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In the present paper, the complete ternary B–Fe–Ti system is thermodynamically modelled based on our own experimental results and information reported in literature. Series of key experiments were performed for the binary Fe-B, Fe-Ti and the ternary B-Fe-Ti systems in order to obtain parameters of invariant reactions. For this, 19 alloys were prepared and analysed in the as-cast and annealed conditions by means of SEM/EDS, SEM/EBSD, XRD and DTA/DSC techniques. A new ternary boride Ti2FeB2 with the crystal structure of Mo2FeB2 (an ordered derivative of U3Si2 crystal structure type) was revealed to exist at temperatures from 1273 K to solidus. The elaborated thermodynamic description was applied to calculate selected phase equilibria as to provide a comparison between calculated and experimental results. The calculations are shown to reproduce available experimental data entirely well.

Intermetallic iron aluminide alloys show various advantages such as low material cost and a good creep resistance that is superior to the P92 martensitic-ferritic steel at 650 °C, nominating them as potential candidates for steam turbine applications. However, cast preforms for hot forging show a rather coarse microstructure and limited workability. Recent research thus introduced Fe-25Al-Ta alloys, where tantalum prevents excessive grain growth during solidification. This paper, for the first time, investigates the possibility of producing the Fe-25Al-1.5Ta (at.%) alloy by spark plasma sintering (SPS) from pre-alloyed powder particles and investigates its deformation behavior under compression in the temperature range of 900–1100 °C using the concept of processing maps. SPS is mainly used to analyze the possibility of inheriting the size of the initial powder particles into the sintered material. The SPSed specimen at room temperature reveals a homogeneous equiaxed microstructure consisting of fine A2-phase grains with an average size of 7 μm surrounded by the ternary (Fe, Al)2Ta, C14, Laves phase particles. Laves phase particles are precipitated predominantly on grain boundaries of the Fe-Al matrix grains. Several particles are also dispersed inside the grains. The presence of a fine-grained equiaxed microstructure at hot working temperature seems to improve workability and leads to a wide processing window. The optimum processing domain for the studied Fe-25Al-1.5Ta alloy locates at 1050–1100 °C/0.0013–0.01 s−1 with a power efficiency of 40–50%, where the material undergoes dynamic recrystallization. At low temperature and high strain rates, dynamic recovery is the major softening mechanism observed for the samples, where the efficiency of power dissipation reaches around 40%. The current study offers a possibility to produce a homogeneous fine-grained Fe-25Al-1.5Ta alloy strengthened by dispersed Laves phase particles using SPS compared to the coarse and columnar microstructure commonly obtained by casting. Such a refined microstructure leads to a good hot forgeability.

This paper investigates the hot forgeability of a TNB-V5 (Ti–45Al–5Nb–0.2B–0.2C, at.%) alloy produced by spark plasma sintering (SPS) from pre-alloyed powder particles using the concept of processing maps. For the first time in this paper, to the best of our knowledge, we report the possibility of the isothermal forging of a TiAl alloy without the necessity to induce the ductile β-phase in the microstructure, by using non-equilibrium phases produced by SPS. At room temperature, the SPSed sample reveals a homogeneous equiaxed microstructure consisting of globular α2-and γ-grains with the α2-phase formed mainly at the necks between powder particles as confirmed by EBSD analyses. The necks contain a lower Al content and thus transform into α-phase upon heating to forging temperature. A stable plastic flow is observed for all ranges of the studied strain rates. The presence of a fine equiaxed microstructure at hot working temperature seems to ensure good workability and leads to a relatively wide processing window. The processing map reveals two safe processing windows for the studied alloy. The lower strain rate domain (10−3-10−2 s−1) corresponding to a strain rate sensitivity value of ≈0.8 represents superplasticity of the fine and uniform (α+γ) equiaxed microstructure. The higher strain rate domain (10−2-10−1 s−1, T > 1215 °C) with a strain rate sensitivity value of ≈0.45 represents dynamic recrystallization of the α-grains at elevated temperatures. The processing map also exhibits a domain of flow instability represented by the deformation conditions of T e ˙ > 10−2 s−1, which might result from the void formation and/or cracking. Although the TNB-V5 alloy was not designed for forging operations, the SPS process can create a homogeneous equiaxed microstructure consisting of globular α- and γ-grains decorating the interfaces and triple junctions between former powder particles leading to a good hot workability. The current study offers a new process design strategy by opening up the possibility of using local non-equilibrium conditions in the material during the forging process, which could stabilize the ductile phases locally.

The microstructure of ternary eutectic Al - Al 2 Cu - Ag 2 Al arranges in several patterns of three solid phases during directional solidification. One key question for understanding the behavior of this system is if and how the patterns depend on crystal orientation relationships (ORs) between the solid phases. In order to study the correlation between the ORs and the evolving patterns for different process conditions, electron backscatter diffraction (EBSD) is performed on samples of directionally solidified ternary eutectic Al - Al 2 Cu - Ag 2 Al which have been processed with different solidification velocities and temperature gradients. The results show that characteristic ORs occur, influencing the type of the evolving pattern, the alignment of the phases and the degree of order. For one specific OR the pattern was observed to change in response to an imposed increase in the growth velocity even though the OR was retained. Based on the obtained EBSD results, an explanation for the observed behavior is proposed. For the other ORs, specific microstructures were observed for each of them. The outcomes demonstrate that knowledge about crystal ORs is essential to improve the understanding of the pattern formation in complex eutectic alloys.

