Corrosion resistance of titanium-chromium diboride and composite material based on it

Abstract

The resistance to electrochemical corrosion and high-temperature oxidation of titanium-chromium diboride and materials with a metal binder based upon it is studied. The mechanism of processes that occur in compacted specimens and powders is studied, and the composition of reaction products in relation to specimen heating temperature is determined. It is established that the oxide films that form at a specimen surface during oxidation are protective and prevent further material oxidation.The expediency of ceramic and cermet materials in various technology is due to their high heat resistance and high-temperature strength in air, corrosion resistance in electrolytes, hardness and wear resistance. Among the considerable number of ceramic materials there is special interest in refractory compounds of titanium: TiC, TiB 2 , TiN, TiCN, TiCrC, TiCrB 2 . The advantage of these ceramic materials is the high hardness, wear-and corrosion-resistance, high density, good electrical conductivity (for this class of materials), and also presence within CIS countries of a rich raw material base for their manufacture.Among the materials listed the greatest interest with respect to properties is titanium-chromium diboride TiCrB 2 [1]. In the majority of work devoted to this material, the mechanism of its contact reaction with metal alloys has been studied [2, 3], mechanical and tribotechnical properties have been determined [4,5], both in pure form, and also with a metal binder, and the possibilities for deposition and surfacing have been determined [6,7].A promising area for using titanium-chromium diboride, composite materials and coatings based on it, is use in corrosive media (chemical industry) and at high temperature. With the aim of determining life under these conditions for titanium-chromium diboride and composite material developed on its basis, the corrosion resistance of these materials in 3% NaCl solution and their resistance to high-temperature oxidation were studied. EXPERIMENTAL PROCEDURE AND MATERIALSElectrochemical corrosion was studied at 20°C in a medium of 3% NaCl solution (sea water) in an electrochemical cell with an anode of the test material and a platinum cathode by a potentiodynamic method of polarization curves using PI50 -1 and P5848 potentiostats. The electrolyte composition after electrolysis was studied by chemical analysis.The corrosion resistance at high temperature was evaluated by differential thermal analysis (DTA). DTA-curves with T-curves (temperature) and thermogravimetric TGcurves were recorded in a derivatograph type Q-1500 (rate of temperature increases 10°C/min) in the range 20 -1000°C at atmospheric air pressure. The sensitivity selected in the records was: DTA -1/10; DTG -1/10; TG -2.0 × 10 -5 kg. The standard sued for DTA measurements was freshly calcined a-Al 2 O 3 . The weight of test material samples was 200 mg.In order to determine the composition of oxidation products at different specimen temperatures a corresponding material was subjected to isothermal heating in air up to a maxi...