Study of the formation and intergrowth of granular eutectic in austenitic steel matrix composite by directional solidification technology

The formation and intergrowth of granular eutectic in austenitic steel matrix composite has been studied by directional solidification technology. The results indicate that the modifying element Si enhances the dendritic segregation of C and Mn. The surface active elements, such as Y and Ca, concentrate highly ahead of the solid-liquid (S-L) interface of the composite due to the nonequilibrium solidification. As a result, the S-L interface of the composite is unstable during solidification. The spatiotemporal condition of the formation and the growth of the granular eutectic is the formation of granular eutectic between austenitic dendrite arms at the end of solidification and its growth restricted by the austenitic dendrites. By the simulating eutectic growth of the granular eutectic by Fe−C−Mn alloy, the Si, Ca, and Y adsorb and enrich on the growing surface of the eutectic during crystallization, which makes the crystallization model of the eutectic turn from facet/nonfacet to nonfacet/nonfacet. The intergrowth of the eutectic can be explained by (1) the influence of the modifying elements on the crystallization of the eutectic, (2) the coarse solidification growth interface of the eutectic and the same growth rate for austenite and cementite ((Fe, Mn)₃C), and (3) the austenite and cementite ((Fe, Mn)₃C) have not lateral branch during eutectic growth.     

Phase Diagram of the Al2O3 – ZrO2 – Nd2O3 System. Part 2. Liquidus Surface

A projection of the liquidus surface has been constructed for the Al₂O₃ – ZrO₂ – Nd₂O₃ system. No ternary compounds and areas of solid solutions based on the components or the binary compounds have been identified. The liquidus surface is formed by eight binary-phase primary crystallization fields. There are four four-phase nonvariant peritectic equilibria, together with two four-phase nonvariant eutectic equilibria as well as one three-phase nonvariant eutectic equilibrium. As the ZrO₂ and NdAlO₃ phases interact with the other phases by a eutectic mechanism, it is possible to determine the composition of the material, to take advantage of the unique properties of the T and F solid solutions based on ZrO₂ with incorporation of the properties of other phases in the ternary system.     

Structure and phase composition of alloys of the Al-Ce-Cu system in the region of the Al-Al<Subscript>8</Subscript>CeCu<Subscript>4</Subscript> quasi-binary join

Phase diagram of the Al-Cu-Ce system is investigated in the region of the quasi-binary join Al-Al₈CeCu₄. The parameter of the eutectic reaction L → (Al) + CeCu₄Al₈ are found: T = 610°C; composition 14% Cu and 7% Ce. This eutectic has a dispersed structure, and the ternary compounds, which is involved in the eutectic, is capable to fragmentation and spheroidism in the course of heating starting from 540°C. It is shown that the region of optimal compositions of alloys based on the eutectic (Al) + CeCu₄Al₈ lies in narrow limits. This is caused by the fact that an abrupt decrease of the solidus and, as a consequence, significant broadening of the crystallization range occurs at a relatively small deviation from the ratio Cu: Ce = 2.     

Modeling structure parameters of irregular eutectic growth: Modification of Magnin-Kurz theory

A new approach to irregular eutectic growth (faceted/nonfaceted crystallization) in Fe-C and Al-Si alloys has been presented in this article. The results of unidirectional crystallization of the irregular eutectic in the Fe-C, Al-Si, and Al-Fe systems were used for the experimental verification of the resulting model. For the oriented graphite, α(Al)-Si and α(Al)-Al₃Fe eutectics, a decrease of the interlamellar spacing λ and in protrusion δ_β of the nonfaceted phase (austenite, α(Al)) by the leading faceted phase (graphite, silicon, and Al₃Fe), the increase of growth rate v was observed. The Magnin-Kurz theory of irregular eutectic growth has been modified in order to better understand the physical mechanisms driving the crystallization process. A comparison of the measured and calculated average λ values has revealed good agreement for the (γ)Fe-graphite, α(Al)-Si, and α(Al)-Al₃Fe eutectics. The developed model also considered the influence of the material constants of the examined alloys on the interlamellar spacing and protrusion of the leading phase—graphite, silicon, and Al₃Fe. It has been found that material constants such as the wetting angle, diffusion coefficient, and Gibbs-Thomson coefficient are of great importance in this eutectic growth.     

