Eutectic Trough Research Articles

Phase-Field Simulation of the Microstructure Evolution in the Eutectic Alloy NiAl-31Cr-3Mo

The directionally solidified eutectic alloy NiAl-(Cr,Mo) is a promising candidate for structural applications at high temperatures, due to its increased creep resistance compared to its single phase B2ordered NiAl counterpart. This system yields an eutectic trough connecting the invariant reactions of the ternary alloys NiAl-Cr and NiAl-Mo. During directional solidification (DS) along this trough the evolved microstructures of the two-phase eutectic is changing from fibrous to lamellar and back to fibrous morphology while increasing and decreasing the amounts of Mo and Cr, respectively. To investigate these effects in the morphology, the phase-field method has proven to be predestined in the last decades. However, as the modeling of quaternary systems is challenging for the simulation with a grand potential based phase-field model, the focus of this work is on the generation of a material model for one defined compound namely NiAl-31Cr-3Mo. The modeling is validated by investigating the microstructure evolution in two- and three-dimensional simulations of the DS process for two different growth velocities and by investigating their undercooling spacing relationships. The evolving microstructures obtained from three-dimensional large-scale simulations are presented and validated with corresponding micrographs from scanning electron microscopy (SEM) of directionally solidified samples with the same growth velocities. The simulation results show the theoretically expected behaviors and are in qualitative and quantitative accordance with DS experiments. The study of NiAl-31Cr-3Mo serves as the basis for a comprehensive data-driven analysis of microstructure properties and system quantities of the entire quaternary material NiAl-(Cr,Mo). With this, an accelerated design of advanced materials is promoted.

Microstructural Investigations of Novel High Temperature Alloys Based on NiAl-(Cr,Mo)

Apart from the reported transition from the fibrous morphology in NiAl-34Cr to lamellae by adding 0.6 at.% Mo, further morphology transformations along the eutectic trough in the NiAl-(Cr,Mo) alloys were observed. Compositions with at least 10.3 at.% Cr have lamellar morphology while the first tendency to fiber formation was found at 9.6 at.% Cr. There is a compositional range, where both lamellae and fibers are present in the microstructure and a further decrease in Cr to 1.8at.% Cr results in fully fibrous morphology. Alongside these morphology changes of the (Cr,Mo)ss reinforcing phase, its volume fraction was found to be from 41 to 11 vol.% confirming the trend predicted by the CALPHAD approach. For mixed morphologies in-situ X-ray diffraction experiments performed between room and liquidus temperature accompanied by EDX measurements reveal the formation of a gradient in composition for the solid solution. A new Mo-rich NiAl-9.6Cr-10.3Mo alloy clearly shows this effect in the as-cast state. Moreover, crystallographic orientation examination yields two different types of colonies in this composition. In the first colony type, the orientation relationship between NiAl matrix and (Cr,Mo)ss reinforcing phase was ( 100 ) NiAl|| ( 100 ) Cr,Mo and ⟨ 100 ⟩ NiAl|| ⟨ 100 ⟩ Cr,Mo. An orientation relationship described by a rotation of almost 60° about ⟨ 111 ⟩ was found in the second colony type. In both cases, no distinct crystallographic plane as phase boundary was observed.

Microstructure and Compression Properties of VSS‑V3B2 Eutectic Alloys in the V-Si-B System.

The present study reports on the microstructural evolution and room temperature plasticity of V(-Si)-B alloys with respect to the V solid solution (VSS)-V3B2 phase region. To investigate the occurring effects systematically, different binary V-B and ternary V-Si-B alloys were produced by conventional arc melting. Scanning electron microscope (SEM) analyses and X-ray diffraction (XRD) measurements were used to characterize the resulting as-cast microstructures. For the first time, the eutectic composition was systematically traced from the binary V-B domain to the ternary V-Si-B system. The observations discover that the binary eutectic trough (VSS-V3B2) seems to reach into the ternary system up to an alloy composition of V-5Si-9B. Room temperature compression tests were carried out in order to study the impact of single-phase and multi-phase microstructures on the strength and plasticity of binary and ternary alloys. The results indicate that the VSS phase controls the plastic deformability in the VSS-V3B2 eutectic microstructure whereas the intermetallic V3B2 acts as a strong hardening phase.

