Phase equilibria investigations on the aluminum-rich part of the binary system Ti-Al

Abstract

The binary system Ti-Al has been reinvestigated in the composition range of 50 to 76 at. pct Al by X-ray diffraction, metallography, electron probe microanalysis (EPMA), and differential thermal analysis (DTA). Heat-treated alloys (600 ЊC to 1300 ЊC) as well as the as-cast alloys were investigated. Seven stable intermetallic phases were observed: TiAl, Ti 1Ϫx Al 1+x , Ti 3 Al 5 , TiAl 2 , Ti 5 Al 11 , TiAl 3 (h), and TiAl 3 (l); two metastable phases, TiAl 2 (m) and TiAl 3 (m), were also found. For each of these phases, the homogeneity range and the crystal chemical parameters were determined. The temperatures of the solid-state phase reactions were re-established. On the basis of the experimental results, an improved version of the equilibrium phase diagram has been drawn and critically compared with earlier versions presented in the literature.

Interfacial Microstructure of Silicon Carbide and Titanium Aluminide Joints Produced by Solid-State Diffusion Bonding

“…The pattern indicates that TiAl 20) and Ti 1ÀX Al 1þX 25) exist. This result agrees well with the detailed Ti-Al binary phase diagram presented by Braun and Ellner, 21) indicating that the high-temperature phases are successfully maintained by quenching. Ti-65.5 at%Al corresponds to the composition of the TiAl 2 layer formed at 1573 K and to that of the matrix region of TiAl 2 formed at 1673 K. Figure 5(b) shows the pattern for Ti-65.5 at%Al quenched from 1673 K. Ti 1ÀX Al 1þX and a small amount of hTiAl 2 26) are detected in the pattern.…”

“…[21][22][23][24] Then, the influence of the cooling rate on the formation process of the interfacial microstructures was investigated at first. Figure 4 shows the influence of the cooling rate on the interfacial microstructure of the SiC/TiAl joints bonded at 1573 K for 32.4 ks.…”

“…Braun and Ellner have mentioned that h-TiAl 2 is a metastable phase observed only in as-cast alloys. 21) Thus, the phase is considered to be a remaining phase of the as-cast alloy. Ti-68.0 at%Al corresponds to the composition of acicular grains of TiAl 2 formed at 1673 K. Ti 5 Al 11 27) and a small amount of TiAl 2 19) are formed in Ti-68.0 at%Al quenched from 1673 K as shown in Fig.…”

Formation of Corundum, Magnesium Titanate, and Titanium(III) Oxide at the Interface between Rutile and Molten Al or AlSi7Mg0.6 Alloy

“…[37] ), which indicates that the chemical composition of the titanium trialuminide deviates from the stoichiometric composition of Al 3 Ti. Local EDX chemical analyses performed on large grains of this intermetallic phase in longtime heat-treated sample (24 h at 750 C) revealed that Al 3 Ti was doped with Si, which replaces aluminum in the crystal structure of Al 3 Ti.…”

Reviewing the class of Al-rich Ti-Al alloys: modeling high temperature plastic anisotropy and asymmetry

“…With melting point of 1463°C, γ -TiAl (L1 0 -type) has a wide solubility range from the near stoichiometry to the Al-rich side (Braun and Ellner 2001;Nakano et al 1999). In the near stoichiometric Ti-rich side, alloys mostly consist of two phases, γ -TiAl and α 2 -Ti 3 Al.…”