Phase diagram of the Al2O3-ZrO2-Sm2O3 system. II. Liquidus surface

A projection has been constructed for the liquidus surface on the plane of the concentration triangle for the Al₂O₃-ZrO₂-Sm₂O₃ phase diagram. There are no ternary compounds, or appreciable regions of solid solutions based on the components and the binary compounds. The liquidus surface is formed by nine fields of primary phase crystallization. There are five four-phase nonvariant peritectic equilibria, as well as two four-phase nonvariant eutectic equilibria, and one three-phase nonvariant eutectic equilibrium. As the ZrO₂ and SmAlO₃ phases interact with other phases by a eutectic mechanism, it is possible to combine the unique properties of the T and F solid solutions based on ZrO₂ with the properties of the other phases in the form of composites. __________ Translated from Poroshkovaya Metallurgiya, Nos. 3–4(448), pp. 28–35, March–April, 2006.     

Crystallization kinetics of amorphous magnesium-rich magnesium-copper and magnesium-nickel alloys

Amorphous magnesium-rich alloys Mg _y X_1-y (X=Ni or Cu and 0.82<y<0.89) have been produced by melt spinning. The crystallization kinetics of these alloys have been determined by in situ X-ray diffraction (XRD) and isothermal and isochronal differential scanning calorimetry (DSC) combined with ex situ XRD. Microstructure analysis has been performed by means of transmission electron microscopy (TEM) and electron energy loss spectroscopy (EELS). Crystallization of the Mg-Cu alloys at high temperature takes place in two steps: primary crystallization of Mg, followed by simultaneous crystallization of the remaining amorphous phase to Mg and Mg₂Cu. Crystallization of the Mg-Cu alloys at low temperatures takes place in one step: eutectic crystallization of Mg and Mg₂Cu. Crystallization of the Mg-Ni alloys for a Mg content, y>0.85, takes place in two steps: primary crystallization of Mg and of a metastable phase (Mg_∼5.5Ni, with Mg content y=0.85), followed by the decomposition of Mg_∼5.5Ni. Crystallization of the Mg-Ni alloys for a Mg content y<0.85 predominantly takes place in one step: eutectic crystallization of Mg and Mg₂Ni. Within the experimental window applied (i.e., 356 K<T<520 K and 0.82<y<0.89), composition dependence of the crystallization sequence in the Mg-Cu alloys and temperature dependence of the crystallization sequence in the Mg-Ni alloys has not been observed.     

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 Mg_0.6Bi_0.4 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 Mg_0.6Bi_0.4 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 Mg_0.6Bi_0.4 at the point of maximum temperature of the eutectic trough. J. D. ESDAILE, formerly Senior Principal Research Scientist, now deceased     

Phase diagram of the Al2O3 - ZrO2 - Nd2O3 system. III. Solidus surface and phase equilibria in alloy crystallization

A projection has been constructed for the solidus surface in the Al₂O₃ - ZrO₂ - Nd₂O₃ phase diagram on the plane of the concentration triangle, which consists of six isothermal three-phase fields corresponding to two nonvariant equilibria of eutectic type and four nonvariant ones of peritectic type, together with five lineated surfaces for the end of crystallization of the monovariant eutectics. The highest solidus temperature in the system is 2710°C, the melting point of pure ZrO₂ , and the least is 1675°C, the temperature of the ternary eutectic L ? β + F + NA. No ternary phases and no appreciable regions of solid solutions based on their components and the binary compounds have been observed. Data on the adjoining binary systems, liquidus and solidus surfaces allowed for construction of the phase equilibrium diagram together with a reaction scheme for the equilibrium crystallization of alloys in the Al₂O₃ - ZrO₂ - Nd₂O₃ system.     

