K. M. Calamba Kwick | Searcharxiv

arXiv2023

High temperature decomposition and age hardening of single-phase wurtzite Ti$_{1-x}$Al$_{x}$N thin films grown by cathodic arc deposition

We investigated the high temperature decomposition behavior of wurtzite phase Ti$_{1-x}$Al$_{x}$N films using experimental methods and first-principles calculations. Single phase metastable wurtzite Ti$_{1-x}$Al$_{x}$N (x = 0.65, 0.75, 085 and 0.95) solid solution films were grown by cathodic arc deposition using low duty cycle pulsed substrate-bias voltage. First-principles calculated elastic constants of the wurtzite Ti$_{1-x}$Al$_{x}$N phase show a strong dependence on alloy composition. The predicted phase diagram shows a miscibility gap with an unstable region. High resolution scanning transmission electron microscopy and chemical mapping demonstrate decomposition of the films after high temperature annealing (950$^{\circ}$C), which resulted in nanoscale chemical compositional modulations containing Ti-rich and Al-rich regions with coherent or semi coherent interfaces. This spinodal decomposition of the wurtzite film causes age hardening of 1-2 GPa.

cond-mat.mtrl-sci↗

arXiv2022

Elucidating dislocation core structures in titanium nitride through high-resolution imaging and atomistic simulations

Although titanium nitride (TiN) is among the most extensively studied and thoroughly characterized thin-film ceramic materials, detailed knowledge of relevant dislocation core structures is lacking. By high-resolution scanning transmission electron microscopy (STEM) of epitaxial single crystal (001)-oriented TiN films, we identify different dislocation types and their core structures. These include, besides the expected primary full a/2{110}<1$\bar{1}$0> dislocation, Shockley partial dislocations a/6{111}<11$\bar{2}$> and sessile Lomer edge dislocations a/2{100}<011>. Density-functional theory and classical interatomic potential simulations complement STEM observations by recovering the atomic structure of the different dislocation types, estimating Peierls stresses, and providing insights on the chemical bonding nature at the core. The generated models of the dislocation cores suggest locally enhanced metal-metal bonding, weakened Ti-N bonds, and N vacancy-pinning that effectively reduces the mobilities of {110}<1$\bar{1}$0> and {111}<11$\bar{2}$> dislocations. Our findings underscore that the presence of different dislocation types and their effects on chemical bonding should be considered in the design and interpretations of nanoscale and macroscopic properties of TiN.

cond-mat.mtrl-sci↗