidation is proposed in this paper,at the same time,the electric conductivity is not reduced.In this paper,the Cu-TiO2-Ti composites were prepared by in-situ reaction using TiO2 as oxygen supply medium.The phase analysis,microstructure observation,tensile properties and electrical properties were tested,the effects of aging time and TiO2 content on the microstructure and mechanical properties of Cu-TiO2-Ti composites were studied.In addition,this paper also changed the oxygen supply medium,added Cu2O to prepare Cu-Cu2O-Ti composite material,through two step internal oxidation method to produce Cu2Ti4O phase,to explore the reaction path and the properties of the composite material.In this paper,Cu-TiO2-Ti composites were prepared by low energy ball milling,pre-pressing and spark plasma sintering(SPS).The effects of aging time on the morphology,structure and properties of Cu-0.42TiO2-1.75Ti composites were studied.The densest and most uniform composite material was obtained by sintering at 900℃ for 1h.It was determined that the Cu0.42TiO2-1.75Ti composites with excellent properties could be obtained after aging at 450℃ for 4 h,the tensile strength and yield strength were 543 MPa and 394 MPa,respectively,and the elongation and conductivity were 13.5%and 24.1%IACS.The results show that fine acicular β’Cu4Ti phase precipitates from the matrix during aging,and the mechanical properties and electrical conductivity of the material are improved significantly.With the aging time increasing,the interface of β’-Cu3Ti with matrix was changed to that of β-Cu4Ti with semi-coherent discontinuous precipitate phase,which resulted in the poor interface adhesion between the second phase and matrix.The electrical conductivity increases with aging time,which is mainly due to the dissolvability of Ti atoms,the recovery of lattice distortion,the decrease of electron scattering and the decrease of electrical resistivity.The effect of TiO2 on the microstructure and properties of Cu-xTiO2-3Ti composites was studied by increasing the content of TiO2 on the basis of keeping the content of Ti unchanged.The results show that Cu2Ti4O nanophase is in-situ formed by the internal oxidation method with the addition of TiO2.Cu2Ti4O is uniformly distributed at the grain boundary of the matrix,and the particle size is about 250 nm,this kind of semi-coherent interface will form dislocations accumulation at the crystal interface,and the lattice dislocations at the semi-coherent interface need to overcome the coherent stress and interface attractive force to slide,so the mechanical properties of the composites can be improved,but it will reduce the elongation of the material.When the amount of TiO2 was 0.73wt.%The tensile strength and yield strength of Cu-xTiO2-3Ti composites can reach 670 MPa and 607 MPa,and the elongation can be kept at 11.4%,and the effect on conductivity is not significant.The strengthening methods of Cu-xTiO2-3Ti composites are solid solution strengthening,precipitation strengthening(precipitated phase),dispersion strengthening(formed phase at grain boundary),fine grain strengthening and working hardening,the contribution of precipitation enhancement was the highest,reaching 65%.On the basis of this study,by changing the oxygen supply medium.Cu-Cu2O-Ti composites were prepared by adding Cu2O to Cu-Ti.Nano oxides are produced by two-step internal oxidation,adding Cu2O as a medium to provide oxygen source,it reacts preferentially with Ti to form TiO2,and then reacts with Cu powder to form Cu2Ti4O phase.The size of the generated nanoparticles is about 100 nm,which is smaller than that of Cu2Ti4O nano phase generated by directly adding TiO2,but the performance is similar.By changing the reaction path,another research idea is provided for the generation of Cu2Ti4O phase reinforced Cu-Ti alloy by internal oxidation. |
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