Coupling of Computational Thermodynamics with Kinetic Models for Predictive Simulations of Materials Properties

We present successful examples of CALPHAD thermodynamics-based precipitation simulations for three important alloy groups: Single-crystal Ni-base superalloy, austenitic stainless steel and hardenable Al-alloy. Underlying physical models for special features, such as, energies of diffuse interfaces between coherent precipitates and matrix, precipitation of incoherent particles at grain boundaries, evolution of excess vacancies during quenching and continuous aging and their role for metastable precipitate nucleation, are discussed.

The Possible Importance of Pressure in Metastable Precipitate Formation in Ion Implanted Metals

ABSTRACTPrompted by the recent discovery that the heavier inert gas atoms implanted into metals precipitate in the solid phase, indicative of very high pressures (,>,1 GPa), the present paper discusses the conditions under which such pressures might be expected. The metal/inert gas results are briefly described and then used as a model to show that the two essential features apart from low or moderate metal temperatures, are the insolubility of the implanted species in the host matrix and its precipitation on a very fine scale. This combination suppresses the bias-driven cavity swelling that would otherwise control vacancy acquisition in an irradiation environment.The extrapolation to other combinations of implanted ion and metal will be discussed. Where the implanted ion is insoluble and precipitates on a scale similar to the inert gas atoms, exact analogy suggests that the precipitates will again be under high pressure. The formation of high pressure phases might not be unexpected and could be a factor in explaining the presence of phases previously thought to be metastable.