Materials World Network: Structures and Mechanical Behavior of Amorphous Solids

Peter K. Liaw, University of Tennessee Knoxville, DMR 0909037

Findings:(1)The high-energy synchrotron diffraction analysis with the pair distribution function (PDF) technique shows that the average atomic distances from load and normal directions (LD and ND) are different during uniaxial compression, indicating an anisotropic deformation behavior for amorphous selenium, as shown in Figure 1. This anisotropic fracture is the result from the anelastisity, and is highly dependent on temperatures and strain rates.(2)Two Zr-based BMGs (Zr50Cu40Al10 and Zr50Cu30Al10Ni10 in atomic percent) are used to study their fatigue behavior at different sample sizes (3x3x25 mm and 2x2x25 mm) using four-point-bend fatigue loading in Figure 2. The stress vs. cycles to failure (S-N) curves demonstrate that BMGs with a large dimension showed longer fatigue lifetime and greater fatigue endurance limits than those with a small size. Above the fatigue-endurance limit, the lifetime of small samples is shorter than that of large samples when the applied stress increases.

Goals and Objectives:(1)The deformation mechanism of amorphous solids is still not clear. People tend to believe in an isotropic deformation mechanism for amorphous solids due to the lack of ordered lattice structures. However, atoms do not always behave isotropically during deformation. To simplify the amorphous solid system, the one-element amorphous selenium was studied in the present work.(2)Significant bend ductility can be obtained when the sample size of bulk metallic glasses (BMGs) is decreased to a critical value. However, the sample size influence on the fatigue behavior of BMGs is still not clear.

Figure 1: Stress relaxation curves at 25% engineering strain at 32 °C. Inserted figures are manipulated diffraction patterns at a certain time. The diffraction ring patterns are obtained at different time: (a) 150 s, (b) 300 s, (c) 450 s, (d) 600 s, and (e) 2,250 s.

0 500 1000 1500 2000 2500

10

20

30

40

50

60

True

Stre

ss (M

Pa)

Holding Time (s)

Amorphous Se Creep at Constant Engineering Strain 25

LDND

a

bc

e

d

%

Anisotropicvisible differences from LD and ND

IsotropicIdentical LD

and ND

Figure 2: The applied maximum stress vs. cycles to failure curves for two BMGs with different-size samples

under four-point-bend loading.

Metallurgical and Materials Transactions A, Vol. 43A, Issue. 8, August 2012 -- Special Issue of Symposium on Bulk Metallic Glasses VIII [The Minerals, Metals & Materials Society (TMS) Annual Meeting, Orlando, FL, 3/11-3/15/2012], edited by P.K. Liaw, G.Y. Wang, H. Choo, & Y.F. Gao of The University of Tennessee

Materials World Network: Structures and Mechanical Behavior of Metallic-Glass Thin Films

Peter K. Liaw, University of Tennessee Knoxville, DMR 0909037

2012 TMS Annual Meeting & Exhibition, Symposium on Bulk Metallic Glasses VIII, sponsored by the TMS/American Society for Metals (ASM) Mechanical Behavior of Materials Committee, and organized by P.K. Liaw, G.Y. Wang, H. Choo, & Y.F. Gao, held at Orlando, FL, 3/11-3/15/2012.

Dr. Peter Liaw teaches a graduate research course using the book on Bulk Metallic Glasses (BMGs), edited by Michael Miller and Peter Liaw. This course covers the development, theories, and applications of late-transition-metal bulk metallic glasses.

Dr. Liaw and an undergraduate student, Wayne Ethan Pratt, work on the fabrication of BMGs/BMG composites, and the thermography studies of shear-banding behavior in compressed metallic glasses and composites.

Liaw Wentz