For the manufacturing of low pressure turbine blades, titanium aluminides are used as structural materials, among them the alloy Ti-43.5Al-4Nb-1Mo-0.1B (at.-%) known as TNMTM alloy. In this study, laser metal deposition (LMD) was investigated as a potential technology to repair defective, damaged or worn blades, and process conditions were successfully optimized. However, post-process heat treatment is required to optimize the microstructure. In this work, different annealing treatments and the resulting microstructures were characterized for bulk LMD samples as well as for investment cast reference samples. Annealing temperatures were selected from 1245 to 1290 °C. The results show that annealing at 1290 °C for a duration of 60 min with subsequent furnace cooling can be used so that the LMD and cast micro-hardness nearly match, albeit with significant differences in microstructure. Nonetheless, yield strength mismatch can be mitigated and LMD can qualify as prospective additive repair technology, but also as a manufacturing technology for functional TiAl parts.

Intermetallic Titanium Aluminides (TiAl) have been designed for high-temperature lightweight applications. Powder-bed additive manufacturing (AM) processes such as laser powder bed fusion (LPBF) or electron beam melting (EBM) allow near-net-shape production of TiAl components. However, TiAl parts produced by LPBF or EBM do not reach the structural integrity and mechanical properties of forged parts. The main post-processing step of TiAl parts made by AM is hot-isostatic pressing (HIP), which has several disadvantages such as a long process time and an undesired coarsening of the microstructure. High-performance TiAl components such as turbine blades are thus still produced by isothermal forging of preforms made by investment casting and hot isostatic pressing. Due to the low workability of TiAl alloys, often more than one deformation step is required, and the tooling costs and the low material yield make this process chain very expensive. This paper explores the feasibility of combining AM with isothermal forming in order to replace HIP by thermomechanical post-processing. The hot forming behavior of the Ti-43.5Al-4Nb-1Mo-0.1B (at. %) TNM-B1 alloy, manufactured by EBM and LPBF, is analyzed concerning the evolution of the voids and grain sizes and compared to hot isostatic pressing. It is shown that the fine microstructure produced by AM yields a much lower flow stress and faster globularization kinetics in comparison to conventional cast and HIPed material. While HIP experiments are shown to significantly coarsen the microstructure, isothermal hot working is shown to convert the AM microstructure to a dense and refined state. Moderate hot working with total strains of ∼1 of AM pre-forms may thus serve as an alternative process chain to conventional large strains forging of cast pre-forms and to AM + HIP in the series production of high-performance TiAl components.

In the present work are reported ground-reference results from a series of transient solidification experiments with the organic eutectic alloys SCN-23.6 DC (wt.%) and SCN-24.2DC-0.5NPG (wt.%), which have been performed in preparation of microgravity experiments using a new multi-user facility called Transparent Alloys or DIRSOL. In 1g lab conditions we investigated the response of rod-like eutectic patterns to imposed transients, involving defined acceleration and deceleration of the growth velocity. The patterns have been recorded in-situ in oblique view using a long distance optics and were analysed for a region of interest of 640 μm x 320 μm over long periods of time. The time dependent growth velocity and the associated acceleration / deceleration were determined using images from a side-view camera. The reported results mainly refer to the spacing distribution and the hexagonal order parameter S0, dynamically attained at a defined time instant, i.e. at the moment when the local growth velocity reaches V = 40 nm s−1 along deceleration 80 → 10 nm s−1 or acceleration 10 → 80 nm s−1 paths. The major result is that the hexagonal order is deteriorating under transient growth conditions compared to steady state conditions. We could not observe an increase of order for either imposed acceleration or deceleration, mainly because spacing adjustment is accomplished by abrupt morphological transitions which destroy the previous order. The abrupt morphological transitions are clearly identified as sharp events along an experiment cycle 80 → 10 → 80 nm s−1 and could conveniently be seen in hysteresis loop diagrams. Upon deceleration the abrupt spacing adjustment event corresponds to a transition from fibrous to vermicular morphology. Upon acceleration the abrupt spacing adjustment event corresponds to spontaneous rod splitting.

International audience; Experiments of directional solidification of TiAl cylindrical samples were conducted within the frame of the ESA GRADECET project. The experiments were performed in the ESA "Large Diameter Centrifuge" using a furnace with a well defined thermal protocol. The furnace was mounted in the centrifuge and free to tilt in such a way that the total apparent gravity (sum of terrestrial gravity and centrifugal acceleration) was aligned to the cylinder centerline. Several centrifugation levels were investigated besides to one reference case out of the centrifuge. In this work, we present 3D numerical simulations of these experiments paying special attention in the liquid thermosolutal buoyancy convection and aluminum macrosegregation. The numerical model accounts for the non-inertial accelerations that appear in the rotating reference frame (centrifugal and Coriolis), motionless solid, the-mosolutal Boussinesq approximation and an infinitely fast microscopic diffusion model between the phases to depict the solid growth. The results showed that the Coriolis acceleration entirely modifies the liquid flow regime during solidification leading to a 3D aluminum segregation pattern with respect to the case solidified under normal terrestrial gravity conditions. Additionally the magnitude of aluminum segregation increases with the level of centrifu-* Corresponding author

In the present paper, the constituent binary B–Mo system is re-modelled in order to reproduce genuine homogeneity ranges of the molybdenum borides. Based on this, available descriptions of the constituent B–Ti and Mo–Ti systems as well as new experimental data reported in the literature for the ternary B–Mo–Ti system are used to model the B–Mo–Ti system in the entire composition and temperature ranges. The elaborated thermodynamic description is further applied to calculate selected phase equilibria as to provide a comparison between calculated and experimental results. The calculations are shown to reproduce the experimental data reasonably well, however for few alloys belonging to the domain of primary (Ti,Mo)B 2 crystallization the computed solidus temperatures are about 200 K higher than incipient melting temperatures measured by pyrometry.

