Computation and validation of weld pool dimensions and temperature profiles for gamma TiAl
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8/30/04
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Computation and Validation of Weld Pool Dimensions and Temperature Profiles for Gamma TiAl K.B. BISEN, M. ARENAS, N. EL-KADDAH, and V.L. ACOFF Previous research by the authors has shown that the welding current has a strong effect on the weld properties and microstructures of gamma TiAl. This article presents the results of experimentally measured and theoretically predicted temperature profiles of gas tungsten arc (GTA) welded gamma TiAl for welding currents of 75 and 100 A. The GTA welding model used in this study accounts for the fluid flow in the weld pool as well as conductive, convective, and phase change heat transfer processes in the solid, liquid, and mushy regions of a metal. The computed temperature fields predicted that as the welding current is increased, the maximum temperature reached in the weld pool also increases. Experimental validation of the computed temperature fields was determined by placing thermocouples at three locations on the specimen, to record the temperatures during welding using computer-based data acquisition hardware and software. The agreement between theoretical predictions and measurements was reasonably good, which provided a direct validation of the model.
I. INTRODUCTION
GAMMA titanium aluminides have emerged as potential candidates for high-temperature applications, owing to their attractive properties such as low density, good hightemperature tensile properties, and acceptable oxidation resistance. In such applications, TiAl will in many instances have to be joined. This can be accomplished using various fusion welding processes in an inert atmosphere, such as gas tungsten arc (GTA) welding, electron beam welding, and laser welding.[1,2] Among these processes, the GTA welding process is the most flexible and cost effective. Despite the extensive use of GTA welding for joining TiAl alloys to date, the scientific basis of the GTA operation has been concerned with the structural characterization of the final weld rather than the physics of the arc welding process. There is much to be understood about the way changes in various operating parameters affect the weld geometry, weld penetration, and mechanical properties of the final weld. Figure 1 shows a sketch of a typical GTA system, where it is shown that an arc is struck between the tungsten electrode and the metal. The thermal energy generated in the arc, which depends on the arc current, melts the local area to form a molten pool. The passage of the arc current through the base metal also dissipates its energy as heat (Joule heating) and gives rise to an electromagnetic force field. This force field produces a recirculating motion opposite that of the natural convection currents. The presence of high-temperature gradients at the free surface will also induce thermocapillary flow from low- to high-surface-tension regions, only if the
K.B. BISEN, Graduate Student, M. ARENAS, Postdoctoral Fellow, N. EL-KADDAH, Professor, and V.L. ACOFF, Associate Professor, are with the Department of Metallurgi
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