Influence of high Si contents in nanocomposite coatings on temperature dependent elastic-plastic properties and damage behavior of milling tools

• Applicant: Professorin Dr.-Ing. Kirsten Bobzin
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 516745377

The tools during milling of high-speed steels undergo thermal and mechanical stresses resulting in reduced machining performance. Hard coatings deposited through physical vapor deposition offer a promising solution for tool protection. CrAlSiN and TiAlSiN coatings consist of (Cr,Al)N and (Ti,Al)N nanocrystals, respectively, embedded in Si3N4 amorphous matrix and are therefore termed as nanocomposites. The Si contents in such coatings influence the elastic-plastic properties and wear behavior of coated milling tools. Currently, an increase in indentation hardness HIT with Si addition until x(Si) = ~10 at. % is reported. The decrease at higher Si contents is associated with the increased volume fraction of amorphous phase in the coating. However, the elastic-plastic properties of these coatings have been determined only at room temperature whereas the tools during milling of high-speed steels are subjected to temperatures of T > 600 °C. Moreover, the higher Si contents can help avoid unfavorable residual stress states in the coatings which may lead to cutting edge fracture in milling tools. Regarding the wear behavior, an increased high temperature wear resistance of the coated compound has been associated with higher Si content of the coating using Pin-on-Disk model tests. The main aim of the proposed research project is to find out the influence of higher Si contents in nanocomposite coatings on residual stress state, temperature dependent elastic-plastic properties and crack resistance of the coatings along with deformation and wear behavior of the coated milling tools. Moreover, the effect of high Si contents on the damage mechanisms of the coated milling tool through targeted combination of residual stress state and temperature-dependent elastic-plastic properties of the coating will be identified. For this purpose, CrAlSiN and TiAlSiN coatings with higher Si contents till x(Si) = 25 at. % will be deposited on carbide substrates and milling tools. The coating properties, microstructure and residual stress state will be analyzed in correlation with the coating’s Si content. The temperature dependent elastic-plastic properties of the coating and deformation behavior of the coated compounds will be investigated using high temperature nanoindentation. Furthermore, the crack resistance of the coatings will be studied using nanoscratch. The coated milling tools will undergo machining tests on high speed steel HS6 5-3C workpieces. Accordingly, the wear behavior and the underlying damage mechanisms of the coated milling tools will be analyzed.

• DFG Programme: Research Grants