High Performance Heavy Alloys by Alloying and Process Control.

This report covers research conducted at RPI prior to the PIs relocation to Penn State, where the focus was on processing optimization for novel compositions fabricated by powder metallurgy. Alloys were fabricated with improved strength and hardness using alloying additions of Mo, Ta, and Re. These results were then applied to the fabrication of injection molded heavy alloys to illustrate the combination of high sintered properties within the context of net shaping without post-sintering deformation processing. Because ductility is sensitive to the processing conditions, special attention was given to identification of useful processing atmospheres. A three stage sintering atmosphere cycle was developed to optimize densification and properties, and demonstrated for times up to 10 h. For comparison, long time vacuum sintering was performed to illustrate the importance of hydrogen and dew point control for this system. Microstructural observations include a drop in the contiguity and the flattening of larger grains with long sintering times, indicative of coalescence contributions to coarsening.