Materials Week '97: Thursday AM 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 Thursday morning, September 18.

P/M CURRENT RESEARCH AND INDUSTRIAL PRACTICES: Session III: Current Research II

Session Chairperson: Burton R. Patterson, Department of Materials and Mechanical Engineering, University of Alabama-Birmingham, AL 35294-4461

METAL POWDER RESEARCH AT NIST: Stephen D. Ridder, NIST, B156, Bldg. 231, Gaithersburg, MD 20899

Powder Metal processing research at NIST includes expert system control of Inert Gas Atomization (IGA), nitrogenated stainless steel powder processing, advanced sensors for diagnostics and control, mechanical alloying, and thermal spray deposition. Recent IGA studies have focused on the measurement and control of process pressures, temperatures, and flow rates of metal and gas and quantifying the effects of controllable parameters on the metal powder particle size. Instrumentation has been developed that allows real-time measurement and control of the gas to metal mass flow ratio, the atomizing gas jet pressure ratio, and the resulting metal powder size distribution. An Expert System driven computer control system incorporating these sensors provides the operator real-time graphical indications of the atomizers performance and allows for the construction of control strategies of arbitrary complexity. In addition to these IGA studies, new DC and RF plasma spray systems are being installed to extend the sensor and expert system control capabilities to include thermal spray processing. This technology, currently used to provide thermal barrier and wear resistance coatings for many high-performance/high-cost products, will require new advanced sensors and control for improved coating reliability and reduced overall cost before it will be accepted in high production industries such as automotive and consumer electronics.

9:00 am INVITED

UNDERSTANDING THE BEHAVIOR OF FULLERENES IN METALS WHEN PROCESSED BY P/M METHODS: E.V. Barrera, Xiayang Sheng, J. Sims and *V. Provenzano, Department of Mechanical Engineering and Materials Science, Rice University, Houston, TX 77005; *Physical Metallurgy, Division of Materials Science and Technology, Code 6320, Naval Research Laboratory, Washington, DC 20375-5343

With the recent awarding of the 1996 Nobel Prize in Chemistry to the discovery and understanding of fullerenes, it is evident that the capability of developing new materials with these molecules is dependent on the ability to process them in various material systems. This talk will focus on the processability of fullerenes in metals, polymers, and ceramics. The focus will be on powder processing methods but will review the range of processing where the fullerene powder has been used. Recent investigations directed toward the use of nanotubes will also be discussed. Fullerenes are seen as a potential dispersoid, reinforcement or second phase in the numerous material systems being explored. This research is supported by a NSF grant: DMR-935705, Texas Higher Education Coordinating Board grant: TATP 3604-056, and an Office of Naval Research grant: N00014-97-1-0391.

9:20 am INVITED

MODELING AND CONSOLIDATION OF NANOCRYSTALLINE CUTTING TOOLS FOR MACHINING TITANIUM: Ram B. Bhagat, Penn State University, Engineering Science and Mechanics Department, 227 Hammon Bldg., University Park, PA 16802

A key issue pertaining to the consolidation of nanocrystalline powders is the grain growth to micrometer size. Addition of grain growth inhibitors such as VC and Cr3C2 has been reported to be useful during the liquid-phase sintering of nanocrystalline WC-Co powder to produce ultra fine grained material, but not truly nanograined material (grain size < 100 nm). This paper deals with modeling and rapid solid-state consolidation techniques (microwave sintering and vacuum hot pressing) for fabricating nanograined cermet (WC-10 wt.% Co) wherein the maximum temperature is kept much below the eutectic temperature of the WC-Co system (~13200°C). In conjunction with the results of the modeling, the processing conditions are optimized to fabricate fully dense samples with minimum grain growth. The fully dense nanograined WC-10 wt.% Co samples (with no dopants) have higher hardness and fracture toughness than those hitherto reported for conventionally processed material of identical composition. Nanograined ball end mills (WC-10 wt.% Co) have been fabricated for machining titanium; initial results appear very promising for improved cutting performance and enhanced tool life.

