Plastic Deformation of Ti 3 Al and Ti 3 Al/TiA1 Polycrystals
- PDF / 1,487,303 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 36 Downloads / 273 Views
PLASTIC DEFORMATION OF Ti3 AI AND Ti3A/TiA1 POLYCRYSTALS S.A.COURT, J.P.A.LOFVANDER, M.A.STUCKE, P.KURATH+ and H.L.FRASER Department of Materials Science and Engineering (+ Materials Engineering Research Lab.), University of Illinois, 1304 W. Green St., Urbana, IL 61801, U.S.A. ABSTRACT Samples of polycrystalline Ti3Al-base alloys, and a two phase Ti3 A1/TiA1 mixture have been deformed at room temperature and at elevated temperatures and examined subsequently by transmission electron microscopy in order to determine the influence of temperature and alloy content on the relative activity of the various slip systems. In particular, the detailed influence of covalent bonding on dislocation mobility in Ti 3A1 has been identified. INTRODUCTION The ductility of titanium aluminides at ambient temperatures has been the subject of study for some period of time. In the case of TiAl, the limited ductility has been attributed to the presence of trailing partials [1], to dislocation core dissociations [2,31, and also to the intersection of twins [4]. For Ti 3A1, the lack of sufficient numbers of independent slip systems and the planarity of slip have been cited [e.g. 5]. It has also been determined that additions of Nb, for example, tend to increase the ambient temperature ductility of this compound. The effect of this alloying addition is not well understood. Furthermore, when a two phase mixture of these two brittle compounds is effected in a lamellar morphology, there is an attendant increase in ductility [6]. The reasons for this are not well understood. The present work has been aimed at understanding the deformation mechanisms in these compounds, and so define more precisely the reasons for the limited ductility at ambient temperatures and the increase in this property with increasing temperatures, alloying additions and phase morphology. In this report, our results concerning the deformation of Ti3 AI and the two phase mixtures are presented. EXPERIMENTAL PROCEDURE Master ingots of each alloy were prepared by non-consumable electrode arc-melting under an argon atmosphere, using elemental starting materials. These ingots were then homogenized under an argon atmosphere. All samples were deformed in compression at temperature to strains of =3%. Slices were cut from the deformed material parallel to the compression axis and discs were punched from these slices. The compression axis was indicated on the discs in the form of an aligned scratch pattern produced during grinding on silicon carbide paper. Thin foil specimens were prepared for examination in either a Philips EM430 or a Philips CM12 transmission electron microscope operating at 250 kV and 120kV, respectively.
RESULTS AND DISCUSSION The results have been divided into two sections, corresponding to the analyses of the deformation microstructures in: (1) Ti3Al-base alloys, and (2) two phase Ti3 AI/TiAl alloys. These results will be described in turn. (1) Deformation of Ti3Al-base alloys Figure 1 shows a typical dislocation array found in grains of a binary Ti-25A1 all
Data Loading...
