NSF-BSF: Designing Damage-Resistant Alloys with Potential Energy Landscape Roughness using Experimental Thermochemistry and Rapid Structural Damage Inference

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

NON-TECHNICAL SUMMARY This US-Israel Binational Science Foundation (BSF) collabortive project seeks to establish, test, and explore the limits of a more universal principle to design damage-resistant metals. Metallic materials form the backbone of an enormous amount of US infrastructure. Keeping their properties from degrading is tantamount to ensuring the safety and economic stability of our citizens which this infrastructure supports. Refractory alloys, or alloys which have very high melting temperatures, are particularly promising for seriously demanding applications such as aerospace, defense, medical devices, and nuclear power. However, the nearly infinite possibility of alloy compositions requires a fast and effective way to screen for the most damage-resistant ones. A combination of detailed calculations, high-temperature formation energy measurements, and ultra-rapid, laser-based ultrasound measurements during irradiation are used in parallel. This measures damage as it happens, comparing predictions of which alloys we expect to incur the least damage to reality. The scientific impact of a more universal principle for damage-resistant materials cannot be overstated – such a principle would slow initial material degradation resulting from corrosion, fatigue, radiation damage, or any other source of defects. The broader impact will be far more damage-resistant materials, which can hold their strength and toughness at higher temperatures, under heavier loads, and in more extreme situations. Examples include higher-temperature rocket and turbine parts for aerospace, more robust and longer-lasting medical implants, stronger, lighter armor for critical defense applications, and more radiation-tolerant components for fission and fusion nuclear reactors. TECHNICAL SUMMARY No fundamental, universal principle yet exists to deterministically design materials resistant to atomic-scale damage. Regardless of its source, the defects responsible must originate with a small ensemble of atoms nucleating into a more stable structure, and it is frustration of these stable structures that is the key to preventing defects from accumulating into stable structures which degrade material properties. What has been fundamentally missing from this more universal descriptor of damage resistance is the atomistic process by which point defects and similarly small defect clusters either find their way to similar clusters, forming larger clusters or recombining to lessen the degree of permanent damage. It is hypothesized that potential energy landscape (PEL) roughness, quantified by variance of migration energy barriers (MEBs), stops the rapid, 1D movement of some defects. First, new methods and principles for predicting which alloys in the (WVTa)xTi1-x family, specifically chosen due to availability of molecular dynamics interatomic potentials, will remain in single phase are devised. This is accomplished via thermodynamic calculations and high temperature drop calorimetry experiments. Next, these single-phase alloys are studied with a combination of density functional theory to compute MEB heights and distributions, to compare to in situ ion irradiation transient grating spectroscopy instrumented ion irradiations to confirm whether the core hypothesis is correct. Finally, by linking observed trends in thermo-elastic property changes with thermodynamic calculations of mixing enthalpies and the variance in PEL migration barriers, a simple design principle is articulated and tested to create the most damage-resistant base material composition, upon which other microstructural features (dispersoids, grain boundaries, secondary phases) can be added to further enhance material performance. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.