Phase diagram of the Al2O3-ZrO2-Er2O3 system. II. Phase diagram liqiudus surface

The liquidus surface for the Al₂O₃-ZrO₂-Er₂O₃ phase diagram is projected for the first time onto a concentration triangle. No ternary compounds are found in the system. The liquidus surface is completed by eight primary crystallization fields. Four four-phase nonvariant eutectic equilibria, one four-phase nonvariant transformation equilibrium, and three three-phase nonvariant eutectic equilibria are found in the system. Since ZrO₂ interacts with other phases eutectically, the unique properties of ZrO₂-based T-and F-solid solutions can be combined with the properties of other phases of the ternary system in composite materials. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 1–2(453), pp. 64–71, 2007.     

Al2O3-ZrO2-Yb2O3 phase diagram. II. Liquidus surface

The liquidus surface for the Al₂O₃-ZrO₂-Yb₂O₃ phase diagram is constructed for the first time. No ternary compounds are found in the system. The liquidus surface is completed by seven primary crystallization fields. Two four-phase invariant eutectic equilibria, two four-phase invariant transition equilibria, and one three-phase invariant eutectic equilibrium are found in the ternary system. Since ZrO₂ interacts with other phases eutectically, composite materials can combine the unique properties of ZrO₂-based T-and F-phases with the properties of other phases of the Al₂O₃-ZrO₂-Yb₂O₃ system.     

Phase diagram of the Al2O3-ZrO2-Sm2O3 system. III. Solidus surface and phase equilibria in alloy crystallization

A projection has been constructed for the solidus surface in the Al₂O₃-ZrO₂-Sm₂O₃ phase diagram on the plane of the concentration triangle, which consists of seven isothermal three-phase fields corresponding to two nonvariant equilibria of eutectic type and five nonvariant equilibria of peritectic type, and also eight lineated surfaces for the end of crystallization of the binary eutectics. The highest temperature on the solidus surface is 2710°C, the melting point of pure ZrO₂, while the lowest is 1680°C, the temperature of the triple eutectic Al + F + SA. No ternary phases or appreciable regions of solid solutions based on the components and the binary compounds are observed. Data on the bounding binary systems, the liquidus and solidus surfaces have been used to construct the phase-equilibrium (melting) diagram together with a reaction scheme for the equilibrium crystallization of alloys in the Al₂O₃-ZrO₂-Sm₂O₃ system. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 56–64, May–June, 2006.     

Al2O3-ZrO2-Yb2O3 phase diagram. III. Solidus surface and phase equilibria in alloy solidification

The solidus surface for the Al₂O₃-ZrO₂-Yb₂O₃ phase diagram is plotted onto the concentration triangle for the first time. It consists of four isothermal three-phase fields that correspond to two invariant eutectic equilibria and two invariant peritectic equilibria. The solidus surface also includes five ruled surfaces representing the end of crystallization in binary eutectics. The highest solidus temperature in the system is 2710 °C, which is the melting temperature for pure ZrO₂, while the lowest temperature is 1765 °C, which is the melting temperature for the AL+F+Yb₃A₅ ternary eutectic. No ternary compounds or noticeable areas of solid solutions based on components and binary compounds are found in the ternary system. The phase equilibrium diagram and reaction scheme for the equilibrium crystallization of Al₂O₃-ZrO₂-Yb₂O₃ alloys are plotted using data on bounding binary systems and liquidus and solidus surfaces.     

