Cuiyun He

Thermodynamic Assessment of the Cr–Al–Nb System

Abstract A thermodynamic assessment of the Cr–Al–Nb system was performed using the CALPHAD technique on the basis of new experimental data on three isothermal sections at 1 150, 1300 and 1 450 °C as well as the available earlier literature data. The ternary phase diagram is dominated by an extended phase field of the Laves phase Nb(Cr, Al)2. Both the cubic C15 and the hexagonal C14 structure type of Laves phases occur as stable phase in the ternary system. A two-sublattice model was used for their thermodynamic description. The ternary solubilities of the (Nb) and (Cr) solid solutions and the binary phases NbAl3, Nb2Al and Nb3Al were taken into account in the ternary assessment. Several isothermal sections were calculated using the evaluated parameters. Good agreement between the calculations and the experimental data is achieved.

Thermodynamic description of the Ni–Si–Ti ternary system

Abstract A thermodynamic modeling of the Ni–Si–Ti system is conducted. All of the experimental phase diagram data available from the literature are critically reviewed and assessed using thermodynamic models for the Gibbs energies of individual phases. The thermodynamic parameters for five ternary compounds (τ1: Ti1Ni1Si1, τ2: Ti4Ni4Si7, τ3: Ti13Ni40Si31, τ4: Ti6Ni16Si7, and τ5: Ti2Ni3Si1), the ternary solution phases (liquid, bcc_A2, bcc_B2, fcc_A1, and L12) as well as the binary phases (Ti5Si3, Ni3Si, Ni5Si2, and TiNi3) showing noticeable solubilities for the third element are adjusted in the optimization. The order/disorder transitions between disordered bcc_A2 and ordered bcc_B2 phases as well as between disordered fcc_A1 and ordered L12 phases are treated using a two-sublattice model. The calculations indicate that the disordered and ordered phases can be described with a single equation. Comprehensive comparisons between the calculated and measured phase diagrams show that in the measured isothermal sections at 750°C, 900°C, 1000°C and 1100°C, most of the observed primary phase regions, as well as 16 out of the 26 experimentally observed invariant reaction temperatures are satisfactorily accounted for by the thermodynamic description. The liquidus projection and reaction scheme for the entire system are also presented. Further experimental work to solve a few discrepancies between calculation and experiment is emphasized.

Thermodynamic Re-Assessment of the Co–Nb System

A new thermodynamic assessment of the Co-Nb system is presented. All experimental phase diagram data available from the literature have been critically reviewed and assessed using thermodynamic models for the Gibbs energies of the individual phases (Thermo-Calc). Compared to previous assessments more elaborate models for the description of the C14 and C36 Laves phases and for the μ phase were employed. Thereby a calculated phase diagram is obtained which satisfactorily agrees with the experimental data.