Investigation On Microstructure And Properties Of Conductive Elastic Cu-Ti-Ni-X(Ag,Y) Alloys

The microstructural evolution and properties of Cu-Ti-Ni-X(Ag,Y)alloy at different states were systematiclly studied.The microstructure and phase constituents was characterized by optical microscopy(OM),X-ray diffractometer(XRD),scanning electron microscope(SEM)and transmission electron microscope(TEM),and the electrical conductivity,hardness and elastic modulus were tested as well.The following conclusions can be drawn from above investigations.(1)The microstructure of as-cast Cu-Ti-Ni-Ag alloy is mainly consisted of ?-Cu,NiTi and Ni2Ti intermetallic.More NiTi and Ni2Ti phase precipitate with the increase of Ag content.Moreover,the increased Ag content decreases the grain size obviously.(2)In the range of experiments,the good comprehensive property of Cu-Ti-Ni-Ag alloy can be obtained after solid solution at 850? for 4h and aging at 500? for 7h.The peak electrical conductivity of Cu-3Ti-3Ni-xAg(x=1,1.5,2)alloys are 31.03%IACS,32.41%IACS and 35.79%IACS,and hardness are 268HV,276HV and 289HV,respectively.The elastic modulus are 143.31GPa,148.86GPa and 158.08GPa,respectively.They are larger than that of aged QBe2 alloy(133 GPa).(3)The increased Ag content promotes the formation of intermetallic and decreases the grain size of Cu-Ti-Ni-Ag alloy.Moreover,the phase at the grain boundry precipitates in a continuous way.The formation of CuNi2Ti,Ni3Ti,NiTi,?'-Cu4Ti and ?-Cu3Ti can efficiently reduce the Ti concentration in the Cu matrix,thus increasing the electrical conductivity.The strengthening effect of the Cu-Ti-Ni-Ag alloy can be attributed to the formation of intermetallic phase such as CuNi2Ti,Ni3Ti,NiTi and fine precipitates of coherent ?'-Cu4Ti.With the increase of the aging time,the precipitates become coarse and incoherent with the Cu matrix,and a discontinuous precipitate? with an lamellar structurestarts to grow inward from the grain boundaries and,thus,decreases the hardness.(4)The microstructure of as-cast Cu-Ti-Ni-Y alloy is consisted of ?-Cu(Ti,Ni,Y)and NiTi phase.An appropriate Y content is beniefical for the formation of the fine grain for Cu-Ti-Ni-Y alloy,but an excessive Y content can lead to grain coarsening.In the range of the experiments,the desired Y content is 0.07wt.%.(5)After solid solution and aging treatment,the electrical conductivity and hardness of Cu-Ti-Ni-Y alloy increase remarkedly.With the icrease of aging time,the electrical conductivity always increases,while the hardness increases at the beginning and then decreases.In the range of experiments,the optimum aging process for Cu-Ti-Ni-Y alloy is 550 ? holding for 7h.The electrical conductivity and hardness of Cu-3Ti-3Ni-0.07Y alloy are 35.66%IACS and 3 10HV,respectively.(6)Though the formation of ?'-Cu4Ti,?-Cu3Ti,Ni3Ti and NiTi can efficiently decrease the Ti concent in the Cu matrix,they increase the electrical conductivity of Cu-3Ti-3Ni-0.07Y alloy.Furthermore,the precipitation of Cu5Y and Cu2Y reduce Y concentration in the Cu matrix,resulting in the improventment on the electrical conductivity of Cu-3Ti-3Ni-0.07Y alloy.The strengthening effect of Cu-3Ti-3Ni-0.07Y alloy can be contibuted to the formation of intermetallic phase such as Ni3Ti,NiTi and fine precipitates of coherent ?'-Cu4Ti.Besides,the amount of intermetallic such as Cu2Y,N3Ti,NiTi and Cu5Y can strengthen Cu-3Ti-3Ni-0.07Y alloy simultaneously.With the increase of the aging time,the precipitates become coarse and incoherent with the Cu matrix,the discontinuous precipitat ? with an lamellar structurestarts to grow inward from grain boundaries,resulting in the decrease of the hardness.