A. G. Illarionov, A. A. Popov, S. M. Illarionova, D. V. Gadeev, O. A. Elkina
THE EFFECT OF MICROALLOYING WITH CHROMIUM, HAFNIUM AND YTTRIUM ON THE STRUCTURE AND MECHANICAL PROPERTIES OF THE VT18U HIGH-TEMPERATURE TITANIUM ALLOY
The effect of microalloying of the VT18U high-temperature near-alpha titanium alloy with rare-earth elements (yttrium and hafnium), simultaneously with chromium, on its phase composition, structure and microindentation hardness is considered. It is demonstrated that additional alloying of the alloy both with chromium and hafnium and with chromium and yttrium decreases the beta-transus temperature (BTT) of the alloy. A higher content of β-stabilizers in the experimental alloys in comparison with the commercial alloy proves to increase the β-phase volume fraction and decrease the elastic modulus from 115 GPa to 104 GPa in the as-received 750 ºC α+β-annealed condition. Additional microalloying with chromium and yttrium is shown to inhibit the β-grain growth during high-temperature holds due to the segregation of yttrium atoms to the boundaries followed by a decrease in free energy, whereas doping with chromium and hafnium proves to have no effect on the grain growth process due to the non-horophilic nature of these elements.
Keywords: microalloying, titanium alloys, rear-earth elements, REM, yttrium