Nucleation and growth kinetics of stable and metastable eutectics in FeSiB metallic glasses

Two iron-based metallic glasses, Fe₇₈Si₁₀B₁₂ and Fe₇₂Si₁₀B₁₈, have been examined in detail after partial crystallization at a series of temperatures. The number and size of the eutectic cells—of both stable and metastable eutectics—have been determined as functions of time and temperature and the results compared with theoretical nucleation models. It has been found that the extent to which quenched-in nuclei from the original planar flow casting operation influence the subsequent crystallization behaviour depends on alloy composition and on the annealing temperature. The results indicate that it is possible to control the type, number and size of the crystallization products in the microstructure by suitable choice of annealing conditions.     

Phase diagram of the Al2O3-ZrO2-Er2O3 system. III. Solidus surface and phase equilibria in alloy crystallization

The solidus surface for the Al₂O₃-ZrO₂-Er₂O₃ phase is projected for the first time onto the concentration triangle. It consists of five isothermal three-phase fields that correspond to four invariant eutectic equilibria, one invariant transformation equilibrium, and six ruled binary eutectic solidus surfaces. The highest solidus temperature in the system is 2710 °C, which is the melting point of pure ZrO₂, and the lowest is 1720°C, which is the melting point of the ternary eutectic AL + F + Er₃A₅. Neither ternary phases nor visible solid solution areas based on components and binary compounds are found in the system. Based on the data on bounding binary systems, liquidus, and solidus surfaces, the phase equilibrium diagram and reaction scheme for equilibrium crystallization of Al₂O₃-ZrO₂-Er₂O₃ alloys are constructed. __________ Translated from Poroshkovaya Metallurgiya, Vol. 46, No. 5–6 (455), pp. 74–83, 2007.     

Kinetics of crystal nucleation and growth in Pd40Ni40P20 glass

Samples of Pd₄₀Ni₄₀P₂₀ glass, produced by cooling the melt at 1 or 800 K/s, are heated in a differential scanning calorimeter to determine the crystallization kinetics. Optical microscopy shows that eutectic crystallization proceeds both by growth from the surface of the samples and by the growth of spherical regions around pre-existing nuclei in the interior. A modified Kissinger analysis is used to obtain the activation energy for crystal growth (3.49 eV). The steady state homogeneous nucleation frequency at 590K is ~ 10⁶ m⁻³ s⁻¹. This is estimated to be the maximum nucleation frequency: it is too low to account for the observed population of quenched-in nuclei, which are therefore presumed to be heterogeneous. The major practical obstacle to glass formation in this system is heterogeneous nucleation.     

Microstructural characteristics of Ni-Sb eutectic alloys under substantial undercooling and containerless solidification conditions

Both Ni-36 wt pct Sb and Ni-52.8 wt pct Sb eutectic alloys were highly undercooled and rapidly solidified with the glass-fluxing method and drop-tube technique. Bulk samples of Ni-36 pct Sb and Ni-52.8 pct Sb eutectic alloys were undercooled by up to 225 K (0.16 T _E ) and 218 K (0.16 T _E ), respectively, with the glass-fluxing method. A transition from lamellar eutectic to anomalous eutectic was revealed beyond a critical undercooling ΔT ₁*, which was complete at an undercooling of ΔT ₂*. For Ni-36 pct Sb, ΔT ₁*≈60 K and ΔT ₂*≈218 K; for Ni-52.8 pct Sb, ΔT ₁*≈40 K and ΔT ₂*≈139 K. Under a drop-tube containerless solidification condition, the eutectic microstructures of these two eutectic alloys also exhibit such a “lamellar eutectic-anomalous eutectic” morphology transition. Meanwhile, a kind of spherical anomalous eutectic grain was found in a Ni-36 pct Sb eutectic alloy processed by the drop-tube technique, which was ascribed to the good spatial symmetry of the temperature field and concentration field caused by a reduced gravity condition during free fall. During the rapid solidification of a Ni-52.8 pct Sb eutectic alloy, surface nucleation dominates the nucleation event, even when the undercooling is relatively large. Theoretical calculations on the basis of the current eutectic growth and dendritic growth models reveal that γ-Ni₅Sb₂ dendritic growth displaces eutectic growth at large undercoolings in these two eutectic alloys. The tendency of independent nucleation of the two eutectic phases and their cooperative dendrite growth are responsible for the lamellar eutectic-anomalous eutectic microstructural transition.     

