1997 TMS Annual Meeting: Tuesday Abstracts

SHAPING AND FORMING OF HIGH PERFORMANCE POWDER PRODUCTS: Session II

Session Chairpersons: Dr. Jeffrey Waldman, Dept. of Materials Engineering, Drexel University, Philadelphia, PA 19104; Dr. William E. Frazier, Naval Air Warfare Center Aircraft Division, Patuxent River, MD 20657

8:00 am

P/M APPLICATIONS IN THE AUTOMOTIVE INDUSTRY: Alan Lawley, Dept. of Materials Engineering, Drexel University, Philadelphia, PA 19104

The North American automotive industry is now a major user of P/M products. In the last sixteen years the weight of P/M parts in a family vehicle has increased from 7.7 to 13.7 kg. and this trend is expected to continue. The results of a recent Delphi Study predict substantial growth over the next decade in power train applications (camshaft lobes, conrods, bearing caps, transmission gears, valve seat inserts, and valve guidelines). In this presentation, three P/M automotive case studies are examined in terms of the technical and economical factors that resulted in commercial viability: (i) the pressed and sintered main bearing cap, (ii) the warm formed turbine hub, and (iii) the powder forged connecting rod. Potential new P/M automotive applications are also discussed.

8:30 am

HIPPING OF P/M PRODUCTS: James H. Hahn, Pressure Technology Inc., Warminster, PA 18974

Abstract not available.

8:55 am

NET SHAPE PROCESSING OF NAVY AIRCRAFT MATERIALS: William E. Frazier, Naval Air Warfare Center Aircraft Division, Patuxent River, MD 20657

New and emerging Navy aircraft systems must satisfy the demanding performance requirements of the 21st Century, and yet, be affordable. This paper examines how advanced, net-shape technology is being implemented and how it can be used to reduce the cost and enhance the performance Navy aircraft.

9:20 am

PRESSURE CYCLING ENHANCED DENSIFICATION IN SEVERAL COMPOSITE COMPACT SYSTEMS: Ching-Yao Huang, G.S. Daehn, Dept. of Materials Science and Engineering, The Ohio State University, Columbus, OH 43210

Recently, it has been observed that pressure cycling can significantly enhance densification of composite powder compacts in the constrained uniaxial consolidation. The simple explanation for this is that differential compressibility in the constituents of composites drives plasticity in the deformable phrase and the net compressive stress biases the resulting strain to fill porosity in compacts. In the present paper, several composites powder systems including Pb, Zn, Al matrices and Al2O3p, TiO2p, SiCw, reinforcements have been studied in room temperature consolidation in static and cyclic loading. Effects of pressure cycle maximum stress, amplitude, and period on the densification of composite powder compacts are observed and analyzed in terms of matrix strength as well as reinforcement properties including size, shape, and agglomeration. Some simple ideas are able to explain the observed results.

9:45 am

HIGH-NITROGEN AUSTENITIC STAINLESS STEEL POWDERS PORDUCED BY GAS ATOMIZATION: G.O. Rhodes, W.B. Eisen, Crucible Research Center, 6003 Campbells Run Rd., Pittsburgh, PA 15205

Nitrogen is increasingly being utilized as an interstitial alloying element in stainless steels due to the intrinsic benefits imparted on the strength and corrosion resistance properties. Using an alloy design model, austenitic stainless steel powders consisting of about 6-12% manganese, 22% nickel, 25-28% chromium, 4-8% molybdenum and having 0.6 to 1.25% nitrogen have been produced using nitrogen gas atomization. The nitrogen contents attained are substantially higher than predicted at a temperature of 1600°C and nitrogen partial pressure of 100kPa using current thermodynamic models. The powders are subsequently consolidated to full density by hot isostatic pressing (HIP), and in the solution annealed condition the materials exhibit tensile yield strengths of up to 700 MPa with good tensile ductility and excellent corrosion resistance. The development and evaluations of the new steel are described in comparison to other established super austenitic stainless steels and nickel base corrosion resistant alloys.

