Microstructure And Mechanical Properties Of Cu-Ni-Co Multi-Principal Alloys

The ocean is rich in energy resources.Facing the extreme environment of the deep sea,the mechanical properties of traditional copper alloy materials are faced with the bottleneck of strength and plasticity improvement.Cu-containing multi-principal alloys have outstanding corrosion resistance,anti-microbial induced corrosion properties and excellent low-temperature mechanical properties.Therefore,the development of new Cu-containing multi-principal alloys and improving their mechanical properties have significant application prospects.In this work,a novel（CuNi）_100-xCo_x（x=15,20,25,30 at.%）multi-principal alloy was prepared by vacuum arc melting,and its phase composition and microstructure were analyzed by XRD,SEM and TEM.The tensile properties of alloys were tested at room temperature.Subsequently,the effects of adding Mn and Al alloying elements on the microstructure and mechanical properties of Cu-Ni-Co multi-principal element alloys were investigated.Finally,the effects of melting method and deformation heat treatment（cold-rolling and annealing）on the microstructure and mechanical properties of a typical Cu-Ni-Co multi-principal alloy(Cu₃₅Ni₃₅Co₃₀)were investigated.The main research conclusions are as follows:（1）The（CuNi）_100-xCo_x alloy was prepared by vacuum arc melting.The alloy has a dual-phase FCC structure,and its microstructure is a typical dendrite structure,in which the inter-dendritic elements are enriched with Cu elements,and the dendrites are enriched with Ni and Co elements.The yield strength and hardness of the alloy increase with the increase of Co content,while the plasticity is opposite.The（CuNi）₇₀Co₃₀ alloy exhibited the highest yield strength,tensile strength and Vickers hardness of 384 MPa,407 MPa and 195 Hv,respectively,but the elongation was lower at 1.9%.The microstructure of（CuNi）₇₀Co₃₀ alloy that was prepared by the magnetic levitation melting method was transformed into a typical equiaxed dendrite structure,the segregation degree of alloy elements was reduced,and the mechanical properties were significantly improved.Its yield strength,tensile strength and elongation are504 MPa,686 MPa and 11.0%,respectively.After homogenization annealing at 1030℃for15h,the segregation of Cu₃₅Ni₃₅Co₃₀ alloy elements is eliminated,and the alloy has a single-phase FCC structure.（2）The(Cu₃₅Ni₃₅Co₃₀)₈₅Mn₁₀Al₅ and(Cu₃₅Ni₃₅Co₃₀)₈₅Mn₈Al₇ alloys formed by adding Mn and Al elements still show a dual-phase dendrite structure after being prepared by vacuum arc melting.The yield strength,tensile strength and elongation of the as-cast(Cu₃₅Ni₃₅Co₃₀)₈₅Mn₈Al₇ alloy were 251 MPa,530 MPa and 43.1%,respectively.Compared with the Cu₃₅Ni₃₅Co₃₀ alloy,the yield strength slightly decreases,the tensile strength increases,and the elongation increases significantly,with excellent overall performance.After the homogenization heat treatment at 1000℃for 15 h,both alloys showed single-phase FCC structure.（3）The as-cast Cu₃₅Ni₃₅Co₃₀ alloy prepared by magnetic levitation smelting method and the single-phase Cu₃₅Ni₃₅Co₃₀ alloy after homogenization annealing at 1030℃for 15 h were cold-rolled with a deformation amount of 75%,and the microstructure of the alloy showed a typical fiber structure.After cold-rolling,the yield strength and tensile strength of the alloy were significantly improved,and the elongation decreased sharply.During the subsequent recrystallization annealing process,the strength of the alloy decreases and the ductility increases with the prolongation of the annealing time.After the single-phase rolled alloy was annealed at 1030°C for 1min,the alloy was almost completely recrystallized,and its yield strength,tensile strength and elongation were 562 MPa,772 MPa and 29.9%,respectively.After the single-phase rolled alloy was annealed at 1030°C for 1.5 min,the alloy was completely recrystallized,and its yield strength,tensile strength and elongation were 433 MPa,692 MPa and 36.4%,respectively.After the as-cast cold-rolled alloy was annealed at 950°C for 1.5 min,the alloy was partially recrystallized,and the yield strength,tensile strength and elongation of the alloy were 622 MPa,780 MPa and 27.7%,respectively.After the as-cast cold-rolled alloy was annealed at 950℃for 3 min,the alloy was completely recrystallized and the deformation structure was eliminated.The yield strength,tensile strength and elongation were 514 MPa,720MPa and 33.7%,respectively.These four alloys all have excellent comprehensive mechanical properties,and their mechanical properties are significantly better than those of traditional nickel-aluminum-bronze alloys.