Numerical simulation on phase stability between austenite and ferrite in steel films sputter-deposited from austenitic stainless steel targets

This contribution presents a theoretical discussion on phase hierarchy stability between face-centered cubic (FCC), austenite, and body-centered cubic (BCC), ferrite, lattice structures of stainless steel (SS) films that are sputter-deposited from austenitic targets under non-reactive atmospheres. Data published in literature on both phase characterization and chemical composition of diverse SS films are interpreted anew in this contribution in the light of lattice stability thermodynamic simulations. For films obtained from 304 and 316 steel targets, thermodynamic simulations predict that the ferrite phase is more stable than the austenite phase at low thermal energies. In contrast, simulations forecast thermodynamic stability at low thermal energies of the austenite phase in films that are sputtered from 330 steel targets. The criterion of lattice stability reveals that structures observed in the experiments cannot be described comprehensively by thermodynamic states where either full atomic partitioning among phases is established or zero atomic partitioning takes place. Thereby, a description of an equilibrium with incomplete atomic partitioning is proposed here, with the aim of depicting the structures reported in the literature. Such an equilibrium with incomplete atomic partitioning adequately describes the gradual destabilization of ferrite and the increased fraction of austenite (up to fully austenitic structures), when either the substrate heating is intensified, or the Ni content of the alloy is increased, with an 73Fe18Cr9Ni, wt%, initial alloy as a basis.