Thermodynamic Analysis and Experimental Study of Composite Structure Formation in Eutectic Alloys α -Al + Mg2Si

The Al ― Mg ― Si phase diagram was studied and the formation conditions for a regular two-phase eutectic structure (α-Al + Mg₂Si) were established. Concentration limits were found for optimum alloy compositions with maximum melting point (～595°C) and a narrow (or zero) melting (crystallization) range (less than 5°C). The structures of these alloys are formed by Mg₂Si monocrystal fibers and lamellae with a high degree of ordering, located in the aluminum matrix.     

Structure and properties of multicomponent eutectic alloys based on chromium and titanium carbide

We have investigated alloys in the Cr-Mo-Ti-C, Cr-Re-Ti-C, and Cr-Mo-Re-Ti-C systems in the eutectic <Cr>+<TiC> crystallization region. We found a four component quasibinary eutectic <Cr, Mo>+<TiC> with 4–8 at. % molybdenum content with melting point 1630°C. Additions of 3–11 at. % Mo or 5–20 at. % Re to the base eutectic alloy Cr₇₉Ti₁₂C₉ doubles the Vickers hardness at 1000°C (to approximately 2000 MPa), and simultaneous introduction of molybdenum and rhenium (the alloy Cr₅₁Mo₈Re₂₀Ti₁₂C₉) raises the hardness to 3000–3500 MPa. Ukrainian Materials Science Institute, National Academy of Sciences, Kiev. Translated from Poroshkovaya Metallurgiya, Nos. 1–2, pp. 15–23, January–February, 1997.     

Grain refinement in aluminum alloyed with titanium and boron

The aluminum corner of the ternary Al-B-Ti diagram was explored. A eutectic: Liq — Al + TiAl₃ + (Al, Ti)B₂ was found at approximately 0.05 wt pct Ti, 0.01 wt pct B; 659.5‡C. TiB₂ and A1B₂ form a continuous series of solid solutions, but no distinct ternary phase was found. The addition of boron to aluminum-titanium alloys expands the field of primary crystallization of TiAl₃ toward lower titanium contents and steepens the liquidus. In equilibrium conditions, pronounced grain refinement is found only in alloys in which TiAl₃ is primary and nucleates the aluminum solid solution before any other impurity can act. The peritectic reaction facilitates this priority but it is not necessary for grain refinement. Because of the low diffusivity of titanium and boron in aluminum, equilibrium is seldom attained and in commercial practice grain refinement by TiAl₃ is found also outside its equilibrium field of primary crystallization.     

Solubility products of metal sulfides in molten salts: II. Measurements and calculations for lead sulfide in the LiCl-KCl and the LiCl-LiF eutectic compositions

The solubilities of lithium sulfide and the solubility products of lead sulfide in the LiCl-KCI and LiCI-LiF eutectic mixtures have been measured by an electrochemical titration method in the temperature range from 673 to 823 K. At 823 K, the solubility of Li₂S in the LiCI-LiF eutectic was much larger than in the LiCI-KCI eutectic (1.95 × 10⁻¹ compared with 3.50 × 10⁻³). The measured solubility product of PbS in the LiCI-KCI eutectic (1.0 × 10⁻¹⁰ at 823 K) did not differ greatly from that in the LiCI-LiF eutectic (6.8 × 10⁻¹¹ at 823 K).A priori calculations were made of the solubility products of PbS and several transition and heavy metal Sulfides in the molten LiCI-KCI eutectic at 723 K. Fundamental theories of reciprocal and additive ternary molten salt solutions are used to explain the influence of the solvent on the solubilities of Li₂S and on the solubility products of PbS. The correlation of experiments with theory illustrates the utility of known theories of ionic systems in making predictions of solubilities and solubility products in ionic systems.