Ultrahigh Temperature Strength of Multi-Principle-Element Alloys
Abstract
Refractory-multi-principal-element alloys (RMPEAs) hold tremendous potential for use as structural materials that can operate at ultrahigh temperatures and in the extreme environments required for energy efficient power generation, hypersonic flight and space access. Targeted use temperatures of 1300-1600oC cannot be met with Co- or Ni-based superalloys and the development of viable RMPEAs would represent a revolution in high temperature materials. Innovative computational and experimental efforts are being pursued to design, explore and understand the processing, properties and environmental behavior of RMPEAs, but the current dearth of high temperate tensile and creep data represents a critical impediment to the realization of this promising new class of alloys. The proposed effort will involve the integration of advanced processing capabilities, novel ultrahigh temperature meso-scale mechanical testing, detailed microstructural characterization, and close collaboration with the existing ONR-sponsored BRC and MURI teams, Beyerleins multiscale modeling effort at UCSB and Clarkes thermomechanical processing effort at the Colorado School of Mines. We will rely on our collaborators to identify promising alloy compositions and place our focus on providing much needed ultrahigh temperature tensile and creep data and developing a fundamental mechanistic understanding of ultrahigh temperature deformation in RMPEAs.Ultrahigh temperature (UHT) tests will be conducted in a high vacuum chamber outfitted with a custom load frame, Joule heating, and quartz windows for pyrometry and DIC strain mapping. Constant strain rate tensile tests will be used to measure the Youngs modulus, yield strength, strain hardening rate, ultimate tensile strength, and strain to failure at temperatures of 1000-1600C and a variety of crystallographic orientations. Interrupted tensile tests and stress relaxation experiments will be used to measure time-dependent creep exponents and activation energies over the same range of temperatures. Experiments will be conducted on three generations of RMPEAs. In the first year, single crystals of the Senkov alloy (HfNbTiTaZr) will be tested. In the second year, the UHT tensile and stress relaxation experiments will be conducted on an alloy identified by the ONR-BRC via machine learning approaches to alloy exploration. Detailed slip trace and TEM observations will be performed to characterize UHT dislocation activity in these single crystalline RMPEAs; the results will form the basis of an interactive collaboration with Beyerlein who has developed a multi-scale methodology for modeling energy minimum pathways for dislocation in RMPEAs. In the third year we will measure and characterize the UHT mechanical response of multi-phase O- and C-containing RMPEAs developed by Clarke. In the fourth year, creep experiments of polycrystalline specimens at low loads and long times will be used to define the conditions associated with grain boundary(Coble) and lattice diffusion (Herring-Nabarro) mediated creep, which will allow us to construct Frost-Ashby deformation mechanism maps for RMPEAs. Taken as a whole, the UHT experiments and detailed microstructural investigations outlined in this proposal will provide the community with a more complete understanding of ultrahigh temperature strength in this new class of structural materials. Approved for Public Release
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- May 05, 2021
- Source ID
- N000142112462
Entities
People
- Kevin Hemker
Organizations
- Johns Hopkins University
- Office of Naval Research
- United States Navy