In the present paper, the ternary Al–Cr–Ti and binary constituent Al–Cr systems are thermodynamically re-modelled based on new experimental information reported in the literature within the past few years. Few key experiments were performed with selected ternary alloys in order to complement data on phase equilibria in the composition range of common TiAl-based alloys. Six sample compositions were prepared and analyzed in the as-cast and annealed conditions by means of SEM/EDS, XRD and DTA techniques. The elaborated thermodynamic description was applied to calculate selected phase equilibria as to provide a comparison between calculated and experimental results. The calculations are shown to reproduce the experimental data reasonably well.

Based on novel experimental data the thermodynamic description of the ternary Al–C–Ti system was subject to optimization using the CALPHAD approach (Thermo-Calc/PARROT). The reaction scheme, the projections of the liquidus and solidus surfaces, as well as a number of isothermal sections and isopleths were calculated using the proposed thermodynamic description and compared with the experimental results. The calculations were shown to adequately reproduce the experimental data. The main feature of the phase equilibria in the system is the existence of three ternary compounds P (Ti3AlC), H (Ti2AlC) and N (Ti3AlC2) forming peritectically from the liquid phase and TiC1−x carbide at 1907, 1865 and 2013 K, respectively. It is shown that these three compounds are thermodynamically stable in a wide temperature interval.

Based on 2D phase-field simulations including fluid flow driven by natural convection, columnar dendritic growth of the β -solidifying Ti-48 at.%Al alloy is characterised for different gravity levels ranging from 0 to ± 15 g. Depending on the direction of the gravity g with respect to the growth direction, different flow regimes emerge which show stable or unstable dendritic growth dynamics. When gravity and growth directions are parallel, the dendrite tips experience downward melt flow and individual dendrites grow in a stable manner with a rather small modification of the operating state. When gravity and growth directions are antiparallel, the impact on the operating state is larger. Eventually, at higher gravity levels the upward melt flow around the dendrite tips “destabilises” the dendritic morphology resulting in tip splitting, branching and local changes in the apparent dendrite growth direction which is an alternative mechanism for the adjustment of the primary dendrite arm spacing in addition to tertiary arm formation.

Potential based molecular dynamics simulations were performed for Al–Al2Cu phase boundaries (PBs) at a temperature of 50 K using a newly designed computation geometry that enables modeling hetero-interface configurations for an arbitrary pair of phases. The computational method and geometry were validated for symmetric grain boundaries in Al, both [0 0 1] and [1 1 0] tilt boundaries, followed by extensive simulations of Al–Al2Cu PBs. For randomly oriented Al and Al2Cu as well as randomly oriented phase boundary planes the average PB energy reaches γav. = 0.456 ± 0.002 J/m2. Two special orientation relationships (ORs), known to prevail in Al–Al2Cu eutectics after unidirectional solidification, were characterized in detail. For each OR the 3D phase boundary energy surface was mapped and the energy minima were carefully analyzed. Computational results were compared to experimental observations based on EBSD measurements and allowed concluding that lamellar eutectic interfaces select a shallow energy minimum γα4 = 0.407 J/m2 for one OR, but a deep, cusp-like energy minimum γβ6 = 0.253 J/m2 for the second OR. The calculations thus substantiate the experimentally observed behavior of lamellar eutectic interfaces, being nearly isotropic in the first case, but strongly anisotropic in the latter.

International audience; Phase equilibria and phase transformations in the ternary Al-B-Nb system were investigated by XRD, SEM/WDS and SEM/EDS techniques, DTA, and optic pyrometry. No ternary compound, including the ternary phases reported in literature, was found. It was experimentally measured that the Al-Nb phases epsilon (NbAl3), sigma (prototype sigma CrFe) and delta (prototype Cr3Si) have evident ternary extensions with maximal solubility of boron amount to 1.2, 10.4 and 3.2 at.%, respectively. The Al solubility in niobium borides is also significant. The obtained results were used to elaborate the thermodynamic description of this ternary system based on recently published thermodynamic models of the constituent binary subsystems using the CALPHAD approach (Thermo-Calc/PARROT). The Al-B-Nb reaction scheme, projections of the liquidus and solidus surfaces as well as a number of isothermal sections and isopleths were calculated using the proposed thermodynamic description and compared with the experimental results. The calculations were shown to reproduce adequate the experimental data. The main features of the phase equilibria in the range of melting/solidification are the existence of two quasibinary sections, NbAl3-NbB and NbB2-AlB12, eutectic L-E - epsilon + sigma + (NbB) at 1850 K and cascades of invariant U-type reactions.