10:10 am

SELF SINTERING AND BONDING USING ELECTROEXPLODED NANOSIZE ALUMINUM POWDERS: Henry R. Piehler, Gennady V. Ivanov, Frederick Tepper, Dept. of Materials Science and Engineering, Carnegie Mellon University, Pittsburgh, PA 15213; Institute of Petroleum Chemistry, Academy of Sciences, Tomsk, Russia; Argonide Corp., Gateway Towers, Pittsburgh, PA 15222

Aluminum powders approximately 100 nanometers in diameter, made by the process of electroexplosion of wire in argon, have stored surface and strain energy that is released at threshold temperatures well below the melting point. This energy release and accompanying temperature increase allows self sintering and bonding to occur at relatively low temperatures. We studied the self sintering of nanosize aluminum powders made by electroexplosion by heating cold compacted pellets to 450C, at which point they exothermed with the generation of light and sufficient heat to partially melt the pellets. Preliminary results are also reported for bonding conventional aluminum powders and sheets using the energy release and temperature increase from exotherming nanosize electroexploded aluminum powders.

10:35 am

FREE FROM FABRICATION OF HIGH STRENGTH METAL COMPONENTS & DIES: C.C. Bampton, K. Newell, S. Fowser, Rockwell Science Center, Thousand Oaks, CA 91358; Rocketdyne, DeSoto Avenue, CA 91303

A two-staged method has been developed for free form fabrication of nickel and iron based alloy parts directly from alloy powders without the need for tooling or machining. The method provides shape and property control equal or superior to investment castings in the same base alloys. A major advantage of the approach is the ability to utilize commercially available selective laser sintering systems with virtually no modification from their standard configurations as intended for plastic model generation direct from CAD data bases. We have demonstrated the feasibility of shape, dimension and property control for complex, low production volume rocket engine components and for tools and dies intended for higher volume commercial production applications in fully hard commercial steels and superalloys. A new finite element model has been developed specifically to aid in control of sinter densification without distortion or cracking.

11:00 am

DEVELOPMENT OF A MANUFACTURING PROCESS FOR AFFORDABLE, COMPLEX NET SHAPE P/M COMPONENTS: Ellen W. Robare, Clifford M. Bugle, Tony E. Zahrah, Phillip A. Parrish, Dynamet, Inc. Washington, PA 15301; MATSYS, Inc., Arlington, VA 22209

This paper describes the background and progress of a research and development effort called Rapid Net Shape Forming. This effort involves the development and reduction to practice of a process, known as the MetalShell process, for manufacturing complex net shape powder metal components. The process involves the use of electroformed nickel to create a net shape HIP canister. One of the outstanding features of the process is that it can be used to make hollow parts with thin walls. Potential applications for this technology include titanium and beryllium components including fan blades, inlet guide vanes, nozzle hardware, prosthetic devices, and intermetallic and composite components. This effort uses recent advances in process modeling and in-process sensing technologies to reduce the lead time and number of iterations required to make a net shape component. This is turn will make components more cost effective. The areas being exploited include rapid prototyping from CAD files to generate patterns and molds, numerical simulation of the electroforming process to optimize shield design and uniformity of canister thickness, and numerical simulation of HIP consolidation to predict final component dimensions.

11:25 am

ENHANCEMENT OF SINTERING KINETICS IN NANOCRYSTALLINE ALUMINA POWDERS BY ELECTRIC PULSING: R.S. Mishra, A.K. Mukherjee, Dept. of Chemical Engineering and Material Sciences, University of California, Davis, CA 95616

Plasma activated sintering (PAS) involves application of electric pulsing before the sintering cycle. A comparative study has been carried out on nanocrystalline alumina powders with y and a starting phases. The results obtained with and without electric pulsing clearly establish the enhanced sintering kinetics due to prior electric pulsing. These results are explained on the basis of dielectric properties of the powders. In addition the present results show that the powder with a-phase sinters better. High densities (>98%) can be obtained in less than 10 minutes at 1573 K. The time and temperature are significantly lower as compared to the conventional sintering parameter of 1773 K and 3 h. The reason for slower sinterability of powder with y-phase is linked to formation of vermicular structuring during transformation to a-phase. Examples of obtaining sintered products with simple shape in one step using PAS would be shown.