Solubility of argon in laser additive manufactured α-titanium under hot isostatic pressing condition

The solubility of Ar in alpha-Ti under temperature and pressure conditions typical to hot isostatic pressing (HIP) of pore-laden laser additive manufactured parts is investigated. The equilibrium pressure and radius of an Ar-containing pore during HIP, as a function of initial pore radius, are evaluated from a thermodynamics perspective. It is found that a reduction in pore radius by one to two orders of magnitude, as well as extremely high pore pressures on the order of GPa, can result from HIP. Using density functional theory (DFT), the formation energies of Ar solutes in the pure Ti matrix are calculated. Several different types of solutes, including interstitial in single crystal and substitutional in both single crystal and (1 0 (1) over bar 1) and (1 0 (1) over bar 2) twin boundaries, are considered in the calculations. The solubility of Ar in Ti is then calculated based on the formation energies as a function of both temperature and pressure. Although the dissolution of Ar in Ti is highly endothermic, substitutional Ar atoms in Ti, especially in crystallographic defects like twin boundaries, have been found to possess significantly lower formation energies than interstitials. The corresponding solubility of Ar within the Ti matrix is found to be very low. However, it increases substantially under the elevated pressure and temperature conditions in the pores during HIP, which further facilitates the removal of Ar. (C) 2017 Elsevier B.V. All rights reserved.