Study on the evolution of phase relations in the Ti–Al–Nb/Cr systems at 0–50 at.% Al region. (December 2022)

• Record Type: Journal Article
• Authors: Huang, Xing-Ming; Zhang, Shun-Xin; Cai, Ge-Mei; Liu, Hua-Shan
• Is Part Of: Calphad. Volume 79(2022)
• Publication Date: 2022-12
• Subjects: Ti-Al-Nb/Cr systems -- Phase equilibria -- ωo-Ti3Al2Nb -- O–Ti2AlNb; Phase diagrams -- Data processing -- Periodicals; Thermochemistry -- Data processing -- Periodicals; Diagrammes de phases -- Informatique -- Périodiques; Thermochimie -- Informatique -- Périodiques; Thermodynamica; Electronic journals; 541.363
• DOI: 10.1016/j.calphad.2022.102461
• Languages: English
• ISSNs: 0364-5916

Abstract

Abstract: β-Solidifying γ-TiAl based alloys have gained scientific attention and showed potential applications as structure materials. When adding the β-stabilizing elements (e.g., Nb and Cr), ordered B2 and ωo phases are often formed during the production process of the TiAl based alloys. The information about the evolution of these phases as the temperature changes is necessary and important for design and preparation of desired TiAl based alloys with excellent properties. In this work, phase relationships and evolvement of Ti–Al–Nb/Cr systems have been investigated in the service temperature ranging from 950 to 700 °C. In the Ti–Al–Nb ternary system, B2 phase will directly transform into ωo phase at the temperature range of 913.6–921.1 °C, which results in an increase of the microhardness (i.e. 460 HV to 530 HV). At 700 °C, ωo phase has the composition of 15.8–20.4 at.% Nb, 29.8–33.3 at.% Al, and 46.3–54.4 at.% Ti. Equilibrium composition of ωo is defined as Ti3 Al2 Nb. The ternary compound O_Ti2 AlNb has been found to be formed via β(Ti)+Ti3 Al + Nb2 Al→O at 981.5 ± 6.5 °C. As for the Ti–Al–Cr ternary system, when temperature decreases from 950 to 900 °C, the center section of the β(Ti) phase region shrinks and separates, resulting in the formation of independent B2 phase region. The island-like B2 region can remain stable at 700 °C. According to the evolution of phase relationship, one solid transition reaction Ti3 Al + C14→B2+C15 at 900–800 °C has been deduced to occur in the Ti–Al–Cr ternary system. Present work provides an important guide for fabricating Ti–Al–Nb/Cr alloys with different ratio and distribution of plastic/brittle phases. Highlights: Phase relations and evolution in the Ti–Al–Nb/Cr systems were studied. B2 transforms into ωo -Ti3 Al2 Nb directly at the range of 913.6–921.1 °C. The cooling rates have a certain impact on transformation of B2→ωo . O–Ti2 AlNb phase occurs via reaction β(Ti)/B2+Ti3 Al + Nb2 Al→O at 981.5 ± 6.5 °C. An isolated B2 decomposing from β(Ti) would be formed at 950–900 °C in the Ti–Al–Cr system.