Although the Ni-Cu system exhibits complete solid solubility, the large difference in melting points between Ni (1455 °C) and Cu (1085 °C) can lead to cu segregation. As a result of this segregation, this study investigated the effect of heat treatment on three different binary Ni-Cu alloy compositions. The process is for cold -compacted Ni and Cu shavings to be melted to produce ingots using state-of-the-art Amazemet ultrasonic equipment operating under an inert atmosphere. Then, followed by a heat treatment process to get different mechanical properties of the alloy. The samples were characterized using an optical microscope (OM) and an X-ray diffractometer (XRD) to track microstructural and phase evolutions, respectively. Microstructural evolution will help with the selection of an alloy suitable for use as a weld filler material at a later stage of the project. This work provides experimental evidence of composition- and cooling-rate-dependent metastable phase formation in Ni–Cu alloys. It was found that through appropriate heat treatment cycle, Cu segregation can be suppressed, which helped the alloys to achieve high strength where high hardness were achieved in water quenched alloys.