9:50 am INVITED Talk by the Secretary of the P/M Committee

THE DEVELOPMENT OF A LIQUID-PHASE-SINTERED, Cu-BASED P/M MATRIX FOR AN SiC REINFORCED COMPOSITE MATERIAL: B. Wang, G.M. Janowski, Department of Materials and Mechanical Engineering, The University of Alabama at Birmingham, Birmingham, AL 35294-4461

A liquid-phase sintered copper-based alloy was developed as a matrix for SiC particle reinforced composite materials. The concentrations of elemental additives (Al, Si, and Mg), sintering temperature, green density, and sintering atmosphere were varied in order to achieve high density and strong matrix/particle bonding. Two satisfactory alloys were developed: Cu-7 Al-2 Mg-2 Si and Cu-8 Al-2 Mg-2 Si (in wt.%), with the latter material having a higher strength (yield strength of 280 MPa compared to 218 MPa). Although the uncombined Mg was likely not present after vacuum sintering, its presence in the elemental powder blends was key in achieving a strong bond between the SiC particles and Cu matrix. A comparison of the particle cracking of these Cu-based composite materials will be made with similar Al-based composites. This research was supported by Alabama-NSF EPSCoR.

10:10 am INVITED

A STUDY OF THE BRAIN GROWTH BEHAVIOR ON NANOCRYSTALLINE Cu AND Cu-Fe ALLOYS PREPARED BY MECHANICAL ALLOYING: Steven C. Axtell, Department of Mechanical Engineering, Center for Materials Research and Analysis, University of Nebraska-Lincoln, Lincoln, NE 68588-0656

Research at the University of Nebraska has focused, in part, on the characterization of the grain growth behavior of nanocrystalline alloys prepared by mechanical alloying. The grain growth behavior of nanocrystalline materials is of interest due to its technological importance in the consolidation of these materials and its scientific importance in determining whether the behavior is similar to that of larger-grained materials. Isochronal and isothermal annealing experiments have been performed on Cu and Cu-Fe alloys using in situ x-ray diffraction. The variation in the diffracting particle size and the grain growth exponent, n, in the normal grain growth equation as a function of grain growth of nanocrystalline Cu prepared by mechanical alloying decreases with increasing temperature and increases with the addition of Fe.

10:40 am INVITED

NEW PROCESS CONTROL AGENTS FOR MECHANICAL ALLOYING AND BALL MILLING: Frank Biancaniello, NIST, Gaithersburg, MD 20899

Prior to about 1970, fine metal powders (<100=B5m) were produced by grinding coarse metal powders in a conventional ball mill. Lubricants such as kerosene or fatty acids were employed to eliminate the cold welding (agglomeration) of the particles during the milling process, thus achieving a higher yield of the fine powders. However, these lubricants, which are presently referred to as process control agents (PCA), often contaminate the powders leading to degradation of the alloy properties following powder consolidation. In the late 1960's, researchers at Inco discovered that metal powders could undergo repeated welding, fracturing, and rewelding when processed in a dry high-energy ball mill using stearic acid (SA) as a PCA. In this study, three new PCA's are investigated and compared with SA. X-ray diffraction analysis results indicate that these new PCA's are as efficient or more so than SA and leave little or no contaminating residue when heated at relatively low temperatures during degassing followed by subsequent consolidation at higher temperatures.

11:10 am INVITED

POWDER METALLURGY AT LOS ALAMOS NATIONAL LABORATORY THEN AND NOW: S.R. Bingert and H. Sbeinberg, P.O. Box 1663, MS G770, Los Alamos National Laboratory, Los Alamos, NM 87545

Powder metallurgy has been an active part of Los Alamos programs for over fifty years. Although not all state-of-the-art, the capabilities represent one of the widest and most unusual collections of processing equipment in the country, most of which has been used for fabrication of components for internal requirements and for research and development, or demonstrations of processing technology. The past, present, and future operational capabilities of the section will be presented and include: powder making, powder characterization, reactive powder handling, powder conditioning, hot and cold uniaxial pressing, hot and cold isostatic pressing, extrusion, powder rolling, sintering and heat treatment facilities, atmospheric and low pressure plasma spray, flame spray, wire arc spray, alloy development, rapid and directional solidification, and consolidation and micromechanics modeling. The team has worked on a large variety of materials over the course of the LANL history including most metals, many oxides, composites, and unusual materials. Some select projects and results from past to present programs will be presented.