DOI: 10.1002/adem.200800313 Mechanical and Fatigue Behavior of Ca 65 Mg 15 Zn 20 Bulk-Metallic Glass** By Gongyao Wang * , Peter K. Liaw, Oleg N. Senkov, Daniel B. Miracle and Mark L. Morrison A number of BMGs, such as Zr-, Fe-, Pd-, Al-, and Ni-based alloys, have been discovered after the rapid development of glass-forming alloys during the early 1990s. [1–4] Ca-Mg-Cu and Ca-Mg-Cu-Ag BMGs were successfully fabricated by Amiya and Inoue in 2002. [5,6] Following these reports, numerous Ca-based BMG systems have been produced and studied. [5–21] Ca-based BMG alloys are of interest because of their unique properties, such as low density (2.0 g cc 1 ), low Young’s modulus (17–20 GPa) that is comparable to the modulus of human bones, low glass-transition tempera- ture (T g  100 8C) and a wide super-cooled liquid temperature range (DT xg ¼ T x  T g  30–80 8C). [15,18] Elements such as Ca, Mg, and Zn are biocompatible, which makes the Ca-Mg-Zn-based alloys attractive for use in biomedical applications. [18] The amorphous structure gives unique properties to BMGs, including high elastic strain, high fracture strength, and high fatigue resistance. Although the mechanical behavior of BMGs is studied widely, [1–4,22,23] there is no fatigue data for Ca-based BMGs. A comprehensive under- standing based on the compression, hardness, and fatigue behavior is critically important for the application of the Ca-based BMGs. In the current paper, the compression behavior, Vickers hardness, and fatigue characteristics of Ca 65 Mg 15 Zn 20 BMGs were investigated at room tempera- ture in air. A mechanistic understanding of the fatigue and fracture mechanisms of Ca-based BMGs is proposed. Experimental The Ca 65 Mg 15 Zn 20 (atomic percent, at%) BMG alloy was fabricated by induction melting pure elements (99.9 wt%) with a water-cooled copper crucible in an argon atmosphere. The prepared alloy was subsequently placed in a quartz crucible with a 2 mm diameter hole at the bottom, induction melted in an argon atmosphere, and injected into a water- cooled copper mold with a 15  15  4 mm 3 cavity. Previous studies demonstrated that the critical thickness of this alloy, below which it is fully amorphous, is 6 mm [9,15,18] . X-ray diffraction and differential scanning calorimetry (DSC) analyses indeed confirmed the fully amorphous state of the produced 4-mm-thick plates. Thermal properties of the cast alloys were determined using a DSC Q1000 differen- tial-scanning calorimeter (TA Instruments Inc., New Castle, DE) at a heating rate of 20 K min 1 . The weight of the DSC samples was in the range of 8–15mg. The DSC results exhibited that this Ca 65 Mg 15 Zn 20 BMG had a very low T g of 91 -C. [18] The ingots were cut into 4  4  4 mm 3 samples for compression and fatigue experiments. All samples were polished to avoid surface effects. Each side of these samples was polished to a 600-SiC-grit-surface finish parallel to the longitudinal axis of the specimens using a polishing fixture (South Bay Technologies, San Clemente, CA) to keep the sides parallel and perpendicular. A computer-controlled Material Test System (MTS Systems Corporation, Eden Praire, MN) servohydraulic-testing machine was employed to study these samples. The load frame was aligned prior to use. The compression experiments were performed at room temperature with strain rates of 10 4 , 10 3 , and 10 2 s 1 . Four to eight specimens were compression tested at each of the three strain rates. Load-controlled fatigue COMMUNICATION [*] Dr. G. Wang, Prof. P. K. Liaw, Dr. M. L. Morrison Department of Materials Science and Engineering, The University of Tennessee Knoxville, TN 37996, USA E-mail: gwang@utlr.edu Dr. O. N. Senkov UES, Inc., Dayton OH 45432-1894, USA Dr. D. B. Miracle Air Force Research Laboratory, Materials and Manufacturing Directorate Wright-Patterson AFB, OH 45433, USA [**] We would like to acknowledge the financial support of the National Science Foundation: the Division of the Design, Manufacture, and Industrial Innovation Program, under Grant No. DMI-9724476; the Combined Research-Curriculum Development (CRCD) Pro- grams, under EEC-9527527 and EEC-0203415; the Integrative Graduate Education and Research Training (IGERT) Program, under DGE-9987548; the International Materials Institutes (IMI) Program, under DMR-0231320; and the Major Research Instrumentation (MRI) Program, under DMR-0421219, to the University of Tennessee, Knoxville, with Dr. D. Durham, Ms. M. Poats, Dr. C. J. Van Hartesveldt, Dr. J. Giordan, Dr. D. Dutta, Dr. W. Jennings, Dr. L. Goldberg, Dr. C. Huber, and Dr. C. R. Bouldin as Program Directors, respectively. Work at the Air Force Research Laboratory (AFRL) was conducted through the AFRL on-site contract No. FA8650-04-D-5233 and through an AFOSR Task (01ML05-COR, Dr. J. Fuller, Program Manager). ADVANCED ENGINEERING MATERIALS 2009, 11, No. 1--2 ß 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 27