Modelling Ti-6Al-4V microstructure by evolution laws implemented as finite element subroutines: Application to TIG metal deposition
C. Charles, D. N. Järvstråt, University West, Trollhattan, Sweden
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 . 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 , 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
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 2005Pine Mountain, GA, United States: ASM International, pp. 65-70.
Summary: A microstructure evolution law has been implemented for finite element simulations of TIG metal deposition; including heating, cooling, as well as successive re-heating. Simulations of phase fractions and alpha lath thickness explain observed banding features and fatigue endurance variations between different manufacturing process settings.