Mohammad Arab Pour Yazdi

Nano-sculptured Janus-like TiAg thin films obliquely deposited by GLAD co-sputtering for temperature sensing

Inclined, zigzag and spiral TiAg films were prepared by glancing angle co-deposition, using two distinct Ti and Ag targets with a particle incident angle of 80° and Ag contents ranging from 20 to 75 at%. The effect of increasing Ag incorporation and columnar architecture change on the morphological, structural and electrical properties of the films was investigated. It is shown that inclined columnar features (βxa0=xa047°) with high porosity were obtained for 20 at% Ag, with the column angle sharply decreasing (βxa0=xa021°) for 50 at% Ag, and steeply increasing afterwards until β = 37° for the film with 75 at% Ag. The sputtered films exhibit a rather well-crystallized structure for Ag contents ≥50 at%, with a TiAg (111) preferential growth. No significant oxidation was detected in all films, except for the one with 20 at% Ag, after two 298-473-298 K temperature cycles in air. The calculated temperature coefficient of resistivity (TCR) values vary between 1.4 and 5.5xa0×xa010-4 K-1. Nano-sculptured spiral films exhibit consistently higher resistivity (ρxa0=xa01.5xa0×xa010-6 Ω m) and TCR values (2.9xa0×xa010-4 K-1) than the inclined one with the same Ag content (ρxa0=xa01.2xa0×xa010-6 Ω m and TCRxa0=xa02.0xa0×xa010-4 K-1). No significant changes are observed in the zigzag films concerning these properties. The effective anisotropy A eff at 473 K changes from 1.3 to 1.7 for the inclined films. Spiral films exhibit an almost completely isotropic behavior with A effxa0=xa01.1. Ag-rich TiAg corexa0+xa0shell Janus-like columns were obtained with increasing Ag concentrations.

The Yttrium Effect on Nanoscale Structure, Mechanical Properties, and High-Temperature Oxidation Resistance of (Ti0.6Al0.4)1–x Y x N Multilayer Coatings

As machine tool coating specifications become increasingly stringent, the fabrication of protective titanium aluminum nitride (Ti-Al-N) films by physical vapor deposition (PVD) is progressively more demanding. Nanostructural modification through the incorporation of metal dopants can enhance coating mechanical properties. However, dopant selection and their near-atomic-scale role in performance optimization is limited. Here, yttrium was alloyed in multilayered Ti-Al-N films to tune microstructures, microchemistries, and properties, including mechanical characteristics, adhesion, wear resistance, and resilience to oxidation. By regulating processing parameters, the multilayer period (Λ) and Y content could be adjusted, which, in turn, permitted tailoring of grain nucleation and secondary phase formation. With the composition fixed at xxa0=xa00.024 in (Ti0.6Al0.4)1–xYxN and Λ increased from 5.5 to 24 nm, the microstructure transformed from acicular grains with 〈111〉 preferred orientation to equiaxed grains with 〈200〉 texture, while the hardness (40.8xa0±xa02.8xa0GPa to 29.7xa0±xa04.9 GPa) and Young’s modulus (490xa0±xa047 GPa to 424xa0±xa050 GPa) concomitantly deteriorated. Alternately, when Λxa0=xa05.5xa0nm and x in (Ti0.6Al0.4)1–xYxN was raised from 0 to 0.024, the hardness was enhanced (28.7xa0±xa07.3xa0GPa to 40.8xa0±xa02.8xa0GPa) while adhesion and wear resistance were not compromised. The Ti-Al-N adopted a rock-salt type structure with Y displacing either Ti or Al and stabilizing a secondary wurtzite phase. Moreover, Y effectively retarded coating oxidation at 1073 K (800xa0°C) in air by inhibiting grain boundary oxygen diffusion.