• PDF / 288,782 Bytes
• 2 Pages / 593.972 x 792 pts Page_size
• 56 Downloads / 150 Views

DOWNLOAD

REPORT

---

Section II: Phase Diagram Evaluations

Al-Co-U (Aluminum-Cobalt-Uranium) V. Raghavan

The early work on this system compiled by [1995Vil] included a liquidus projection, three isothermal sections at 800, 700, and 600
C, three vertical sections along the AlCoU-CoU, AlCoU-Co2U, and AlCoU-U joins from [1968Sam] and a pseudobinary section along the Al2UCo2U join from [1964Pet]. Recently, [2005Noe] determined an isothermal section at 900
C for the entire composition region, which depicts three new ternary compounds in addition to the ones known earlier.

Binary Systems The Al-rich region of the Al-Co phase diagram was reinvestigated by [1996God]. Three modifications of Co4Al13 occur in a narrow range of composition between 24 and 24.7 at.% Co [1996God]. The other intermediate phases are: Co2Al9 (D8d-type monoclinic), CoAl3(D011, Fe3C-type orthorhombic), Co2Al5 (D811-type hexagonal), and CoAl (48-78.5 at.% Co; B2, CsCl-type cubic). The Al-U phase diagram [Masssalski2] depicts three compounds:

Table 1

UAl2 (C15, MgCu2-type cubic), UAl3 (L12, AuCu3-type cubic), and UAl4 (D1b, UAl4-type orthorhombic). The Co-U system [Massalski2] has six intermediate compounds: CoU6 (D2c, MnU6-type tetragonal), CoU (Ba, CoU-type cubic), Co2U (C15, MgCu2-type cubic), Co3U (PuNi3-type rhombohedral), CoU4, CoU5 (CoU5-type rhombohedral).

Ternary Compounds In addition to the three previously-known ternary compounds, UCo1+xAl1 x (x £ 0.1) (s4), U2Co2Al (s5), and U2Co3+xAl1 x (x £ 0.1) (s6), [2005Noe] found three more stable ternary compounds, U2Co6Al19 (s1), U2Co3Al9 (s2), and U3Co4+xAl12 x (0.4 < x < 0.7) (s3), plus a metastable compound UCoAl4. The structural details of these compounds are listed in Table 1. The notations s1, s2, etc. given above in brackets correspond to the numbers 1, 2, etc. used by [2005Noe]. The metastable compound UCoAl4 occurs only in cast samples and decomposes on annealing [2005Noe].

Al-Co-U crystal structure and lattice parameter data [2005Noe]

Phase

Composition, at.%

Pearson symbol

U2Co6Al19 (s1)

70.4 Al 22.2 Co 7.4 U

mC108

C2/m

U2Co3Al9 (s2)

64.3 Al 21.4 Co 14.3 U 61.1-59.5 Al 23.2-24.7 Co 15.8 U 33.3-30 Al 33.3-36.7 Co 33.3 U 20 Al 40 Co 40 U 16.7-15 Al 50-51.7 Co 33.3 U 66.7 Al 16.7 Co 16.7 U

oC56

Cmcm

Y2Co3Ga9

hP?

P63/mmc

Gd3Ru4Al12

hP9

P62m

ZrNiAl

a = 0.6677 c = 0.3965

tP10

P4/mbm

Mo2FeB2

a = 0.71061 c = 0.34641

hP12

P63/mmc

MgZn2

a = 0.5120 c = 0.7692

hP?

P62m

…

a = 0.9161 c = 0.4114

U3Co4+xAl12

x

UCo1+xAl1

(s4) (x £ 0.1)

x

(s3) (0.4 < x < 0.7)

U2Co2Al (s5)

U2Co3+xAl1

x

(s6) (x £ 0.1)

UCoAl4 (metastable)

268

Space group

Prototype

Lattice parameter, nm

…

a = 1.44617 b = 1.20474 c = 0.82003 b = 103.9
a = 1.2789 b = 0.7477 c = 0.9258 a = 0.86518 c = 0.92620

Journal of Phase Equilibria and Diffusion Vol. 30 No. 3 2009

Phase Diagram Evaluations: Section II

Fig. 1 Al-Co-U isothermal section at 900
C [2005Noe]. Narrow two-phase regions are omitted

Ternary Isothermal Section

References

[2005Noe] vacuum-melted alloys in silica tubes and annealed them at 900