al-fe-ti system

Al-Fe-Ti (Aluminum-Iron-Titanium)V. Raghavan

Practical interest in the phase equilibria of this ternarysystem has focused on the search for ternary phases of highcrystal symmetry with acceptable mechanical properties, ascompared to the brittle Al-Ti compounds of low crystalsymmetry. In addition, the stabilization of the ordered formsof body-centered cubic (bcc) Fe (such as Fe3Al) by theaddition of Ti has evoked interest in their possible use forhigh-temperature applications.

The previous review of this system by [1987Rag] pre-sented a liquidus projection, a full isothermal section at800 °C, partial isothermal sections at 1100 and 550 °C anda reaction scheme. A vertical section at 5 at.% Ti and apartial isothermal section at 1200 °C were presented in theupdate by [1993Rag]. Several significant new results havebeen reported recently, which include the work of [1995Pal]and [2000Kai1 and 2000Kai2].

Binary Systems

The Al-Fe phase diagram reviewed by [1993Kat] showsthat the face-centered cubic (fcc) solid solution based on Fe

is restricted by a � loop. The bcc solid solution (�Fe)exists in the disordered A2 and the ordered B2 and D03forms. The A2 → B2 transition is second-order in naturedown to ∼660 °C [1993Kat]; below 660 °C, a two-phasefield of (A2 + B2) intervenes, indicating a change-over to afirst-order transition. The B2 → D03 transition is secondorder and occurs below ∼550 °C. Apart from the high-temperature phase �, there are three other intermediatephases in the system with restricted ranges of homogeneity:FeAl2, Fe2Al5, and FeAl3.

The Al-Ti system was updated by [1993Oka]. The up-dated phase diagram was quite different from the versionof [Massalski2] and showed that (�Ti) and liquid under-go a peritectic reaction to yield (�Ti) at a high temperatureof 1490 °C. More recently, [2000Ohn] found additionallythat (�Ti) undergoes the A2 → B2 transition in the tem-perature range of ∼1425-1125 °C. This finding was sup-ported by differential scanning calorimetric measure-ments and by extrapolation of the ternary data on theAl-Fe-Ti and Al-Cr-Ti systems. The ordered B2 phasecould not be retained by quenching due to the interven-

Fig. 1 Al-Ti computed binary phase diagram [2000Ohn]

Phase Diagram Evaluations: Section II

Journal of Phase Equilibria Vol. 23 No. 4 2002 367

tion of the martensitic transformation of bcc (�Ti) tohexagonal close-packed (hcp) (�Ti) [2000Kai2]. The Al-Tiphase diagram computed by [2000Ohn] is shown in Fig. 1.The intermetallic compounds in this system are Ti3Al (D019type, hexagonal), TiAl (L10 type, tetragonal), TiAl2 (Ga2Hf

type, tetragonal), Ti2Al5 (tetragonal), and TiAl3 (D022 type,tetragonal).

In the Fe-Ti system, there are two intermediate phases:Fe2Ti (C14, hexagonal) and FeTi (B2, cubic). [1998Dum]presented a comparison of the recent Fe-Ti assessments.

Fig. 2 Al-Fe-Ti tentative liquidus projection

Fig. 3 Al-Fe-Ti isothermal section at 1000 °C [after 1995Pal]

Section II: Phase Diagram Evaluations

368 Journal of Phase Equilibria Vol. 23 No. 4 2002

The homogeneity range of Fe2Ti used in this review isfrom the tentative new assessment of [1998Dum]. Thesmall homogeneity range of FeTi is from [1993Mur]. Formore structural details on the binary compounds, see[Pearson3].

