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Title:Effect of low energy ion irradiation during growth on the composition, nanostructure, and physical properties of epitaxial metastable zirconium aluminum nitride
Author(s):Mei, Antonio Rodolph
Advisor(s):Rockett, Angus A.
Department / Program:Materials Science & Engineerng
Discipline:Materials Science & Engr
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):transition metal nitride
metastable alloy
spinodal decomposition
ion bombardment
reactive magnetron sputtering
Abstract:Protective coatings synthesized from pseudo-binary metastable transition-metal nitride (TMN) alloys account for the majority of the world’s coating market. The popularity of these films owes to their intrinsic nanostructure, which are well known to enhance physical properties such as hardness and oxidation resistance. Since these alloys may be deposited en mass at relatively low costs by physical vapor depositions (PVD) processes such as cathodic arc evaporation and reactive magnetron sputtering, nanostructured TMN alloys have dominated the market at competitive prices. The origin of the nanostructure in TMN alloys may be traced to the immiscibility of the constituents forming the alloy. Pseudo-binaries with large miscibility gaps readily undergo spinodal decomposition when exposed to processing temperatures, giving rise to a nanoscale composition modulation. Consequentially, appropriately selecting pseudo- binaries which have maximize miscibility gap may lead to greater enhancements in physical properties. In this dissertation, I investigate Zr1-xAlxN alloys, which exhibits a larger driving force for spinodal decomposition than the current industry standard, Ti1-xAlxN. Single-phase epitaxial metastable Zr1-xAlxN/MgO(001) (x ≤ 0.25) thin films and Zr1-xAlxN/ZrN(001) superlattices are grown at 650°C by ultra-high vacuum magnetically- unbalanced reactive magnetron sputtering from a single Zr0.75Al0.25 target. The AlN concentration x is controlled by varying the ion energy (5 < Ei < 55 eV) incident at the growth surface while maintaining the ion-to-metal flux ratio constant at Ji/JMe = 8. The net incorporated Al flux decreases from 3.4 to 1.1×1014 atoms cm-2s-1, due to resputtering and backscattering of deposited Al atoms (27 amu) from heavy Zr atoms (91.2 amu). High- resolution x-ray diffraction θ-2θ scans, reciprocal lattice maps, and selected-area electron diffraction revealed that all films are NaCl structure with a cube-on-cube orientation relative to the substrate, (001)Zr1-xAlxN||(001)MgO. The relaxed alloy lattice parameter varies from 0.458 with x = 0.25 to 0.450 nm with x = 0.01. Nanoindentation measurements show that hardness decreases from 28.6 to 23.3 GPa, while the elastic modulus increases from 263 to 296.8 GPa, as x is varied from 0 to 0.25. Z-contrast scanning transmission electron microscopy and nanobeam electron diffraction reveal the presence of a spinodal nanostructure with a constant characteristic lattice modulation period of 1.1 nm for alloy films with x > 0.18. Zr0.75Al0.25N/ZrN(001) superlattices with equi-thick layers have hardness H which range from 27 GPa with a bilayer period Λ = 9.2 nm to a maximum of 29 GPa at Λ = 2.3 nm.
Issue Date:2013-02-03
Rights Information:Copyright 2012 Antonio Rodolph Mei
Date Available in IDEALS:2013-02-03
Date Deposited:2012-12

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