Introduction: High Entropy Alloys (HEAs) provide a transformative opportunity to design materials that are custom tailored to the distinct needs of a given application. HEAs enable manufacturers to realize products that have extraordinary and unique combinations of material properties, and new choices to replace expensive, rare, or hazardous elements. Researchers have generated HEA samples and prototypes that set the stage for advancing national energy, security, and health goals. United States investments have generated essential research, expertise, and resources that underlie HEAs. However, manufacturing HEAs, especially at scale, faces a plethora of challenges in alloy identification, high-throughput experimentation, feedstock quality, alloy processing, impurities, sharing of HEA data, intermediate scale manufacturing, and cohesion across the HEA manufacturing community. Seizing the opportunity of HEAs critically relies on translating promising research to materials and products manufactured at scale.
Recommendations: MForesight: Alliance for Manufacturing Foresight (MForesight.org) convened U.S. industry, research, and government experts and practitioners to gather insights and identify cross-cutting prospects and challenges for manufacturing HEAs in the United States. The resulting report, High Entropy Alloy Manufacturing, showcases four actionable recommendations for translating HEA research into HEA manufacturing competitiveness:
1. Invest in critical translational research for HEA manufacturing, including the alloy production processes of melting, casting, thermomechanical processing and joining, and wire-, powder-, and coating-based manufacturing methods. Additionally, it is critical to advance alloy identification and modeling methods.
2. Establish a National Testing Center for HEAs that provides a centralized location for advancing and conducting high-throughput testing to accelerate discovery and validation of HEAs and associated manufacturing processes. The center should collaborate with governing bodies and national facilities to develop property and testing standards critical to HEAs.
3. Develop a central database for HEA data that empowers U.S. researchers to avoid duplicate efforts, expand analysis methods, develop high-fidelity models, consider unfavorable results, and accelerate research progress. Leveraging a range of stakeholders, the database should collect, validate, organize, and provide access to HEA alloy, manufacturing, and modeling data. The database should be made available to all U.S. based researchers.
4. Enhance collaborative efforts through programs that connect stakeholders in industry, universities, and federally funded research and development centers. This includes creation of an interdisciplinary advisory group for HEA manufacturing roadmapping exercises and needs prioritization.
Technical Focus: The MForesight report highlights opportunities for translational research on technologies and challenges in need of national attention. Alloy identification research should focus on connecting layers of models and experiments that are at different fidelities, streamlining diverse toolsets, and expanding tools to address refractory alloys. High temperatures and complex chemistries in HEAs require novel high temperature melt processes and stirring technologies, cleaner master alloys, and better manufacturing analysis tools. Reducing defects and undesirable microstructures during casting can be enhanced through improved hot top casting and rheocasting methods, as well as enhanced control of cooling rate. The high temperatures of refractory HEAs and challenges in homogeneity drive the need for research on high-temperature roll and die materials and novel hot rolling methods. Mini-mills, such as those used for steel, would greatly accelerate HEA production scale-up and testing. Direct HEA fabrication methods such as additive manufacturing, sputtering, cold spray, and other powder-, wire-, and coating-based methods require improved powder and wire production, novel and improved additive process, highly-controllable multi-element sputtering, and improved understanding of the relationship between processes parameters and alloy performance.
Modeling spans the entirety of HEA identification, development, and manufacturing, with research needed to understand the relationships between manufacturing processes, microstructure, and the resulting alloy performance. Established methods such as CALPHAD (CALculation of PHAse Diagrams) show immense promise, as well as emerging methods such as Special Quasi-random Structure (SQS) approaches, atomistic potential methods, and Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA). Machine learning presents another viable path for model generation.
High-throughput testing requires overcoming challenges in sample fabrication, testing method for varying size & scale, testing of complex conditions, high-throughput testing processes, and a lack of standardization. “Alloy-on-demand” through additive manufacturing provides a potential route to rapid sample production. Advancement of high-throughput HEA assessment is needed to ascertain mechanical, chemical, microstructure, environmental, and functional properties. This will be aided by miniaturization and mass parallelization of traditional materials testing methods.
Conclusion: HEAs are a tremendous opportunity for both economic growth and realization of national priorities, but swift action is needed by key stakeholders. A focused effort by public and private members of the HEA manufacturing community is paramount to overcoming cross-cutting barriers and realizing the vison of ubiquitous utilization of HEAs.
For the full report of findings, recommendations, and contributorsReference Bishop-Moser and Miracle1 please visit MForesight.org.
MForesight: Alliance for Manufacturing Foresight is a federally-funded, independent, nonprofit technology-driven organization focused on accelerating technological innovation to enhance U.S. manufacturing competitiveness. Serving as the voice of the nation’s advanced manufacturing community, MForesight connects researchers and practitioners and harnesses their collective wisdom to forecast and develop recommendations on emerging technologies and cross-cutting challenges. Through its timely reports, MForesight serves as a continuous source of intelligence on advanced manufacturing trends and opportunities to policy makers, business leaders and researchers.
