Optimizing Transmission Kikuchi Diffraction for Analysing Grain Size and Orientation of Nanocrystalline Coatings

• Main Author: Tryblom, Axel
• Format: Others
• Language: English
• Published: Uppsala universitet, Tillämpad materialvetenskap 2015
• Subjects: TKD; t-EBSD; Kikuchi diffraction; coating; nanocrystalline; sample preparation; in situ lift-out; DualBeam; precision mechanical polishing; SEM
• Online Access: http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-266442

In order to increase efficiency and lifetime of cutting tools it is typical to apply thin coatings by physical or chemical vapour deposition. Applying coatings on cutting tools has shown an increase in both efficiency and lifetime and are of large interest in further development. The study of coatings and their mechanical properties is a very active research area and produces tools extensively used in the industry.  The behaviour of materials on a macroscopic scale can typically be related to microscopic properties. Some coatings produced by Chemical Vapour Deposition (CVD) but especially Physical Vapour deposition (PVD) have crystal structures which are difficult to analyse by conventional methods due to crystal sizes in the nanometre scale. For nanocrystalline materials standard methods fall short due to a limited resolution of the methods.  Recently a method for electron diffraction of crystalline samples was suggested to be used differently in order to achieve a higher resolution. Unlike earlier when electrons were reflected from the sample, using Electron Backscattering Diffraction (EBSD), the electrons were transmitted through thin samples with thicknesses in the magnitude of 100 nm, which enabled the crystal structure to be determined. The new method is typically referred to as either Transmission Kikuchi Diffraction (TKD) or transmission EBSD (t-EBSD) with a resolution down to approximately 10 nm.  The goal with this master thesis has been to evaluate sample preparation methods and TKD studies on PVD samples. Each step has been divided into parameters which govern the sample preparation and analysis and optimized accordingly in order to achieve best possible results of the crystal structure of PVD coatings. From this it has been possible to show how TKD is optimally performed and which difficulties and limitations that are present.  In this thesis two coatings, TiN and (Ti,Al)N, have been studied with TKD and two different preparation methods have been attempted. These were precision mechanical polishing and in-situ lift out with a Dual Beam System. Mechanical polishing did not succeed in producing samples for TKD but was not ruled out as a possibility while the in-situ lift out method could both produce samples and achieve a crystallographic indexing around 80 %. The only areas which were difficult to index were crystal boundaries and crystal clusters where individual crystals were in the range of <30 nm. In these areas overlapping Kikuchi patterns were observed due to the resolution limit of TKD.