Regulation of Ni–Si intermetallics in Cu–Ni–Si alloys and its influence on electrical breakdown properties

Microstructure of Cu–Ni–Si alloys, especially morphology, amount and size of Ni–Si intermetallics, was controlled by heat and thermal–mechanical treatment, and then its influence on electrical breakdown behavior was investigated systematically. Results show that first breakdown is prior to occur on the Ni₃Si phase at the grain boundary and δ-Ni₂Si in the inner of Cu matrix in Cu–Ni–Si alloys. The decrease of Ni₃Si size by using thermal–mechanical treatment can significant enhance the breakdown behavior of Cu–Ni–Si alloys since it can change the total area of preferred phase within the action area of cathode spot. As a result, the chopping current and erosion depth decrease but arc life, breakdown field and erosion area increase with the decrease of Ni₃Si size, while the precipitation δ-Ni₂Si phase has limited effect on breakdown properties. On the whole, Cu–Ni–Si alloy by solution, hot forging and aging treatments in sequence has the best breakdown properties due to the uniform dispersion of Ni₃Si phase.