A microstructure evolution law has been formulated for use in finite element simulations of TIG metal deposition. State variables representing the relative phase contents are included, as well as the Widmanstätten alpha lath thickness. The phases considered are beta, alpha, colony/grain boundary alpha, Widmanstätten alpha and martensite. For phase evolution laws, the traditional diffusional Johnson-Mehl-Avrami and martensitic Koistinen-Marburger formulations are discretised [1]. Heating, cooling, as well as successive re-heating involved in the process of metal deposition are appropriately treated, taking care of the different phase interactions.

The metallurgical model is implemented as a set of subroutines, employing a point-wise and fully deterministic logic. The model is applied to TIG metal deposition of Ti-6Al-4V component-like features, and in comparison with similar work on laser metal deposition [2], provides further understanding of the underlying metallurgical process. The simulation of phase fractions and a lath thickness are exploited to explain observed banding features and fatigue endurance variations between different manufacturing process settings.

Figure 1 - Microstructure and morphology modelling logic

Figure 2. Experimental setup for TIG metal deposition and transversal cross-cut of the deposited wall

1. Charles, C., and Järvstråt, N. (2007) Development of a Microstructure Model for Metal Deposition of Titanium Alloy Ti-6Al-4V. In: The 11th World Conference on Titanium, Ti‑2007, Kyoto, Japan: To be published December 2007.

2. Kelly, S.M., Babu, S.S., David, S.A., Zacharia, T., and Kampe, S.L. (2005) A microstructure model for laser processing of Ti-6Al-4V. In: 7th International Conference on Trends in Welding Research, May 16-20 2005 Pine Mountain, GA, United States: ASM International, pp. 65-70.