High temperature mechanical behavior of refractory alloys and novel manufactured specimens with digital image correlation

Gas turbine efficiency is typically limited by the maximum allowable temperature for components at the inlet side and in the hot gas flow. One path to improving efficiency is the development of materials that can withstand greater stresses and higher temperatures than those currently implemented. Refractory alloys are promising candidates for advancing efficiency due to a high melting point, as well as greater toughness and ductility. However, it is well known that refractory alloys suffer from poor oxidation behavior. The ARPA-E ULTIMATE program has set out to combine new alloys with advanced coatings to mitigate oxidation effects, while maintaining the mechanical performance benefits of refractory materials. Low oxygen (inert gas) or vacuum systems are needed to assess high temperature mechanical performance of developed alloys. To investigate the environmental sensitivity of candidate alloys and develop high temperature testing capabilities, four argon tensile frames were upgraded as well as a single vacuum system at Oak Ridge National Laboratory. Digital image correlation (DIC) was incorporated into the vacuum frame allowing for surface strain determination and subsequent insight into thermomechanical response. Creep testing was performed at 1300 °C on predominantly two alloys, C-103 (Nb-10Hf-1Ti) and MHC (Mo-1.1Hf-0.1C) in vacuum and high purity Ar environments. The Mo-based alloy showed less sensitivity to oxygen, indicating that testing in Ar may be suitable. The C-103 testing demonstrated a stronger sensitivity to oxygen in the Ar environment, illustrating the need for the developed vacuum testing capabilities. This high temperature infrastructure with DIC will also be used to investigate novel graded tensile specimen produced by additive manufacturing. Opportunities for unique, high temperature and throughput DIC data will also be discussed.