Effects of cooling rate and initial composition on the solidification path and microstructure of Al-Cu-Si alloys

ABSTRACTThe influences of cooling rate and initial composition on solidification path, microstructure and hardness of Al-Cu-Si alloys were investigated. The results indicate that the solidification paths of alloys Al-3.7Cu-6.5Si, Al-5.2Cu-2.6Si and Al-15.1Cu-6.2Si were (L + α-Al)→(L + α-Al+ β-Si)→(L + α-Al+ β-Si+ θ-Al2Cu), and the solidification paths of alloys Al-4.6Cu-0.9Si, Al-24.2Cu-3.9Si and Al-26.9Cu-2.1Si were (L + α-Al)→(L + α-Al+ θ-Al2Cu)→(L + α-Al+ β-Si+ θ-Al2Cu). Furthermore, it is found that the further the initial compositions from the binary eutectic trough and the slower the cooling rate was, the second dendrite arm spacing was larger and the volume percent of phase θ-Al2Cu was fewer, and then influence the hardness. There were three kinds of (α-Al+ θ-Al2Cu) binary eutectic, two kinds of (α-Al+ β-Si+ θ-Al2Cu) ternary eutectic and one kind of (α-Al+ β-Si) binary eutectic morphologies existed in the solidification specimens.

Experimental Investigation and CALPHAD Assessment of the Eutectic Trough in the System NiAl-Cr-Mo

NiAl-based alloys are promising candidates for high-temperature structural applications but their use is restricted by the limited mechanical properties. However, an improved performance can be achieved by strengthening the NiAl matrix with embedded fibers of refractory metals, such as Cr and Mo. Such composites can be manufactured in-situ by directional solidification of alloys with eutectic composition. For these processes the location of the eutectic trough in the NiAl-Cr-Mo system has to be known. The determination of the respective compositions was achieved by combining experimental investigations with computational thermodynamics. Thus, a series of melts in the NiAl-Cr-Mo system were prepared and their microstructures were investigated after solidification. The information on the primary phases was used to model the liquidus surface of the system NiAl-Cr-Mo using the CALPHAD approach. For this purpose, the thermodynamic datasets of the respective sub-systems from the literature have been combined into a quaternary database. The database will be used in the development of NiAl-based alloys for directional solidification. The dataset allows the calculation of the eutectic temperatures, the phase fractions and further thermodynamic properties along the eutectic trough. The present dataset will provide a reliable description for the NiAl-Cr-Mo system, but other regions of the Al-Cr-Mo-Ni system have an inferior representation.

Constitution of the ternary system Cr–Ni–Ti

Abstract The nature of solid–liquid phase equilibria in the ternary system Cr–Ni–Ti was investigated using electron microscopy, energy dispersive spectroscopy, X-ray diffraction, and differential thermal analysis. Literature data on solid state phase equilibria are confirmed. The Cr2Ti Laves phase modifications coexisting with Ni–Ti phases are clarified to be hexagonal C14-type and cubic C15-type. The C14-type Laves phase γCr2Ti is found to coexist with the liquid phase. It forms in the pseudobinary peritectic reaction pmax1 from L + β(Cr,Ti) at 1389 °C. On further cooling γCr2Ti + NiTi solidify at 1202 °C in the pseudobinary eutectic emax2. In the Cr-rich part of the system ternary eutectics occur at 1216 °C (E1: L = Ni3Ti + (Ni) + β(Cr,Ti)) and 1100 °C (E2: L = NiTi + Ni3Ti + β(Cr,Ti)), respectively. No ternary eutectic is found in the Ti-rich part. Rather the eutectic trough ends in the binary eutectic L = NiTi2 + β(Ti).

A novel concept for the preparation of alloy nanowires

AbstractA novel concept for the preparation of alloy nanowires has been developed. By combining two pseudobinary eutectic systems NiAl–W and NiAl–Cr with a completely miscible system Cr–W, a pseudoternary system was created in which there is large two‐phase field between NiAl and W(Cr) solid solutions, separated by a eutectic trough. This enables the fabrication of nanowires with compositions from pure W to pure Cr allowing a free change of the ratio. The directional solidification in the pseudoternary system has been carried out. For the first time alloy nanowires in the W–Cr system have been reported. In addition, nanowires of pure W and Cr were fabricated as well. Moreover, an electrochemical procedure for the release of nanowires from the matrix has been established. magnified image High yield of W–Cr alloy nanowires with equiatomic composition.

