Shliakhetka K. Modification of surface layers of porous titanium VT1-0 for increasing anticorrosive properties

The dissertation presents a solution of an actual scientific and technical task: development of the approaches to modification of surface layers of porous titanium VT1 0 on the basis of the established general regularities of formation of structure and properties for providing anticorrosive protection against corrosive environment. The comparative investigations of porous and nonporous titanium VT1-0 showed that the residual porosity is a key structural factor that determines the corrosion resistance of titanium fabricated by powder metallurgy (PM) : the higher the porosity, the lower the corrosion resistance of titanium in solutions of hydrochloric and sulfuric acids of a wide concentration range. At the porosity ≤4.2% in 10% and 60% aqueous solutions of hydrochloric and sulfuric acids, respectively, and porosity ≤3.4% in 20% hydrochloric acid solution, the corrosion rate of titanium VT1-0 fabricated by PM method is at the level of nonporous material traditionally fabricated. At higher porosity titanium VT1-0 fabricated by PM method requires the additional anticorrosive protection. It was proposed the methods of modification for decreasing porosity of titanium VT1-0 fabricated by PM method in volume and surface layer in order to improve the an-ticorrosive characteristics. It was found that the additional operations of cold pressing and vacuum sintering during the synthesis of porous titanium VT1-0 have a positive effect on anticorrosive characteristics, and their effectiveness of protection increases with decreasing the initial porosity of the material. The consolidation of surface layer by cold surface plastic deformation reduces the porosity in surface layer and promotes healing of the pores under the action of applied loads, that increases the corrosion resistance of porous titanium by one order. The morphology of the modified layer to increase the anticorrosive properties of porous titanium VT1-0 is regulated and oxidation and nitriding regimes for its formation are developed. It is shown that under the regulated morphology of the modified layer the corrosion rate of porous titanium in acid solutions decreases by one or three orders of magnitude. The technology of obtaining titanium VT1-0 does not affect the corrosion properties.