Effect Of Atomic Ratio And Content Of Ni And Ti On Microstructure And Properties Of Cu-Ni-Ti Alloys

With the development of society,not only the excellent strength,hardness and conductivity of Cu alloy,but also the high anti softening temperature of Cu alloy are needed in various fields.In this paper,the effects of Ni/Ti atomic ratio and total Ni/Ti content on the properties of Cu-Ni-Ti alloy were investigated,including hardness,conductivity and softening temperature.The microstructure of the alloy was analyzed by thermodynamic calculation and scanning transmission.The main results are as follows:(1)The thermodynamic calculation shows that Ni₃Ti phase exists in CuNiTi+FCC+Ni₃Ti three-phase region and FCC+Ni₃Ti two-phase region,and the solid solubility of Ni₃Ti phase is0.4%and 2.8%at 600?and 950?,respectively.Therefore,Ni₃Ti phase is likely to precipitate during aging;(2)The effect of Ni/Ti ratio on the properties of Cu-Ni-Ti alloy was studied when the total content of Ni+Ti was 4 wt.%.When Ni/Ti ratio increases from 1 to 5.8,Cu-Ni-Ti alloy has obvious age hardening characteristics,The peak aging hardness and maximum conductivity of Ni/Ti=4 and 5.8 alloys are low,Ni/Ti=1 and 1.5 alloys have higher peak aging hardness,but the maximum conductivity is less than 45%IACS,The peak aging hardness of Ni/Ti=2 and2.5 aged alloys is the highest,and the electrical conductivity is greater than 55%IACS,In addition,the tested alloy has good high temperature softening resistance,and the softening temperature is between 680? and 720?;(3)The effect of Ni and Ti content on the properties of Cu-Ni-Ti alloy was studied under the condition of Ni/Ti=2.The total content of Ni and Ti increases from 1 wt%to 6 wt%,and Cu-Ni-Ti alloy has obvious age hardening characteristics.Although the conductivity of Ni+Ti=1 wt.%alloy is higher than 60%IACS,the hardness is below 110 HV,The hardness of Ni+Ti=7 wt.%alloy is higher than 180 HV,but its conductivity is lower than 50%IACS.The hardness and conductivity of Ni+Ti=2,3,4,5 and 6 wt.%alloys are higher than 160 HV and50%IACS,respectively.In addition,the tested alloys have good high temperature softening resistance,and the softening temperature is between 680? and 750?;(4)The grain structure and phase composition of Cu-Ni-Ti alloy were analyzed.With the increase of Ni and Ti atom proportion,the as cast grains are refined and the solid solution grains are coarsened gradually.With the increase of Ni and Ti content,the as cast and solution grains are refined;There is no diffraction peak of the second phase in the XRD pattern.Scanning electron microscopy(SEM)showed that the second phase appeared in shape of strip and sphere,and mostly distributed along the grain boundary.The segregation of Ni and Ti in the second phase was found by surface scanning,while the content of Ni and Ti in the middle of the second phase was higher than that in the edge by line scanning.The point energy spectrum shows that the atomic ratio of Ni to Ti in the second phase is close to 3:1,which indicates that the second phase is Ni₃Ti;(5)The Cu-Ni-Ti alloy with peak aging and heat preservation at 720? for 1 h was analyzed by TEM.There are a lot of dispersed spherical nano precipitates in the structure,which are identified as Ni₃Ti phase by elemental analysis and diffraction spot calibration,The results show that the nano spherical precipitates are coarsened obviously after heat preservation,but the interface relationship with the matrix is still semi-homogeneous,which is the key reason for the alloy to have high softening resistance.