Metastability in high-entropy alloys: A review
- PDF / 980,518 Bytes
- 14 Pages / 584.957 x 782.986 pts Page_size
- 80 Downloads / 222 Views
REVIEW This section of Journal of Materials Research is reserved for papers that are reviews of literature in a given area.
Metastability in high-entropy alloys: A review Shaolou Weib) Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
Feng Heb) Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA; and State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an 710072, People’s Republic of China
Cemal Cem Tasana) Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA (Received 23 April 2018; accepted 6 August 2018)
Classical alloy design strategies often aim to benefit from metastability. Examples are numerous: metastable transformation- and twinning-induced plasticity steels, cobalt or titanium based alloys, age hardenable aluminum alloys, and severe plastic deformed nanostructured copper. In each of these cases, superior engineering property combinations are achieved by exploring limits of stability. For the case of high-entropy alloys (HEAs), on the other hand, majority of present research efforts focus on exploring compositions that would yield stable single-phase structures. HEA metastability and its effects on microstructure and property development constitute only a relatively small fraction of ongoing work. To help motivate and guide a corresponding shift in HEA research efforts, here in this paper, we provide an overview of the research activities on metastability in HEAs. To this end, we categorize the past research on the topic into two groups based on their focus, namely, compositional and structural stability, and discuss the most relevant and exciting findings.
I. INTRODUCTION
High-entropy alloys (HEAs), or compositionally complex alloys, have arguably become the fastest growing research direction in metallurgy in the last decade.1–3 Majority of the research efforts in the initial part of this period focused on assessing the validity of the originally proposed HEA concept, i.e., configurational entropymaximization can stabilize heavily alloyed single-phase solid solutions. While these proof-of-principle investigations have significantly contributed to the fundamentals of solid solution thermodynamics, the widely studied single-phase HEA microstructures are often not promising from the perspective of property requirements for engineering applications. It is known from decades of optimization of traditional alloy systems (e.g., Fe-, Al-, Ni-, and Ti-) that single-phase alloys can rarely exhibit competitive property combinations. In fact, exceptional toughness, ductility, and strength levels are usually
a)
Address all correspondence to this author. e-mail: [email protected] b) These authors contributed equally to this work. DOI: 10.1557/jmr.2018.306 J. Mater. Res., 2018
achieved by utilizing different states of metastability.4–7 Despite the apparent importance
Data Loading...
