The Yttrium Effect on Nanoscale Structure, Mechanical Properties, and High-Temperature Oxidation Resistance of (Ti 0.6 A
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d TIMOTHY J. WHITE are with the School of Materials Science and Engineering, Nanyang Technological University, Singapore 639798, Singapore, and also with the Energy Research Institute @ NTU, Interdisciplinary Graduate School, Nanyang Technological University, Singapore 637141, Singapore. MOHAMMAD ARAB POUR YAZDI and ALAIN BILLARD are with the Institut FEMTO-ST, UMR 6174, CNRS, Universite´ Bourgogne Franche-Comte´, UTBM, Site de Montbe´liard, 90010 Belfort, France. FERNANDO LOMELLO is with the DenService d’Etudes Analytiques et de Re´activite´ des Surfaces (SEARS), CEA, Universite´ Paris-Saclay, 91191, Gif sur Yvette, France. ANDRA´S KOVA´CS is with the PGI-5, Forschungszentrum Ju¨lich GmbH in the Helmholtz Association, 52425 Julich, Germany. FRE´DE´RIC SCHUSTER is with the CEA CrossCutting program on Advanced Materials Saclay, 91191 Gif-sur-Yvette, France. YVES WOUTERS and CE´LINE PASCAL are with the SiMaP, UMR CNRS/UJF/Grenoble INP, 38402 Saint-Martin d’He´res, France. FRE´DE´RIC SANCHETTE is with LRC CEA-ICD-LASMIS-UTT, Antenne de Nogent-52, 52800 Nogent, France. ZHILI DONG is with the School of Materials Science and Engineering, Nanyang Technological University. Contact e-mail: [email protected] Manuscript submitted October 6, 2016. Article published online July 12, 2017 METALLURGICAL AND MATERIALS TRANSACTIONS A
INTRODUCTION
TITANIUM aluminum nitride (Ti-Al-N) coatings processed by physical vapor deposition (PVD) exhibit high hardness, good wear resistance,[1] and less oxidation,[2] which are essential for protecting high speed machining tools.[3,4] Fine-scale TiN/Ti-Al-N multilayer superlattices improve mechanical properties[5–8] by layering rock-salt face-centered-cubic (fcc) TiN and Ti-Al-N, which have slightly different lattice parameters. By adjusting the bilayer period (K), a hardness higher than the rule-of-mixtures value is achieved. Further improvements in oxidation resistance are achieved by alloying elements with a high oxygen affinity, such as Si,[9,10] Cr,[11] V,[12] Y,[13] and Hf,[14] as these dopants form dense oxides in Ti-Al-N coatings that inhibit oxygen migration. It has been reported that adding 1 at. pct yttrium (in Ti0.45Al0.54Y0.01N) decreased oxide thickness from 4.9 to 3.1 lm after annealing at 1173 K (900 C) for 210 minutes, because at elevated VOLUME 48A, SEPTEMBER 2017—4097
temperature, Y segregates to grain boundaries and impedes oxygen inward diffusion and cation outward diffusion. Simultaneously, the Ti0.45Al0.54Y0.01N monolayer coating hardness improved by 24 pct compared to Ti0.45Al0.55N due to a combined effect of solid solution hardening from Y substitution and reduced grain size.[15] The physical-vapor-deposited Ti-Al-Y-N coatings are commonly fabricated using Ti-Al-Y alloy targets with various yttrium contents. The Ti0.45Al0.54Y0.01N, as reported, is composed of single rock-salt phase with low yttrium content.[15] However, secondary wurtzite phase may appear with increased yttrium content in Al-rich Ti-Al-N (Al atomic fraction > 0.5), which will affect mechanical properties.[16]
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