Abstract
A CrAlSiN-AlSiN coating with periodically modulated composition was investigated regarding dependence of the mechanical properties and toughness, morphology, composition, and structure on thermal treatment in the interval of 600–900 °C in argon ambience. The coating exhibited superhardness and high toughness up to 800 °C. A very slight decrease in the nanohardness, resistance to elastic strain to failure, and plastic deformation were observed. The coating had enhanced elastic recovery stable up to 700 °C. It was found that the coating morphology was not substantially influenced by the thermal treatment. X-ray diffraction (XRD) analysis revealed that the modulated coating had a nanocomposite structure, which did not change after annealing, even at 900 °C. The grains were composed mainly of fcc-CrN and h-AlN phases embedded into an amorphous Si3N4 matrix. A small amount of an h-Cr2N phase appeared after heating at temperatures above 700 °C. The coating composition was examined by energy-dispersive X-ray spectroscopy (EDS). The coating was stoichiometric up to 800 °C. It became sub-stoichiometric with respect to nitrogen after annealing at 800 °C and 900 °C. It is thus concluded that the CrAlSiN-AlSiN coating with a periodically modulated structure keeps the combination of superhardness (45.3 GPa) and improved toughness (H3/E*2 = 0.362 GPa, elastic recovery 57%) at temperatures up to 800 °C, and is suitable for high thermal applications.
Highlights
The needs of present-day industry are posing demanding requirements for the mechanical and tribological properties of the tools, details, and pieces used in machining and forming technologies, high-speed machining, hard turning, micro-manufacturing, dry machining, and so on
This study aims to investigate the stability of the coating superhardness and enhanced toughness under high thermal treatment in the interval of 600–900 ◦ C, for high-temperature industrial applications
The surface morphology is the typical one of coatings deposited by cathodic arc evaporation and was not affected significantly by the thermal treatment
Summary
The needs of present-day industry are posing demanding requirements for the mechanical and tribological properties of the tools, details, and pieces used in machining and forming technologies, high-speed machining, hard turning, micro-manufacturing, dry machining, and so on. Modern coatings are required to combine incompatible properties, such as superhardness with high toughness, thermal stability, and wear resistance. This goal is unachievable in conventional monolayer coatings based on nitrides and carbides of transition metals, despite the useful properties they possess [1,2,3,4]. Graded and multilayer structures offer an appropriate approach to overcome the limited potential of monolayer coatings. These configurations allow changes in the structure and composition of the coating period so that several properties are strengthened simultaneously [5,6,7]
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