Injection Moulding of Low Expansion Fe-Ni-Co Alloys

Low-expansion alloys (Fe-Ni-Co) are used in specific applications that require accurate dimensional control, such as standards for length measurement, radar resonant cavities, components for nuclear reactors, and parts for ceramic-metal joining. This work investigates the production of the Fe-28 percent Ni-18 percent Co and Fe-28 percent Ni-23 percent Co alloys by powder injection moulding. The mixtures were characterized in a capilar rheometer. The microstructure was characterized with SEM and XRD, and the coefficient of thermal expansion determined with a linear dilatometer. The mixtures exhibited a pseudoplastic rheological behavior and a viscosity level adequate to the injection moulding. The microstructure of the two alloys was comprised of an austenitic phase and the residual porosity (8.5 percent). Dilatometric behavior of two alloys is characterized by two distinct regions, demonstrating the presence of the Invar effect and different transition temperature as a function of the cobalt content. Coefficients of thermal expansion for both alloys can be considered adequate for brazing with alumina. (Author)