Reaction Scheme and Liquidus Surface of the Ternary System Aluminum-Chromium-Titanium

The constitution of the ternary system Al-Cr-Ti is investigated over the entire composition range using X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), differential thermal analysis (DTA) up to 1500 °C, and metallography. Solid-state phase equilibria at 900 °C are determined for alloys containing ≤75 at. pct aluminum and at 600 °C for alloys containing >75 at. pct Al. A reaction scheme linking these solid-state equilibria with the liquidus surface is presented. The liquidus surface for ≤50 at. pct aluminum is dominated by the primary crystallization field of bcc β(Ti,Cr,Al). In the region >50 at. pct Al, the ternary L12-type phase τ forms in a peritectic reaction pmax at 1393 °C from L + TiAl. Furthermore, with the addition of chromium, the binary peritectic L + α(Ti,Al) = TiAl changes into an eutectic L = α(Ti,Al) + TiAl. This eutectic trough descends monotonously through a series of transition reactions and ternary peritectics to end in the binary eutectic L = Cr7Al45 + (Al).

Reaction Scheme and Liquidus Surface in the Al-Rich Section of the Al-Cr-Ni System

The constitution of the ternary system Al-Cr-Ni is investigated over the entire composition range using X-ray diffraction (XRD), energy dispersive X-ray analysis (EDXA), differential thermal analysis (DTA) up to 1500 °C, and metallography. The ternary phase τ1 is confirmed. Its crystal structure, homogeneity range, and melting temperature are corroborated. Two additional ternary phases, labeled τ2 and τ3, are stable at 700 °C. Their compositions are Al77.5Cr12.5Ni10 and Al80Cr15Ni5, respectively. Their XRD powder patterns are shown. The isothermal section at 700 °C and the reaction scheme linking it with the liquidus surface are presented. The Al-rich part of the liquidus surface is characterized by an eutectic trough, which descends monotonously from the pseudobinary maximum emax1: L = NiAl + (Cr) at 1433 ± 1 °C through a series of transition reactions and ends in the ternary eutectic E2: L = Cr7Al45 + NiAl3 + (Al) at 639 °C.

On the reaction scheme and liquidus surface in the ternary system Al–Si–Ti

Abstract The constitution of the ternary system Al–Si–Ti is reinvestigated over the entire composition range using X-ray diffraction, energy dispersive X-ray analysis, differential thermal analysis up to 1500 °C and metallography. The ternary phases τ1 and τ2 are confirmed and their crystal structures and solid state phase equilibria are corroborated. The compositions observed confirm previous literature. The phase τ1 (I41/amd, Zr3Al4Si5-type) melts incongruently at 953 °C < T < 1000 °C into L + τ2 + TiSi2. The phase τ2 (Cmcm, ZrSi2-type) melts incongruently at 1338 °C into L + TiSi + TiSi2. The liquidus surface is characterized by a eutectic trough, which descends monotonically from the pseudobinary maximum emax1 L = βTi + Ti5Si3 at 1540 ± 5 °C through a series of transition reactions and ends in the ternary eutectic L = τ1 + (Si) + (Al) at 573 °C.

Oxidation behavior of multiphase Mo–Si–B alloys

The oxidation behavior of multiphase Mo, Mo 3Si, and Mo 5SiB 2 (T2) alloys was examined at 800 and 1300 °C. The alloys were cast and heat treated at 1600 °C before the cyclic oxidation tests were performed. The compositions of the alloys with Si/B ratios of 0.5, 0.71, and 1.0 were chosen near the L=(Mo)+T2 eutectic trough to produce a fine dispersion of the different phases. The multiphase alloys showed poor oxidation resistance at 800 °C while a protective glass scale formed at 1300 °C. At 800 °C the oxidation resistance improved as the volume fraction of the T2 phase increased. Conversely, at 1300 °C, the glass scaled that formed on the alloys with a Si/B ratio of 0.5 was not protective. However, a protective glass scale did form on the alloys with a higher Si/B ratio. The near eutectic alloy with a Si/B=1 was found to have the best oxidation resistance at 1300 °C. The results indicate the Mo 3Si phase provides a source of silicon for controlling the composition of the glass scale at 1300 °C.

