Determination of proof stress and strain-hardening exponent for thin film with biaxial residual stresses by in-situ XRD stress analysis combined with tensile test

A new method is put forward to measure the proof stress and strain-hardening exponent of polycrystalline films (Cu, TiN) under a biaxial residual stresses state on the substrates. The Cu and TiN films were deposited on the steel substrates by ion beam-assisted magnetron sputtering and plasma-assisted chemical vapor deposition (PACVD), respectively. During the tensile test, the longitudinal stress (σ1) and transverse stress (σ2) of the films were determined by in-situ X-ray diffraction, and the applied strain (εa) of the films were measured by a strain gauge. Based on the experimental results, the equivalent stresses σ̄ and equivalent uniaxial strains εt can be obtained. From the σ̄-εt curves, the proof stresses σ0.1 of the Cu and TiN films have been calculated. The results indicate that the values of σ0.1 of the Cu and TiN films are 328 MPa and 4.2 GPa, respectively, and the values of the strain-hardening exponents for them are 0.62 and 0.36, respectively. In addition, evidence that the plastic flow of TiN film occurred under the tensile load is also obtained.