Microstructures and Mechanical Properties of Dual Phase Alloys Consisting of the Intermetallic Phases Ti 3 (Al, Si) and
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MICROSTRUCTURES AND MECHANICAL PROPERTIES OF DUAL PHASE ALLOYS CONSISTING OF THE INTERMETALLIC PHASES Ti,(Al,Si) AND Ti,(Si,Al), J.S. Wu, P.A. Beaven, R. Wagner, Ch. Hartig* and J. Seeger* GKSS Research Center, Institute for Materials Research, 2054 Geesthacht, FRG
* Technical University Hamburg-Harburg, 2100 Hamburg 90,
FRG
ABSTRACT Alloying additions of silicon to the intermetallic titanium-aluminide Ti,Al lead to two-phase microstructures consisting of a 2 -Ti 3 (Al,Si) and Ti,(Si,Al) , . Although details of the ternary Ti-Al-Si phase diagram are not available, theoretical analysis and experimental screening have indicated the existence of a eutectic line in the Ti-rich region of the Ti 3 Al + TiSi 3 two-phase region. The eutectic alloys display dual phase structures with Ti 3 (AI,Si) being the matrix and Ti 5 (Si,Al) 3 the second phase. In this paper the microstructures of the eutectic as well as hypoeutectic and hyper-eutectic alloys, which contain additionally primary Ti,(Al,Si) and Ti,(Si,Al) 3 needles, respectively, are described. The influence of the particular microstructure on various temperature-dependent mechanical properties such as strength, ductility, creep and fracture behaviour has been investigated. Alloys with hypo-eutectic microstructures show promising high temperature mechanical properties. INTRODUCTION Silicon is a common alloying addition to conventional a-based alloys destined for elevated temperature applications since it has been shown to improve creep properties [i]. However, no systematic investigations have been reported on the effect of silicon on the behaviour of intermetallic alloys based on c 2-TiAl in the Ti-Al-Si system. Since further potential exists for the development of useful intermetallic alloys based on TiAl, an investigation of the influence of additions of silicon on the microstructure and mechanical properties of Ti 3 Al has been made. The binary Ti-Si phase diagram [2] indicates that silicon additions which exceed the solid solubility limit in 8-Ti result in the formation of an additional phase TisSi. via a eutectic reaction. As a reasonable inference, in the Ti-Al-Si ternary system alloying additions of silicon to the intermetallic alloy Ti3 Al perhaps lead to two-phase microstructures consisting of Ti 3 (Al,Si) and Ti 5 (Si,Al) , . EXPERIMENTAL PROCEDURE Materials The alloys were made as 60 g ingots by arc melting high purity elements in an argon atmosphere using more than 5 remelts to ensure homogeneity. Weight losses during melting were less than 0.2 wt %. Specimens were studied in the as-cast condition.
Mal. Res. Soc. Symp. Proc. Vol. 133. L11989Materials Research Society
762
Microstructural analysis Microstructures and phase relationships were characterized by lography, X-ray diffraction and electron microscopy (SEM and TEM). rized illumination for the metallography allows the identification phase Ti,(Si,AI) 3 . The composition of the eutectic and the primary was obtained by point count analysis using an EDS system on a SEM. bending tests, fracture surfac
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