Liquidus surface of the Mg-Sm-Tb phase diagram

Differential thermal, electron microprobe, and X-ray diffraction analyses and metallography are used to study Mg-Sm-Tb alloys containing up to 30% Sm or Tb. Polythermal sections and the solidification surface of the Mg-Sm-Tb phase diagram are constructed for the Mg-rich region. In the composition range under study, nonvariant transition-type equilibrium L + Mg₂₄Tb₅ = (Mg) + Mg₄₁Sm₅ is found to exist at a temperature of 539°C.     

The Dy-Zn phase diagram

The dysprosium-zinc phase diagram has been investigated over its entire composition range by using differential thermal analysis, (DTA) metallographic analysis, X-ray powder diffraction, and electron probe microanalysis (EPMA). Seven intermetallic phases have been found and their structures confirmed. DyZn, DyZn₂, Dy₁₃Zn₅₈, and Dy₂Zn₁₇ melt congruently at 1095 °C, 1050 °C, 930 °C, and 930 °C, respectively. DyZn₃, Dy₃Zn₁₁, and DyZn₁₂ form through peritectic reactions at 895 °C, about 900 °C and 685 °C, respectively. Four eutectic reactions occur at 850 °C and 30.0 at pct Zn (between (Dy) and DyZn), 990 °C and 60.0 at pct Zn (between DyZn and DyZn₂), 885 °C and 76.0 at pct Zn (between DyZn₃ and Dy₃Zn₁₁), and 875 °C and 85.0 at pct Zn (involving Dy₁₃Zn₅₈ and Dy₂Zn₁₇). The Dy-rich end presents a catatectic equilibrium; a degenerate invariant effect has been found in the Zn-rich region. The phase equilibria of the Dy-Zn alloys are discussed and compared with those of the other known RE-Zn systems (RE=rare earth metal) in view of the regular change in the relative stabilities of the phases across the lanthanide series     

The Nd-Zn phase diagram

Metallographie, thermal, and X-ray techniques were used to determine the phase relations in the Nd-Zn system. Eight compounds, three eutectics and a eutectoid were found. The compounds NdZn, NdZn₂, and Nd₂Znn melt congruently at 923°, 925°, and 981°C respectively. The compounds Nd₃Zn₁₁, NdZn_4.46, and Nd₃Zn₂₂ undergo peritectic decomposition at 870°, 902°, and 950°C respectively, while NdZn₃ undergoes peritectoid decomposition at 849°C. The eutectics occur at 12 wt pct Zn and 630°C, 38 wt pct Zn and 868°C, and 56 wt pct Zn and 854°C. The eutectoid occurs at 4 wt pct Zn and 622°C. The existence of a NdZn₁₂ phase of the SmZn₁₂ type structure has been confirmed. An allotropie transformation between the tetragonal NdZn₁₁ structure and the hexagonal NdZn₁₂ defect structure is proposed.     

The neodymium-gold phase diagram

The Nd-Au phase diagram was studied in the 0 to 100 at. pct Au composition range by differential thermal analysis (DTA), X-ray diffraction (XRD), optical microscopy (LOM), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). Six intermetallic phases were identified, the crystallographic structures were determined or confirmed, and the melting behavior was determined, as follows: Nd₂Au, orthorhombic oP12-Co₂Si type, peritectic decomposition at 810 °C; NdAu, R.T. form, orthorhombic oP8-FeB type, H.T. forms, orthorhombic oC8-CrB type and, at a higher temperature, cubic cP2-CsCl type, melting point 1470 °C; Nd₃Au₄, trigonal hR42-Pu₃Pd₄ type, peritectic decomposition at 1250 °C; Nd₁₇Au₃₆, tetragonal tP106-Nd₁₇Au₃₆ type, melting point 1170 °C; Nd₁₄Au₅₁, hexagonal hP65-Gd₁₄Ag₅₁ type, melting point 1210 °C; and NdAu₆, monoclinic mC28-PrAu₆ type, peritectic decomposition at 875 °C. Four eutectic reactions were found, respectively, at 19.0 at. pct Au and 655 °C, at 63.0 at. pct Au and 1080 °C, at 72.0 at. pct Au and 1050 °C, and, finally, at 91.0 at. pct Au and 795 °C. A catatectic decomposition of the (βNd) phase, at 825 °C and ≈1 at. pct Au, was also found. The results are briefly discussed and compared to those for the other rare earth-gold (R-Au) systems. A short discussion of the general alloying behavior of the “coinage metals” (Cu, Ag, and Au) with the rare-earth metals is finally presented.     

The coherent phase diagram of Cu-Ni-Zn

The phase diagram for the f.c.c. part of the CuNiZn system has been derived using the tetrahedron approximation of the Cluster Variation Method. The pair-wise interaction potentials have been obtained from a pseudopotential model for the stoichiometric Cu₂NiZn composition. The results obtained are combined with the cluster variation method in order to make predictions on the phase diagram of the CuNiZn system. In particular, this paper reports the influences which the various more-body forces exert on the shape of the regions in the phase diagram where ordering occurs. The predictions on the phase diagram of the ternary system CuNiZn are in reasonable agreement with experiments and are the least topologically correct.     

The ternary phase diagram,Fe-Ni-P

In order to provide the necessary phase equilibria data for understanding the development of the Widmanstatten pattern in iron meteorites, we have redetermined the Fe-Ni-P phase diagram from 0 to 100 pct Ni, 0 to 16.5 wt pct P, in the temperature range 1100° to 550°C. Long term heat treatments and 130 selected alloys were used. The electron microprobe was employed to measure the composition of the coexisting phases directly. We found that the fourphase reaction isotherm, where α+ liq ⇌ γ+ Ph, occurs at 1000° ± 5°C. Above this temperature the ternary fields α+ Ph + liq and α+ γ+ liq are stable and below 1000°C, the ternary fields ⇌+ γ + Ph and γ + Ph + liq are stable. Below 875°C a eutectic reaction, liq → γ + Ph, occurs at the Ni-P edge of the diagram. Altogether nineteen isotherms were determined in this study. The phase boundary compositions of the two-and three-phase fields are listed and are compared with the three binary diagrams. The α + γ + Ph field expands in area in each isotherm as the temperature decreases from 1000°C. Below 800°C the nickel content in all three phases increases with decreasing temperature. The phosphorus solubility in α and γ decreases from 2.7 and 1.4 wt pct at 1000°C to 0.25 and 0.08 wt pct at 550°C. The addition of phosphorus to binary Fe-Ni greatly affects the α/α + γ and γ/α + γ boundaries below 900°C. It stabilizes the α phase by increasing the solubility of nickel (α/α +γ boundary) and above 700°C, it decreases the stability field of the γ phase by decreasing the solubility of nickel(@#@ γ/α + γ boundary). However below 700°C, phosphorus reverses its role in γ and acts as a γ stabilizer, increasing the nickel solubility range. The addition of phosphorus to Fe-Ni caused significant changes in the nucleation and growth processes. Phosphorus contents of 0.1 wt pct or more allow the direct precipitation ofa from the parent γ phase by the reaction γ ⇌ α + γ. The growth rate of the α phase is substantially higher than that predicted from the binary diffusion coefficients. Formerly at Planetology Branch, Goddard Space Flight Center