Influence of Oxidation on the Corrosion Resistance of Sintered Titanium
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INFLUENCE OF OXIDATION ON THE CORROSION RESISTANCE OF SINTERED TITANIUM A. A. Skrebtsov,1 I. M. Pohrelyuk,2, 3 O. H. Luk’yanenko,2 and A. T. Pichuhin2
UDC [669.295+621.762.8]:620.193.41:621.785
We study the corrosion resistance of sintered titanium specimens obtained by the methods of powder metallurgy in a 40% aqueous solution of sulfuric acid and in a 20% aqueous solution of hydrochloric acid at room temperature. It is shown that the modification of the surface layers of sintered titanium specimens by interstitial elements and, especially oxygen, increases their corrosion resistance. The maximum protection effect against aggressive media is provided by an oxide film obtained by thermodiffusion oxidation under the conditions of saturation in the oxygen-containing controlled atmosphere and by the oxidation in air: the corrosion resistance increases by three orders of magnitude as compared with the corrosion resistance of the unprotected surface. Keywords: sintered titanium, thermodiffusive saturation, oxidation, corrosion resistance, sulfuric and hydrochloric acids.
Due to their unique properties, titanium alloys are quite useful for the chemical industry [1, 2]. They are used in the production of various articles, such as cases, caps of valves, disks of gates, working wheels of centrifugal pumps, etc., intended for operation under the simultaneous action of corrosive media, high temperatures, and contact loads. The technologies of casting with welding are extensively used for their production [3]. The materials of blanks are mostly low-alloy α - and pseudo- α -titanium alloys. The procedure of pressing of powders with subsequent sintering allows one to significantly decrease their cost as compared with the cost of cast specimens and to decrease the number of technological transitions to the mechanical treatment. Despite the intense development of the technologies of powder metallurgy [4–8], the list of products manufactured by using these technologies for chemical applications is now quite small. The main obstacle for a more extensive application of powder metallurgy is connected with much higher porosity of these materials as compared with the porosity of cast materials. Due to the presence of a developed structure of open surface pores and interparticle boundaries in powder blanks, the corrosion resistance of these blanks is becomes lower. It can be increased as a result of surface engineering, e.g., by the method of thermodiffusion saturation with interstitial elements and, in particular, with oxygen (oxidation). The experience accumulated in the development of these coatings for compact titanium alloys cannot be completely transferred to objects produced by the powder technologies because it is necessary to take into account the specific features of these materials. The aim of the present study is to evaluate the efficiency of thermodiffusion oxidation for the enhancement of the corrosion resistance of specimens of sintered VT1-0 titanium in extremely aggressive media of inorganic acids. 1 2 3
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