Quantification of the heat transfer during the plasma arc re-melting of titanium alloys

This paper summarizes the development and application of an Inverse Heat Conduction Code (IHCC) to determine the surface heat flux distribution from an industrial plasma torch applied to heat a sample of Ti-6wt%Al-4wt%V (Ti64) alloy. The test (trial) was conducted within an industrial scale plasma arc furnace and the sample was instrumented with 15 thermocouples embedded below the top surface. The sample was heated for 278 s, which allowed sufficient time for a liquid pool to form within the sample. Following the trial, the sample was sectioned to obtain the liquid pool profile. The IHCC analysis method described in the paper is based on the future time-step approach and uses the commercial finite element code ABAQUS™ as the forward conduction engine. The IHCC analysis was conducted with both isotropic thermal conductivity and anisotropic thermal conductive in the liquid. The later, was used to approximate the effect of fluid flow on heat transport in the liquid. Additionally, the method used linear interpolation to vary the estimated heat flux between the discrete heat flux evaluation points associated with the thermocouple positions. The results indicated that it is critical to account for fluid flow and suggest that the heat flux distribution can be accurately described by two over-lapping Gaussian distributions: one narrow distribution associated with convective heat transfer; and a second, broader distribution, associated with radiation. An overall heat transfer efficiency of 28% was estimated from the heat flux distribution.