Heat-resistant Cu-Ni-Al(Fe) Films With γ’ Phase Precipitation Strengthening

Copper is widely used in electrical,mechanical,national defense and other fields because of its excellent conductivity（heat）,plasticity and ductility.In recent years,due to more complex and harsh operating conditions in service,many problems of Cu have limited its use,such as low strength and hardness,poor wear resistance,poor high temperature stability and so on.The surface strengthening method can improve the surface properties of Cu with good thermal and electrical conductivity.γ′phase coherent precipitation has good resistance to high temperature and creep.Therefore,this paper intends to prepare（?’+?）phase films on the surface of Cu to improve the surface mechanics and temperature resistance.To obtain Cu-Ni-M films withγ′phase precipitation strengthening,the bulk alloys were used to select coherent precipitation strengthening.In this paper,Ni/M（at.%）is fixed as 3 at first,The microstructure,conductivity and hardness of Cu-Ni-M（M=Al,Cr,Fe and Mo）alloys were studied systematically in a large range of compositions.The results showed that different microstructure could be obtained by adding different M.Cu-Ni-Cr alloy is an spinodal decomposition structure.Cu-Ni-Fe alloy also is composed of a quasi-spinodal decomposition and a small amount ofγ′-Ni₃Fe phase.The structure of Cu-Ni-Mo alloy is disordered,and there is large NiMo phase,nanoscale Ni₂Mo and Ni₄Mo phases,elemental Mo.The microstructure of Cu-Ni-Al alloy is simple.By comparing the conductivity and hardness,it is found that the conductivity and hardness of Cu-Ni-Al alloy are at a high level.Therefore,the Cu-Ni-Al system was selected in this paper for the subsequent study of thin films.A series of Cu-Ni-Al ternary films with fixed Ni/Al ratio（at.%）of 3 and different Cu contents were prepared on single crystal Si（100）and pure Cu substrates by magnetron sputtering.The analysis showed that the as-depositied film was in the form of nano-columnar crystal,and theγ′-Ni₃Al phase was embedded in the thin film with smaller nano-state.As the content of Ni and Al increased,the hardness of Cu-Ni-Al film on Si substrate increased gradually from 6.25 GPa to 9.31 GPa,and the friction coefficient decreased from 0.06 to 0.02.The hardness of Cu-Ni-Al film on Cu substrate increases from 4.7 GPa to 7.05 GPa,and the friction coefficient decreases from 0.08 to 0.05.Compared with pure Cu film and block,the hardness increases greatly,and the friction coefficient decreases greatly.However,compared with pure Cu film,The electrical conductivity of Cu-Ni-Al films decreases to different degree,which is due to many grain boundaries,defects,and alloying elements in the sputtering state film,increasing the scattering of electrons.The strengthening mechanism of films is a combination of fine crystal strengthening,γ′-Ni₃Al precipitation strengthening,solid solution strengthening and crystal microdistortion strengthening.After 450°C/20 h annealing treatment of Cu-Ni-Al films on Cu substrate,due to stress relieving,grain combined growth,some decline in hardness,but compared to pure Cu thin film and block of pure Cu hardness can still maintain a high level,with the increase of Ni and Al content,the hardness increases by 4.1 GPa to 6.2 GPa;The wear resistance of most thin films became better,and the friction coefficient decreased from 0.09 to 0.05,indicating the good stability of thin films.In conclusion,heat-resistant Cu-Ni-Al films withγ′precipitation strengthening were successfully prepared.It opens up a new way for surface strengthening of Cu materials.