Effect of Ni and Mn contents on the microstructure and properties of Cu-Ni-Mn-P alloy

The microstructure of Cu-Ni-Mn-P alloys prepared with different contents of Ni and Mn was explored by using EBSD、TEM、HADDF STEM and HRTEM. The findings revealed that the hardness of the Cu-Ni-Mn-P alloy was significantly increased by addition Ni or Mn. However, the conductivity was declined to vary degrees. The peak hardness of Cu-0.78Ni-0.32Mn-0.21P (NMP211) and 0.4Ni-0.81Mn-0.19P (NMP121) alloys were 176.8 and 178.1 HV，respectively, which is 9.1 and 10.4 HV higher than that of Cu-0.39Ni-0.29Mn-0.18P (NMP111) alloy. In addition, the softening temperature of NMP121 alloy was 530 °C, which is 25 °C higher than that of NMP111 alloy.TEM observation demonstrated that after aging the precipitates of NMP111, NMP211, and NMP121 alloys were calibrated as NiP phase. The phase relationship between the NiP phase and matrix was as (11̅1)NiP // (02̅2)Cu. With the addition of Ni, the precipitation phase became fine and dispersed, resulting in the improvement of the hardness of NMP211 alloy. XRD analysis showed that the addition of Mn increased the lattice distortion and hardness of NMP121 alloy and sharply decreased its conductivity. The addition of Mn inhibited coarsening of precipitates in high temperature environment, and increased the softening temperature of NMP121 alloy.