Papers by Author: Waldyr Ristow

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.

Abstract: In order to obtain specific magnetic properties, it is of paramount importance to increase the alloy density of components fabricated by powder metallurgy. An alternative to increase the density of alloys such as Fe-49Co-2V would be the use of elemental Fe and Co instead of the prealloyed powder. Trying to give some insight on the industrial application of this strategy, this paper investigates the replacement of more conventional pre-alloyed Fe-49Co-2V powders with elemental Fe and Co. A previous analysis shows that it is possible to achieve higher densities using elemental Fe and Co powders sintered at the same temperature than Fe-49Co-2V. It is also shown that this leads to a noticeable improvement in some important magnetic properties such as permeability and magnetic induction.

Abstract: this paper describes the PADS process and equipment, which has been developed to produce PIM components. The use of a hybrid system of plasma discharge and Mo heating elements makes debinding and sintering PIM components in the same heating cycle possible. The use of an abnormal discharge between a cathode and anode under low-pressure provides reactive specimens that break the polymeric chains of the binder of the molded parts. By the combination of these features it was possible to use heating rates of 2,0º C/min during the debinding step. The hydrocarbons, resulted from debinding, are pumped out through vacuum pumps, without traps. The clean environment makes possible to sinter the parts in the same cycle, as well as execute a surface treatment during cooling. The results present short process times as 6 hours to Fe2Ni0,6C low alloy steel and 7 hours to 316-L stainless steel. Characteristics as density, carbon content and mechanical properties are similar to traditional PIM process. The reduction of energy and gas consumption and shorter lead-times are economic advantages of PADS system. The clean environment of PADS is also an ecological advantage.