Ternary Phases

The three ternary compounds of this system discussed by[1987Rag] are those reported by [1981Sei]. Among these,the existence of the cubic phase AlFe2Ti (�1) remaineddoubtful. Recent results of [1995Pal] have established that�1 does not exist. The solidification reactions postulatedby [1981Sei] for the formation of �1 could possibly be re-lated to the heat effects associated with the order-disorderreactions in (�Fe) in the ternary region, but no evidencein this regard is available. The �1 phase stands deleted inthis update. The second ternary phase Al2FeTi (�2) hasthe Mn23Th6 type (D8a) cubic structure. [1995Pal] madea detailed study of the homogeneity range and the latticeparameter variations of this phase. The homogeneity rangeincreases with decreasing temperature. It covers a rangeof 21-50 at.% Ti at 800 °C. At 1000 °C, two separatecomposition islands with Ti ranges of 21-31.5 at.% and37.5-44 at.% exist. At Ti concentrations above 30 at.%, thestructure of �2 at room temperature is the cubic Mn23Th6type, with the lattice parameter increasing from 1.2038 nmat ∼31 at.% Ti to 1.2110 nm at 51 at.% Ti. Below 30 at.%Ti, the structure at room temperature is indexed tetragonal,with a � 1.1973 nm and c � 1.2768 nm at 24 at.% Ti. It

is not known whether the tetragonality exists at high tem-peratures or occurs at lower temperatures during cooling.Al8FeTi3 (�3) is cubic L12 type with a � ∼0.3944 nm at 27at.% Ti. The phase field of �3 is roughly circular with awidth of ∼5 at.% at 800 and 1000 °C [1995Pal, 1995Yan],increasing to ∼7 at.% Fe at 1200 °C [1989Maz, 2000Mab].[1995Pal] found no evidence for the low-symmetry ternary

Fig. 4 Al-Fe-Ti isothermal section at 800 °C [after 1995Pal]

Fig. 5 Al-Fe-Ti isothermal section at 900 °C [1998Ohn]



phase at the composition Al69Fe25Ti6, as already ruled out in[1987Rag].

The binary phases FeTi and Fe2Ti show high solubilitiesfor Al. At 1000 °C, most of Fe in FeTi can be replaced byAl. The lattice parameter of FeTi varies linearly accordingto the equation: a � 0.2970 + 0.000507 (50 − XFe) nm,where XFe is in at.% [1995Pal]. In Fe2Ti, the maximum Alcontent is 47.5 at.% at 1000 °C and the lattice parametersvary according to the equations: a � 0.4770 + 0.000506 (70− XFe) nm and c � 0.7783 + 0.001406 (70 − XFe) −[6.78532 × 10−6 (70 − XFe)

2] nm. (�Ti) containing 15 at.%Fe dissolves up to 22 at.% Al at 1000 °C. In fact, the largesolubility of Al in FeTi and (�Ti) results in a continuoussolid solution between them, separated by an order-disorder

transition line at 1000 °C [2000Kai2]. In the Al-Ti com-pounds, the solubility of Fe is <0.5 at.% in (�Ti), 2.5 at.%in TiAl, and TiAl2 and ∼1.5 at.% in Ti3Al and TiAl3. Thesolubility of Ti in Fe-Al compounds is 1.8 at.% in FeAl2, 2.5at.% in Fe2Al5, and 6.5 at.% in FeAl3 [1995Pal]. In Fe-richFe-Al alloys, the addition of Ti strongly stabilizes the B2(FeAl) and D03 (Fe3Al) structures, increasing the successiveorder-disorder transition temperatures [1995Ant, 1995Pal,1997Nis, 1998Ohn, 1999Mek]. For example, the addition ofabout 11 at.% Ti to Fe3Al increases the D03→B2 transitiontemperature of Fe64Ti11Al25 to 1027 °C (1300 K)[1997Nis].

