Temperature Dependence of Deformation Behaviour and Dislocation Structure of Al 67 Mn 8 Ti 26 L1 2 Intermetallic Alloy
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TEMPERATURE DEPENDENCE OF DEFORMATION BEHAVIOUR AND DISLOCATION STRUCTURE OF AlohMneTi26 LI 2 INTERMETALLIC ALLOY XIAOHUA WU, SHIPU CHEN, YONGHUA RONG, XIAOFU CHEN AND GENGXIANG HU Department of Materials Science, Shanghai Jiao Tong University, Shanghai 200030, China ABSTRACT The AhTi-based Li2 alloy AlhTMnsTias shows different temperature dependence of the yield stress and ductility from that of the model Li 2 alloy NisAl. The dislocation structures and dissociation modes of the alloy deformed at room temperature, 673 and 873K were investigated by TEM. It is determined that at room-temperature and 673K, a(il0) dislocation dissociated into two a/3(112> superpartials with SISF between them on {111} plane, while at 873K, the dissociation is a/2(l10> pairs on {111} planes separated by APB. The temperature dependence of yield stress and ductility may be related to the dislocation structures at various temperatures. INTRODUCTION Recently, the Li 2 ordered AhTi-based alloys have attracted much attention because of their low density, relatively good strength, excellent oxidation resistance and potential ductility. The transformation of DO 22 AhTi into L12 structure by alloying has developed considerable ductility in compression, but these Li 2 alloys still remain brittle in tension at ambient temperatures [1-2]. The temperature dependence of yield strength of the LI 2 AhTi alloys has been reported by several investigators. Unlike some Li 2 compounds such as Ni3AI, which exhibit a strong positive temperature dependence of strength, these alloys only show a weak positive temperature dependence [3-4] or a plateau [5-6] in the anomalous regime. The dislocation structure of the deformed LI 2 AhTi alloys studied by transmission electron microscopy (TEM) so far is controversial. Earlier observations on room temperature deformed Al. 7NioTi 2 s [7-8] or AlsTi2Fe [9] samples suggested that the a(il0> dislocations moving on {111} planes are undissociated. Further work on the Fe-modified LI 2 alloy have shown that at room temperature the a(ll0> dislocations tend to dissociate into a/2 partials on {111} planes separated by an antiphase boundary (APB) [10-12], while others cited that the dissociation is of the a/3(ll2>-type with the superlattice intrinsic stacking faults (SISF) between two partials on {111) planes [13,14]. TEM studies on the dislocations in AlsTi-based Li 2 alloy deformed at elevated temperatures are very limited. Lerf and Morris 0[9] reported that majority of the dislocations in the Fe-modified alloy after 500 C deformation are dissociated as pairs of a/2(110> on {111} planes with APB between, and the result of Inui et al [14] showed also the APB-coupled a/2(l10) superpartials at 600'C but on {001} planes. In the present study, the temperature dependence of yield stress and ductility of a Mn-modified L1 2 alloy was examined by compression tests conducted at temperatures ranging from R.T. to 1023K. The dislocation structures of the samples deformed at selected temperatures were investigated by TEM in order to elucidate
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