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1997 TMS Annual Meeting: Session Abstracts


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Room: 240B

Session Chairperson: David H. Carter, Los Alamos National Laboratory, MS G770, Los Alamos, NM 87545

8:30 am

A TEM STUDY ON THE MICROSTRUCTURALEFFECTS ON PLASTIC DEFORMATION IN ALUMINUM ALLOY2219: Carlos D. Rincon, Roy Arrowood , Department of Metallurgical and Materials Engineering and Materials Research Institute, The University of Texas at E1 Paso, E1 Paso, TX 79968-0520

A fundamental transmission electron microscopy (TEM) investigation is being conducted on the effects of microstructure on the plastic deformation of 2219-T87 aluminum. A previous study showed inhomogeneous and locally extreme work hardening in the heataffected-zone (HAZ)- regions in Variable Polarity Plasma Arc (VPPA) 2219-T87 butt welds, which strongly suggests that the HAZ microstructure plays a major role in the deformation and fracture process. Due to the small size of these butt welds, it can be quite difficult to accurately quantify the stress-strain behavior of the HAZ. Therefore, precipitate structures similar to ones found in the HAZ are being produced by heat treatment of tensile specimens machined from 2219-T87 plate. Heat treatments involve varying the aging time and temperature to obtain GP zones followed by the precipitation of transition phases. Uniaxial tensiIe tests will be performed on the heat treated specimens at low strain rates (0.01 mine-1 and 5.0 min-1') at room temperature in order to quantify the effect of precipitate structure on the stress-strain behavior. This work was supported by the General Electric Faculty of the Future Program.

8:50 am

COMPREHENSIVE FLOW STRESS DETERMINATION IN EXTRUDED ALUMINUM PRODUCTS: Michael S. Paulson, Roger N. Wright, Materials Science and Engineering Department, Rensselaer Polytechnic Institute, Troy NY 12180

Physical modeling of the aluminum extrusion process e reductions is difficult due to the large reductions and the complex extrudate shapes. Conventional machines flow stress specimens are not likely to be representative of the metal as it is extruded. A method of directly testing the total cross section is needed to properly represent extrudate flow stresses for process modeling purposes. Such a method is presented, as applied to rapidly heated commercial aluminum extrudates at temperatures and strain rates pertinent to die exit conditions. Resulting constitutive equations are compared to those developed for starting billet stock from the same lot of metal. Sponsored by the Rensselaer Aluminum Processing Program.

9:10 am

EFFECT OF REDISTRIBUTING RESIDUAL STRESS ON THE FATIGUE BEHAVIOR OF SS330 WELDMENT: Yong-Bok Lee, Chin-Sung Chung, Dept. of Mechanical Eng., Hong-Ik University of Seoul; Nam-Ik Cho, Dept. of Mech. Eng. Chon-Ju Tech. College; and Ho-Kyung Kim, Dept. of Automotive Eng., Seoul National Polytechnic University, 172 Kongnung-dong, Nowon-ku, Seoul, Korea

Effect of residual stress and its redistribution in weldment on the fatigue crack propagation was investigated. Fatigue tests were conducted using center notched specimens machines from welded plats. The residual stress and its redistribution were measured by a magnetizing stress indicator and hole drilling method. The residual stresses were found to be redistributed during crack propagation. Crack growth rates were predicted and compared with the experimental results. It has been found that the predicted crack growth rates have a better agreement with the experimental results when the redistributing residual stress, rather than residual stress, was considered. Also when the concept of partial crack closure was adopted in the analysis of crack growth rates, fatigue crack growth rates were a good agreement with, in spite of variation of stress ratio.

9:30 am

COMPRESSIVE STRENGTH AND FATIGUE PROPERTIES OF BE-A1 ALLOYS: R. Schneeberger, B. Bavarian, School of Engineering and Computer Science, California State University at Northridge, Northndge, CA 91330; R. Hayes, Metals Technology, Inc., 19080 Nordhoff St., Northridge, CA 91330

Both 40 and 62 wt.% beryllium compositions were evaluated for ambient and elevated temperature compressive strength at low and high strain rates. Data indicated a strong influence of beryllium percentage along with an increase of yield point for fast strain rates of 0.5-1 inch/minute. Fatigue properties of a ternary BeAl-Ag cast and extruded material were determined for full reversal and standard tension fatigue conditions. Typical S-N curve behavior including endurance limit was observed.

