Effect of Mo, W and Cr over the mechanical properties of clean and sustainable magnetron sputtered AlTiN layers

This study investigates the microstructure and the mechanical performance of Mo, W and Cr doped AlTiN coatings. The coatings have been produced by magnetron sputtering, a waste-free thin film production technology. It will be discussed whether the Mo and W containing AlTiN based coatings could be qualified as medium/high-entropy nitrides as the dominant phase is a solid solution. In this frame, the research is part of the Horizon Europe project M2DESCO (grant agreement 101138397), aimed to develop novel computational models for the design of safe & sustainable high-entropy coatings. The ultimate goal is to achieve coatings which allow the lifespan_enhancement of machining tools by 50%, which would substantially reduce the consumption of raw materials used in these items.

The coatings have been deposited on high-speed steel AISI-M2 (60 HRC) by co-sputtering a Al₃₃Ti₆₇ target in DC_pulsed mode with a Mo or a dual-tile Mo/W or Mo/Cr target in HIPIMS mode, thus obtaining TiAlMoN, TiAlMoWN and TiAlMoCrN coatings respectively. The coating series presented in this study were prepared for different HIPIMS power, while keeping constant the DC sputtering power over the AlTi target. In addition, the influence of the N₂ mass flow has also been investigated. The adhesion of the films was optimized with a combination of Ti and TiN cladding layers.

The effect of the Mo, Mo/W and Mo/Cr co-sputtering, and the N₂ mass flow significantly affects the structure and hardness of the coatings. The dominant face-center-cubic (FCC) structure of the Mo-free AlTiN is also affected upon the increase of the Mo, Mo/W and Mo/Cr sputtering powers, as reflected in notable changes in the crystallite domain sizes and the cell lattice parameters, while the indentation hardness of the coatings notably increases. In addition, the sputtering of dual-tile Mo/W target leads to even higher hardnesses over these of the TiAlMoN coatings.