Study On Microstructure And Mechanical Properties Of Cu-15Ni-8Sn-xMo Alloy

Cu-Ni-Sn alloys with high elastic modulus,hardness,electrical conductivity and good wear resistance are widely used in Marine engineering,mining,aerospace and electronics industries.However,the Sn-segregation and discontinuous precipitation in the subsequent aging process of high Tin Cu-15Ni-8Sn alloy are very easy to occur,resulting in a sharp decline in the overall performance of the alloy.In this paper,the influence of Mo element on the microstructure and mechanical properties of Cu-15Ni-8Sn alloy under different states is systematically studied by combining the simulation and experimental characterization.The main research contents are as follows:(1)Based on Pandat software,the phase diagram and phase fraction diagram of alloy are calculated,and the design criteria of alloy composition are proposed.It is found that Mo element has very low solubility in Cu matrix,so it should be melted at high temperature for a long time.Ni and Mo can form intermetallic compounds only at low temperature(Below250℃),and no Ni-Mo intermetallic compounds are formed after solution aging treatment.The results of phase field simulation of Cu-15Ni-8Sn-x Mo alloy confirm that Mo is easy to enrich in the front of Cu solid-liquid interface,which slows down the solidification of the alloy and improves the segregation of Sn element during solidification.(2)For the as-cast microstructure of Cu-15Ni-8Sn-x Mo alloy,Mo element exists in two forms.When the addition amount of Mo element is 0.3 wt.%,Mo element exists in the matrix as solid solution atom.When the content of Mo element in the alloy is 0.6-1.5 wt.%,Mo element will produce segregation phenomenon and exist in the structure in the form of second phase.Compared with other alloys with Mo content,the addition of 0.3 wt.% Mo in Cu-15Ni-8Sn alloy can significantly refine grain and improve segregation,and has better microstructure.(3)After solution treatment(at different temperatures for 4 h),Cu-15Ni-8Sn-x Mo alloy did not obtain single phase solid solution.When the content of Mo element is low(0.3wt.%),Mo element exists in the matrix in the form of solid solution atom.When Mo element is high(0.9,1.5wt.%),Mo phase appears in the tissue,and there are many Ni-rich phases around.In particular,when the content of Mo element is 1.5 wt.%,γ phase and discontinuous precipitation still exist in the microstructure after solution treatment,which is due to the high content of Mo has a curing effect on the alloy,resulting in poor solid solution strengthening effect.(4)In the aging process at 400℃,the addition of 0.3 wt.% Mo can effectively inhibit the formation of discontinuous precipitation,but excessive Mo element will promote the formation of discontinuous precipitation.After aging at 400℃ for 4 h,Cu-15Ni-8Sn-0.3Mo alloy has the best comprehensive properties,Vickers hardness is 379 HV,tensile strength is 854 MPa,corrosion rate is the slowest,passivation film stability is high.