thermal barrier coatings (tbcs) are used to provide thermal insulation to the hot section components of gas turbines in order to enhance the operating temperature and turbine efficiency. hot corrosion and thermal shocks are the main destructive factors in tbcs which comes as a result of oxygen and molten salt diffusion into the coating. in this thesis atmospheric plasma spraying was used to deposition of three types of coatings: (a) usual csz (ceria-stabilized zirconia), (b) layer composite of (csz/micro al2o3) and (c) layer composite of (csz/nano al2o3) in which al2o3 was as a topcoat on csz layer. thermal shock test at 1100?c and hot corrosion test were carried out on the surface of coatings in molten salt (45wt%na2so4+55wt%v2o5) at 1050?c for 40 h. the microstructure, phase and elemental analysis after hot corrosion and thermal shock tests were examined by scanning electron microscopy (sem) equipped with energy dispersive spectrometer (eds) and x-ray diffraction (xrd) machine. moreover, microhardness test was carried out to evaluate the mechanical properties of the coatings. usual csz coating showed little resistance during thermal shock cycles, while layer composite of (csz/nano al2o3) coating showed the highest resistance to thermal shock. phase analysis after the hot corrosion revealed monoclinic zro2, rod-type yvo4+cevo4 and semi-cubic ceo2 crystals as hot corrosion products. usual csz coating and micro alumina layar as outer layer in (csz/micro al2o3) coating were destroyed during hot corrosion, while no hot corrosion product and degradation were observed in layer composite of (csz/nano al2o3). results of hot corrosion test indicated that creation of a dense nano al2o3 layer over the usual csz had a significant effect on increasing hot corrosion resistance. also micro hardness tests demonstrated that the hardness values of the csz coating increased substantially after hot corrosion.