Thermal Conductivity Designed Hard Protective Thin Films
Abstract
The main objective was to design hard coatings with directionally-dependent thermal transport properties. Coatings with layered arrangement of CrN and AlN layers were developed, as CrN typically has a thermal conductivity of ~2 W/mK whereas AlN can reach up to 300 W/mK at room temperature. This arrangement allows for high lateral thermal conductivity through the continuous AlN layers, and low thermal conductivity across the layers due to the periodic arrangement of the CrN layers. We have developed and studied various CrN/AlN layer combinations. The influence of the individual layer thickness was investigated by preparing multilayer coatings composed of 1-3 nm thin AlN layers and 1-10 nm CrN layers. Based on x-ray diffraction, transmission electron microscopy, and high resolution TEM, we can conclude that full stabilization of the AlN layers in their metastable cubic structure can be achieved up to layer thicknesses of 3 nm with the condition that the CrN layers need to be at least as thick as the AlN layers. Otherwise the AlN layers crystallize also in their stable ZnS (wurtzite type) structure. The superlattice coatings exhibit a characteristic hardness profile as a function of the bilayer period with a pronounced hardness maximum of 31 and 28 GPa. Highest thermal stability for these superlattice coatings is obtained when the columnar growth is inhibited. Based on our study we can conclude that a knowledge-based combination which is derived from this project of CrN and AlN layers leads to outstanding mechanical properties as well as thermal stability.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 01, 2014
- Accession Number
- ADA602572
Entities
People
- Paul H Mayrhofer
Organizations
- TU Wien