The Liquidus Surface

The report by [1981Sei] on the solidification reactions ofthis system needs modifications on the basis of the newresults. The nonexistence of the �1 phase requires that thereaction corresponding to its peritectic formation bedropped. In addition, the much wider homogeneity range of�2 and its occurrence as two separate composition islands athigh temperatures [1995Pal] imply an additional ternaryperitectic reaction for its formation at higher Ti contents. Atransition reaction is necessary near Ti2Al5 to eliminate thisphase from the liquid equilibrium. With Al present, theordered form of (�Ti) forms a continuous solid solutionwith FeTi; this implies that the three-phase equilibrium(�Ti) + FeTi + L must start at a critical point (C2 in Fig. 2)and move down to the binary eutectic reaction on the Fe-Tiside (e5 in Fig. 2). With these modifications, a tentativeliquidus surface is drawn in Fig. 2, which retains the otherfeatures of the surface of [1981Sei] as reviewed in[1987Rag]. The phases of primary crystallization aremarked in Fig. 2.

Fig. 6 Al-Fe-Ti partial isothermal sections at (a) 1300 °C and (b)1200 °C [2000Kai1]

Fig. 7 Al-Fe-Ti vertical sections along the Fe3Al-Fe2AlTi andFe2AlTi-FeAl joins [1998Ohn]



Table 1 A Reaction Scheme for the Al-Fe-Ti System



Table 1 A Reaction Scheme for the Al-Fe-Ti System (continued)



Isothermal Sections

There are several new reports of isothermal sections de-termined for this system. Those published after the reviewof [1987Rag] are: [1989Maz], a partial section at 1200 °C;[1991Nwo], partial sections at 800 and 700 °C; [1995Pal],full sections at 1000 and 800 °C; [1995Yan], partial sectionat 800 °C; [1998Ohn], partial sections at 900 and 800 °C;[1999Gor], full isothermal sections at 1000, 900, and800 °C; [2000Kai1], partial sections at 1300, 1200, and1000 °C; [2000Kai2], partial section at 1000 °C; and[2000Mab], partial sections at 1150 and 1000 °C.

Using starting metals of purity of 99.99% Al, 99.97% Feand 99.77% Ti, [1995Pal] prepared 59 ternary alloy com-positions by levitation melting. Sample were annealed at1000 and 800 °C for 100 and 500 h, respectively, andquenched in brine solution. In addition, diffusion coupleswere prepared, which were heat treated at 1000 °C for500 h. The phase equilibria were studied by metallography,x-ray powder diffraction, electron probe microanalysis, andenergy-dispersive analysis with the scanning electron mi-croscope The isothermal sections determined by [1995Pal]at 1000 and 800 °C are redrawn in Fig. 3 and 4 to agree withthe accepted binary data. The Ti-rich region at 1000 °C(Fig. 3) is drawn according to the results of [2000Kai2],where the (�Ti) phase is divided between A2 and B2 by asecond-order transition line and the B2 region becomes con-tinuous with the FeTi field. The FeTi-(�Ti) two-phase equi-librium is seen at low Al contents; with increasing Al, or-dering occurs in (�Ti). Beyond this point, a miscibility gapis present where two differing compositions of the orderedphase (B2 and B2*) coexist, till the gap closes. The phaserelationships in the (�Fe) region indicate a tie-triangle of(B2 + Fe2Ti + D03) [1998Ohn, 1999Gor].

At 800 °C (Fig. 4), the continuous B2 region between(�Ti) and FeTi has disappeared, giving rise to a three-phasefield of FeTi + (�Ti) + Ti3Al. The phase relationships in the(�Fe) region show that A2, D03, and Fe2Ti are in three-phase equilibrium [1998Ohn]. Pending confirmation of thepersistence at high temperatures of the tetragonality of the�2 phase, it is represented as one homogeneous region inFig. 4 [1995Pal]. This region is marked as �2 at higher Ticontents. At lower Ti, where the tetragonal polymorph maybe present, it is marked �2*. Because of the absence of the�1 phase and the wider homogeneity range of �2, the phasedistribution seen in Fig. 4 is quite different from that givenby [1981Sei].

Figure 5 is a partial isothermal section at 900 °C for theFe-rich region from the results of [1998Ohn]. The (A2 +Fe2Ti + D03) three-phase field at 800 °C (Fig. 4) is replacedby (B2 + Fe2Ti + D03). A full isothermal section at 900 °C[1999Gor] has the same triangulation as that at 800 °C.

