Effect Of Heat Treatment On Microstructure And Mechanical Properties Of Cu-15Ni-8Sn(-0.3Si-0.1Ti) Alloy

Cu-15Ni-8Sn alloy is a high-strength,wear-resistant and corrosion resistant copper alloy.The spinodal decomposition,ordered-disorder transformation,discontinuous precipitation and other phase transition processes occur when the Sn atoms are sufficiently soluted in the matrix,which significantly affects the mechanical properties of the alloys.It has been particularly concerned as beryllium bronze alternative materials early and recently as a wear-resistant materials.In this paper,Cu-15Ni-8Sn and Cu-15Ni-8Sn-0.3Si-0.1Ti alloys prepared by permanent mold casting were studied by mechanical properties testing,metallographic microscope,scanning electron microscope and energy dispersive spectroscope,transmission electron microscope,differential scanning(DSC)analysis.The effects of heat treatment on the microstructures and mechanical properties of Cu-15Ni-8Sn,Cu-15Ni-8Sn-0.3Si-0.1Ti alloy were studied.The results are as follows:The microstructures of Cu-15Ni-8Sn-0.3Si-0.1Ti and Cu-15Ni-8Sn alloys under as-cast,homogenization-annealed and hot-extruded alloys were investigated.The results show that the as-cast Cu-15Ni-8Sn alloy is a developed dendritic structure with serious dendrite segregation,By addition of elements Si and Ti,the volume of bone-like phases in the alloy significantly increased and the dendrites and bone-like transition layer is no longer lamellar distribution;The ?-phase in the annealed Cu-15Ni-8Sn alloy is in the form of lamellar distribution,and its thickness is about 150 nm,and nano-scale ?-phase particles evenly distribute on the substrate between the lamellar phases.Under the same homogenization annealing system,the alloy containing Si and Ti still retains a part of the bony-like structure,indicating that the addition of Si and Ti delayed the homogenization annealing process;Under the same hot extrusion process conditions,When Si and Ti is added recrystallization grains are smaller and grain size is more uniform.It was found that a large amount of the second phase particles were distributed in the alloy grain boundaries and matrix.Besides the rod-shaped ? phase,there are some Ni3 Si phases with the surrounded dislocations.The effects of different heat treatment processings on the microstructure and mechanical properties of the annealed Cu-15Ni-8Sn-0.3Si-0.1Ti and Cu-15Ni-8Sn alloys were investigated.The results show that the solution treatment of Cu-15Ni-8Sn alloy is sufficient todissolve the second phase in the alloy at 800?/1h,and the mechanical properties of the alloy after 340?/3h aging treatment are the best with tensile strength of 722 MPa,yield strength of640 MPa and elongation of 9.4%;Under the same heat treatment processing,the Cu-15Ni-8Sn-0.3Si-0.1Ti alloy has the tensile strength of the alloy is 755 MPa,the yield strength is 653 MPa,and the elongation is 8.2%.Si and Ti have little effect on the mechanical properties of the alloy.The effects of different heat treatment processing on the microstructure and mechanical properties of hot-extruded Cu-15Ni-8Sn-0.3Si-0.1Ti and Cu-15Ni-8Sn alloys were investigated.The results show that the best solution treatment for hot-extruded Cu-15Ni-8Sn alloy can be obtained by 840?/1h.after aging treatment at 340?/3h the tensile strength of the alloy is 863 MPa,the yield strength is 665 MPa and elongation is 14.5%;For the hot-extruded Cu-15Ni-8Sn-0.3Si-0.1Ti alloy,the tensile strength is 970 MPa,the yield strength is 757 MPa and the elongation is 23.3% under the same heat treatment processing.The effect of Si and Ti on the mechanical properties of the alloy is significant.