High-Entropy Alloys in Hexagonal Close-Packed Structure
- PDF / 2,225,726 Bytes
- 11 Pages / 593.972 x 792 pts Page_size
- 47 Downloads / 281 Views
INTRODUCTION
THE core concept of high-entropy alloys (HEAs)[1,2] is to maximize the configurational entropy of solid solution phases via equi-molar compositions among multi-principal elements (for a comprehensive review, see References 3, 4). To date, there are very limited single-phase HEAs reported, and arbitrary mixing of four or more principal elements at equi-molar compositions usually does not render formation of disordered solid solutions.[1,5–7] This has posed great difficulty in understanding HEA formation mechanisms or establishing HEA formation rules (for a recent review in this topic, see Reference 8). The vast majority of reports pertaining to HEAs are focused on face-centered cubic (FCC) structures, body-centered cubic (BCC) structures, or their mixtures. Early work on FCC HEAs is based on CoCrFeMnNi[1] and its derivatives such as CoCrFeNi,[9] CoFeMnNi,[5,10] and CoCrMnNi,[10] and excessive addition of BCC stabilizers such as Al to them causes the formation of BCC and/or ordered BCC (i.e., CsCl-type B2) structures.[11–14] Recently, by inspecting phase diagrams and performing ab initio molecular dynamics (AIMD) simulations, Gao and Alman[5] suggested new single-phase FCC HEAs based on noble metals including CuNiPdPtRh and CuNiPdPt. Other BCC HEAs reported in the literature are centered on refractory metals.[15–19] In contrast, the progress in the design and fabrication of the hexagonal close-packed (HCP) HEAs has been
M.C. GAO, Principal Materials Scientist, is with the AECOM at National Energy Technology Laboratory, P.O. Box 1959, Albany, OR 97321. Contact e-mail: [email protected] B. ZHANG, Graduate Student, and S.M. GUO, Professor, are with the Department of Mechanical & Industrial Engineering, Louisiana State University, Baton Rouge, LA 70803. J.W. QIAO, Professor, is with the Department of Materials Science and Engineering, Taiyuan University of Technology, Taiyuan 030024, China. J.A. HAWK, Group Leader, is with the Structural Materials Development Division, National Energy Technology Laboratory, Albany, OR 97321. Manuscript submitted May 25, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS A
slow. Chen et al.[20] prepared BeCoMgTi and BeCoMgTiZn alloys that are entirely composed of HCP elements using mechanical milling, but no crystalline solid solutions and compounds formed before full amorphization. Detailed analysis on the formation of HCP HEAs was performed by Zhang et al.[3] who stated that the difficulty in forming HCP HEAs was because most elements in the periodic table prefer a BCC or FCC structure. Elements Cd, Mg, Os, Re, Ru, Tc, and Zn possess only one stable structure in HCP lattice below their melting points, while Be, Sc, Ti, Zr, and Hf transfer from the HCP to BCC structure and Co from the HCP to FCC structure at high temperatures. While HCP CoOsReRu HEA was suggested in Reference 5, Youssef et al.[21] reported that Al20Li20Mg10Sc20Ti30 transformed from FCC to HCP structure after annealing at 773 K (500 C) for 1 hour. However, it is not known whether the FCC and HCP phases formed
Data Loading...
