Enhancing the Thermoelectric and Mechanical Properties of CuNiMn Alloys by Introducing Si Impurity Atoms and Twins

Constantan (Cu-Ni alloy) has been successfully applied in precision resistors, thermocouples, and other devices because of its low-temperature coefficient of resistivity and favorable thermoelectric properties. The high power factor of CuNiMn alloys endows them with a higher output power density than those of conventional thermoelectric materials. However, as an alloy with intrinsic metallic properties, its high thermal conductivity is also an important factor that limits further improvement in its thermoelectric properties. In this study, CuNiMn alloys doped with Si atoms were prepared by melting and rolling. The thermal conductivity of the cryorolled CuNiMn-2.0 atom % Si alloy decreased effectively to 29.96 W m^-1 K^-1 at 773 K, which is 36.2% lower than that of the pristine alloy. Moreover, the thermoelectric figure of merit of the cryorolled Cu₅₆Ni₄₂Mn₂-2.0 atom % Si alloy reached 0.17 at 773 K, which is 47% higher than that of the as-cast Cu₅₆Ni₄₂Mn₂ sample. The decreased thermal conductivity of the alloy is attributed to intensified phonon scattering at various frequencies due to the introduction of solid-solution atoms, dislocations, and twin boundaries. These results provide a solution to optimize simultaneously the thermoelectric and mechanical properties for CuNiMn-based alloys.