Materials Week '97: Monday PM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Monday afternoon, September 15.

DEFORMATION AND MICROSTRUCTURE: General Abstract Session II

Session Chair: Sriram Seshagiri, Wright Patterson Air Force Base, OH

X-RAY TOPOGRAPHIC STUDIES OF DISLOCATIONS IN ICE: I. Baker, X. Hu, D. Cullen, X. Pierron, Thayer School of Engineering, Dartmouth College, Hanover, NM 03755; M. Dudley, Dept. of Materials Science, State University of New York at Stony Brook, Stony Brook, NY 11794; D. Black, U.S. Dept. of Commerce, National Institute of Standards and Technology, Gaithersburg, MD 20899

THIS PAPER HAS BEEN WITHDRAWN

2:20 pm

DEFORMATION AND FRACTURE BEHAVIOR OF A BULK AMORPHOUS Zr-Ti-Ni-Cu-Be ALLOY: Peravudh Lowhaphandu, Lorie Ludrosky, John J. Lewandowski, The Case School of Engineering, Department of Materials Science and Engineering, Case Western Reserve University, Cleveland, OH 44106

The deformation and fracture behavior of a bulk amorphous Zr-TiNi-Cu-Be alloy were investigated. The effects of changes in stress state on the subsequent mechanical behavior were determined via a variety of test techniques, including compression, notched bend, and microhardness. SEM fractography was utilized to characterize the fracture surfaces, while X-ray diffraction and optical metallography were used to characterize the structure and evolution of deformation, respectively.

2:40 pm

FRACTURE TOUGHNESS AND FATIGUE-CRACK PROPAGATION IN A Zr-Ti-Ni-Cu-Be BULK METALLIC GLASS: C.J. Gilbert, R.O. Ritchie, Department of Materials Science and Mineral Engineering, University of California, Berkeley, CA 94720-1760; W.L. Johnson, Department of Materials Science, California Institute of Technology, Pasadena, CA 91125

The recent development of several alloy systems which readily form metallic glasses at low cooling rates (~10 K/s) has permitted novel measurements of both fracture toughness and fatigue-crack growth properties. Specifically, bulk plates of a Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 alloy were machined into compact-tension specimens with thicknesses and widths of ~7 mm and ~38 mm respectively. Fracture measurements on fatigue-precracked samples indicate that the fully amorphous structure has a fracture toughness of ~55 MPa. Heat treatments at 360°C for 12h and 450°C for 24h to form partially and fully crystallized microstructures, however, drastically reduce the fracture toughness to ~1.2 MPa and 1.0 MPa. Furthermore, the fully amorphous alloy is indeed susceptible to fatigue-crack growth, with a Paris-exponent and fatigue-threshold comparable to ductile crystalline metallic alloys such as high-strength aluminum or steel. Possible microstructural mechanisms for such behavior are discussed. Material supplied by A. Peker and M. Tenhover at Amorphous Technologies International.

3:00 pm

MECHANICAL AND STRUCTURAL PROPERTIES OF Mg ALLOY AZ31 IN HOT WORKING: A. Mwembela, E.V. Konopleva, H.J. McQueen, Mechanical Engineering, Concordia University, 1455 De Maisonneuve Blvd. W., H-549-34, Montreal, Quebec H3G 1M8, Canada

Alloys AZ31 (Mg-2.8Al-0.88Zn-0.OlMn) and AZ31-Mn (Mg-3.2Al-1.lZn0.34Mn) in torsion testing at temperatures T of 180 to 450°C at strain rates of 0.01, 0.1 and 1.0s^-1 exhibited flow curves with a peak and progression towards a steady state regime above about 300°C. The alloy AZ31-Mn exhibited higher ductility while alloy AZ31-Mn exhibited higher strength. The flow stress dependence could be described by the sinh relation and the T dependence by an Arrhenius function with activation energies of 125 and 138 kJ/mol for the two solute levels agreeing with those during creep in the range 300-400°C. When compared with die cast specimens of AZ91 tested earlier, these alloys exhibit less ductility, higher strength and activation energy. Optical microscopy revealed that dynamic recrystallization (I)RX) had nucleated at the grain boundaries and progressed more extensively above 300°C, but never completely replaced the original grains. The occurrence of DRX improved the ductility considerably. Below 300°C there was increasing evidence of twinning.