High Elasticity Cu-Ni-Sn Alloys Compositional Interpretation And Multi-componentization Studies

The high-elasticity Cu-Ni-Sn alloy has high strength,excellent wear and corrosion resistance,stress relaxation resistance and electrical conductivity,and is widely used in aerospace,mechanical precision instrument manufacturing and the electronics industry.However,the Cu-Ni-Sn alloy has serious anti-segregation and discontinuous precipitation phase during long time low temperature aging,which seriously affects the mechanical properties of the alloy.For the above problems,composition optimization design is a good way to solve them.However,the research process always faces the problem that the precipitation phase size is too small to obtain accurate feedback of precipitation phase and matrix composition.To this end,this paper introduces the cluster-plus glue-atom model to describe the near-procedural structure of the alloy phase,firstly adjusts the ideal cluster formula of the alloy according to the actual study,and then uses the cluster formula to resolve the actual alloy composition to establish the connection between the composition and properties of the ternary Cu-Ni-Sn alloy,and establishes a method to seek the change trend of conductivity and hardness predicted by the alloy composition.Further,the Cu-Ni-Sn-Zn（Co）system and a similar Cu-Ni-Al system alloy were used to verify the correctness of the actual clustered composition.Subsequently,the possibility of designing a series of multi-componentization of Cu-Ni-Sn-Ti alloy with Ti element as the fourth cluster element was investigated,and the presence form of Ti element and its influence on the microstructure and properties of the alloy were systematically studied.The main findings of this thesis are as follows.The Cu-Ni-Sn alloy cluster formula was optimized based on the measured phase composition,and the cluster formula of the high-elasticity Cu-Ni-Sn alloy reinforced with the D0₂₂ or L1₂ typeγ’phase was obtained as{[Sn-Ni₈Cu₄]Sn₃}_m+{{[Cu-Cu₁₂]Cu₃}_18-（a+b）+{[Sn-Ni₁₂]Cu₃}_b+{[Cu-Cu₁₂]Ni Cu₂}_a}_n（m,n,a,b≥0,and all are integers）,and each actual alloy composition could be calculated to find a matching cluster formula with clear values of m,n,a and b.In the Cu-Ni-Sn alloy,increasing the Ni/Sn value or appropriately reducing the Sn content is beneficial to suppress the generation of discontinuous precipitation phases.Both theoretical and empirical results verified that the strength of the high-elastic Cu-Ni-Sn alloy strengthened byγ’phase precipitation mainly depends on the amount of Sn precipitation,and the electrical conductivity mainly depends on the amount of Ni solid solution.In the Cu-Ni-Sn-Zn（Co）alloy,the closer the value of（Ni+Co）/Sn is to 3 and the higher the content of Sn,the greater the strength to resistance ratio of the alloy,and the more likely to produce discontinuous precipitation.Therefore,it is necessary to combine other alloying components to suppress discontinuity precipitation in the first place,i.e.,multi-componentization is an effective way to improve the comprehensive performance of Cu-Ni-Sn alloys,rather than relying solely on lowering the（Ni+Co）/Sn value to enhance alloy performance.In the Cu-Ni-Sn-Ti alloy,the Ti element will significantly suppress the discontinuous precipitation phase and improve the segregation of Sn in the alloy ingot.With the addition of Ti content of 0.1875 at.%,the alloy has the highest strong resistance ratio and the best overall performance;as the Ti content increases to 1.875 at.%,Ti is not only solid soluble in theγphase,but also forms the L1₂-Ni₃Ti phase which is co-grid with the matrix with Ni,and the disc-like or long rod-like phase which has a certain orientation relationship with the matrix.The enthalpy interaction between Ti element and Cu and Ni is strong,and its solid solution in the matrix and precipitation phase will improve the stability of both,but its existence in the form of long-rod D0₂₄-Ni₃Ti phase is not conducive to the mechanical properties of the alloy.Therefore,the amount of Ti addition should be strictly controlled.The laws of alloy composition and properties summarized in this paper,as well as the cluster cluster composition interpretation and calculation methods,are of practical significance for property prediction and composition design of alloy systems where the precipitated phase size is small and accurate feedback of the precipitated phase and matrix composition is not available.