Effect of Annealing Temperature on the Surface Structure and Properties of Porous TiNi

• Published in: Inorganic materials Vol. 57; no. 12; pp. 1242 - 1249
• Main Authors: Dubovikov, K. M., Garin, A. S., Marchenko, E. S., Baigonakova, G. A., Shishelova, A. A., Kovaleva, M. A.
• Format: Journal Article
• Language: English
• Published: Moscow Pleiades Publishing 01.12.2021; Springer Nature B.V
• Subjects: Annealing; Chemistry; Chemistry and Materials Science; Free energy; Industrial Chemistry/Chemical Engineering; Inorganic Chemistry; Intermetallic compounds; Materials Science; Nickel base alloys; Nickel compounds; Nickel titanides; Oxidation; Phase composition; Self propagating high temperature synthesis; Shape memory alloys; Surface layers; Surface structure; Thickness; Titanium; Titanium compounds; Titanium dioxide; Wettability; surface free energy; titanium nickelide; contact angle; surface; titanium oxides
• ISSN: 0020-1685; 1608-3172
• DOI: 10.1134/S0020168521120050

— The phase composition of porous titanium nickelide alloys annealed at temperatures from 500 to 1000°C with a 100°C step has been determined by X-ray diffraction, energy dispersive X-ray spectroscopy, and scanning electron microscopy. Annealing at temperatures in the range 900–1000°C was shown to result in the formation of a double surface layer 4 μm in average thickness as a consequence of titanium segregation and oxidation. The outer layer, up to 2 μm in thickness, consisted of TiO 2 , and the inner, intermetallic layer, up to 3 μm in thickness, was titanium-deficient. A comparative analysis led us to conclude that the outer protective layer formed on the porous alloy as a result of self-propagating high-temperature synthesis effectively prevented oxidation of the TiNi matrix and titanium segregation during annealing in air at temperatures of up to 900°C. Captive bubble wettability measurements showed that the growth of a surface TiO 2 phase at increased annealing temperatures led to higher surface hydrophilicity and an increase in surface free energy.