SiC ceramics were fabricated by spark plasma sintering technique with the use of Al2O3 additive. The sintering process was carried out at three dierent temperatures in the range of 17001800• C applying two dierent pressures 40 and 80 MPa under vacuum atmosphere. The eect of additive, dierent temperatures and pressures on densication behaviour, density, Vickers hardness, fracture toughness, and microstructure were examined. The hardness and fracture toughness of the samples were evaluated by the Vickers indentation technique. Microstructure of spark plasma sintered SiC samples were characterized by using scanning electron microscopy technique. The highest value of fracture toughness 5.9 ± 0.2 MPa m 1/2 was achieved with the addition of 5 vol.% Al2O3.

Air oxidation behavior of a Ti6Al7Nb alloy was examined over the temperature range of 873 –1173 K for different time intervals ranging in between 12 and 72 h. The rate of oxidation evaluated according to the weight gain measurements, fitted parabolic kinetics by yielding oxidation activation energy of 226 kJ/mol. Rutile and anatase modifications of TiO2 formed on the surface as the result of air oxidation. Oxidation temperatures higher than 923 K encouraged rutile formation rather than anatase. As temperature of oxidation was increased, the thickness of the oxide layer increased. Thicker oxide layer provided higher surface hardness and better protection against a corrosive media (5 M HCl solution) was provided.

Processing and mechanical characterisation of monolithic silicon carbide ceramic consolidated by sparkp lasma sintering(SPS) Silicon carbide ceramics were fabricated using the spark plasma sintering technique withoutt he use of additives. The sintering process was carriedout at four differenttemperatures in the range of 2073 -2223 Kunder two different pressures, 40 MPa and 80 MPa, under vacuum. The effects of different temperatures and pressures on the density, Vickers hardness, fracture toughness, and microstructure were examined.F ully dense monolithics iliconc arbide ceramicsw itharelative density of approximately 99 % were obtained. Increasingt he pressure from 40 to 80 MPa and the temperature from 2073 to 2223 Kresulted in an increase in the relative densities of spark plasma sintered ceramicsfrom 87 %to97.5 %and 95.5 %to99.7 %, respectively. The results revealed that the silicon carbide ceramic spark plasma sintered at 2223 Kwhile applying 80 MPa of pressure with a5 -minute soaking time under vacuum has the highest hardness and fracture toughness valueso f 31.9 GPa and 3.6 ±0.3 MPa ·m 1/2 ,respectively.