Mechanical Properties and Dislocation Structures in TiAl Alloys with Varying Aluminum Contents
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MECHANICAL PROPERTIES AND DISLOCATION STRUCTURES IN TiAI ALLOYS WITH VARYING ALUMINUM CONTENTS S. Sriram*,Vijay K. Vasudevan* and Dennis M. Dimiduk**. *Dept. of Materials Science and Engineering, University of Cincinnati, Cincinnati, OH, 45221 "**Wright Laboratory, Materials Directorate, Wright-Patterson AFB, Dayton, OH, 45433. ABSTRACT Binary, coarse-grained polycrystalline Ti-48, 50 and 52 Al (in at.%) alloys, containing low (-250 wt.ppm) levels of interstitials (O+N) have been deformed at various temperatures in compression and four-point bending. The 0.2% proof strength-temperature profiles are observed to comprise of three distinct regimes. Differences in the material response between bending and compression modes of deformation have been observed. Importantly, in both cases a flow stress anomaly is observed in the 50 and 52 Al alloys. Dislocation fine structures of samples deformed in compression, have been observed in the TEM. Analyses suggests the possible influence of Al contents on the line directions of dislocations, superdislocation dissociation modes, SISF dissociation distances and hence planar fault energies. Distinct0 differences in the deformation structures at RT and at the flow stress peak temperature (800 C) have been observed. These results are presented and discussed in relation with the observed mechanical properties. INTRODUCTION There have been several studies [1-5] aimed at understanding the fundamental deformation behavior of TiA! as a function of temperature. The initial observation of a flow stress anomaly in single crystals of Ti-56AI [5] has been followed by observations of the same in polycrystalline binary alloys [6-8]. The presence of the flow anomaly in the latter has been suggested to be dependent on the grain size [6,7], the heat treatment temperature and Al content [8]. On the basis of dislocation fine structure investigations [3,4] it has been suggested that the flow anomaly is due to thermally activated cross slip of the
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