Effect Of Ni And Sn Content On Aging Process Of Cu-Ni-Sn Alloy

Cu-Ni-Sn alloy is a typical am decomposition strengthening alloy,which is widely used in electronic information industry,mechanical manufacturing and precision instruments and meters because of its high strength,high elasticity,excellent wear resistance,electrical conductivity and high temperature stability.At present,researchers at home and abroad have done a lot of experimental research to improve the properties of Cu-Ni-Sn alloy and clarify its phase transformation process and mechanism,but few scholars have made in-depth research on the influence of Ni or Sn content change on the thermodynamics and kinetics of aging process of Cu-Ni-Sn alloy.Based on the above problems,the microstructure evolution and mechanical properties of aged Cu-xNi-6Sn(x=7.5,12.5,15 wt.%)alloy and Cu-9Ni-xSn(x=3,4,6wt.%)alloy were studied by changing the Ni or Sn content in this paper.According to the microstructure and properties of the aged alloy,the coarsening process of the modulated structure and discontinuous precipitation process in the aging process were characterized by using advanced testing methods.Then the calculation and analysis were carried out.At the same time,the coarsening process of the modulated structure and discontinuous precipitation process were discussed.The effect of Ni or Sn content on the coarsening process of the modulated structure of Cu-Ni-Sn alloy was studied by TEM and XRD.In the early stage of aging at 400 ?,the hardness of Cu-12.5Ni-6Sn and Cu-9Ni-6Sn alloys increases faster than that of Cu-15Ni-6Sn and Cu-9Ni-4Sn alloys,respectively.The results show that the activation energy of Cu-12.5Ni-6Sn alloy(94.8 k J/mol)is less than that of Cu-15Ni-6Sn alloy(134.7 k J/mol)when Ni content is changed,that is to say,the coarsening process of Cu-12.5Ni-6Sn alloy is easier than that of Cu-15Ni-6Sn alloy;the activation energy of Cu-9Ni-6Sn alloy(66.2 k J / mol)is less than that of Cu-9Ni-4Sn alloy(79.4 k J/mol)when Sn content is changed,that is to say,the coarsening process of Cu-9Ni-6Sn alloy is easier than that of Cu-9Ni-4Sn alloy.Therefore,the higher the Ni content is,the more difficult the coarsening process of modulated structure of Cu-(12.5,15)Ni-6Sn alloy is;the higher the Sn content is,the easier the coarsening process of amplitude modulated structure of Cu-9Ni-(4,6)Sn alloy is.The effect of Ni or Sn content on the discontinuous precipitation process of Cu-Ni-Sn alloy was studied and analyzed.The results of microstructure observation of discontinuous precipitation process show that when the content of Ni or Sn remains unchanged,the interlamellar spacing of discontinuous precipitation increases with the increase of aging temperature;under the same aging conditions,the interlamellar spacing of discontinuous precipitation decreases with the increase of Ni content or Sn content.The thermodynamics and kinetics of discontinuous precipitation process are calculated,the results show that the higher the Ni content is,the more difficult it is for the atoms to diffuse at the grain boundary during the discontinuous precipitation process of Cu-xNi-6Sn alloy.The higher the Sn content is,the more easily it is for the atoms to diffuse at the grain boundary during the discontinuous precipitation process of Cu-9Ni-xSn alloy.The phase transformation process of Cu-Ni-Sn alloy during aging was discussed and analyzed.The results show that the sum of the interfacial energy and the elastic strain energy at the grain boundary of Cu-12.5Ni-6Sn and Cu-9Ni-6Sn alloys is larger than that of Cu-15Ni-6Sn and Cu-9Ni-4Sn alloys,respectively,when the coherent relationship of the modulating structure disappears.That is to say,the driving force of the discontinuous precipitation of Cu-12.5Ni-6Sn and Cu-9Ni-6Sn alloys is greater during aging,which is consistent with the thermodynamic calculation results of discontinuous precipitation process.Combined with the above,it can be seen that the discontinuous precipitation morphology in the microstructure of Cu-12.5Ni-6Sn and Cu-9Ni-6Sn alloy appears earlier than that of Cu-15Ni-6Sn and Cu-9Ni-4Sn alloy respectively when aging at 400 ?.