Program Organizers: M.G. McKimpson, Institute of Materials Processing, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931; S. Axtell, Dept. of Mechanical Engineering, University of Nebraska-Lincoln, 225 WSEC, Lincoln, NE 68588
Monday, AM Room: Grand G
February 5, 1996 Location: Anaheim Marriott Hotel
Session Co-Chairpersons: M.G.McKimpson, S. Axtell, Department of Mechanical Engineering and Center for Materials Research and Analysis, University of Nebraska, 255 WSEC, Lincoln, NE 685880656
8:30 am
GRAIN GROWTH IN NANOCRYSTALLINE MATERIALS PREPARED BY MECHANICAL ALLOYING: S.C. Axtell, Department of Mechanical Engineering and Center for Materials Research and Analysis, University of Nebraska, 255 WSEC, Lincoln, NE 685880656
Although commercial quantities of nanocrystalline powders can be produced by mechanical alloying, a consolidation step is required to produce usable parts and devices from these materials. Mechanically alloyed powders are generally consolidated at temperatures where grain growth occurs; therefore an understanding of the grain growth behavior of nanocrystalline materials produced by this method is desirable. This talk will present an overview of studies of grain growth in mechanically alloyed materials. The presentation will include, in part, a discussion of the work being performed at the University of Nebraska on Cu and Cu-based alloys using in-situ and non in-situ x-ray diffraction techniques. Support for this work was provided by NSG EPSCoR grant OSR-255225.
9:00 am
PHASE TRANSFORMATION & STRUCTURAL EVOLUTION OF MECHANICALLY ALLOYED Fe-Zn-A1 PHASES: O. Uwakweh, Z. Liu, R. Edwards, Department of Materials Science & Engineering, University of Cincinnati, Cincinnati, OH 45221-0021
Fixed composition ratios of Fe and Zn corresponding to Fe3Zn10, Fe5Zn2l, FeZn7, and FeZn13, with the addition of 5% Al (wt.) were mechanically alloyed. Nonisothermal kinetic analyses based on DSC measurements of the milled alloys revealed two diffusion controlled processes for the FeZn7 + 5% Al with activation energies of 227 +/- 12kJ/mole and 159 +/- llkJ/mole respectively. The formation of FeAl2 phase at 440deg.C during the evolution of FeZn13 + 5% Al suggests the need for a re-evaluation of the existing Fe-Zn-Al equilibrium diagrams. The Fe3Zn10 + 5% Al and Fe5Zn21 + 5~ Al compositions evolved similarly except at 400deg.C where the former decomposed to Fe + FeZn7 + Fe3Znl0, and the latter to Fe + FeZn7.
9:20 am
INVESTIGATION OF THE MICROSTRUCTURE AND MAGNETIC PROPERTIES OF MECHANICALLY MILLED SmCo5/Fe: R. L. Schalek, S.C. Axtell, Department of Mechanical Engineering, University of Nebraska, 225 WSEC, Lincoln, NE 68588- 0656; Alice M. Milton and Diandra L. Leslie- Pelecky, Department of Physics and Astronomy, University of Nebraska, Lincoln, NE 68588-0656
Theoretical calculations indicate that hard magnets (SmCo5) can exchange couple across soft magnets (Fe) producing large coercivity materials exhibiting enhanced remanence and saturation magnetization. We have produced (SmCos)x:Fe100-x, with x = 90, 70 and 50 vol.% via mechanical milling of SmCo5 and iron powders. X-ray diffraction, scanning electron microscopy, and magnetic hysteresis measurements are used to characterize the materials. To investigate the effects of the lamellar microstructure on the magnetic properties, as-received iron powder or iron premilled for 6 hours was milled with the SmCo5. Powders containing the premilled iron have significantly different magnetic properties than powders consisting of as- received iron. Furthermore, increasing the iron concentration decreases the coercivity and remanence, but increases saturation magnetization. Results of powders annealed at temperatures between the Curie temperatures of Fe and SmCo5 will also be presented. Support for this work was provided by NSG EPSCoR grant OSR- 9255225.
9:40 am
CHARACTERIZATION AND CONSOLIDATION OF CuAlNiMnTi SHAPE MEMORY ALLOY POWDER PREPARED BY MECHANICAL ALLOYING: W.G. Liu*, C.Y. Chung, Dept. of Physics & Materials Science, City University of Hong Rong, Tat Chee Avenue, Kowloon, Hong Kong. * also Dept. of Materials Engineering, Dalian University of Technology, Dalian 116023, China
The elemental powder mixtures of Cu-12Al-5Ni-2Mn-lTi(wt%) have been processed by mechanical alloying (MA), cold pressing and sintering with the aim of fabricating a Cu-based high temperature shape memory alloy. The mechanically alloyed powders as well as consolidated products in compacted, sintered and quenched states have been characterized by X-ray diffraction, SEM, DSC and hardness testing. The MA process, which was carried out in a hlgh energy ball mill for up to 40h, was found to be a typical one like that which generally occurs in the MA of ductile/ductile systems. The final product of MA was a single phase of fcc structure with lattice parameters close to that of Cu. The green densities of cold pressed compacts strongly depended on the MA time with a maximum value after 10 hours milling. As the MA time increases, the size of pores in compacts formed during sintering reduced and the expansion which occurred in sintering decreased. All the sintered compacts gave the same dual phase structure conslsting of and Y2 phase regardless of the milling time. The dominant structure of the quenched compacts from powder milled for less than lh was martensite with the same crystal structure as observed in conventional cast CuAlNiMnTi alloy. With longer MA processing, the amount of martensite in quenched compacts reduced and little martensite was found when MA time exceeded 20h. The martensite demonstrated no reversible transformation during heating from 50-590deg.C
10:00 am BREAK
10:20 am
CONSOLIDATION OF MECHANICALLY ALLOYED MATERIALS-AN OVERVIEW: M. G. McKimpson, Institute of Materials Processing, Michigan Technological University, 1400 Townsend Drive, Houghton, MI 49931
Mechanical alloying is widely used to produce powders exhibiting a variety of novel microstructures and physical properties, including nanoscale structures, extended solid solutions and dispersion-strengthened alloys. Frequently there is a need to process these powders to nearly full density while retaining as much of the as- milled structure as possible. Achieving this goal often requires extended-and expensive-iterative process development efforts. In this overview presentation, phenomenological changes likely to be observed during consolidation processing of mechanically alloyed powders will be reviewed, and possible guidelines for minimizing consolidation process development efforts will be suggested.
