Correlation of Magnetic Permeability and Microstructure in Cupro-Nickel Alloys

AbstractThe magnetic permeability of a series of complex, high-strength cupro-nickel alloys is shown to be strongly dependent on the composition and degree of order of the strengthening γ′ (Ni3Al-type) precipitate. Electron metallography and X-ray-diffraction techniques were used to study the precipitation occurring in such alloys in the quenched, slowly cooled, and aged conditions. The composition of the γ′ precipitate varied with both alloy content and heat-treatment but was of the general form (NiCuh)3(AlFeMn). The effect of precipitate composition and degree of order on magnetic permeability was examined in a number of synthetic alloys with compositions similar to those of precipitates extracted from the original alloys. A direct correlation of magnetic permeability with the ordered state of these precipitates was possible by means of dark-field microscopy. The alloys have high magnetic permeability when ordered ferromagnetic precipitates are formed within a limited composition range. Magnetic permeab...