Synchrotron nano-diffraction for advanced CVD coatings

Purpose and goal

The aim of the joint project between Sandvik Coromant and Chalmers was to demonstrate that synchrotron nano-diffraction can provide critical information about residual stresses distribution through the thickness in thin coatings on cutting tools. Joint experiments show that stress profiles can be measured with a spatial resolution of 100-300 nm, more than enough to follow stress changes through the thickness. Through the project, the Sandvik Coromant was trained in the implementation of the experiments, and have obtained the necessary tools and knowledge for evaluation the data.

Expected results and effects

The project has shown that the technology is very useful for measuring residual stress profiles in thin coatings, and is a good complement to the in-house methods used at Sandvik Coromant. Several coatings made in different ways have been tested, which makes it possible to correlate residual stress and performance. The measured data enters the industrial R&D process and is thus expected to contribute to increased knowledge and, in the long run, more sustainable coatings. If possible, it will also be of interest in the future to perform similar measurements on MAX IV.

Planned approach and implementation

Samples were prepared from coatings with different manufacturing parameters through a combination of mechanical cutting and focused ion beam milling. Nanodiffraction was performed at NanoMAX (MAX IV) with a beam size of 60 nm and step size of 100 nm. Diffraction patterns were collected as a function of position in the layer using a downstream area detector in transmission geometry. Open source software (pyFAI) was used to reduce the data, and dedicated Matlab scripts were developed to correct the data, fit diffraction peaks and evaluate stresses using the sin2psi methodology.