Near the Al-Ti side of the composition triangle,[2000Kai1] investigated the phase equilibria between (�Ti),(�Ti), and TiAl. Using starting metals of purity of 99.99%Al, 99.99% Fe, and 99.7% Ti, [2000Kai1] melted alloycompositions in an arc furnace under Ar atmosphere. Thealloys were annealed at 1300 °C for 24 h and at 1200 °C for168 h and then quenched in an ice-water mixture. The phase

equilibria were studied by metallography and electron probemicroanalysis. The partial isothermal sections determinedby them at 1300 and 1200 °C are redrawn in Fig. 6(a) and(b). As the temperature decreases, the solubility of Fe in(�Ti) decreases and the three-phase equilibrium in Fig. 6shifts to higher Ti contents.

The strong influence of Ti in raising the order-disordertransition temperatures in bcc Fe is illustrated in Fig. 7 bytwo vertical sections along the Fe3Al-Fe2AlTi, and Fe2AlTi-FeAl joins [1998Ohn].

The Reaction Scheme

With the significant changes in the solidification reac-tions and in the phase distribution on the isothermal sectionsas discussed above, the scheme of invariant reactions re-viewed by [1987Rag] needs substantial revision. A newreaction scheme is written in Table 1 that is consistent withthe tentative liquidus projection in Fig. 2 and the isothermalsections in Fig. 3-6. The course of the reactions between1000 and 800 °C outlined by [1995Pal] is adopted. No dis-tinction is made in the table between �2 and �2*. The pos-tulated reactions are placed in boxes outlined by brokenlines. The temperatures shown for the postulated reactionsare notional values. They merely indicate the likely se-quence. The order-disorder (second-order) transitions in the(�Fe) region are not incorporated in the reaction scheme.Correspondingly, the tie-triangle present in this region in-volving more than one form of (�Fe) is unaccounted. Thetemperatures of the binary invariant reactions of the Al-Tisystem shown in the reaction table are from [1993Oka].Underlined three-phase equilibria are expected not to un-dergo further reactions during cooling.

The following are the noteworthy features of the reactionscheme:

• The independent formation of the �2 phase at higher Ticontents by an additional ternary peritectic reaction P3at ∼1230 °C;

• The disappearance of the [L + (�Ti) + �2] and the (L +FeTi + �2) phase fields at the lower critical point C1(∼1200 °C), as the (�Ti) and FeTi fields are continuous;

• The start of the three-phase equilibrium [L + FeTi +(�Ti)] at C2 at ∼1150 °C and its termination on theFe-Ti binary side;

• The appearance of the three-phase equilibrium [(�Ti) +FeTi + Ti3Al] at C3 (∼950 °C), as the (�Ti) and FeTibecome separate phases;

• The disappearance of the two (Fe2Ti + TiAl + �2) fieldsat C4 (∼930 °C), as the two islands of the �2 phasemerge.

References

1981Sei: A. Seibold: “Phase Equilibria in the Ternary SystemsTi-Fe-O and Ti-Al-Fe,” Z. Metallkd., 1981, 77(10), pp. 712-19(in German).

1987Rag: V. Raghavan: “The Al-Fe-Ti (Aluminum-Iron-Titanium)System” in Phase Diagrams of Ternary Iron Alloys, ASM In-ternational, Materials Park, OH, 1987, pp. 9-21.



1989Maz: S. Mazdiyasni, D.B. Miracle, D.M. Dimiduk, M.G.Mendiratta, and P.R. Subramanian: “High Temperature PhaseEquilibria of the L12 Composition in the Al-Ti-Ni, Al-Ti-Fe andAl-Ti-Co Systems,” Scr. Metall., 1989, 23(3), pp. 327-31.

1991Nwo: A. Nwobu, T. Maeda, H.M. Flower, and D.R.F. West:“The Constitution of Ti-Rich Alloys of the Ti-V-Fe-Al System,”Proc. User Aspects of Phase Diagrams, Institute of Metals,London, 1991, pp. 102-11.

