A model for the yield strength of a thin polycrystalline film

Abstract

A simple expression for the yield strength of a thin polycrystalline film attached to a substrate and with a passivated layer has been derived from a relationship between stress work for dislocation moving and strain energy. It is shown that, the yield strength of a polycrystalline film is determined by two affecting factors (orientation of grains and type of dislocations) and three strengthening factors (passivated layer strengthening, substrate strengthening, and grainsize strengthening). Predictions from the expression are in agreement with reported experimental results. This shows that the model is reasonable.

Yield strength of attached copper film

“…These can be attributed to the substrate strengthening, grain size strengthening and film thickness effects. In previous papers, [17,18] we assumed that a polycrystalline film was composed of columnar grains with an average grain diameter d in the film plane and height h (equal to the film thickness). A simple expression for the yield strength of the polycrystalline film attached to a substrate with a passivated layer was derived from a work-energy relationship for dislocation movement,…”

“…for which the parameters were described in our previous papers. [17,18] It is shown that the yield strength of a polycrystalline film is determined by two affecting factors (grain orientation and dislocation type, corresponding to the first and second factor, respectively) and three strengthening factors (substrate strengthening, passivated layer strengthening, and grain size strengthening, corresponding to the first, second, and third terms in square brackets, respectively). For pure copper film on a steel substrate studied here, the second term in square brackets should be omitted in Eq.…”