An investigation of novel methods of preparing dense,homogeneous, spinodally decomposable copper-nickel-iron alloys

The densification behaviour of four different powder metallurgical alloying techniques have been studied in two spinodally decomposable alloys, Cu 24.5-Ni 48.5-Fe 27.0 at. % and Cu 35.5-Ni 19.5-Fe 45.0 at. %. Three of the techniques involve variations in producing the alloy by the direct reduction of mixed oxides. The fourth technique uses mixed commercial elemental powders. Within short sintering times (2.5 to 4.5 h) at 1000° C, the first three techniques produced microstructurally homogeneous and very dense (96 to 99% theoretical density) alloys. Within the same times and temperatures, the fourth technique showed no increase in the as-pressed (∼ 60%) densities. The difference in densification kinetics is believed to be due to the marked difference in specific surface area between alloy particles produced by the reduction of submicrometer oxide powders and atomized elemental powders ranging between 15 and 30 μm in size. The first three techniques are concluded to be useful and promising as means to produce homogeneous, high density Cu-Ni-Fe alloys.