Dependence of resistivity on temperature and the mechanism of strengthening in a single-phase Cu-12Mn-3Ni alloy

The microstructural evolution of a single-phase Cu-12Mn-3Ni alloy during rolling and annealing has been investigated using electron backscatter diffraction and X-ray diffraction techniques. We have established the effects of microstructural characteristics on material strength and the temperature coefficient of resistance (TCR). The yield strength increased to 682 MPa after cold rolling with a strain of 0.87 due to an increase in the density of dislocation and low-angle grain boundary. A significant annealing softening is observed for the cold-rolled Cu-Mn-Ni alloy at temperatures above 400 degrees C, caused by recrystallization. The difference in yield strength for fully recrystallized alloys is mainly attributed to a difference in grain size, consistent with the Hall-Petch relationship. The addition of Ni and Mn enhanced the degree of difficulty in dislocation passing through the grain boundary, resulting in a higher Hall-Petch constant (274 MPa mu m1/2) for Cu-12Mn-3Ni alloys when compared with pure copper. The TCR is related to grain size, dislocation and Cu-12Mn-3Ni alloy texture. Grain coarsening and reduced dislocation density can effectively enhance the resistance temperature stability. In addition, the strong copper texture formed during cold rolling results in a difference in TCR associated with the rolling di-rection (RD) and transverse direction (TD) of the cold-rolled sheet. The Cu-Mn-Ni alloy crystal exhibits a lower resistance sensitivity to temperature when the [110]Cu direction is parallel to the current direction compared with the [111]Cu direction parallel to the current direction. The absolute value of the TCR in the TD of the cold-rolled sheet is 10.2 x 10-6 degrees C-1, lower than that in the RD (19.3 x 10-6 degrees C-1).