The eutectic spacing (λ) was investigated in three alloys of succinonitrile–neopentylglycol–(D)camphor–aminomethylpropanediol (SCN–NPG–DC–AMPD) system over a wide range of temperature gradients (G) and growth velocities (V), both in thin ⩽5 μm (two-dimensional (2-D)) samples and in bulk (three-dimensional (3-D)) samples. The compositions were selected such that fraction of rod-forming phase (f) was equal to 11.5 vol.% for the invariant SCN–12.2 wt.% NPG alloy, 23.3 vol.% for the univariant SCN–24.2 wt.% DC–0.5 wt.% NPG alloy and 29.8 vol.% for the bivariant SCN–33.0 wt.% DC–6.0 wt.% NPG–3.0 wt.% AMPD alloy. For high G/V conditions significant deviations from growth at minimum undercooling were found with spacing selection closer to the pinch-off limit. The experimental results show that confining the 3-D eutectics to 2-D growth conditions invariably leads to larger values of the mean rod spacing, but to smaller values of the mean rod diameter. The 2-D/3-D ratio of the square of mean rod diameters η = d 2 D R / d 3 D R 2 was found to be independent of the phase fraction of the rod-forming phase f and equal to η = 0.80 ± 0.02. The 2-D/3-D ratio of square of rod spacing k = λ 2 D R / λ 3 D R 2 was found to dependent on f following k = ( 2 f ) - 1 or else k = η 3 8 π f - 1 . These findings are discussed in terms of the Jackson–Hunt model of eutectic growth and simple geometrical considerations.

Lamellar eutectic growth was investigated in the transparent organic alloy neopentylglycol-(D)camphor of eutectic composition (NPG-45.3 wt% DC) using bulk (3D) and thin (2D) samples. Two types of eutectic grains were observed in the polycrystalline samples, either with lamellae well aligned to the direction of solidification or inclined at an angle of 21.5±1.5°. The well aligned grains were used for determining lamellar spacing as function of growth velocity V and temperature gradient G . Based on these data the Jackson–Hunt constant was evaluated to be K JH =1.60±0.15 μm 3 s −1 . For low growth velocity experiments the contact angles for (DC) and (NPG) lamellae at eutectic triple junctions were also evaluated, being θ (DC) =50.9±4.1° and θ (NPG) =41.8±4.7°, respectively. Using these values, as well as phase diagram data and the Gibbs–Thomson coefficients, the chemical coefficient of diffusion of (D)camphor in the eutectic liquid at eutectic temperature 53 °C was estimated to be D L =97±15 µm 2 s −1 .

Alloys from the succinonitrile–(D)camphor (SCN–DC) system are widely used as model alloys for the in situ investigation of solidification using light optical microscopy, but literature on the binary phase diagram is contradictory with respect to the solubility limit of DC in (SCN). Phase equilibria of the system were therefore revisited experimentally and critically assessed in the present work. The results prove that the maximum solubility of DC in the succinonitrile solid solution (SCN) is far less 1 wt% and the volume fraction of the (DC) phase in the eutectic solid is 23.3%. On this basis and on recently reported experimental data the CALPHAD description of the SCN–DC system was re-optimized.

An experimental method for the in-situ observation of solidification in eutectic metallic alloys growing at moderate temperatures, i.e. 500–600 °C was developed. It is based on unidirectional solidification of thin samples (200 to 700 μm thick) contained in rectangular quartz glass tubes allowing for in-situ observation of growth on the sample surface by means of light microscopy using a long-distance microscope. The method is illustrated for two-phase eutectic growth in Al–17.5Cu–1.0Ag, Al–11.8Si and Al–11.8Si–0.025Sr as well as for three phase growth in Al–13.3Cu–5.7Si, all at%. Coupled growth of lamellar Al–Al2Cu eutectic in Al–17.5Cu–1.0Ag was investigated in more detail with regard to spacing selection: experiments were performed in a temperature gradient of 38±1 K cm−1 using different, but constant withdrawal velocities ranging from 0.025 to 1.8 μm s−1. Measured spacing was compared with literature data and discussed with reference to the Jackson–Hunt theory and the recent amendment proposed by Akamatsu, Faivre, Karma and Plapp. In-situ observations were complemented by post-mortem metallographic analysis using SEM and EBSD in transverse sections.

A new experimental method for in-situ observation of microstructure formation in top view during unidirectional solidification of bulk, transparent, organic alloys is presented. This method allows observing growth patterns over an extended interface area with high resolution and minimal optical aberrations. With (D)camphor – neopentylglycol – succinonitrile (DC–NPG–SCN) alloys a series of unidirectional solidification experiments were performed in order to validate the set-up. By means of multi-focus exposition eutectic cells were observed over a depth of several millimeters, followed by 3D reconstruction of their shape. The method also allows capturing the integral interface dynamics and measuring its relative undercooling.

In the present paper a thermodynamic description of the entire ternary Al–Ta–Ti system is proposed, being obtained by CALPHAD modelling. Dedicated experiments were performed in order to complement literature data on phase equilibria reported mainly for the temperature interval from 1273 to 1723 K. As-cast and annealed samples were investigated by means of DTA, pyrometry after Pirani–Alterthum, SEM/EDS, SEM/EBSD and XRD techniques in order to prove the phase relations in ranges of invariant equilibria at melting, α 2 + γ alloys and low-temperature ternary phases. The experiments revealed that two ternary phases exist in the Al–Ta–Ti system: the orthorhombic O-phase (Ti 2.17 Ta 0.77 Al 1.06 , Pearson symbol oC16 ) and the ordered B8 2 -phase (Ti 3.00 Ta 0.89 Al 2.11 , Pearson symbol hP6 ) are thermodynamically stable below 1123 K and 1171 K, respectively. The obtained and literature data were employed throughout the optimization work, using the PARROT module of Thermo-Calc. The elaborated thermodynamic description was applied to calculate selected phase equilibria as to provide a comparison between calculated and experimental data. The calculations are shown to reproduce correctly experimental data. They revealed the presence of a miscibility gap for the ternary (βTi,Ta,Al) solid solution in the temperature interval from 1461 to 813 K.

