Properties of multilayered and multicomponent nitride alloys from first principles [thesis]

Fei Wang
This thesis is a theoretical exploration of properties of multilayered and multicomponent nitride alloys, in particular their mixing thermodynamics and elastic behaviors. Systematic investigation of properties of a large class of materials, such as the multicomponent nitride solid solutions, is in line with the modern approach of high-throughput search of novel materials. In this thesis we benchmark and utilize simple but efficient methodological frameworks in predicting mixing thermodynamics,
more » ... ng thermodynamics, Young's moduli distribution of multilayer alloys and the linear thermal expansion of quaternary nitride solid solutions. We demonstrate by accurate ab-initio calculations that Ti 1−x Al x N solid solution is stabilized by interfacial effects if it is coherently sandwiched between TiN layers along (001). For TiN/AlN and ZrN/AlN multilayers we show higher thermodynamic stability with semicoherent interfaces than with isostructural coherent ones. Accurate 0 Kelvin elastic constants of cubic Ti x X y Al 1−x−y N (X=Zr, Hf, Nb, V, Ta) solid solutions and their multilayers are derived and an analytic comparison of strengths and ductility are presented to reveal the potential of these materials in hard coating applications. The Young's moduli variation of the bulk materials has provided a reliable descriptor to screen the Young's moduli of coherent multilayers. The Debye model is used to reveal the high-temperature thermodynamics and spinodal decomposition of Ti x Nb y Al 1−x−y N. We show that though the effect of vibration is large on the mixing Gibbs free energy the local spinoal decomposition tendencies are not altered. A quasi-harmonic Debye model is benchmarked against results of molecular dynamics simulations in predicting the thermal expansion coefficients of Ti x X y Al 1−x−y N (X=Zr, Hf, Nb, V, Ta). v Preface
doi:10.3384/diss.diva-145091 fatcat:lmbtdj345rhxrnqhdpk5o3u4kq