Towards an improvement of performance of TiAlN hard coatings using metal interlayers
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Towards an improvement of performance of TiAlN hard coatings using metal interlayers J. M. Castanho and M. T. Vieira ICEMS – Grupo de Materiais e Engenharia de Superfícies Departamento de Engenharia Mecânica Universidade de Coimbra 3030 Coimbra, PORTUGAL
ABSTRACT TiAlN sputtered coatings have been used with success in high-speed cutting tools in the last few years. However, the adhesive failures of the coatings refrain its application in more severe wear conditions like as high-speed machining. The assumptions for the present research were based on the hypothesis that thin metal interlayers will behave as shear stress sinkers, which could decrease the delamination of the thin films. In the present work, coatings of TiAlN with thin ductile metallic interlayers (Al, Ti, Cu and Ag) were deposited by reactive d.c. magnetron sputtering. Multilayer coatings with aluminum, titanium and silver interlayers achieve higher adhesion values (70N) than TiAlN monolithic coating (40N). Three and five metal ductile layers contribute to an increase of hardness and Young’s modulus without change the residual stresses of the monolithic coating. Contrarily, the introduction of copper layers reduces all the studied mechanical properties of the TiAlN monolithic coatings, which are related to the different deformation mechanisms of the ductile interlayers.
INTRODUCTION Multilayer coatings with short bilayer period have been widely studied [1-4]. High values of hardness attained by the coatings with a superlattice structure have been reported, but this mechanical property seems to be only the unique reason for the intense investigation in such kind of materials. However, these coatings does not fulfill the fundamental needs to be used in severe mechanical applications, particularly high speed machining, and their behavior is even worse than monolithic coatings [5]. From this statement, it is necessary to improve the mechanical properties of the monolithic coatings, and this can be performed introducing very thin metallic ductile interlayers, that are expected do not interfere with the mechanical properties of the monolithic coatings, and increase the adhesion and fracture resistance of the coatings. This based on the ability of the metal interlayers to be deformed and deflect the cracks induced by the mechanical constraints applied in during coated tool life. Thus, the aim of the present research work was to study the behavior of different ductile metals were used as interlayers: aluminum, titanium, copper and silver; aluminum and titanium (A1-f.c.c. and A3-h.c.p, and have high affinity to nitrogen) and copper and silver (both A1-f.c.c. and low reactivity to nitrogen).
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EXPERIMENTAL DETAILS Multilayer coatings were deposited on heat-treated (quenching and tempering), polished (Ra < 0.02 µm) high-speed steel M2 (AISI) with hardness of 9GPa, by a two d.c. magnetron semi- industrial sputtering prototype (HARTEC). A titanium aluminide target (55.3 %at. of Ti, 43.2 %at. of Al, 1.5 %at. of Cr) and N2 as reactive gas with a pa
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