Manufacturing of nitinol parts and forms

Abstract

The invention includes processes and products made by the processes. The processes include making forms and parts by friable mold casting or die casting using molten Nitinol poured or injected into the mold or die. After the Nitinol has cooled to a solid state, it is removed from the mold by disintegrating the friable material of the mold and is heated to an elevated temperature under high pressure to consolidate the Nitinol and remove any internal voids. The parts and forms are then heat treated to reduce brittleness and improve toughness and impact strength. The part may be hot machined to reduce it to near net size, and may be ground to reduce the part to the exact specified part size. For example, cylindrical parts can be centerless ground; balls can be ground in a conventional ball grinder; flat stock can be surface ground. For parts requiring a smooth surface finish, polishing or lapping provides the specified surface finish on the part, down to 0.5 microinch RMS or finer. The part may be heat treated to obtain the desired hardness, from RC40 to RC65. An integral surface oxide of any of several colors can be formed on the surface of the part. The oxide surface may itself be polished to an even finer surface finish. Shape memory effect may be obtained in Type 60 Nitinol parts and forms that have been hot-worked by heat treating to about 675° C.-700° C. and oven cooling slowly over 8-10 hours to ambient temperature.