1993Kat: U.R. Kattner and B.P. Burton: “Al-Fe (Aluminum-Iron)” in Phase Diagrams of Binary Iron Alloys, ASM Interna-tional, Materials Park, OH, 1993, pp. 12-28.

1993Mur: J.L. Murray: “Fe-Ti (Iron-Titanium)” in Phase Dia-grams of Binary Iron Alloys, ASM International, Materials Park,OH, 1993, pp. 414-25.

1993Oka: H. Okamoto: “Al-Ti (Aluminum-Titanium),” J. PhaseEquilib., 1993, 14(1), pp. 120-21.

1993Rag: V. Raghavan: “Al-Fe-Ti (Aluminum-Iron-Titanium),”J. Phase Equilib., 1993, 14(5), pp. 618-19.

1995Ant: L. Anthony and B. Fultz: “Effects of Early TransitionMetal Solutes on the D03-B2 Critical Temperature of Fe3Al,”Acta Metall. Mater., 1995, 43(10), pp. 3885-891.

1995Pal: M. Palm, G. Inden, and N. Thomas: “The Fe-Al-Ti Sys-tem,” J. Phase Equilibria, 1995, 16(3), pp. 209-22.

1995Yan: T.Y. Yang and E. Goo: “Phase Stability and Micro-structure of Al-Ti-Fe Near Al3Ti,” Metall. Mater. Trans. A,1995, 26A, pp. 1029-033.

1997Nis: Y. Nishino, C. Kumuda, and S. Asano: “Phase Stabilityof Fe3Al with Addition of 3d Transition Elements,” Scr. Mater.,1997, 36(4), pp. 461-66.

1998Dum: L.F.S. Dumitrescu, M. Hillert, and N. Saunders: “Com-parison of Fe-Ti Assessments,” J. Phase Equilib., 1998, 19(5),pp. 441-48.

1998Ohn: I. Ohnuma, C.G. Schoen, R. Kainuma, G. Inden, and K.Ishida: “Ordering and Phase Separation in the bcc Phase of theFe-Al-Ti System,” Acta Mater., 1998, 46(6), pp. 2083-094.

1999Gor: A. Gorzel, M. Palm, and G. Sauthoff: “ConstitutionBased Alloy Selection for the Screening of Intermetallic Ti-Al-Fe Alloys,” Z. Metallkd., 1999, 90(1), pp. 64-70.

1999Mek: A.O. Mekhrabov and M.V. Akdeniz: “Effect of Ter-nary Alloying Elements Addition on Atomic Ordering Charac-teristics of Fe-Al Intermetallics,” Acta Mater., 1999, 47(7), pp.2067-075.

2000Kai1: R. Kainuma, Y. Fujita, H. Mitsui, I. Ohnuma, and K.Ishida: “Phase Equilibria Among � (HCP), � (BCC) and � (L10)Phases in Ti-Al Base Ternary Alloys,” Intermetallics, 2000,8(8), pp. 855-67.

2000Kai2: R. Kainuma, I. Ohnuma, K. Ishikawa, and K. Ishida:“Stability of B2 Ordered Phase in the Ti-Rich Portion of Ti-Al-Cr and Ti-Al-Fe Ternary Systems,” Intermetallics, 2000, 8(8),pp. 869-75.

2000Mab: H. Mabuchi, H. Nagayama, H. Tsuda, T. Matsui, andK. Morii: “Formation of Ternary L12 Intermetallic Compoundand Phase Relation in the Al-Fe-Ti System,” Mater. Trans. JIM,2000, 41(6), 733-38.

2000Ohn: I. Ohnuma, Y. Fujita, H. Mitsui, K. Ishikawa, R.Kainuma, and K. Ishida: “Phase Equilibria in the Ti-Al BinarySystem,” Acta Mater., 2000, 48, pp. 3113-123.



al-fe-ti system

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