arXiv subjects

Nidhin George Mathews

Publications and source records attributed to Nidhin George Mathews.

4 recordsLinked to original sources

arXiv2026

A correlation of structural changes with nanomechanical properties in TiN-AlN multilayer films

The present work investigates the changes in overall nanomechanical properties of reactively sputtered TiN-AlN multilayer films arising due to phase transformation in the AlN layers. Multilayered TiN-AlN films were sputter deposited with constant TiN layer thickness of 5 nm while the AlN layer thickness varied between 1-5 nm. The AlN underwent a phase transition from cubic rock salt to hexagonal wurtzite above 3 nm thickness due to the lattice strains. The hardness and indentation modulus of the multilayers decreased with increasing AlN film thickness, up to 3 nm, due to increased volume fraction of softer AlN layer and then stabilized for 4 nm and 5 nm thickness films. Micropillar compression of these multilayers showed a transition from columnar brittle to partially ductile failure associated with crack deflection with increasing AlN film thickness. Interestingly, nanoindentation scratch resistance of 3 nm AlN multilayer was observed to be superior compared to all other films. The crack propagation behavior in scratching showed increased microcracking tendency towards higher AlN film thickness. This shows that cubic to hexagonal transformation in AlN is beneficial for improving the damage tolerance of the multilayer system.

cond-mat.mtrl-sci↗

arXiv2026

Microscale bending plasticity and fracture behavior of amorphous aluminum oxide films

Recent work has demonstrated microscale compressive plasticity in pulse laser deposited (PLD) amorphous alumina (a-Al2O3). This work explores microscale bending plasticity and fracture behavior of a-Al2O3 films deposited using three different methods-PLD, atomic layer deposition (ALD) and sputter deposition (SD). The three deposition routes produced amorphous films with similar stoichiometric compositions. We demonstrate, for the first time, bending plasticity in PLD and ALD a-Al2O3 films at microscale using in situ microcantilever bending experiments at room temperature. All tested PLD a-Al2O3 microcantilevers showed substantial ductile behavior in bending by accommodating total strains >10% without fracture. Half of the tested ALD a-Al2O3 cantilevers exhibited elastic brittle fracture while the other half showed bending plasticity, indicating that the observed deformation behavior is strongly influenced by the presence and distribution of defects within the tested volume. All SD a-Al2O3 microcantilevers showed elastic brittle failure attributed to their columnar growth microstructure. The microscale bending response was found to be highly dependent on the film deposition method highlighting the role of defects in suppressing plasticity mechanisms. Notched microcantilever bending tests on all three films showed brittle failure with similar fracture toughness value of 3.1 +/- 0.2 MPa.m0.5, effectively ruling out any localized crack tip plasticity. These findings underscore the importance of minimizing defects during fabrication in order to develop damage tolerant amorphous oxides. Nonetheless, the observation of bending plasticity in both PLD and ALD microcantilevers, which include a tensile stress component as well, suggests that the plastic deformation mechanisms in amorphous alumina are more general and are not exclusively governed by the deposition method.

cond-mat.mtrl-sci↗

arXiv2025

The effect of elastic-plastic mismatch and interface proximity on the fracture toughness of Ti-TiN thin films

Magnetron sputtered titanium nitride (TiN) thin films are widely used as protective coatings due to their high hardness, but suffer from inherent brittleness and low fracture toughness, limiting their applicability. The multilayering of TiN films with metallic titanium (Ti) interlayers in the form of bi-layer and tri-layer systems have been studied using microcantilever fracture tests. Plastic dissipation in the Ti layer is shown to lead to an increase in crack growth resistance. The effect of the elastic-plastic mismatch between the two materials on the crack driving force, as well as the size of the fully developed plastic zone in Ti have been quantified in this work for the first time. It is shown that incorporating a Ti layer thickness of 250 nm can improve the fracture resistance by nearly ten times compared to the initiation fracture toughness in TiN, preventing catastrophic fracture of these multi-layered films. These results will aid in physics informed design of optimised thickness of metallic interlayers in multi-layered thin films.

cond-mat.mtrl-sci↗

arXiv2025

Deformation and adiabatic heating of single crystalline and nanocrystalline Ni micropillars at high strain rates

The deformation behavior of single crystal and nanocrystalline nickel were studied using in situ micropillar compression experiments from quasi-static to high strain rates up to 10^3 s-1. Deformation occurred by dislocation slip activity in single crystal nickel whereas extensive grain boundary sliding was observed in nanocrystalline nickel, with a shift towards more inhomogeneous, localized deformation above 1 s-1. The strain rate sensitivity exponent was found to change at higher strain rates for both single crystal and nanocrystalline nickel, while the overall strain rate sensitivity was observed to be of the same value for both. With increasing high strain rate micropillar compression tests being reported, the issue of adiabatic heating in micropillars becomes important. We report crystal plasticity based finite element modeling to estimate the adiabatic heating, spatially resolved within the pillar, at the highest tested strain rates. The simulations predicted a significant temperature rise of up to 200 K in nanocrystalline Ni at the grain boundaries, and 20 K in single crystalline Ni due to strain localization. Transmission Kikuchi Diffraction analysis of nanocrystalline nickel pillar post compression at 10^3 s-1 did not show any grain growth.

cond-mat.mtrl-sci↗