Acta metall, mater. Vol. 41, No. 10, pp. 2867-2876, 1993 0956-7151/93 $6.00 + 0.00 Printed in Great Britain. All rights reserved Copyright ~ 1993 Pergamon Press Ltd MICROSTRUCTURE OF A ~)--0~2--]~ Ti-A1 ALLOY CONTAINING IRON AND VANADIUM B. J. INKSON, C. B. BOOTHROYD and C. J. HUMPHREYS Department of Materials Science and Metallurgy, Cambridge University, Pembroke St, Cambridge CB2 3QZ, England (Received 2_? March 1993) Abstract--Ordered fl-phase (B2 CsC1 structure) has been identified in a Ti~45.5at.%A1 1.6 at.% Fe 1.1 at.% V-0.7 at.% B alloy being developed for high temperature applications. Selected area electron diffraction has been used to identify the orientation relationships and interface planes of the fl-phase with the bulk 7-TiA1 and ~2-TiaA1 phases. Energy dispersive X-ray spectroscopy indicates that the fl-phase has approximately the same Ti/Al ratio as the ~t2-Ti3A1phase, and is stabilized within the microstructure by Fe and V. Channeling enhanced microanalysis studies (ALCHEMI) show that the Fe and V both occupy the same sublattice as the A1 atoms in the cubic fl-phase structure, and that Fe occupies the Al sites in the y-phase. Fe and V are concentrated in the fl-phase, which effectively getters these dopants from the 7 and cq phases. Titanium ferride precipitates, probably FeTi, have been observed within the fl-phase. R4sum~-La phase ordonn6e fl (structure B2, CsC1) 6t6 identifi6e dans un alliage Ti- 45.5 at.% A1-1.6 at.% Fe 1.1 at.% V~3.7 at.% B developp6 pour des applications fi haute temp6rature. La diffraction des 61ectrons en selection d'aire a 6t6 utilis6e dans le but d'identifier les relations d'orientation et les plans de l'interface entre la phase fl et les phases volumiques TiA1- 7 et Ti3Al-~ v Des mesures par spectrom&rie des rayons X en s61ection d'6nergie montrent que la phase fl pr6sente, approximativement, le m6me rapport Ti/Al quc la phase TiaAl-ct 2 et qu'elle est stabilis6e dans la microstructure par la pr6sence de Feet V. Par microanalyse intensifi6e par la canalisation des 61ectrons (ALCHEMI), nous montrons que le Fe et le V occupent le m6me sousr6seaux des atomes de A1 dans la structure cubique de la phase fl, et que les atomes de Fe occupent les sites de AI dans la phase y. Le Feet le V sont concentr6s dans la phase fl qui agit comme pi6ge de ces dopants pr6sents dans les phases 7 et ct 2. Des precipit6s contenant Feet Ti, probablement FeTi, ont 6t6 observes dans ta phase ft. Zusammenfassung--Die geordnete fl-Phase (B2, CsC1-Struktur) wurde in einer f/ir Hochtemperaturan- wendungen entwickelten intermetallischen Legierung, Ti-45.5 at.% A1 1.6at.% Fe-l.l at.% V 0.7at.% B, identifiziert. Dutch Analyse yon Beugungsbildern konnten die Orientierungsbeziehungen zwischen den Kristallgittern der fl-Phase und den Matrixphasen 7-TiAI und ~2-Ti3Al festgestellt werden. Energiedispersive R6ntgenspektroskopie (EDS) deutete darauf hin, dab die fl-Phase Ti und Al etwa im gleichen Verhfiltnis wie die ~t2-Ti3A1-Phase enth/ilt und durch die Fe- und V-Zus/itze in der Mikrostruktur stabilisiert wird. ALCHEMI ("Atom Location by channeling enhanced microanalysis") zeigte, dab die Fe- und V-atome das A1-Ubergitter in der B2-Struktur der fl-Phase besetzen und dab Fe in der 7-Phase auf A1 Gitterpl/itzen zu finden ist. Fe und V wurden in erh6hter Konzentration in der fl-Phase nachgewiesen, welche die Zus/itze aus den Matrixphasen 7- und ~t 2 'gettered'. Titanium-Eisen-Verbindun- gen, wahrscheinlich FeTi, wurden in der fl-Phase beobachtet. 1. INTRODUCTION The TiA1 based alloys have been considered as prom- ising advanced aerospace alloys for many years due to their low density, good high temperature strength and oxidation resistance. Their Achilles' heel however is the brittleness [1] and poor fracture toughness that they exhibit at ambient temperatures. Attempts to improve the ductility by alloying have concentrated on adding elements such as Mo, V and Nb. These elements are known to improve the ductility of Ti3AI based alloys by stabilizing ordered fl-phase within the microstructure [2, 3]. Recently, Nakagawa et al. [4] have shown that the addition of V, Fe and B produces TiAl based alloys of good castability for turbine component manufacture. In the present study the effect of Fe and V on the stabilization of fl-phase within the ?-TiAl/cq- TiaA1 system is considered. The microstructure of the alloy used is characterized, determining the crys- tallographic relationships of the phases observed and the segregation of the Fe and V between them. The site occupations are investigated using channeling enhanced microanalysis. 2. EXPERIMENTAL The alloy used for this work had composition Ti-45.5 at.% Al-l.6 at.% Fe-l.1 at.% V4).7 at.% B. It was annealed at 1473K (1200°C) for 3h then furnace cooled. Transmission electron microscopy specimens were electropolished using 6% perchloric AM 4t/L~ v 2867