The influence of erosion of an AISI 304 stainless steel target during long-term magnetron spraying on the structural and chemical homogeneity of the obtained thin films

Abstract

As a result of this study, it was found that the erosion of the surface of an AISI 304 austenitic steel target during magnetron sputtering leads to significant changes in its chemical and phase composition. During the first hour of target sputtering, the surface is enriched in Cr by ∼4 wt% due to the loss of Fe by ∼3 wt% and Ni by ∼1 wt%, which persists over the next 4 h of sputtering. Changes in the phase composition are also observed, with the formation of a highly dispersed ferrite phase reaching 46 wt% within 5 h of target sputtering. This stationary state of the target surface promotes the formation of thin films with controlled phase and chemical composition at the nanoscale. They are a three-phase system including austenite, ferrite and intermetallic σ-phase (60 wt% austenite, 30 wt% ferrite, and 10 wt% σ -phase) with different but time-stable (stationary) chemical compositions.

A mechanism for the formation and stabilization of such a three-phase system is proposed. This is associated with the manifestation of a phase size effect, which ensures the preferential formation of ferrite at nanoparticle sizes up to 13 nm, and an isomorphic size effect, which is responsible for chemical and phase heterogeneity at the nanoscale, when the structure and chemical composition of nanoparticles (NPs) depend on the shape and size of the particles.

Data from local methods of surface analysis (electron probe microanalysis and scanning tunneling microscopy) indicate the presence of subtle chemical and phase heterogeneity at the nanoscale. It has been shown that the films consist of NP ferrite phases α and α₁, which exhibit distinct chemical compositions: Fe – 66 at.%, Cr - 27 at.%, Ni – 7 at.% and Fe – 80.4 at.%, Cr −19.6, respectively; σ-phases: Fe 80.4 at%, Cr 19.6 at% and γ-phases: Fe 70.0 at%, Cr 16.3 at%, Ni 13.7 at%.