Davide Sangiovanni

Toughness enhancement in hard ceramic thin films by alloy design

Hardness is an essential property for a wide range of applications. However, hardness alone, typically accompanied by brittleness, is not sufficient to prevent failure in ceramic films exposed to h ...

Large-scale molecular dynamics simulations of TiN/TiN(001) epitaxial film growth

Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200K are carried out using incident flux ratios N/Ti -1, 2, and 4. The films are analyzed as a fu ...

Experimental and computational studies on toughness enhancement in Ti-Al-Ta-N quaternaries

Design of hard ceramic material coatings with enhanced toughness, which prevents crack formation/propagation leading to brittle failure during application, is a primary industrial requirement. In this work, experimental methods supported by ab initio density functional theory (DFT) calculations and electronic structure analyses are used to investigate the mechanical behavior of magnetron sputtered Ti-Al-Ta-N hard coatings. The as-deposited Ti1-x-yAlxTayN (y = 0–0.60) films exhibit a single phase cubic sodium chloride (B1) structure identified as TiAl(Ta)N solid solutions. While the hardness H of Ti0.46Al0.54N (32.5 ± 2 GPa) is not significantly affected by alloying with TaN (H of the quaternary nitrides varies between 26 ± 2 and 35 ± 4 GPa), the elastic stiffness monotonically decreases from 442 to 354 GPa with increasing Ta contents, which indicates improved toughness in TiAlTaN. Consistent with the experimental findings, the DFT results show that Ta substitutions in TiAlN reduce the shear resistance due...

Effects of incident N atom kinetic energy on TiN/TiN(001) film growth dynamics: A molecular dynamics investigation

Large-scale classical molecular dynamics simulations of epitaxial TiN/TiN(001) thin film growth at 1200 K, a temperature within the optimal range for epitaxial TiN growth, with an incident N-to-Ti flux ratio of four, are carried out using incident N energies EN = 2 and 10 eV and incident Ti energy ETi = 2 eV. To further highlight the effect of EN, we grow a bilayer film with EN = 2 eV initially and then switch to EN = 10 eV. As-deposited layers are analyzed as a function of composition, island-size distribution, island-edge orientation, and vacancy formation. Results show that growth with EN = 2 eV results in films that are globally overstoichiometric with islands bounded by N-terminated polar 110 edges, whereas films grown with EN = 10 eV are flatter and closer to stoichiometric. However, EN = 10 eV layers exhibit local N deficiency leading to the formation of isolated 111-oriented islands. Films grown by changing the incident energy from 2 to 10 eV during growth are more compact than those grown entirel...

Effects of surface vibrations on interlayer mass transport: Ab initio molecular dynamics investigation of Ti adatom descent pathways and rates from TiN/TiN(001) islands

We carried out density-functional ab initio molecular dynamics (AIMD) simulations of Ti adatom (

Thermally induced age hardening in tough Ta-Al-N coatings via spinodal decomposition

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Growth, nanostructure, and optical properties of epitaxial VNx/MgO(001) (0.80 ≤ x ≤ 1.00) layers deposited by reactive magnetron sputtering

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Efficient and accurate determination of lattice-vacancy diffusion coefficients via non equilibrium ab initio molecular dynamics

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Electronic mechanism for toughness enhancement in Ti{sub x}M{sub 1-x}N (M=Mo and W)

epitaxial islands on TiN(001) at temperatures (

Electronic mechanism for toughness enhancement in TixM1-xN (M=Mo and W)

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