9:50 am

CREEP BEHAVIOR OF TWO BERYLLIUM-ALUMINUM ALLOYS: R. Schneeberger, B. Bavarian, School of Engineering and Computer Science, California State University, Northridge; 18111 Nordhoff St., Northridge, CA 91330; R. Hayes, Metals Technology, Inc., 19080 Nordhoff St., Northridge, CA 91330

Creep testing performed on 40 and 62 wt.% beryllium compositions of a powder metallurgy composite alloy at several elevated temperatures indicated a dependence of steady state creep rates and times to rupture on beryllium content, test direction, stress, and test temperature. A stress exponent of 8.5 for 40% beryllium and 10 for 62% beryllium was obtained from tests at 550 degrees F. A lower stress exponent of 6.7 was found for 62% beryllium at 630 degrees F. Activation energies for creep were somewhat higher than for self-diffusion in either pure metal, and exhibited significant anisotropy.

10:10 am BREAK

10:20 am


Neutron diffraction measurements of internal elastic strains during mechanical deformation are performed on Be-50%Al. The material is produced from hot isostatically pressed powder which is rapidly solidified using a gas atomization process. Under rapid solidification, Be-A1 undergoes liquid phase separation, and upon complete solidification two intimately interpenetrating phases exist. The resulting microstructure can be described as a three-dimensional interpenetrating composite, where each phase is continuous. Strain measurements are taken at the Los Alamos Neutron Scattering Center (LANSCE) using a pulsed neutron source, which provides time-of-flight diffraction data. The elastic strains in the individual phases are measured as a function of applied stress. This data is used to quantify the deformation behavior of each phase. The A1 phase is highly constrained by the Be phase due to the morphology of the composite as well as the high stiffness and low Poisson's ratio of Be. The results provide more insight into the overall deformation behavior of Be-Al.

10:40 am

DEFORMATION OF Al70Pd21Mn9 ICOSAHEDRAL QUASICRYSTAL WITH DECAGONAL PHASE LAMELLAE: Hisatoshi Hirai, Mater. Eng. Dept., Kyushu National Indust. Res. Inst., 807-1 Shuku, Tosu, Saga 841, Japan; Fuyuki Yoshida, Hideharu Nakashima, Dept. Mater. Sci. & Tech., Grad. Sch. Eng. Sci., Kyushu Univ., Kasuga, Fukuoka 816, Japan

In our previous work, we prepared Al70Pd21Mn9 icosahedral quasicrystal by zone melting technique. The obtained sample contained fine lamellae of decagonal phase Al69Pd13Mn18. The Vickers indentation test revealed that the existence of fine lamellae and annealing improved the fracture toughness of the sample to be about 2.1 Mpam1/2 which is about 1.5 times as large as those without lamellae. In this paper, we will report the results of high temperature creep test of the sample with fine lamellae. We will also discuss the effects of decagonal lamellae on the high temperature plastic deformation of icosahedral phase, if possible. Detailed results will be presented at the meeting.

11:00 am

THE PROCESSING AND PROPERTIES OF P/M FE-MN-AL ALLOYS: Chun Sien Lin, Materials Research Laboratory, ITRI, Hsinchu, Taiwan ; Shih-Chin Chang, Dept. Materials Science and Eng., Tsing Hua University Hsinchu, Taiwan

Powder metallurgy processing of Fe-Mn-Al alloys was studied. FeMn-Al alloy powder was produced by mechanical alloying of commercially available pure Fe, Mn, Al and C powder. The effect of ball milling, composition, pressure and sintering conditions on the microstructure and mechanical properties of resulted specimens were studied. For standard Fe-30Mn-lOAl-lC composition, 12 hour ball-milling is enough for producing the fcc structure of Fe-Mn-Al alloy after compaction and sintering at a temperature of 1240°C or higher. It is found that the hardness, strength and ductility of the sintered specimens increase with sintering density. The specimen compacted with 800 MPa and sintered at 13260°C for one hour in Ar have a sintered density of 6.18 g/cm3 (94.3% of theoretical density), hardness of HRC 32, and 0.2% offset yield strength of 1026 MPa. These mechanical properties are comparable to that of conventional casted material and are much better than that of the P/M carbon or stainless steels.

11:20 am

LOAD RELAXATION AND SUPERPLASTIC DEFORMATION BEHAVIOR OF A PB-SN ALLOY: Tae Kwon Ha, Young Won Chang, Center for Advanced Aerospace Materials, Pohang University of Science and Technology, Pohang 790-784, Korea

The deformation characteristics of Pb-Sn eutectic alloy, a typical microduplex superplastic material, has been investigated. For this purpose, a series of load relaxation tests has been conducted to obtain the flow curves under the condition of a constant structure and the results have consequently been analyzed based on the recently proposed internal variable theory of structural superplasticity. The effects of grain size and volume fraction of constituent phases on superplastic deformation behavior of this eutectic alloy has also been examined. The boundary sliding in this two phase alloy was characterized as a viscous flow process with the power index value of Mg=0.5. This value is much less than the previously reported value of Mg=1.0 for GBS obtained in several single phase alloys. The optimum strain rate is found to shift into a faster region as the grain size decreases.

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