Abstract
Because of the tremendous variability of crystallite sizes and shapes in nano-materials, it is challenging to assess the corresponding size-property relationships and to identify microstructures with particular physical properties or even optimized functions. This task is especially difficult for nanomaterials formed by self-organization, where the spontaneous evolution of microstructure and properties is coupled. In this work, two compositionally graded TiAlN films were (i) grown using chemical vapour deposition by applying a varying ratio of reacting gases and (ii) subsequently analysed using cross-sectional synchrotron X-ray nanodiffraction, electron microscopy and nanoindentation in order to evaluate the microstructure and hardness depth gradients. The results indicate the formation of self-organized hexagonal-cubic and cubic-cubic nanolamellae with varying compositions and thicknesses in the range of ∼3-15 nm across the film thicknesses, depending on the actual composition of the reactive gas mixtures. On the basis of the occurrence of the nanolamellae and their correlation with the local film hardness, progressively narrower ranges of the composition and hardness were refined in three steps. The third film was produced using an AlCl3/TiCl4 precursor ratio of ∼1.9, resulting in the formation of an optimized lamellar microstructure with ∼1.3 nm thick cubic Ti(Al)N and ∼12 nm thick cubic Al(Ti)N nanolamellae which exhibits a maximal hardness of ∼36 GPa and an indentation modulus of ∼522 GPa. The presented approach of an iterative nanoscale search based on the application of cross-sectional synchrotron X-ray nanodiffraction and cross-sectional nanoindentation allows one to refine the relationship between (i) varying deposition conditions, (ii) gradients of microstructure and (iii) gradients of mechanical properties in nanostructured materials prepared as thin films. This is done in a combinatorial way in order to screen a wide range of deposition conditions, while identifying those that result in the formation of a particular microstructure with optimized functional attributes.
Highlights
In nanomaterials with crystallite sizes below 100 nm, the physical properties significantly differ from those of bulk materials
As already indicated in x2.1, film A was prepared by using varying deposition conditions, namely the precursor ratio AlCl3/TiCl4 was changed in steps of about 0.1 during the deposition process
In the region near the film– substrate interface, with a thickness of about 1.5 mm, film A possessed the composite grain microstructure visible in the scanning electron microscopy (SEM) image in
Summary
In nanomaterials with crystallite sizes below 100 nm, the physical properties significantly differ from those of bulk materials. The properties of nanomaterials can be correlated with (i) the variation of lattice spacing and corresponding chemical bonding nature, especially at nanocrystal surfaces, and/or (ii) the large volume fraction of grain boundaries in polycrystalline materials (Arzt, 1998; Gleiter, 1989). Hard nanocrystalline thin films based, for example, on TiN, CrN and TiAlN (used in metal cutting applications) represent a typical example of a technological system in which small crystallites decisively contribute to enhanced functional properties such as high hardness, high wear resistance and toughness (Veprek & Argon, 2002; Zhang et al, 2003). The microstructural design is important, especially in the case of hard films where fracture toughness can be significantly enhanced by grain boundary engineering (Mayrhofer et al, 2006; Zhang et al, 2007)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