Macrosegregation development during solidification of a multicomponent alloy with free-floating solid particles

The macrosegregation patterns and convective behavior of a Pb–5wt%Sb–35wt%Sn alloy are studied using numerical treatments of solid particle motion and of transport phenomena occurring during the solidification of ternary metal systems. At this composition, the solidification in the (Pb)–(SbSn) binary eutectic trough has a significant effect on these phenomena. The effects of this solidification path on fluid flow and macrosegregation are compared to the more familiar binary alloy patterns and the effect of solid particle transport is evaluated. The final predictions of macrosegregation are compared to measured composition profiles.

Effects of microstructure on the oxidation behavior of multiphase Mo–Si–B alloys

Abstract The oxidation behavior of multiphase Mo–Mo 5 SiB 2 (T2)–Mo 3 Si alloys was examined in terms of different starting morphologies and volume fractions of the phases. The multiphase alloys were cast and heat-treated at 1600 °C before performing the cyclic oxidation tests at temperatures between 600 and 1300 °C. Alloys compositions were chosen near the Mo–T2 eutectic trough resulting in microstructures containing either primary Mo-dendrites or primary T2-dendrites. After cyclic oxidation tests at 800 °C, a Mo interfacial layer was found adjacent to the T2 phase along the oxide/matrix interface while a Mo 5 Si 3 interfacial layer was found adjacent to the Mo 3 Si phase. For specimens tested at 1300 °C, a Mo+glass interfacial region was found. The multiphase alloys have a poor oxidation resistance at 800 °C due to the competing oxide formation of the Mo oxides and a silicate glass. However, a protective glass scale can form on these alloys at 1300 °C. The presence of Mo 3 Si was found to be an import source of Si in addition to the T2 phase in controlling the composition of the protective glass scale. The near-eutectic alloys with a fine dispersion of T2, Mo, and Mo 3 Si phases displayed the best overall oxidation resistance for the temperatures tested.

Variation of fiber morphology and crystallographic orientation relationship in directionally solidified NiAlMo alloys

In directional solidification of NiAlMo alloys solidifying along the monovariant eutectic trough L→γ + α, the morphology of α-Mo fibers and their crystallographic orientation relationship with the γ-NiAlCr matrix depend on growth rate and misorientation between the crystallographic [001] growth axis of the matrix and the local heat flow direction. At high growth rates and misorientations of more than 6 degrees, fibers can adopt a ribbon like shape but fibers and ribbons generally remain faceted, preserving the standard orientation relationship with the matrix. At low growth rates (< 2 cm/ h) and misorientations by more than about 10 degrees fibers become non-faceted and follow the Pitsch orientation relationship. Spacing of faceted fibers increases with increasing misorientation. If it is assumed that interface undercooling in eutectic growth is associated with maximum interface curvature and that eutectic growth occurs at minimum interface undercooling, spacing and morphological variations in faceted growth can be explained in terms of misorientation and interface energy. Simple structural criteria do not allow to identify the boundaries between matrix and fibers as well developed low-energy interfaces. There is evidence, however, that eutectic α fibers crystallize at the limit between faceted and non-faceted growth, and that fiber morphology is controlled by nucleation of new growth layers at the triple points between the γ-, α- and liquid phases. Solid state transformations change the volume fraction of fibers without much influencing fiber morphology. Concerning the phase diagram reported by Wakashima et al. [ Acta metall. 31, 1937 (1983)], displacement of phase boundaries in the vicinity of the ternary γ + γ' + α eutectic is proposed.

Crystallization studies in the lead-rich corner of the system Pb−Mg−Bi

Crystallizing experiments using slow cooling rates and uninterrupted stirring while periodically sampling the liquid phase are used to determine the areas of primary crystallization of Mg0.6Bi0.4 and lead in Pb−Mg−Bi alloys and the location of the line of the eutectic trough which separates these areas. The procedure involves the use of highly sheared and relatively large baths of lead alloys under a protective atmosphere of argon over a layer of silicone fluid, and a close approach to equilibrium conditions is demonstrated by approaching the eutectic trough from both sides. A maximum temperature in the eutectic trough occurs at 589.4 K, 0.18 pct Mg, and 1.84 pct Bi, and the ternary point occurs at 525.2 K, 2.334 pct Mg, and 0.0247 pct Bi. The solubility data are correlated using a thermodynamic procedure, and the equations obtained are used to calculate lines representing the Mg0.6Bi0.4 isotherms and the eutectic trough in satisfactory agreement with the experimental data. Calculated tie lines representing equilibrium between lead crystals and liquid along the eutectic solidus and trough at appropriate temperatures are also given, including that which is collinear with Mg0.6Bi0.4 at the point of maximum temperature of the eutectic trough.