A crystallographic model is used to predict the nucleation potencies of TiB2 particles during solidification of TiAl-based alloys. Two nucleation scenarios are investigated. In scenario 1, primary TiB2 grows in the melt before formation of the body-centred cubic β phase. In scenario 2, secondary TiB2 precipitates after the first β phase but before formation of the hexagonal close-packed α phase. The model predicts high α and β nucleation potencies of TiB2 in both scenarios. However, pre-existing β grains in scenario 2 are predicted to be preferred α nucleation sites. The experimentally observed β refinement by primary TiB2 agrees with the model predictions. Grain refinement in scenario 2 is attributed to α nucleation on β, which is interleaved with secondary TiB2.

Phase relations in the binary Al–Ta system were re-assessed taking into account recent experimental data. Alloys of different composition were prepared and analyzed by means of DTA, DSC, pyrometry after Pirani–Alterthum, SEM/EDS and SEM/EBSD techniques in order to prove the phase relations in the system. Both, as-cast and annealed samples were investigated. A new thermodynamic description of the binary Al–Ta system was obtained by CALPHAD modeling of the Gibbs energy of all accepted individual phases, taking into account the above experimental data as well as assessed published data. Applying the results, calculations of the phase diagram and thermodynamic properties were performed with the Thermo-Calc software. They are shown to reproduce properly experimental data.

The thermodynamic description of the ternary system Al–B–Ti is obtained by modelling the Gibbs energy of all individual phases in the system using the CALPHAD approach. The model parameters have been evaluated using the computer optimization technique PARROT based on the available descriptions of the constituent binary systems Al–B, B–Ti and Al–Ti recently published and relevant experimental information on phase equilibria for the ternary system. For the ternary system Al–B–Ti the reaction scheme, projection of the liquidus, solidus and solvus surfaces, selected vertical and isothermal sections are calculated using the proposed thermodynamic description. An acceptable agreement between the calculations and experimental data is achieved.

The thermodynamic description of the entire ternary Al–Nb–Ti system is obtained by CALPHAD modelling of the Gibbs energy of all individual phases, taking into account experimental data on phase equilibria and thermodynamic properties published and complemented by own experiments. The description includes a re-evaluation of the constituent binary Al–Nb system. Selected equilibrium calculations were performed with the Thermo-Calc software using the proposed description. They are shown to well reproduce experimental data on both, phase equilibria and thermodynamic properties in the entire Al–Nb–Ti system.

The grain refinement achieved with low boron additions to selected TiAl-based alloys was investigated in unidirectional solidified samples by means of EBSD-orientation mapping of the α(Ti) phase, retained by quenching. The analysis shows that excellent grain refinement is achieved during the solid state transformation of the body centred β(Ti) into the hexagonal close packed α(Ti). It leads to a fairly random orientation of the α(Ti) grains which indicates that heterogeneous nucleation of α(Ti) on borides is at the origin of refinement. The borides were identified to be orthorhombic (Ti,Nb)B monoboride ribbons with the crystal structure of NbB. The refinement is severely impeded by peritectic growth of α(Ti): peritectic α(Ti) grains almost completely invade the microstructure by imposing their crystal orientation through all subsequent solid state transformations.

The thermodynamic description of the ternary system B–Nb–Ti is obtained by modelling the Gibbs energy of all individual phases in the system using the CALPHAD approach. The model parameters have been evaluated by means of a computer optimization technique based on the available descriptions of the constituent binary systems B–Nb, B–Ti and Nb–Ti and relevant experimental information on phase equilibria for the ternary system. The thermodynamic descriptions of both systems with boron, B–Nb and B–Ti, were published in the first part of the work. For the ternary system B–Nb–Ti several vertical and isothermal sections as well as the projection of the liquidus and solidus surface are calculated using the elaborated thermodynamic description. A tolerable agreement between the calculations and experimental data is achieved.

The temperature of phase transformations, as well as the enthalpy of melting of 29 different alloys from the Bi–In–Sn system were measured by DSC using a Perkin–Elmer DSC-7 instrument. The following tie-triangles were characterized in terms of analysing the chemical composition of the phases in equilibrium, using energy dispersive X-ray analysis (EDX): (Bi)–BiIn–(Sn) at 77 °C, BiIn 2 -β-γ at 59 °C including the composition of the liquid phase at 59 °C and the tie-line BiIn 2 -γ at 59 °C. A new thermodynamic description is presented for the ternary Bi–In–Sn system in the entire composition range. The parameters for the thermodynamic models of the constituent binary systems Bi–In, Bi–Sn and In–Sn are adopted from earlier assessments, and those for the Bi–In–Sn system are optimized in this study using experimental data on phase equilibria and data on the enthalpy of melting of different alloys available in the literature and measured in the present work. Several vertical and isothermal sections as well as the liquidus surface and selected thermodynamic properties are calculated using the thermodynamic description. They show reasonably good agreement with reported experimental data.

