Grain growth inhibition in refractory metal alloys by a combination of Field Assisted Sintering (FAST) and nanoparticle addition

Researchers from Pennsylvania University are engaged in the development of new materials and the demonstration of near net-shaped component production via the powder metallurgical method of Field Assisted Sintering Technology (FAST). While the basic geometry of a FAST system (Fig. 1) is similar to that of hot pressing, FAST makes use of high electric current density to heat the metallic powder compact through Joule heating, leading to volumetric heating of the entire sample. Nanopowder additions of transition metal oxides, carbides, and nitrides offer one potential solution to the problem of grain growth. Addition of these powders act as grain growth inhibitors due to an effect known as Zener pinning. In Zener pinning, the presence of a second phase material at a grain boundary acts to produce a drag force which impedes the motion of the grain boundary outward. Nanopowder addition also results in improved hardness and yield strength. While this increased hardness can partially be attributed to the high hardness of titanium carbide itself, this hardness well exceeds that predicted by a simple Rule of Mixtures approach, suggesting additional strength increase due to solid solution strengthening and the Hall?Petch effect.