Formation and magnetic properties of Fe-B-Si metallic glasses

The equilibrium solidification behaviour of Fe-rich Fe-B-Si alloys has been characterized in terms of primary and secondary crystallization, and correlated to metallic glass formation and properties. A eutectic trough extends from the binary eutectic on the Fe-B edge of the ternary composition diagram toward the binary eutectic on the Fe-Si edge. Metallic glass forming compositions closely follow the path of the eutectic trough, extending from the Fe-B edge to compositions containing approximately 20 at% Si. The relative ease of glass formation and the thermal stability of the glassy state are maximized at compositions along the eutectic trough. The magnetic coercive forces of both as-cast and annealed metallic glasses are minimized along the eutectic trough.

Crystallization kinetics in Fe−B−Si metallic glasses

Crystallization kinetics of Fe-B-Si metallic glasses, as characterized by the effective activation energy Ec and the Avrami exponent n have been studied using Differential Scanning Calorimetry. The data show that in the hypoeutectic (Fe-rich) region, the glasses crystallize into α-(Fe,Si) and Fe3B in that order. The growth of crystallites is diffusion controlled, and Ec falls off rapidly away from the eutectic trough. In the hypereutectic region, both crystalline phases are obtained simultaneously. Thermal stability is greatly enhanced by addition of Si(∼3 at. %) and the growth process is no longer purely diffusion controlled. The behavior of Ec and n versus composition is discussed. Effects on Ec and n of additions of small amounts of Ni and Mo are also reported. Such additions have direct relevance to the design of new glasses for applications at high frequencies.

The yttrium-rich side of the yttrium-niobium-titanium system

The ternary Nb-Ti-Y system was examined at the yttrium-rich corner and the position of the eutectic trough was determined. The compositions of the two binary eutectics Nb-Y and Ti-Y were shown to be slightly lower in solute content than previous literature data have indicated. It was demonstrated that aligned Nb-Ti filaments can be grown in an yttrium matrix by directional freezing of ternary Nb-Ti-Y alloys.

The cryoprotective properties of hydroxyethyl starch investigated by means of differential thermal analysis

Phase transition temperatures of the water-rich part of the H 2O-NaCl-HES ternary system have been studied by means of differential thermal analysis. The experimental data indicate that the protective action of the macromolecular agent HES is different from that of DMSO and glycerol which seems essentially to be due to colligative properties. As expected, there is no evidence of a significant freezing-point depression caused by HES concentrated up to 40 wt%. The occurrence of a ternary eutectic point may therefore be excluded. Instead, an isothermal eutectic trough is observed. The extrapolated course of its projection onto the basal composition triangle indicates that a certain portion of water is absorbed by HES and kept from freezing, i.e., appears to be thermally inert within the range of temperatures studied. The protective action of HES against solution effects, therefore, is attributed to its water-absorptive capacity and kinetics instead of a postponement of lethal salt enrichment to lower temperatures as caused by DMSO or glycerol. Consequently, it is possible to determine a minimum initial HES concentration that completely prevents lethal salt enrichment during cooling. For the case of red blood cells, the derived algebraic expression yields an initial HES fraction of 11 wt% if the respective values are inserted.

The constitution of copper-hardened samarium-cobalt permanent magnets

A study has been made of the constitution of copper-hardened samarium-cobalt alloys lying between SmCo 5 and Sm 2Co 17 and containing up to 20 at.% copper. It is found that copper exerts a strong influence; the 2:17 phase is repressed in favour of the 1:5 phase with the peritectic line changing to a eutectic trough. The solvus line of the 1:5 phase is displaced towards the 2:17 phase in the composition range studied. SmCu 5 and the 1:5 phase are mutually soluble above the latter's eutectoid transformation temperature, which falls as the copper level increases. Finally, the cobalt solid solution comes into direct equilibrium with a wide range of composition of the 1:5 phase in the ternary alloys (in the region of 800°C).