An inverse problem in estimating fracture toughness of TiAlN thin films by finite element method based on nanoindentation morphology

The fracture toughness of TiAlN thin films on AISI 304 austenitic stainless steel was inversely investigated by combining nanoindentation experiment with finite element method (FEM) and extended FEM (XFEM) simulation. The TiAlN thin films were deposited by deep oscillation magnetron sputtering (DOMS) with the oscillation pulse on and off times of 12 mu s and 30 mu s at a peak power of 136.1 kW. A completely dense TiAlN thin film with the thickness of 1500 nm has a face-centered-cubic microstructure with (200) preferred orientation. The displacements of the nanoindenter were intentionally interrupted by 1200 nm and 1800 nm, latter is thin filmcrossing to induce an apparently cracking. The cross-sectional samples of TiAlN thin films with the cracks were fabricated by focused ion beam. The experimental crack number and position in the cross-sectional samples were observed by scanning electron microscopy. The maximum damage initiating stress (sigma max) and corresponding crack separation distance (delta c) in the Griffith-Irwin relationships were fitted using the XFEM calculation based on the crack morphology to match the crack number and position of TiAlN thin films. The fracture toughness of TiAlN thin films on AISI 304 austenitic stainless steel was calculated to be 1.09 MPa m1/2 according to the fitted parameters of 5.5 GPa for sigma max and 1.5 nm for delta c. Therefore, an alternative method by the nanoindentation morphology and the inversely calculation fitting was developed to estimate the fracture toughness of thin films.

Automated summary

The fracture toughness of TiAlN thin films on AISI 304 austenitic stainless steel was inversely investigated using nanoindentation experiment and simulation methods. By controlling the displacement of the nanoindenter and observing the crack number and position, the fracture toughness of TiAlN thin films was calculated to be 1.09 MPa m1/2.