Jiang, Y: Growth and Thermal Stability of V-Al-C Thin Films

The goals of the current thesis is to contribute towards understanding (1) the growth of V2AlC MAX phase thin films and (2) the influence of temperature on the thickness homogeneity of alpha-Al2O3 that is infiltrated into open porous cellular iron.V-Al-C thin films were deposited on Al2O3 ( 1120) substrates at 500°C by DC magnetron sputtering using a powder metallurgical composite target with 2:1:1 MAX phase stoichiometry. TEM and XRD results suggest that a hexagonal Al-containing vanadium carbide solid solution (V,Al)2Cx was formed. The films exhibited a strong basal plane texture. The lattice parameter of the hexagonal solid solution was dependent on the annealing temperature: the c lattice parameter decreased by 3.45% after annealing for 1 hour at 750°C compared to the as deposited film. Based on the comparison between experimental and theoretical lattice parameter data, it is reasonable to assume that this annealing induced change in lattice parameter is a consequence of atomic ordering. Meanwhile, the formation of V2AlC MAX phase was observed at 650°C and phase-pure V2AlC was obtained at 850°C. TEM images support the notion that V2AlC forms by nucleation and growth.V-Al-C thin films were deposited from a powder metallurgical composite target by DC magnetron sputtering and High Power Impulse Magnetron Sputtering (HIPIMS) at 500°C with an average power of 250 W. The effect of pressure, distance, substrate bias potential as well as duty cycle of HIPIMS on the film composition was investigated. The results show that nano crystalline V2AlC MAX phase is formed in a (V,Al)2Cx matrix at 500°C during HIPIMS at 3-10% duty cycle. Film composition and ion energy flux appear to be prerequisites for MAX formation at this temperature.The second part of this thesis focuses on chemical vapour deposition/infiltration and oxidation.