Deformation of a Burgers oriented bimetallic bicrystal of alpha-beta (Ti-13Mn)
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I.
INTRODUCTION
DEFORMATION of c~-/3 interfaces plays an important role in the behavior of c~//3 titanium alloys. In low cycle fatigue extrusions form at c~-/3 interfaces.~': Very early in plastic deformation triaxiality develops at c~-/3 interfaces 3 and this triaxiality assists in the breakdown of compatibility slip which, in turn, leads to void formation there. 4 Elastic interaction stresses between Burgers oriented a and /35 across the a-/3 interface were predicted to assist slip in a on (0001) (1120). 6 This research was undertaken to test this prediction and examine plastic deformation at the a-/3 interface. A Burger's oriented a-/3 bicrystal was produced for these purposes. The stress axis was parallel to the interface and was oriented to produce maximum interaction stress. Companion single crystals of c~ and /3 of the same orientation as was employed to make the bicrystal were produced for comparison purposes. As it turned out, it was not possible to test the prediction6 because basal slip did not occur. This paper then presents an examination of the plastic behavior of the Burger's oriented5 bicrystal, with special attention being paid to the interface. II.
EXPERIMENTAL PROCEDURE
A. Material The composition of the a-Ti and/3-Ti-13Mn is given in Table I. The c~-Ti was received as 19.1 mm square bar stock and the/3-Ti-13Mn was obtained as 12.7 mm rounds. CHONG SOO LEE, formerly a Graduate Student in the Department of Physical and Engineering Metallurgy at Polytechnic Institute of New York, Brooklyn, NY, is now Research Associate in the Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN. HAROLD MARGOLIN is Professor in the Department of Metallurgy and Materials Science, Polytechnic University, 333 Jay Street, Brooklyn, NY 11201. Manuscript submitted January 31, 1985.
METALLURGICALTRANSACTIONSA
B. Production of Suitable Size Crystals for Bicrystals 1. a-Ti Bar segments, 7.6 mm in length, were cold square rolled 55.5 pct to 13 mm square. At this point the bars were flat rolled to a thickness of 6.4 mm. These materials were recrystallized for one hour at 600 ~ to produce grain sizes in the range 50 to 60/xm. The annealed bars were encapsulated in 19 mm diameter quartz capsules which were either evacuated or partially filled with argon. The bars were then cycled through the transformation, one cycle requiring 72 hours. As many as six cycles were used, but in the interests of efficiency four cycles were most frequently employed. Crystals up to 50 m m x 12.7 mm • 6.3 mm were produced. Following cycling the specimens were annealed in the ~ field at 850 ~ for three days to remove transformation structure.
2. /3-Ti Bar segments, 14 cm in length, were initially annealed at 715 ~ for one hour and the initial grain size was approximately 50/xm. A taper was machined over a 7.62 cm length to produce a reduction from 8.97 to 8.81 mm, a 0.2 pct taper. The specimens were then extended 2 to 4 pct over a 25.4 mm length measured from the smallest diameter. The bars were then
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