There are 19 such centers across the nation. Each of them addresses research of a scope and complexity requiring the scale, synergy and research talent provided by a campus-based research center. The MRSECs essentially support the materials research infrastructure in the United States; promote collaboration between universities, industry and international organizations; and contribute to the development of a national network of university-based centers in materials research, education and facilities.

Recently, the University of California, Irvine (UCI) was awarded an MRSEC for the establishment of a Center for Complex and Active Materials (CCAM). The primary mission of CCAM is to establish foundational knowledge toward the development of new materials that may offer unique functionalities and superb performance. CCAM’s Director is Professor Xiaoqing Pan, and Professor Tim Rupert is the lead of the interdisciplinary research group (IRG) working on the interfacial science of complex concentrated materials. The Advanced Casting Research Center (ACRC) is part of the CCAM team and contributes to the processing of complex concentrated alloys (CCAs), both FCC and BCC systems.

One of the alloys being studied is the equiatomic CrCoNi ternary alloy. Derived from the CoCrFeNiMn Cantor alloy, the CrCoNi alloy has a single-phase FCC structure and is known for its exceptional mechanical properties, particularly at cryogenic temperatures. Defying the strength-ductility trade-off, this alloy shows a simultaneous increase in yield strength, ductility and fracture toughness as the temperature decreases, which is attributed to the ease of twinning activation in this CCA system.

In addition, chemical short-range order and FCC-HCP transitions prove to be key factors contributing to the alloy’s properties. The team at UCI is studying the interfaces at these twins and dislocation structures, the effect of processing kinetics on such interfaces and the overall microstructural evolution in the CrCoNi system. Furthermore, a dual-phase (FCC+L12) structure can be promoted through the addition of Al and Ti to the base ternary, which will aid the formation of secondary phases. The study of chemical ordering, grain boundary and interphase segregation in the (CrCoNi)100-x-yAlxTiy will be crucial in understanding the effect of alloying additions in the CrCoNi ternary CCA system.

Much like conventional superalloys, CCAs can be compositionally and structurally designed to operate at high temperatures. Conventional superalloys rely on a single principal element, but CCAs make use of several principal elements in near equiatomic ratios. This has opened the compositional space to the design of CCAs based on refractory-metal elements such as Hf, Zr, Nb, Mo, etc. By developing refractory complex concentrated alloys (RCCAs), new alloys that retain higher strengths at higher temperatures than conventional superalloys can be achieved.

Some RCCAs have already been shown to retain their strength up to 1300-1600°C, which is much higher than the temperature capabilities of Ni-based superalloys.[2] Thanks to the vast, unexplored compositional space of RCCAs, combinations of unique properties – such as lowered density and improved oxidation resistance, in addition to high-temperature strength – are achievable. More severe operating environments than conventional superalloys can withstand will be unlocked with the development of RCCAs.

Through compositional design of RCCAs, complex microstructural features are being developed to achieve improved mechanical properties. Most RCCAs developed today have made use of a single or multiple BCC phases, which retain strength at high temperature. By combining multiple principal elements in distinct, chemically ordered and disordered solid-solution phases, RCCA designs can unlock more complex deformation mechanisms such as twinning or transformation-induced plasticity.

The team at UCI is actively pursuing these projects and many others. For more information on CCAM at UCI, please visit: https://ccam.uci.edu.

 

About Advanced Casting Research Center

ACRC provides a collaborative environment in which members, faculty and students discuss challenges in the metal casting and manufacturing industry, specifically in two main domains: alloy development and novel processes. ACRC was founded in 1985 with a small group of companies to advance the use of light metals. Over the years, ACRC has grown to be one of the larger industry-university alliances in North America and has been an exemplar for carrying out fundamental research with clear industrial applications. To date, ACRC consists of 35 corporate members. Now headquartered in southern California, ACRC will expand the consortium to meet the needs of manufacturing industries on the West Coast – aerospace and major DOD OEMs.

 

About the University of California, Irvine

Founded in 1965, UCI is the youngest member of the prestigious Association of American Universities. The campus has produced three Nobel laureates and is known for its academic achievement, premier research, innovation and anteater mascot. Led by Chancellor Howard Gillman, UCI has more than 36,000 students and offers 222-degree programs. It is located in one of the world’s safest and most economically vibrant communities and is Orange County’s second largest employer, contributing $5 billion annually to the local economy. The National Science Foundation recently awarded $18 million to UCI in support of a new materials research science and engineering center. https://news.uci.edu/2020/07/14/nsf-grants-18-million-to-uci-for-materials-science-and-engineering-center/.

Diran Apelian is founding director of ACRC. He was recently appointed Distinguished Professor at UCI’s Department of Materials Science and Engineering after retiring as Alcoa-Howmet Professor of Mechanical Engineering at WPI. Apelian is widely recognized for his innovative work in metal processing and for his leadership as a researcher and educator. He is a member of the National Academy of Engineering, National Academy of Inventors, European Academy of Sciences and the Armenian Academy of Sciences. He has received numerous honors and awards; has over 700 publications; and serves on several technical, corporate and editorial boards.

 

References

  1. [1] Gludovatz, B., Hohenwarter, A., Thurston, K. et al., “Exceptional damage-tolerance of a medium-entropy alloy CrCoNi at cryogenic temperatures,” Nat Commun 7, 10602 (2016
  2. [2] O. N. Senkov, D. B. Miracle, and S. I. Rao, “Correlations to improve room temperature ductility of refractory complex concentrated alloys,” Materials Science and Engineering: A, 2021, doi: 10.1016/j.msea.2021.141512

Images supplied by author.