Nastac Laurentiu, Pang Yuan, Shamblen Clifford E

Abstract: To ensure accuracy of modeling predictions for understanding and optimizing the Plasma Arc Cold Hearth Melting (PAM) process, a methodology for calculating the solidification parameters of Ti-base alloys was developed. This methodology is based on a deterministic solidification-kinetics approach for multicomponent and pseudo-binary alloy systems. It allows calculation of liquidus and solidus temperatures, liquidus slopes, partition coefficients, equiaxed and columnar grain-growth coefficients, as well as primary and secondary dendrite arm spacing coefficients. For computing the aforementioned solidification parameters, dynamic coarsening, microsegregation at the scale of dendrite arm spacing, and diffusion in both liquid and solid phases are considered. The present methodology is then applied to Ti-6Al-4V (Ti-6-4) and Ti-5Al-2Sn-2Zr-4Mo-4Cr (Ti-17) alloys used for high performance aerospace applications. The effect of Fe content on the solidification parameters of Ti-6-4 and Ti-17 alloys is discussed. Calculated results for primary and secondary dendrite arm spacings as related to solidification conditions in remelt processes are presented. The microsegregation profiles of Al, Sn, Zr, Mo, Fe, and Cr were measured by Energy Dispersive X-ray Spectroscopy (EDS) as a function of cooling rate for a PAM processed Ti-17 ingot provided by Allvac, in Monroe, NC, USA. The experimentally measured microsegregation profiles were used to calculate the effective partition coefficients and to estimate the secondary dendrite arm spacing.

Keywords: Estimation, Parameters, Solidification, Titanium alloys.