Transparent metal-analog materials offer a great opportunity for in situ investigation of the morphological dynamics that govern the formation of microstructure in metallic alloys. There are, however, several experimental factors that must be controlled or considered for proper and reproducible interpretation. We examine some of these issues here, summarizing our recent findings related to the case of rod-type eutectic solidification, for which we examine the importance of ampoule geometry and initial conditions. Employing directional solidification experiments with thin-slab specimens, we look specifically at finite-size effects on growth morphology and the influence of initial structure on the mechanisms of eutectic onset.

Real-time high-energy X-ray diffraction (HEXRD) was used to investigate the crystallization kinetics and phase selection sequence for constant-heating-rate devitrification of fully amorphous Cu50Zr50, using heating rates from 10 K/min to 60 K/min (10 °C/min to 60 °C/min). In situ HEXRD patterns were obtained by the constant-rate heating of melt-spun ribbons under synchrotron radiation. High-accuracy phase identification and quantitative assessment of phase fraction evolution though the duration of the observed transformations were performed using a Rietveld refinement method. Results for 10 K/min (10 °C/min) heating show the apparent simultaneous formation of three phases, orthorhombic Cu10Zr7, tetragonal CuZr2 (C11b), and cubic CuZr (B2), at 706 K (433 °C), followed immediately by the dissolution of the CuZr (B2) phase upon continued heating to 789 K (516 °C). Continued heating results in reprecipitation of the CuZr (B2) phase at 1002 K (729 °C), with the material transforming completely to CuZr (B2) by 1045 K (772 °C). The Cu5Zr8 phase, previously reported to be a devitrification product in C50Zr50, was not observed in the present study.

Solution-based thermodynamic descriptions of the Ni–Ta and Ni–Mo–Ta systems are developed with supporting first-principles calculations and reported experimental data for parameter evaluation. For the Ni–Ta system, the liquid, bcc and fcc phases are described with a random solution model, D022–Ni3Ta is treated as a stoichiometric compound, and the remaining compounds are modeled as solid solutions on multiple sublattices. The resulting model for the Ni–Ta system is integrated with reported treatments of the Ni–Mo and Mo–Ta systems, and a thermodynamic model for the ternary Ni–Mo–Ta system is developed. The zero-Kelvin enthalpies of formation for the intermetallic compounds in the Ni–Mo–Ta system and the enthalpies of mixing for the bcc and fcc special quasirandom structures (SQS) in the binary Ni–Ta system are computed using the Vienna Ab-initio Simulation Package (VASP). Phase equilibria modeling results for the ternary Ni–Mo–Ta system are summarily presented in the form of isothermal sections and liquidus projections, with appropriate comparisons with available experimental data.

The local solidification conditions and mechanisms associated with the flake-to-fiber growth mode transition in Al–Si eutectic alloys are investigated here using Bridgman-type gradient-zone directional solidification. Resulting microstructures are examined through quantitative image analysis of two-dimensional sections and observation of deep-etched sections, showing three-dimensional microstructural features. Several microstructural parameters were investigated in an attempt to quantify this transition, and it was found that the particle aspect ratio is effective in objectively identifying the onset and completion velocity of the flake-to-fiber transition, whereas traditional spacing parameters are not effective indicators of the transition. For a thermal gradient of 7–14 K/mm, the transition was found to occur in two stages, appearing over velocity regimes from 0.10 to 0.50 mm/s and from 0.50 to 0.95 mm/s. The initial stage is dominated by in-plane plate breakup and rod formation within the plane of the plate, whereas the second stage is characterized by the onset of out-of-plane silicon rod growth, leading to the formation of an irregular fibrous structure. The boundary between the two stages is marked by widespread fibrous growth and the disappearance of the remnant flake structure, indicating a transition in the structural feature that governs the relevant diffusion length, from inter-flake spacing to inter-rod spacing.

X-ray diffraction (XRD) experiments and first-principles calculations were employed to investigate the martensitic transformation products formed upon rapid cooling of the CuZr-B2 phase. Candidate intermetallic compound structures were selected, and calculations show that CuZr-B11 (CuTi prototype), CuZr-B27 (FeB), CuZr-B19′ (NiTi) and CuZr-B33 (BCr) are more stable than the B2 phase at 0 K. Computed XRD patterns, based on first-principles calculations, were compared with experimental XRD measurements. The results indicate that the CuZr martensite consists of the CuZr-B33 and CuZr-B19′ phases.

The thermodynamic properties and associated phase equilibria for the Al-Sm binary system are examined, and experimental results regarding the stability of the Al3Sm, Al11Sm3, and Al4Sm intermetallics are incorporated. In the analysis presented, the liquid phase is described using a three-species association model, the intermediate phases are treated as stoichiometric compounds, and the terminal phases are treated as solid solutions with a single sublattice model. In addition to the stable phases, thermodynamic descriptions of the metastable Al11Sm3-α and Al4Sm-γ phases are employed, and both stable and metastable phase equilibria are presented over the full composition range, providing a general model, which is consistent with available experimental data. Metastable liquidus curves are examined with respect to the observed crystallization behavior of amorphous Al-Sm alloys.

The relative stability of Al11Sm3 (Al4Sm) intermetallic phases was experimentally investigated through a series of heat treatments followed by microstructural, microchemical, and X-ray diffraction (XRD) analyses. The principal findings are that the high-temperature tetragonal phase is stable from 1655 to 1333 K and that the low-temperature orthorhombic phases, α and γ, have no range of full stability but are metastable with respect to the crystalline Al and Sm reference states down to 0 K. Thermodynamic modeling is used to describe the relative energetics of stable and metastable phases along with the associated two-phase mixtures. Issues regarding transition energetics and kinetics are discussed.

Differential thermal analysis (DTA) is used for liquidus and solidus measurements in binary Fe–Si alloys. The heating-rate and composition dependence of the DTA response is quantified, and we report phase boundaries that differ considerably from previous reports. Implications of A2–B2 ordering and thermodynamic treatments are discussed.