Effect of Strain Rate on Deformation Behavior of Semi-Solid Dendritic Alloys
- PDF / 4,661,296 Bytes
- 11 Pages / 594 x 774 pts Page_size
- 12 Downloads / 209 Views
I.
INTRODUCTION
E N G I N E E R I N G alloys are processed either in the fully liquid state, such as in die casting, or in the fully solid state, such as in forging. The possibility of processing in the semi-solid state is attractive because, among other benefits, it may increase the die life in die casting operations because of the lower temperatures involved, and it may reduce the force during forging operations. Extensive studies were conducted at Massachusetts Institute of Technology and elsewhere in achieving this result using a technique that has come to be known as the "Rheocasting" process. ~-10 A recent study ]~ on the deformation behavior of semisolid nondendritic ("Rheocast") Sn-15 pet Pb alloy was carded out using a parallel plate viscometer type apparatus, and it was shown that the material deformed homogeneously without cracking to very large strains under very low pressures. The pressure required was less than about 0.2 MPa for fraction solid up to 0.60. Only a few experiments were performed for comparison using samples with a dendritic structure. The aim of the work described herein was to study the behavior in compression of ordinary (dendritic) Sn-Pb alloys using the same kind of apparatus over a wide range of strain-rates and deformations. One practical purpose of the work is to determine if there is a set of conditions under which semi-solid dendritic alloys can be homogeneously deformed in a forging operation. Another is to understand better the process variables underlying purification by fractional solidification or melting, tl,12,~3
II.
APPARATUS AND PROCEDURE
Figure 1 is a schematic diagram of the compression apparatus used in this investigation. The semi-solid alloy was
M. SUERY, formerly Visiting Scientist, Materials Processing Center, Massachusetts Institute of Technology, is now Associate Professor, Laboratoire de Physique et de Technologie des Materiaux-L.A., 155 Universite de Metz, lie de Saulcy, Metz, France. M. C. FLEMINGS is Ford Professor of Engineering, Department of Materials Science and Engineering, and Director, Materials Processing Center, Massachusetts Institute of Technology, Cambridge, MA 02139. Manuscript submitted October 5, 1981. METALLURGICALTRANSACTIONS A
9
stoinless steel compressionshaft
~ thermocouple~
[ ~ t hermocouple
- - TOp compression plate
,~_.___._.~ s peci m e n iJ ii I: ii
cooling water inlet thermocouple . ~
I'
~-"
bottom compression plate 3
cooling water inlet control thermocouple
Fig. 1--Schematic diagram of the compression apparatus.
squeezed between two parallel discs heated to the desired temperature with a small 250 watt band heater. Four chromel-alumel thermocouples embedded in the bottom and the top plate were used to assure temperature control and uniformity in the specimen during deformation. Low deformation rates were obtained using a standard Instron testing machine of 22,000 N (5,000 pounds) capacity. The deformation was performed at constant velocities ranging from 8.5 x 10 -3 m m s - l ( 0 . 0 2 inch per minute) to 0.85 mm
Data Loading...
