Accelerated Design of New Materials to Survive Extreme Environments
Motivation
Reducing fossil fuel consumption while achieving the societal desire for increased global connectivity and quality of life requires the development of more efficient transportation and energy conversion technologies. Progress toward this goal is limited by the capabilities of existing materials to survive in the extreme service environments encountered in systems like spacecraft and jet engines, chemical processing facilities, and nuclear reactors.
Discovering materials and architectures with the right combination of toughness, thermal stability, and chemical inertness is critical to advancing technologies to meet society’s grand challenges. The interrelated nature of these stressors means that no single material property or characteristic is an adequate predictor of material performance. Instead, performance depends on a combination of individual properties as well as factors related to the thermodynamics (the driving forces for chemical reactions) and kinetics (the rate at which those reactions occur) in a specific environment.
Approach
To design resilient new materials, our approach couples experiments with analytical and computational models to understand why materials fail and to accelerate the discovery and design more durable materials. We use computational thermodynamics tools to predict driving forces for chemical reactions and identify stable structures, and mechanics models to predict mechanical stresses developed in service. In the lab, we synthesize new materials, measure their properties, and test them in complex thermal-chemical-mechanical environments.
Focus Areas
Our research spans a variety of material systems including oxide and non-oxide ceramics, metal alloys, and intermetallic compounds. We study these as pure materials and consider their integration into layered structures (coatings) and 3-dimensional composites. Ongoing research is divided into several primary areas:
Durable Ceramic Coatings for Turbine Engines
Ceramic coatings play a crucial role in protecting superalloy and ceramic composite (CMC) components in turbine engines powering aircraft and generating electricity. Critical properties include the thermal conductivity, coefficient of thermal expansion, thermal stability, mechanical toughness, and resistance to degradation by corrosive deposits. One thrust of our research in this area focuses on the development of new multi-phase coating materials offering improved resistance to calcium magnesium aluminosilicate (CMAS) corrosion. Another thrust is focused on the design of multi-layer coating architectures to protect next-generation refractory alloys.
Design, Processing, and Surface Enhancement of Multi-Principal Element Alloys
Simultaneously achieving desirable internal strength and toughness, with surface resistance to wear and corrosion is a longstanding challenge in alloy design. Many of the elements that can be added to control the surface reaction chemistry (such as Al, Cr, and Si) also stabilize crystal structures (phases) that reduce the fracture resistance of the alloys. Our approach leverages the extended solid-solution homogeneity ranges in recently discovered multi-principal element alloys (MPEA) to dial-in the desired chemistry. We are developing an alloy design framework that uses computational thermodynamics to identify how specific substitutions of one atom for another change the chemical activity of each constituent. In conjunction with experimental measurements of reaction rates and diffusion, we can then predict how the alloy will respond during processing, and what the final properties will be.
Mitigating the Effects of Microstructure Defects on the Durability of Ceramic Composites
Ceramic matrix composites (CMC) use reinforcing fibers to overcome the brittle nature of ceramics and enable higher use temperatures and longer lifetimes for thermo-structural applications. However, CMCs experience premature strength degradation if oxygen penetrates through defects such as small cracks, pores, and chemical impurities left behind during processing. Current research in my group seeks to understand how these defects facilitate oxygen transport, and how we can improve the processing methods or material chemistry (such as by using additives to generate a ‘self-healing’ behavior) to improve performance.
Decoupling Anion Effects Contributing to Alloy Hot Corrosion
We encounter corrosion (the destruction of material by chemical reactions) every day when we see rusting steel or crumbling concrete. Corrosion reactions are accelerated at high temperatures, especially when pollutants present in the environment adhere to metal alloy surfaces. Prior research on these hot corrosion phenomena has often considered the effects of oxide, chloride, and sulfate pollutants separately. However, based on evidence of more severe corrosion in the presence of multiple anions, my group is now developing a framework to understand why, and under what conditions, the corrosion is accelerated. In this work, our application of automated image analysis to generate large datasets allowed us to easily identify relatively scarce features (comprising just a few percent of the alloy surface) that are important to differentiating the effect of pollutants on the corrosion process.
Funding
Our research is funded by a variety of federal agencies, often with either direct collaboration or advisory input from industrial partners. Current or past support includes:
