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.

MECHANICAL BEHAVIOR OF BULK NANO-MATERIALS: Session I

Session Chair: Walter W. Milligan, Department of Metallurgical and Materials Engineering; Michigan Technological University, Houghton, MI 49931-1295

Naresh N. Thadhani, School of Materials Science and Engineering, Georgia Institute of Technology; Atlanta, GA 30332-0245

2:05 pm INVITED

DEFORMATION CHARACTERISTICS OF NANOCRYSTALLINE METALS, INTERMETALLICS, AND COMPOSITES: Shankar Sastry, W.E. Buhro, R.L. Axelbaum, Washington University, St. Louis, MO 63130

Nanocrystalline powder compacts of metals- Cu, Ni, and W; intermetallics - NiAl and MoSi₂, and composites - Cu-TiB₂ and Ti-TiB_D, were prepared by hot pressing and hot isostatic pressing of nanoparticles produced by solution phase synthesis and gas-phase combustion synthesis. The compacts were characterized by microhardness measurements, compression tests, three-point bend tests, and indentation creep measurements. Nanocrystalline MoSi₂, NiAl, Ni, and Cu exhibit significant creep at T < 1/2T_m. Nanocrystalline copper exhibits superplasticity over a narrow temperature/strain rate window. Nano-grained tungsten exhibits anomalous strain rate dependence of flow stress and ductility. These unique characteristics will be discussed in terms of the extent of dislocation activity in nanograined materials, role of grain boundary diffusion and sliding, and adiabatic shear band formation at high strain rates. This research was conducted under NSF and AFOSR grants.

2:35 pm

FABRICATION OF NANO-GRAINED BULK NICKEL ALUMINIDES FROM MECHANICALLY ALLOYED PRECURSOR: T. Aizawa, Department of Metallurgy, University of Tokyo, 7-3-1 Hongo, Bunky-ku, Tokyo 113, Japan

Bulk mechanical alloying was first used to yield fine-grained powder mixture and compact; both aluminum and nickel powders are refined into lamellar structured mixture with the mutual distance less than 1 m. After densification of this compact by uniaxial compression at room temperature, this Ni-Al mixture is reactively sintered into nano-grained, bulk nickel aluminides. 3 Ni+1Al system is employed here to experimentally demonstrate that Ni₃Al billet and wire can be directly fabricated by the above procedure from the mechanically alloyed precursor.

3:00 pm

MECHANICAL BEHAVIOR OF CONSOLIDATED, ATTRITOR MILLED, NANOCRYSTALLINE Fe, Fe Al, AND Fe - C ALLOYS: J. Rawers, R. Krabbe, N. Duttlinger, U.S. Dept. of Energy, Albany (Oregon) Research Center, 1450 Queen Ave. SW, Albany, OR 97321

Although numerous studies have been conducted and reported on the production and characterization of nanostructured powders, there have been few studies that have characterized the macroscopic properties of consolidated nanostructured materials. Much of this difficulty results from the limited nanomaterial production capability and from the difficulty in retaining the nanostructure during consolidation. In this study, attritor milled Fe, Fe-Al and Fe-C powders were consolidated by hot-pressing. The effect of differing processing conditions (time, temperature, and pressure) on the resulting compact and nanostructure are presented. Compacted samples were of sufficient size that macroscopic properties such as density, hardness, and tensile and compression strengths could be evaluated. Relationships between (a) the milled and the consolidated microstructure, and (b) between nanostructure and macroscopic properties are explored and explained.

3:25 pm BREAK

3:40 pm

BULK ULTRAFINE GRAINED MATERIAL OBTAINED BY INTENSE PLASTIC STRAINING: P.B. Berbon,¹ N.K. Tsenev,² R.Z. Valiev,³ M. Furukawa,⁴ Z. Horita,⁵ M. Nemoto,⁵ and T.G. Langdon;^{1 1}University of Southern California, Los Angeles; ²Ufa State Petroleum University, Ufa, Russia; ³Ufa State Aviation University, Ufa, Russia; ⁴Fukuoka University of Education, Munakata, Japan; ⁵Kyushu University, Fukuoka, Japan

Using the Equal-Channel Angular Pressing (ECAP) technique, a large bulk piece of material can be transformed into Ultrafine Grained (UFG) structure through the introduction of intense plastic deformation. This paper describes the microstructural characteristics and mechanical properties of pressed Al-Mg alloys and a commercial Al-Mg-Li-Zr (01420) alloy having UFG structures. Mechanical testing was performed at temperatures up to 603 K and at strain rates from 10^-4 to 10^-2 s^-1. The strength was found to be stable for the 01420 alloy and it increased for the Al-Mg alloy. The elongation to failure was improved in all cases after ECAP, and there was a very substantial improvement in the ductility of 01420 alloy. The microstructure of 01420 was also found to be remarkably stable upon annealing.

4:05 pm

CHARACTERIZATION OF Cu-BASED MULTILAYERED STRUCTURES PRODUCED BY ELECTRODEPOSITION: F. Ebrahimi, Q. Zhai, D. Kong, Materials Science and Engineering Department, University of Florida, Gainesville, FL

Copper-silver and copper-nickel multilayered structures with nano-size layer thickness were produced using electrodeposition techniques. Low temperature heat treatments were conducted to investigate the microstructural stability of the layers. The microstructure was evaluated using electron microscopy techniques. Mechanical properties were studied using tensile testing at room temperature. Electrical resistivity measurements and x-ray diffraction analysis were performed for evaluation of defect structure and crystallographic texturing, respectively. The results of this study indicate that very high strength levels can be obtained in these structures. The strength and fracture mechanism were found to be a complex function of residual stresses, continuity of the layers, and interface structure.

4:30 pm

MECHANICAL PROPERTIES OF ELECTRODEPOSITED NANOCRYSTALS: D. Clark,¹ G. Palumbo,² K.T. Aust,³ and U. Erb,^{3 1}Nanometals Corporation, Queen's University, Kingston, Ontario, Canada K7L 3N6; ²Ontario Hydro Technologies, 800 Kipling Ave., Toronto, Ontario, Canada M8Z 5S4; ³Department of Metallurgy and Materials Science, University of Toronto, Ontario, Canada M5S 3E4

The mechanical properties of fully dense bulk nanostructured metals and alloys produced by electrodeposition will be reviewed. Particular emphasis will be on the transition from regular to inverse Hall-Petch behavior which is typically observed in hardness measurements on these materials for grain sizes less than 30 nm. The effect of annealing on the hardness of some of the alloys will also be discussed.