Several key experiments were performed to determine the temperature of transformations of organic alloys from the ternary systems 2-amino-2-methyl-1,3-propanediol–(D)camphor–succinonitrile (AMPD-DC-SCN) and 2-amino-2-methyl-1,3-propanediol–neopentylglycol–succinonitrile (AMPD-NPG-SCN) by means of differential scanning calorimetry (DSC). The phase diagrams of these ternary systems were assessed via the CALPHAD approach using Thermo-Calc and the experimental data on phase equilibria were determined by the above key experiments. Good agreement between the experimental and the calculated data was achieved for both ternary systems. Combining the obtained thermodynamic descriptions with those obtained for two other ternary systems, AMPD–DC–NPG and DC–NPG–SCN, published earlier, the thermodynamic description for the entire quaternary system was created. In order to identify the phases involved in solid–liquid equilibria and the nature of coupled eutectic growth in quaternary alloys, several unidirectional solidification experiments were performed: two quaternary alloys with composition 37.5SCN–44.5DC–16.5NPG–1.5AMPD (wt%) and 34SCN–44DC–19NPG–3AMPD (wt%) were used for the experiments on monovariant eutectic growth. We find that in the last alloy the monoclinic NPG phase is fully suppressed by the addition of AMPD and three solid phases show coupled eutectic growth at the solid/liquid interface: the hexagonal phase (DC solid solution), the FCC phase (NPG–AMPD solid solution) and the BCC phase (SCN solid solution). The quasi-2D eutectic patterns obtained in a thin sample show the stacking sequence –BCC–Hex–FCC–Hex–. The volume ratio of Hex:BCC:FCC phases equals 4:3:2. In the quaternary alloy with 1.5 wt% AMPD the monoclinic NPG phase is present at the solid/liquid interface and the eutectic growth is rather irregular.

The temperature and enthalpy of transformations of organic alloys from the ternary system 2-amino-2-methyl-1,3-propanediol–(D)camphor–neopentylglycol (AMPD–DC–NPG) were measured by means of differential scanning calorimetry (DSC). The phase diagram of this ternary system was assessed via the CALPHAD approach using Thermo-Calc based on the thermodynamic descriptions of the constituent binaries published earlier and on the thermodynamic and phase equilibrium data measured in the present work for ternary alloys. Good agreement between the experimental and calculated data was achieved. Experiments and calculations show that the AMPD–DC–NPG exhibits a nonvariant quasiperitectic reaction at 336.1 K and composition AMPD-17.5 mol% DC-42.56 mol% NPG, with all solid phases being nonfaceted. Unidirectional solidification experiments were performed with three different alloys selected such that each exhibits a small amount of the primary BCC (AMPD solid solution), the FCC (NPG solid solution) and the hexagonal (DC solid solution) phase, respectively, in order to verify the nature of the phases involved in solid–liquid equilibria and the nature of coupled growth in this ternary system. We find that in all these cases once steady state growth is reached two solid phases grow at the solid–liquid interface with a rod-like coupled growth pattern: The hexagonal phase (DC solid solution) and the FCC phase (NPG solid solution).

The temperature and enthalpy of transformations of organic alloys from the ternary systems (D)camphor–neopentylglycol–succinonitrile (DC–NPG–SCN) were measured by means of differential scanning calorimetry (DSC). The phase diagram of this ternary system was assessed via the CALPHAD approach using Thermo-Calc based on the thermodynamic descriptions of the constituent binary systems published earlier and the thermodynamic and phase equilibrium data for the ternary alloys measured in the present work. Proper agreements between the experimental and the calculated data were achieved. Experiments and calculations show that the DC–NPG–SCN exhibits a nonvariant eutectic reaction with the eutectic point at 297.0 K, 26.3 mol%DC and 14.8 mol%NPG. This eutectic reaction involves the ordered monoclinic crystals (OCs) of NPG and the orientationally disordered crystals (ODICs) of both, SCN (BCC_A2 phase) and DC (hexagonal phase). Unidirectional solidification experiments were performed with the nonvariant eutectic DC–NPG–SCN alloy in order to verify the phases involved in the solid–liquid equilibrium and the nature of eutectic growth. We find that in the eutectic alloy the eutectic growth is irregular: the extremely facetted monoclinic phase (NPG) grows as thin and long needle-like crystals that protrude far into the liquid and are then decorated with nonfacetted eutectic of BCC_A2 (SCN) and hexagonal (DC) lamellae, which mainly grow perpendicular to the growth direction of the monoclinic (NPG) needles. Few unidirectional solidification experiments were performed with dilute ternary alloys with composition close to the univariant eutectic reactions that extend from the constituent binary systems NPG–DC and SCN–DC, respectively. The destabilisation of planar eutectic interfaces due to constitutional supercooling were qualitatively monitored.

A technique widely used for the in situ observation of microstructure formation in transparent organic systems was applied to metallic alloys with low melting temperature. In the ternary eutectic alloy system In–Bi–Sn, we observed by light microscopy steady state and transient eutectic microstructure formation during unidirectional solidification in thin (5–10 μm) glass capillaries. Starting from an equilibrated planar single-phase front in a slightly off-eutectic alloy we studied the dynamic processes like nucleation of univariant, and finally invariant ternary eutectic when the liquid transforms into three distinct solid phases. Numerical microstructure simulation was performed by applying a general multiphase and multi-component phase field model which couples directly to the complete thermodynamic dataset of the In–Bi–Sn alloy system. Via comparison of the experimental to the simulated data some thermo-physical values like diffusion coefficients and critical undercooling for nucleation have been evaluated.

