Date

August 1985

Document Type

Dissertation

Degree Name

Ph.D.

Department

Dept. of Materials Science and Engineering

Institution

Oregon Graduate Center

Abstract

It is not currently possible to weld titanium alloys to iron alloys by any conventional fusion welding process. When titanium and iron are fused or melted together, they normally form the intermetallic phases TiFe and TiFe2. These phases are inherently brittle and tend to embrittle the materials in which they occur, even when they are present in only small amounts. One possible method of overcoming the formation of these brittle intermetallic phases involves the addition of a third element to the weld fusion zone. The function of the third element is to destabilize the undesirable intermetallic phases, without forming other undesirable phases in the process. A review of the alloying characteristics of several candidate elements indicated that vanadium offers the best potential for being able to destabilize the TiFe and TiFe2 intermetallic phases, without forming other undesirable phases. While vanadium does form the equilibrium FeV intermetallic or σ phase, it does so sluggishly and rarely under non-equilibrium conditions. The objective of this thesis, then, was to investigate selected properties of as-cast V-Ti-Fe alloys, with a view toward determining their suitability for use in the fusion zone of a conventional capacitor discharge weld. To achieve this objective, an approach consisting of both a theoretical and an experimental effort was employed. The theoretical effort consisted of a consideration of the elements vanadium, titanium, and iron, the Ti-Fe binary system, the Ti-V binary system, the Fe-V binary system, the V-Ti-Fe ternary system, and fusion weld interfacial phenomena. The experimental effort consisted of the fabrication, testing, and analysis of twenty six representative V-Ti-Fe alloys. The testing and analysis included chemical analysis, hardness testing, x-ray energy dispersion analysis, microstructure analysis, x-ray diffractometry analysis, bend testing, and fracture analysis. The results of this investigation indicated that the strengths and ductilities of as-cast V-Ti-Fe alloys vary greatly with interstitial impurity content, but that it is possible to obtain such alloys that possess useful levels of both strength and ductility. In addition, the results indicated that the predominant solidification structure is the columnar dendritic structure, with a simple columnar structure occurring only in the nominally pure vanadium and an equiaxed structure occurring in alloys near the V-Fe equiatomic composition. Finally, the results indicated that the predominant phase that occurs is the retained β (Ti) phase. although the VTiFe ternary intermetallic or γ phase and the TiC phase do occur in small amounts in some compositions.

Identifier

doi:10.6083/M4862DC1

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