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ection II: Phase Diagram Evaluations

Al-Ce-Cu (Aluminum-Cerium-Copper) V. Raghavan

The experimental data on this system were reviewed recently by [2004Ria] and [2007Rag]. This update pertains to the new results reported by [2006Bel, 2007Bel], clarifying the phase relationships in the Al-rich region during solidification and in the solid state.

Binary Systems The Al-Ce phase diagram was recently reassessed thermodynamically by [2005Gao], using new experimental results as additional input. The intermediate phases in this system are: aCe3 Al ðD019 , Ni3Sn-type hexagonal), bCe3 Al (L12, AuCu3-type cubic), Ce2Al (stable between 775 and 648 °C; Co2Si-type orthorhombic?), CeAl (orthorhombic), CeAl2 (C15, MgCu2-type cubic), aCeAl3 ðNi3 Sn-type hexagonal), bCeAl3 (stable between 1192 and 973 °C), CeAl4 or bCe3 Al11 (D13, Al4Ba-type tetragonal), and aCe3 Al11 ðaLa3 La11 -type orthorhombic). The Al-Cu phase diagram [1998Liu] depicts a number of intermediate phases: CuAl2 (h, C16-type tetragonal), CuAl (g1 , orthorhombic), CuAl (g2 , monoclinic), Cu5Al4(LT) (f2 , orthorhombic), e1 (bcc), e2 ðB82 , Ni2In-type hexagonal), Cu3Al2 (d, rhombohedral), Cu9Al4(HT) (c0 ; D82 , Cu5Zn8-type cubic), Cu9Al4(LT) (c1 ; D83 -type cubic), and Cu3 Al ðb, bcc). In the above, HT = high-temperature and LT = low-temperature. The Ce-Cu phase diagram [Massaslki2] has the following intermediate phases: Cu6Ce (orthorhombic, space group Pnma), Cu5Ce (D2d, CaCu5-type hexagonal), Cu4Ce (orthorhombic, space group Pnnm), Cu2Ce (orthorhombic, space group Imma), and CuCe (B27, FeB-type orthorhombic).

with optical and scanning electron microscopy, x-ray powder diffraction, electron probe microanalysis, and differential scanning calorimetry at heating/cooling rates of 5 °C per min. [2007Bel] constructed for Al-rich alloys the liquidus and solidus projections, three isothermal sections at 590, 540, and 200 °C and five vertical sections along the Al-s1 join, at 20 and 14 mass% Cu and at 12 and 5 mass% Ce, respectively. The pseudobinary nature of the Al-s1 join earlier determined by [1991Yun] was confirmed by [2002Bel, 2007Bel], except that the eutectic temperature on this join was reported to be 610 °C, higher by 35 °C than that reported by [1991Yun]. Moreover, [2007Bel] did not find a pseudobinary section along the Al-s2 join as reported by [1991Yun]. They concluded that a separate phase labeled Al4CuCe (or Al3CuCe) did not exist, but only a solid solution based CeAl4. As discussed above, CeAl4 (Al4Batype tetragonal) is not stable below 1000 °C, even though the addition of Cu could have a stabilizing effect on the tetragonal structure. This contradiction needs to be resolved by more detailed experiments on the effect of progressive Cu addition to CeAl4. The liquidus projection is shown in Fig. 1 [2007Bel]. The primary phases of crystallization are (Al), CuAl2, CeAl4, and Al8 CeCu4 ðs1 Þ. The eutectic temperature and composition on the Al-s1 pseudobinary section are 610 °C and 14Cu-7Ce in mass%. In the Al-CuAl2 -s1 region, the final solidification is through the tern