Liquid phase formation in the system AlN–Al2O3–Y2O3. Part I: Experimental investigations

The liquid phase formation in the system AlN–Al₂O₃–Y₂O₃ was investigated via differential thermal analysis (DTA) combined with thermogravimetry (TG). For this purpose 17 samples covering a broad composition area of the quasi-ternary system were densified and heat-treated to achieve the equilibrium state. Melting temperatures were determined by DTA. SEM, EDX and XRD were used to study the phase assemblages and microstructures formed. The results were compared with thermodynamic calculations.     

Liquid phase formation in the system Al2O3–Y2O3–AlN: Part II. Thermodynamic assessment

The mixing parameters of liquid phase in the Al₂O₃–Y₂O₃–AlN system were assessed based on differential thermal analysis (DTA) and scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM/EDX) investigations of selected compositions. Phase diagram of the Y₂O₃–AlN system was calculated. Liquidus surface of the Al₂O₃–Y₂O₃–AlN system was constructed and compared with experimental results on primary crystallisation fields. Calculated temperatures of invariant reactions were in agreement with DTA results. Vertical sections of the Al₂O₃–Y₂O₃–AlN system were calculated and compared with experimental data     

Constitution of the high-Al region of Al–Cu–Rh

Phase equilibria between 540 and 1010 °C were studied in Al–Cu–Rh alloys containing more than 50 at.% Al. Congruent equiatomic AlRh dissolves more than 40 at.% Cu and extends up to 58 at.% Al at the high-Cu part of its compositional range. High-temperature cubic C-Al₅Rh₂ (C-phase) dissolves up to 13 at.% Cu, “Al₃Rh” (₆-phase) up to 15 at.% Cu and Al₉Rh₂ up to 1.5 at.% Cu. The solubility of the third element in other binary Al–Rh and Al–Cu phases is below 0.5 at.%. Close to the high-Cu limit of the C-phase region the fcc C₂-phase structurally related to the C-phase is formed. Stable decagonal phase (D₁-phase) is formed below 1005 °C in a compositional range extending from Al₆₅Cu₁₆Rh₁₉ to Al₆₂Cu₂₃Rh₁₅, which shifts to higher Cu concentrations with decreasing temperature. An additional ternary phase forming around the Al₇₀Cu₂₀Rh₁₀ composition below 660 °C was revealed. Partial 1010, 990, 900, 800, 700, 600 and 540 °C isothermal sections were determined.     

Investigation of the Al-Ti-Pt alloy system at 1100 °C

The 1100 °C isothermal section of the Al-Ti-Pt system was experimentally studied in the compositional region below 50 at.% Pt. Most of the binary Al-Ti and Al-Pt intermetallics dissolve about 1.5-3.5 at.% of the third element. Only TiAl and Ti₃Al contain up to ∼5.5 at.% Pt and Al₂Pt ∼13 at.% Ti. The Ti₃Pt, Ti₃Pt₄ and TiPt phases extend up to 7.5, 9 and 30 at.% Al, respectively. The homogeneity range of the ternary phase τ₁ extends from Al_63.3Ti_30.6Pt_6.1 to Al_69.0Ti_24.2Pt_6.6 and that of τ₂ from Al_44.1Ti_34.0Pt_21.9 to Al_55.1Ti_20.9Pt_24.0. The τ₃-phase is formed in the compositional region from Al₃₇Ti_37.5Pt_25.5 to Al₄₂Ti₃₂Pt₂₆. Only the Nb(Ir,Al)₂-type structure of the latter was revealed. The τ₄-phase exists between Al_31.3Ti_33.7Pt₃₅ and Al_36.6Ti_29.4Pt₃₄ while the τ₅-phase exists between Al_12.9Ti_58.9Pt_28.2 and Al_27.3Ti_57.3Pt_15.4. Apart from these previously reported phases, five new ternary compounds designated τ₆ to τ₁₀ were revealed. The τ₆-phase exists between the Al_25.5Ti_54.2Pt_20.3 and the Al₃₀Ti₅₄Pt₁₆ compositions, and probably has a primitive cubic structure with a = 0.68477(6) nm. The τ₇-phase was found to be formed around the Al₁₂Ti₅₁Pt₃₇ composition, τ₈, τ₉ and τ₁₀-phases exist in the compositional ranges of Al_28.5Ti₅₅Pt_27.5 to Al_33.7Ti₄₀Pt_26.3, Al_34.5Ti₄₈Pt_17.5 to Al₃₈Ti₄₄Pt₁₈ and Al_32.6Ti_44.3Pt_23.1 to Al_37.4Ti₄₁Pt_21.6, respectively.