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ection II: Phase Diagram Evaluations

Fe-Sb-Ti (Iron-Antimony-Titanium) V. Raghavan

An isothermal section for this system was determined recently by Melnyk et al. [2003Mel], which depicts four ternary compounds.

Binary Systems The Fe-Sb phase diagram [1993Oka] has two intermediate phases. The ␧ phase with the NiAs type hexagonal structure, has a homogeneity range of 40-47 at.% Sb. FeSb2 is a line compound with orthorhombic symmetry. The Fe-Ti system has two intermediate phases: Fe2Ti (C14, hexagonal) and FeTi (B2, cubic). [1998Dum] presented a comparison of the recent Fe-Ti assessments. A schematic and partial phase diagram of the Sb-Ti system is given in [Massalski2], which depicts seven intermediate compounds: Ti4Sb, Ti3Sb, Ti2.5Sb, Ti5Sb3, Ti6Sb5, TiSb and TiSb2. Among these, only the following four were found by [2003Mel]: Ti3Sb, Ti5Sb3, TiSb, and TiSb2. The crystallogaphic data on the intermediate phases of these binary systems are summarized by [2003Mel].

Ternary Compounds Four ternary compounds are known in this system [1998Sko, 2000Mel, 2003Mel]. The crystallographic data

on these phases are summarized in Table 1 from the results of [2003Mel]. TiFe1−xSb (␶1) (0.64 ⱕ x ⱕ 0.70) has the Co 2 Si (TiNiSi) type of orthorhombic structure. Ti1.18Fe0.57Sb (␶2) has the Ni2In type hexagonal structure. Ti1+xFeSb (␶3) (−0.20 ⱕ x ⱕ 0.25) has the AlLiSi type of face centered cubic structure. Ti5FexSb3−x (␶4) (0.45 ⱕ x ⱕ 1.0) has the W5Si3 type tetragonal structure. Table 1 also lists the structural data for the ternary solid solutions based on the binary compounds of Ti3Sb and Fe2Ti.

Ternary Isothermal Section With starting metals of purity ⱖ99.9%, [2003Mel] melted 138 alloys in an arc furnace under Ar atm. The alloys were annealed for 350 h at 797 °C for compositions in the Fe-FeSb-TiSb2-Ti region and at 597 °C for compositions in the FeSb-Sb-TiSb2 region. The samples were quenched in water after the anneal. The phase equilibria were studied by x-ray powder diffraction. The isothermal section redrawn in Fig. 1 corresponds to 597 °C for the Sb-rich region and 797 °C for the lower region. The four ternary compounds ␶1, ␶2, ␶3, and ␶4 are present at 797 °C. The binary compound Fe2Ti

Fig. 1 Fe-Sb-Ti isothermal sections at 797 °C (lower part) and 597 °C (upper part) [2003Mel]

92

Journal of Phase Equilibria and Diffusion Vol. 25 No. 1 2004

Phase Diagram Evaluations: Section II Table 1

Fe-Sb-Ti Crystal Structure and Lattice Parameter Data

Phase

Composition at:%

Pearson Symbol

TiFe1−xSb (␶1)

42.4–43.5 Ti 42.4–43.5 Sb

oP12

Ti1.18Fe0.57Sb (␶2) Ti1+xFeSb (␶3) Ti5FexSb1−x (␶4) (Ti1−xFex)5Sb

42.9 Ti 36.4 Sb 28.6–38.5 Ti 35.7–30.8 Sb 62.5 Ti 31.9–25.0 Sb 75–73.6 Ti 25 Sb

(Fe1−xSbx)2+yTi

Space Group

Structurbericht Designation

Prototype

Pnma

C23

Co2Si

hP6

P63/mmc

B82

Ni2In

cF12

F4¯ 3m

tI32

I4/mcm

D8m

W5Si3

cP8

Pm3¯ n

A15

Cr3Si

hP12

P63/mmc

C14

MgZn2

AILiSi

Lattice parameter, nm a ⳱ 0.64272 to 0.63758 b ⳱ 0.40501 − 0.40258 c ⳱ 0.70918 − 0.70209 a ⳱ 0.41653 c ⳱ 0.62594 a ⳱ 0.59429 to 0.60182 a