An experimental method is presented for the in situ observation of microstructure evolution during solidification or solid phase transformations in metallic alloys with low melting temperature. It is based on the direct observation of a thin metallic sample embedded between polished glass plates using a light microscope. The sample is placed in a Bridgman type furnace that enables unidirectional solidification under well defined conditions. As examples we show microstructures obtained during coupled, lamellar eutectic growth in two alloys with compositions close to the non-variant eutectic T E = 332 K from the Bi–In–Sn system for different solidification conditions. Stable lamellar patterns with an ABCB stacking sequence are found to be dominant for 2D-samples (∼10 μm in thickness), where A ≡ γ-Sn, B ≡ BiIn 2 and C ≡ β-In phase. The spacing of this stacking sequence was determined as a function of growth rate. The results are compared with the data for bulk (3D) samples of the same composition, taken from the literature. The direct observation of the microstructures at the solid/liquid interface allows the verification of the validity of two different descriptions of the Bi–In–Sn phase diagram proposed earlier, namely a description with eutectic and a second with peritectic reactions involving BiIn 2 , γ-Sn, β-In and liquid. All observed solidification patterns are consistent with the eutectic description.

The temperature and enthalpy of transformations of organic alloys from the binary systems neopentylglycol–succinonitrile (NPG–SCN) and 2-amino-2-methyl-1,3-propanediol–succinonitrile (AMPD–SCN) were measured by means of differential scanning calorimetry (DSC). The phase diagrams of these binary systems were assessed via the CALPHAD approach using Thermo-Calc by simultaneously optimizing the thermodynamic and phase equilibrium data measured in the present work. Proper agreements between the experimental and calculated data for the phase diagrams as well as for the thermochemical properties were achieved. Experiments and calculations show that both the NPG–SCN and the AMPD–SCN systems exhibit a non-variant eutectic reaction with the eutectic point at 90.45 mol% SCN (318.0 K) and at 97.39 mol% SCN (325.7 K), respectively. In the NPG–SCN system the temperature of the eutectic reaction is about 3 K higher than the temperature of the transformation from the ordered crystals (OCs) to the orientationally disordered crystals (ODICs), whereas the eutectic reaction in the AMPD–SCN involves the OCs of AMPD and the ODICs of SCN. Unidirectional solidification experiments were performed with selected NPG–SCN and AMPD–SCN alloys in order to verify phases involved in solid–liquid equilibria and the nature of eutectic growth in these systems. We find that eutectic growth in NPG–SCN eutectic alloy occurs with both solid phases being non-facetted and with a rod-like eutectic structure. The eutectic as well as some hypo-eutectic alloys from the AMPD–SCN system show irregular eutectic growth with a non-facetted BCC_A2 phase of SCN and a facetted monoclinic phase of AMPD.

Aiming to obtain a reliable description of the ternary Ag–Al–Cu system the thermodynamic evaluation of the constituent binaries Ag–Al, Ag–Cu and Al–Cu are revised by modelling of the Gibbs energy of all individual phases using the CALPHAD approach. The model parameters have been evaluated using a computer optimisation technique based on the established descriptions of the systems and taking into account the data on thermodynamic properties and phase equilibria both reported in recent publications and obtained by own measurements. The phase diagrams and the thermodynamic properties calculated with the evaluated parameters are in good agreement with the corresponding experimental data.

The thermodynamic description of the Ag–Al–Cu system is obtained by modelling the Gibbs energy of all individual phases in the system using the CALPHAD approach. The model parameters have been evaluated, by means of a computer optimisation technique, based on the descriptions of the constituent binaries proposed in the first part of the work and relevant experimental information for ternary alloys both from literature and own experimental measurements. Several vertical and isothermal sections, the liquidus surface and some thermodynamic properties are calculated using the evaluated parameters. A good agreement between the calculations and the experimental data is achieved.

Multiphase solidification in multicomponent alloys is pertinent to many commercial materials and industrial processes, while also raising challenging questions from a fundamental point of view. Within the past few years, research activities dedicated to multiphase solidification of ternary and multicomponent alloys experienced considerable amplification. This paper gives an overview of our present understanding in this field and the experimental techniques and theoretical methods research relies on. We start with an introduction to thermodynamic databases and computations and emphasize the importance of thermophysical property data. Then, we address pattern formation during coupled growth in ternary alloys and cover microstructure evolution during successive steps of phase formation in solidifying multicomponent alloys. Subsequently, we review advances made in phase field modeling of multiphase solidification in binary and multicomponent alloys, including various approaches to crystal nucleation and growth. Concluding, we address open questions and outline future prospects on the basis of a close interaction among scientists investigating the thermodynamic, thermophysical and microstructural properties of these alloys.

The temperature and enthalpy of transformation of organic alloys from the binary systems neopentylglycol-( d )camphor (NPG-DC) and 2-amino-2-methyl-1,3-propanediol-( d )camphor (AMPD-DC) were measured by means of differential scanning calorimetry (DSC). The phase diagrams of these binary systems were assessed via the CALPHAD approach using Thermo-Calc by simultaneously optimizing the thermodynamic and phase equilibrium data measured in the present work. Proper agreements between the experimental and calculated data for the phase diagrams as well as for the thermochemical properties were achieved. Experiments and calculations show that both the NPG-DC and the AMPD-DC system exhibit a nonvariant eutectic reaction with the eutectic point at 36.2 mol% DC and 326.0 K and at 9.3 mol% DC and 362.0 K, respectively. In each system the temperature of the eutectic reaction is higher than the temperature of the transformation from the ordered crystals to the orientationally disordered (plastic) crystals. Unidirectional solidification experiments were performed with several alloys in order to verify the nature of eutectic growth: We find that in both systems eutectic growth occurs with both solid phases being non-facetted and with a lamellar or rod-like eutectic structure. Due to the optical activity of DC its distribution in the solid samples is well detectible in polarised light.

