Yong-Tailee

Bio: Yong-Tailee is an academic researcher. The author has contributed to research in topics: Creep & Phase (matter). The author has an hindex of 1, co-authored 1 publications receiving 113 citations.

Alloying mechanism of beta stabilizers in a TiAl alloy

Abstract: The effects of beta stabilizers such as Fe, Cr, V, and Nb on the microstructures and phase constituents of Ti52Al48-xM (x=0, 1.0, 2.0, 4.0, or 6.0 at. pct and M=Fe, Cr, V, and Nb) alloys were studied. The dependence of the tensile properties and creep resistance of TiAl on the alloying elements, especially the formation of B2 phase, was investigated. Fe is the strongest B2 stabilizer, Cr is second, V is an intermediate stabilizer, and Nb is the weakest stabilizer. The composition partitioning of Fe, Cr, V, and Nb in the γ phase is affected by the formation of B2 phase. The peaks of the tensile strengths and creep rupture life of Ti52Al48-xM generally occur at the maximum solid solution of these elements in the γ phase, which is just before the formation of B2 phase. Ti52Al48-0.5Fe shows an attractive elongation of 2.5 pct at room temperature, and the Ti52Al48-1V, Ti52Al48-Cr, and Ti52Al48-2Nb alloys have about 1.1 to 1.3 pct elongation at room temperature. The increase of tensile strengths and creep resistance with increasing Fe, Cr, V, and Nb contents is chiefly attributed to the solid-solution strengthening of these elements in the γ phase. The appearance of B2 phase deteriorates the creep resistance, room-temperature strengths, and ductility. With respect to the maximum solid-solution strengthening, an empirical equation of the Cr equivalent [Cr] is suggested as follows: [Cr]=Cr+Mn+3/5V+3/8Nb+3/2 (W+Mo)+3Fe=1.5 to 3.0. The solid-solution strengthening mechanism of Fe, Cr, V, and Nb at room temperature arises from the increase of the Ti 3s and Al 2s binding energies in Ti-Ti and Al-Al bonds, and the retention of the strength and creep resistance at elevated temperatures in Ti52Al48-xM is mainly attributed to the increase of the Ti 3s and Al 2s binding energies in Ti-Al bonds in γ phase. The decrease of the Ti 3p and Al 2p binding energies in Ti-Ti, Ti-Al, and Al-Al bonds benefits the ductility of TiAl.

Design, Processing, Microstructure, Properties, and Applications of Advanced Intermetallic TiAl Alloys†

Abstract: After almost three decades of intensive fundamental research and development activities, intermetallic titanium aluminides based on the ordered γ-TiAl phase have found applications in automotive and aircraft engine industry. The advantages of this class of innovative high-temperature materials are their low density and their good strength and creep properties up to 750 °C as well as their good oxidation and burn resistance. Advanced TiAl alloys are complex multi-phase alloys which can be processed by ingot or powder metallurgy as well as precision casting methods. Each process leads to specific microstructures which can be altered and optimized by thermo-mechanical processing and/or subsequent heat treatments. The background of these heat treatments is at least twofold, i.e., concurrent increase of ductility at room temperature and creep strength at elevated temperature. This review gives a general survey of engineering γ-TiAl based alloys, but concentrates on β-solidifying γ-TiAl based alloys which show excellent hot-workability and balanced mechanical properties when subjected to adapted heat treatments. The content of this paper comprises alloy design strategies, progress in processing, evolution of microstructure, mechanical properties as well as application-oriented aspects, but also shows how sophisticated ex situ and in situ methods can be employed to establish phase diagrams and to investigate the evolution of the micro- and nanostructure during hot-working and subsequent heat treatments.

Hot deformation behavior and dynamic recrystallization of a β-solidifying TiAl alloy

Abstract: Hot deformation behavior and dynamic recrystallization (DRX) of a β-solidifying TiAl alloy Ti–43Al–2Cr–2Mn–0.2Y (at%) were investigated by means of isothermal compression tests in a temperature range of 1100–1225 °C and strain rate range of 0.01–0.05 s−1. A processing map at a true strain 0.8 was developed based on the dynamic materials model. The current alloy possesses a wide processing window, and the optimum deformation condition is 1175–1225 °C/0.05 s−1. The main softening mechanism is DRX of γ grains. The DRX proceeded preferentially at triangle boundaries, and subsequently in the lamellae. Both deformation temperature and strain rate have an obvious impact on the microstructural evolution. The partial DRX occurred when the alloy deformed at low temperature and high strain rate. Some remnant lamellar structures existed due to the plastic anisotropy of lamellar colony. With the increase of temperature and /or the decrease of strain rate, the lamellae were effectively broken down into fine grains, and a relatively complete DRX occurred. Dynamic recovery is the main deformation mechanism for β0 phase, which promotes the compatible deformation between γ and α2 phases and prevents premature cracks. Additionally, the DRX mechanism of γ phase was investigated through TEM observations. The DRX of γ grains begins with the formation of sub-boundaries, followed by a process of rearrangement of sub-boundaries to form new grains.