Structure And Elastic Properties Of TiAlN And TiAlSiN Studied By Ab Initio

TiAlN and TiAlSiN are widely used in the field of surface protection because of their highhardness, excellent mechanical properties, high temperature oxidation resistance, abrasionresistance, high membrane-binding strength, thermal stability, corrosion resistance and othercharacteristics. The thesis is about both TiAlN and TiAlSiN studied by first-principlescalculations based on density functional theory. First, Ti, Al, Si, N single atomic energy werecalculated. The lattice constant, elastic properties, electronic structure of TiN and AlN wereanalysised. A series TiAlN model of Ti, Al contents in the NaCl structure and wurtzitestructure were constructed. Their crystal structure has been optimized, and I found that thelattice constant of NaCl structure TiAlN is dropped than TiN, with the increase of Al elementcontent to a further reduction, and the cohesive energy have declined. The elastic calculationresults showed that added Al made the elastic moduli decreased. The electronic structure ofTiAlN showed metal. The lattice constants a and c of wurtzite structure TiAlN are increasedwith the increasing content of Ti. The cohesive energy has increased, the elastic propertiesshows the moduli droped. The addition of Ti element reduced the bandgap. I Found that67at%of Al content by theoretical calculation is the TiAlN structural phase transition point.Two TiAlSiN structures were studied, one is the replacement structure, the other is thereplacement interface structure. Lattice constant of TiAlSiN is reduced the than TiAlN, andthe elastic properties were enhanced with varying degrees, but the the replacement interfacestructure performance is better. The replacement interface structure TiAlSiN has high elasticproperties with lower Al content, and Ti0.75Al0.125Si0.125N’s elastic properties are best. Itsbulk modulus is290.9GPa, the shear modulus is197GPa, Young’s modulus is482GPa thetheoretical hardness value is48.2GPa. All of these moduli are the maximum values in thecalculation of TiAlSiN. Electronic structure is shown that TiAlSiN is a metallic conductor.