Srinath Viswanathan

Gelcast Tooling: Net Shape Casting and Green Machining

Abstract Gelcasting is an advanced powder forming process. It is most commonly used to form ceramic or metal powders into complex, near-net shapes. Turbine rotors, gears, nozzles, and crucibles have been successfully gelcast in silicon nitride, alumina, nickel-based superalloy, and several steels. Gelcasting can also be used to make blanks that can be green machined to near-net shape and then high fired. Green machining has been successfully applied to both ceramic and metal gelcast blanks. Recently, we have used gelcasting to make toolinj; for metal casting applications. Most of the work has centered on H13 tool steel. We have demonstrated an ability to gelcast and sinter H13 to near net shape for metal casting tooling. We have also been successful in green machining gelcast blanks using a three-axis CNC milling machine.

Effect of thermomechanical processing on the room-temperature tensile properties of an Fe3Al-based alloy

The poor room-temperature ductility of Fe[sub 3]Al-based iron aluminides has limited their use in structural applications. Increased ductilities are obtained in the presence of a partially recrystallized microstructure in the specimen. In a previous study, samples of an Fe[sub 3]Al-based alloy were subjected to final rolling at a temperature of 650C and annealed at various temperatures; room-temperature tensile elongations of 15 to 20% were achieved as a result. This paper documents attempts to improved the room-temperature ductility of FA-129 alloy, designated for high-temperature use, through an optimization of the final rolling temperature.

Using solidification parameters to predict porosity distributions in alloy castings

Quality criteria used in the computer-aided design and analysis of casting processes typically relate geometric, thermal, or solidification parameters to structural features such as centerline shrinkage and microporosity. Quality criteria for the prediction of porosity in castings have been used successfully in steel, but the application of criteria functions to nonferrous alloys has been less successful. Recent work suggests that the dominating mechanism that determines the amount and distribution of porosity in castings is strongly dependent on the solidification mode of the alloy and the solidification conditions. Accordingly, casting processes and alloy types are divided into four groups, and a different set of criteria functions are obtained for each group.

Acceptable Aluminum Additions for Minimal Environmental Effect in Iron-Aluminum Alloys *

A systematic study of iron-aluminum alloys has shown that Fe-16 at. % Al alloys are not very sensitive to environmental embrittlement. The Fe-22 and -28 at. % Al alloys are sensitive to environmental embrittlement, and the effect can be reduced by the addition of chromium and through the control of grain size by additions of zirconium and carbon. The Fe-16 at. % Al binary, and alloys based on it, yielded over 20% room-temperature (RT) elongation even after high-temperature annealing treatments at 1100[degree]C. The best values for the Fe-22 and -28 at. % Al-base alloys after similar annealing treatments were 5 and 10%, respectively. A multicomponent alloy, FAP, based on Fe- 16 at. % Al was designed, which gave an RT ductility of over 25%.

Industrial applications of solidification technology

Industrial solidification technology is concerned essentially with the removal of heat from a molten material or alloy in a controlled manner, resulting in its transformation from liquid to solid, thereby giving rise to a particular product or component with desired properties or performance. In general, controls may be applied to the liquid, to the solid, to the solid-liquid mixture, at the solidliquid interface, to the mold, and to the mold-metal or external interface. For example, casting processes commonly control fluid flow in the liquid and heat transfer in the mold or at the metal-mold interface by varying pouring techniques or mold materials, by stirring, and by the application of external cooling such as water lines or sprays; crystal growth processes primarily control the solidliquid interface; semi-solid processes utilize and control the solid-liquid mixture; and rapid solidification processes utilize and control rapid heat extraction to a mold or the ambient. Increasingly, the extent and manner in which control in solidification technology is designed or applied in industry is performed in conjunction with the computer, either by the analysis of fluid flow, heat transfer, and microstructural evolution or by the use of process sensing and control. Consequently, an important part of todays industrially oriented casting and solidification research is concerned with the development or application of computational techniques to the analysis of solidification. Even when fundamental solidification phenomena are the subject of inquiry, they are driven by the need for improved physical models for computational process analysis. Not surprisingly, this is also reflected in the content of current symposia on solidification technology, in those organized by TMS as well as other organizations. In this issue, five papers are presented on the state of the art in solidification. Four of the five papers are directly concerned with the application of computational analyses to solidification problems or investigate phenomena for their subsequent application to computational