Papers by Author: Bernardo N. Nobrega

Abstract: The gelcasting process is a forming technique originally developed for the shaping of advanced ceramics into final products in attempts to overcome some of the limitations of conventional forming techniques used in powder metallurgy. It is based on preparing a high solids loading suspension of powder dispersed in an aqueous organic monomers solution, which is poured into a mold and gelled through a chemically initiated polymerization. This work describes the gelcasting of HK-30 stainless steel, a type of powder commonly processed by injection molding. Large (70 x 30 mm) and geometrically complex green compacts with outstanding form retention and stability were obtained. Sintered parts showed good surface finishing and reached 96% of theoretical density, yield strength of 418.5 MPa, and ultimate strength of 701.5 MPa. These results compare favorably with those typically obtained through conventional powder injection molding of HK-30 feedstocks. They support the growing view that gelcasting may soon become an industrial, low cost alternative for near net shaping metallic powders into small or large parts with complex geometries

Abstract: A PADS (Plasma Assisted Debinding and Sintering) reactor developed by Lupatech S.A. has been employed to MIM process two Ni-based superalloys under Argon, at temperatures in the 1280 -1310 °C range, and for 2 to 3 hours. Both materials have chemical compositions similar to that of standard Nimonic® 90 but differ considerably in their powder characteristics. One type of powder was gas-atomized whereas the other was water-atomized. Samples of both materials in as-sintered states as well as subject to different HIP and heat treating conditions have been characterized mechanically in tensile tests and by HV measurements. The best overall results are attained by the water-atomized material sintered at lower temperatures. The PADS processing of these superalloys shows marked advantages over more conventional PM processing technologies. These results are particularly relevant to the development of turbine components for the automotive and aerospace industries.