Improvement of mechanical and tribological properties in steel surfaces by using titanium-aluminum/titanium-aluminum nitride multilayered system

摘要

Improvement of mechanical and tribological properties on AISI D3 steel surfaces coated with [Ti-Al/Ti-Al-N]_n multilayer systems deposited in various bilayer periods {A) via magnetron co-sputtering pulsed d.c. method, from a metallic binary target; has been studied in this work exhaustively. The multilayer coatings were characterized in terms of structural, chemical, morphological, mechanical and tribological properties by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM), scanning electron microscopy, nanoindentation, pin-on-disc and scratch tests, respectively. The failure mode mechanisms were studied by optical microscopy. Results from X-ray diffraction analysis revealed that the crystal structure of TiAl/TiAIN multilayer coatings has a tetragonal and FCC NaCl-type lattice structures for Ti-Al and Ti-Al-N, respectively, i.e., it was found to be non-isostructural multilayers. An enhancement of both hardness and elastic modulus up to 29 GPa and 260 GPa, respectively, was observed as the bilayer periods (△) in the coatings were decreased. The sample with a bilayer period (△) of 25 nm and bilayer number n -100 showed the lowest friction coefficient (~0.28) and the highest critical load (45 N), corresponding to 2.7 and 1.5 times better than those values for the coating deposited with n-1, respectively. These results indicate an enhancement of mechanical, tribological and adhesion properties, comparing to the [Ti-Al/Ti-Al-N]_n multilayer systems with 1 bilayer at 26%, 63% and 33%, respectively. This enhancement in hardness and toughness for multilayer coatings could be attributed to the different mechanisms for layer formation with nanometric thickness such as the novel Ti-Al/Ti-Al-N effect and the number of interfaces that act as obstacles for the crack deflection and dissipation of crack energy.