Precipitation Behavior and Properties of Cu-Ti Alloys with Added Nitrogen

The effects of adding nitrogen (N) to age-hardenable Cu-Ti alloys on their microstructure, hardness, and conductivity have been investigated. It was found that the aging of Cu-Ti-(0.06-0.6) mol% N alloys resulted in the continuous formation of finely precipitated needle-shaped alpha-Cu4Ti grains and the discontinuous formation of coarse cellular components composed of a stable beta-Cu4Ti and Cu solid solution at the grain boundaries, in a manner similar to that in the case of conventional Cu-Ti alloys without any N. Furthermore, a small amount of granular TiN particles was also formed in Cu-Ti-N alloys. The hardening behavior of Cu-Ti-N alloys was similar to that of Cu-Ti alloys without N. This similarity was attributed to the finely dispersed precipitation of alpha-Cu4Ti that was similar between Cu-Ti alloys with and without N. The electrical conductivity of Cu-Ti-N alloys increased more steeply than that of Cu-Ti alloys without N. This is because in the case of Cu-Ti-N alloys, the co-precipitation of alpha-Cu4Ti, beta-Cu4Ti, and TiN efficiently reduced the Ti concentration in the matrix. Thus, the conductivity of peak-hardened Cu-Ti-N alloys can be improved by optimizing the N concentration and aging temperature.