Supporting Online Material for

Transcription

1 Supporting Online Material for Super Plastic Bulk Metallic Glasses at Room Temperature Yan Hui Liu, Gang Wang, Ru Ju Wang, De Qian Zhao, Ming Xiang Pan, Wei Hua Wang* *To whom correspondence should be addressed. This PDF file includes: Materials and Methods Figs. S1 to S3 References Published 9 March 2007, Science 315, 1385 (2007) DOI: /science

2 Supporting Online Material Materials and Methods Fabrication of Materials The BMGs were prepared in following steps: The master alloys with nominal compositions were prepared by arc-melting of the mixture of constituent elements with purity better than 99.99% under a Ti-gettered argon atmosphere. Then the master alloys were remelted and in situ suck into a Cu mould to cast cylinders of different diameters. Composition scanning with a step less than 1% was started from Inoue Zr 65 Cu 15 Ni 10 Al 10 BMG and ended at the composition which shows poor glass formation ability, e.g. the Zr Cu Ni Al 10 BMG near the left edge of the green composition region in Fig.1A. The poor glass-forming alloy could only be cast in glassy rods with 2 mm diameter. The amorphous nature of the rods was ascertained by using x-ray diffraction (XRD). Each composition is repeated for at least 2 times. The formations of S1-S3 have been repeated more than 5 times. The elastic moduli including Poisson s ratio of these BMGs were monitored by ultrasonic method. We found that the compositional dependence of the Poisson s ratio is anomalous considering the element alloying. The BMGs of Zr Cu 18 Ni Al 10, Zr Cu Ni Al 10 and Zr 62 Cu 15.5 Ni 12.5 Al 10 (labeled as S1, S2 and S3 in text, respectively) exhibit larger v relative to that of others in this composition range. Elastic moduli measurements Elastic moduli of the BMGs were monitored using ultrasonic method (S1). The amorphous rod (φ=3 mm) was cut to a length of about 8 mm, and its ends were carefully polished flat and parallel. The acoustic velocities (longitudinal and transverse velocities v l, v s ) were measured using a pulse echo overlap method by a MATEC 6600 model ultrasonic system with a measuring sensitivity of 0.5 ns (S2). The excitation and detection of the ultrasonic pulses were provided by X- or Y- cut (for longitudinal and transverse waves, respectively) quartz transducers. The frequency of the ultrasonic is 10 MHz. This system was capable of resolution of the velocity changes to 1 part in 10 5 and particularly well suitable to determine the subtle changes in velocities. The density was determined by the Archimedean technique and the accuracy lies within 0.1 %. The velocities measurements were performed for the each sample for several times to examine the reproducibility and minimize error. Elastic constants (e.g., the Yong s modulus E, the shear modulus G, and the bulk modulus B and Poisson s ratio ν) were derived from the 2

3 density and acoustic velocities (S3) as follow: G=ρv s 2 ; B = ρ (v l 2 4/3 v s 2 ); ν= ρ(v l 2 2v s 2 )/2(v l 2 v s 2 ); E= 2G(1+ν). The obtained elastic data for various BMG materials are in good agreement with that measured by different methods (S2). XRD was performed using a MAC M03 diffractometer, and differential scanning calorimeter (DSC) was carried out on Pekin Elmer DSC-7. Uniaxial compression tests at room temperature were performed on an Instron 5500R1186 machine. Tests were carried out in a constant-crosshead-displacement-rate controlled manner. The samples with gauge aspect ratio (height/diameter) of 2:1 were cut out of the as-cast 2 mm rods, and the two ends were polished to make them parallel to each other prior to the compression test. For each sample, especially for S1 to S3, sets of five measurements are repeated in compression tests. Transmission electron microscopy (TEM) specimens were prepared by ion milling at liquid nitrogen temperature using a Gatan 691 Precision Ion Polishing System. High resolution TEM (HRTEM) observation was conducted on a Philips CM200EG machine operated at 200 kv. Scanning electron microscope (SEM) investigation was by performed using a Philips XL 30 SEM. 3

4 Supplementary Figures Figure S1 TEM bright-field image and selected area electron diffraction of sample S3 (A). The microstructure of S3 is similar to that of S1 and S2 which is composed of hard regions surrounded by soft regions. However, such structure was not observed in the BMGs shown in Fig.4D. In addition, the structure is also not found in other conventional BMGs such as Vitalloy series, Cu-, Ti-, and Mg-based BMGs, (B) shows an example of our newly developed TiCu-based BMGs. The TEM investigations confirm that the unique structure of our super plastic BMGs is not resulted from artifact during TEM sample preparation. 4

5 Figure S2 Composition mapping on as-cast specimen S2 by using Energy dispersive x-ray spectroscopy attached on SEM. Uniform distributions of components were clearly observed, confirming the compositional homogeneity of the BMG. Energy dispersive x-ray spectroscopy attached on TEM was used to determine the compositions of the soft regions and hard regions. The overall distribution of compositions was mapped by Energy dispersive x-ray spectroscopy attached on SEM. 5

6 36 Strain rate: 0.05/s Load at 500 nm depth ( µn) Indentation No. S2 Figure S3 Instrumented nanoindentation tests on the as-cast S2. All indentation penetrates into the sample surface by 500 nm. This depth corresponds to an indentation size about 4 µm which is comparable to the scale of hard regions. The spacing between indentations is 20 µm. The large fluctuations of load at 500 nm indicate that the strength inside the sample is inhomogeneous, that is, some regions are softer than other regions. Supplementary References S1. Wang, W.H. Correlations between elastic moduli and properties in BMGs. J. Appl. Phys. 99, (2006). S2. W.H. Wang, C. Dong, C.H. Shek, Bulk metallic glasses. Mater. Sci. Eng. R 44, 45 (2004). S3. D. Schreiber, Elastic Constants and Measurement (McGraw-Hill, New York, 1973). 6