10:40 am
COMPACTION MICROSTRUCTURE OF MECHANICALLY PROCESSED IRON POWDER: J. Rawers, G. Slavens, Albany Research Center, U.S. Bureau of Mines, 1450 Queen Ave SW, Albany, OR 97321; J. Groza, University of California Davis, Davis, CA
Although much has been written about high-energy milling of powders and the properties of these powders, there has been limited information about consolidation of these materials. This study describes the microstructure of mechanically processed iron and mechanically alloyed iron and 2 wt% carbon powder that have been compacted using two different techniques: conventional hot-pressing and a new technique plasma activated slntering. Compact characterization will include: density, hardness, grain slze, and microstructure as a functlon of processing time, temperature, and pressure. This study will show that fully dense materials can be produced while retaining the mechanically milled nanostructure.
11:00 am
THE EFFECT OF PROCESSING HISTORY ON SECONDARY RECRYSTALLIZATION IN MA754: Thomas R. Bieler, R. Saminathan, J. McDougall, Department of Materials Science and Mechanics, Michigan State University, East Lansing, MI; S.K. Mannan, INCO Alloys International, Huntington, WV 25720
MA754 is a Ni-Cr based superalloy with relatively few additional alloying elements. Past work has shown that a directional anneal is effective for obtaining elongated large grains in a secondary recrystallization anneal at temperatures above 0.9Tm. However, directional anneals are not convenient for sheet metal structures that could be fabricated out of sheet material; a static anneal is desirable. Sheet forms of MA754 must be hot rolled, and the history of hot rolling conditions affects the potential for a large grain secondary recrystalization. The microstructures and textures were investigated for MA754 with various hot rolling histories. When it is hot rolled near 2000deg.F, partial secondary recrystallization occurs during rolling, resulting in cube texture. Subsequent secondary recrystallization anneals do not result in large grain sizes. When it is hot rolled at temperatures near 1700deg.F, secondary growth is much less, and a diffuse FCC rolling texture is formed. This condition will provide large elongated grains in a static anneal above 0.9Tm, with a strong (110)<001> texture. Precipitation of carbides during hot rolling, and subsequent cold work before annealing strongly affect the kinetics of microstructural evolution.
11:20 am
HOT ISOSTATIC PRESS CONSOLIDATION OF NANO- SCALE TITANIUM TRIALUMINIDE POWDERS: E A. Laitila, D.E. Mikkola, Department of Metallurgical and Materials Engineering, Michigan Technological University; M. G. McKimpson, Institute of Materials Processing, 1400 Townsend Drive, Houghton, MI 49931
Reactive mechanical alloying has been used to produce nanoscale (Al,Cr)3Ti-TiC composites containing nominally 10 wt.% TiC. Powders milled in air or argon were consolidated in a hot isostatic press (HIP) at pressures of 414 MPa, temperatures from 600deg.C to 1000deg.C, and times of either 15 or 120 minutes in an attempt to preserve the nanoscale microstructure of the powders and optimize the mechanical properties. Near full density was achieved by HIPing the powders at 800deg.C for 15 minutes, but all materials consolidated at 800deg.C showed limited resistance to cracking during hardness testing. Powders milled in argon and consolidated at 414 MPa/1000deg.C showed significant improvements in cracking resistance, and increasing consolidation time from 15 to 120 minutes increased the load required for cracking from 2kg up to 5kg. This increase occurred with only a slight decrease in hardness. The results of compression testing the consolidated material will also be reported.
11:40 am
MECHANICAL ALLOYING FOR PREPARATION OF MAGNESIUM MATRIX DEFORMATION PROCESSED COMPOSITES: J.A. Jensen, A.M. Russell, L.S. Chumbley, Ames Laboratory nd Iowa State University, T. W. Ellis, Ames Laboratory, U.S. Department of Energy, Ames, Iowa 50011
Although the conventional precipitation hardened alloys of Mg dominate
today's engineering use of Mg, advantages in mechanical properties can be
achieved by use of immiscible refractory metal phases as strenghtening
particles in an Mg matrix. Since the low melting and boiling points of Mg
preclude use of crdlnary melt processing of Mg with refractory metals, the
authors have preparead Mg-20 vol.% Fe, Mg-20 vol.% Nb, and Mg-20 vol.% Ti
composites by mechanical alloying of the pure metal powders in liquid nitrogen
followed by deformation processlng to increase the strength of the composites.
The resulting composites possess ultimate tensile strengths of 300 MPa (44 ksi)
at room temperature and show no change in microstructure and no loss of room
temperature strength after exposure to 400deg.C (750deg.F) for 500 hours.
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