The temperature and enthalpy of melting of organic alloys from the binary system 2-amino-2-methyl-1,3-propanediol (AMPD) and neopentylglycol (NPG) were measured by means of differential scanning calorimetry (DSC) within the entire composition range. The analytical description of the Gibbs energies of pure AMPD and pure NPG was derived utilizing the data on temperature and enthalpy of transformations, and temperature dependencies of the heat capacity available in the literature. The phase diagram for the binary AMPD–NPG system was assessed via the CALPHAD approach using Thermo-Calc by simultaneously optimizing the thermodynamic and phase equilibrium data available in the literature and measured in the present work. An excellent agreement between the experimental and calculated data for the phase diagram as well as for the enthalpy of melting of the organic alloys was achieved. Experiments and calculations show that the binary AMPD–NPG system exhibits an eutectic reaction with the eutectic point at 378.3 K and 42.2 mol% NPG. The enthalpy of formation of the liquid, BCC and FCC phases derived from the optimisation proves an attractive interaction between dissimilar molecules in these phases. Unidirectional solidification of the eutectic alloy was performed in order to check the nature of the eutectic growth: We find that both solid phases grow with a non-facetted solid/liquid interface, but growth of a regular lamellar eutectic structure could not be observed.

The temperature and enthalpy of transformations of organic alloys from the binary system succinonitrile-( d )camphor were measured by means of differential scanning calorimetry (DSC) within the entire composition range. The analytical description of the Gibbs energies of pure succinonitrile (SCN) and pure ( d )camphor (DC) were derived utilizing the data on temperature and enthalpy of transformations, and temperature dependencies of heat capacity available in the literature. The phase diagram for the binary SCN-DC system was assessed via the CALPHAD approach using Thermo-Calc by simultaneously optimizing the thermodynamic and phase equilibrium data available in the literature and measured in the present work. A good agreement between the experimental and calculated data for the phase diagram as well as for the thermochemical properties was achieved. Experiments and calculations show that the binary system SCN-DC has an eutectic reaction with the eutectic point at 311.5 K and 13.9 mol% DC. The enthalpy of mixing derived in the optimisation proves weak attractive interaction between dissimilar molecules. Unidirectional solidification of the eutectic alloy was performed in order to verify the nature of the eutectic: we find that eutectic growth occurs with both solid phases being nonfacetted and with a rod-like eutectic structure consisting of 23 vol% (DC) and 77 vol% (SCN). Due to the optical activity of DC its distribution in the solid sample is well detectible in polarised light.

Transparent organic alloys showing a plastic crystal phase were investigated experimentally using differential scanning calorimetry and directional solidification with respect to find a suitable model system for regular ternary eutectic growth. The temperature, enthalpy and entropy of phase transitions have been determined for a number of pure substances. A distinction of substances with and without plastic crystal phases was made from their entropy of melting. Binary phase diagrams were determined for selected plastic crystal alloys with the aim to identify eutectic reactions. Examples for lamellar and rod-like eutectic solidification microstructures in binary systems are given. The system ( d )Camphor–Neopentylglycol–Succinonitrile is identified as a system that exhibits, among others, univariant and a nonvariant eutectic reaction. The ternary eutectic alloy close to the nonvariant eutectic composition solidifies with a partially faceted solid–liquid interface. However, by adding a small amount of Amino-Methyl-Propanediol (AMPD), the temperature of the nonvariant eutectic reaction and of the solid state transformation from plastic to crystalline state are shifted such, that regular eutectic growth with three distinct nonfaceted phases is observed in univariant eutectic reaction for the first time. The ternary phase diagram and examples for eutectic microstructures in the ternary and the quaternary eutectic alloy are given.

The partial enthalpies of mixing of the components of liquid ternary Ag–Al–Cu ( T =1252±5 K) and Ag–Cu–Zn ( T =1068–1113 K) alloys have been determined using a high-temperature isoperibolic calorimeter. Measurements were performed starting from both pure Al and Zn and from binary liquid Ag–Cu alloys along sections with constant Ag:Cu ratios 1:3, 1:1, 3:1 (Ag–Al–Cu system) and 2:3, 3:2 (Ag–Cu–Zn system). The integral enthalpies of mixing of these ternary alloys are calculated from the partial enthalpies of mixing using different methods. The composition dependences of the partial and integral enthalpies were simultaneously analytically described according to a Redlich–Kister–Mugianu equation using a least-squares fit by Gauss–Newton method. In case of Ag–Al–Cu alloys square- and higher order terms in excess ternary part are needed to adequately describe the surfaces of enthalpies of mixing. Enthalpy data for the constituent binaries were adopted from latest calorimetric measurements and thermodynamic assessments of the phase diagrams. The evaluated integral enthalpy of mixing demonstrates that the minima for the Ag–Al–Cu (−17.1 kJ mol −1 ) and Ag–Cu–Zn (−10.0 kJ mol −1 ) correspond to binary compositions Al 0.40 Cu 0.60 and Cu 0.50 Zn 0.50 , respectively.