Peritectic Reaction Research Articles

Insights into dendrite growth and phase transition during Cs2LiLaBr6 crystal growth

The lanthanum crystal Cs2LiLaBr6 (CLLB) has excellent scintillation properties for gamma/neutron discrimination. The initial melt with hyper-peritectic ratios (55 < LiBr/mol.% < 61) was found beneficial for CLLB crystal growth. The hyper-peritectic melt would pass though the peritectic point. However, the detailed process was still unknown. Herein, the dendrite growth and peritectic reaction were discovered near the peritectic point in CLLB single crystal ingots for the first time. The mechanism of dendrite growth was analyzed. The Cs2LaBr5-LiBr phase diagram was modified according to these results. The understanding of phase transition and dendrite evolution can guide crystal growth of CLLB and other similar elpasolite crystals.

Precipitation of TCP phases with R/P intergrowth structure during directional solidification in a Ru-containing nickel-based single crystal superalloy

The topologically close-packed (TCP) phases with R/P intergrowth structure formed at the final stage of directional solidification in a Ru-containing nickel-based single crystal (Ni-SX) superalloy were investigated. The nodular TCP phases were distributed in the interdendritic regions of the as-cast microstructure. Precipitation of the β-NiAl phases and the subsequent incomplete peritectic reaction (Liquid + β-NiAl → γ′ + β-NiAlresidual) resulted in the accumulation of the TCP-forming elements (Cr, Co, Mo, W, Ta, and Re) in the residual liquid around the β-NiAl phase, which provided a favorable nucleation condition, leading to the precipitation of TCP phase in the vicinity of the β-NiAl phases. In addition, the TCP phases were found to be the R/P intergrowth structure with an orientation relationship of [2,7,10]R//[001]P and (322¯)R//(200)P, (44¯2)R ∼3.2° from (11¯0)P. Further, the formation mechanism of these TCP phases with R/P intergrowth structure was systematically discussed in terms of crystal structure, interface characteristics, and chemical composition. The result can provide theoretical guidance and experimental data for the composition design and heat treatment process optimization of the novel Ru-containing high-generation Ni-SX superalloys.

Ultra-fine Nbss/Nb5Si3 in situ composites with remarkable properties prepared by ultrasonic melt treatment

In order to refine coarse silicide and improve mechanical performance of ternary Nb-20Si-5Mo alloy, ultrasonic vibration treatment for ultra-high temperature melt is successfully applied. The results show that the vibration can improve the fluidity and reduce the shrinkage defects. The hypereutectic microstructure transforms into the fine rod-like eutectic. Due to the solute redistribution in ultrasound field, the Mo-rich layer at Nbss and β-Nb5Si3 phase boundary and the semi-coherent relation can be observed. Mo tends to dissolve in Nbss the matrix phase and inhibit the peritectic reaction. The average size of primary silicide is refined from 49.1 to 2.2 µm with 95.52% refinement efficiency, the compressive strength and fracture toughness of 100 s ultrasonic treated specimen improved 6.84% and 50.75% compared with the as-cast specimen, respectively. The heightened constitutional supercooling and the accelerated nucleation caused by cavitation effect are the main reasons of grain refinement.

Changes in the physical and mechanical properties of aluminum depending on the composition of the alloying elements

Subject of research: the influence of the concentration and composition of alloying elements Mn, Ti, Cr, Y, Mo, W, V on the change in the aluminum recrystallization temperature.&#x0D; Purpose of research: to find the optimal concentration of alloying additives, at which the recrystallization temperature reaches its maximum value.&#x0D; Methods and objects of research: using the methods of thermodynamic analysis of binary state diagrams of aluminum with alloying additives, it has been established that the nature of the change in the recrystallization temperature depends on what type of eutectic or peritectic reaction the formation of intermetallic compounds belongs to. It is shown that aluminides act as alloy modifiers and impart high mechanical properties to products.&#x0D; Main results of research: it was found that for the AlMn system, the optimal content of Mn should be considered 0.2%, for the AlCr system, the maximum increase in the Al recrystallization temperature is observed at 0.6% Cr, for the AlY system, the mechanical properties of Al at elevated temperatures maximum at 1% Y.

Thermodynamic modeling of the Fe-Sn system including an experimental re-assessment of the liquid miscibility gap

The usage of low-grade ferrous scrap has increased over decades to decrease CO2 emissions and to produce steel products at a low cost. A serious problem in melting post-consumer scrap material is the accumulation of tramp elements, e.g., Cu and Sn, in the liquid steel. These tramp elements are difficult to remove during conventional steelmaking processes. Sn is considered as one of the most harmful tramp elements because, together with Cu, it sometimes induces the liquid metal embrittlement in high-temperature ferrous processing, e.g., continuous casting and hot rolling. Furthermore, the chemical interaction between Fe and Sn plays an important role in the Sn smelting process. The raw material used in the Sn smelting process is SnO2 (cassiterite), in which Fe3O4 is a gangue in the Sn ore. In the process, the reduction of Fe3O4 is unavoidable, which results in forming a Fe-Sn alloy (hardhead). The recirculation of the hardhead decreases the furnace capacity and increases the energy consumption in the smelting. The need to efficiently recover Sn from secondary resources is therefore inevitable. The CALculation of PHAse Diagrams (CALPHAD) approach helps to predict the equilibrium state of the multicomponent system. Previously reported studies of the Fe-Sn system show inconsistencies in the calculations and the experimental results. Mainly the miscibility gap in the liquid phase was under debate, as experimental data of the phase boundary are scattered. Experimental study and re-optimization of model parameters were carried out with emphasis on the correct shape of the miscibility gap. Three different experimental techniques were employed: differential scanning calorimetry, electromagnetic levitation, and contact angle measurement. The present thermodynamic model has higher accuracy in predicting the solubility of Sn in the body-centered cubic (bcc), compared to previous assessments. This is achieved by re-evaluating the Gibbs energies of the FeSn and FeSn2 compounds and the peritectic reaction related to Fe5Sn3. Also, the inconsistencies related to the miscibility gap around XSn = 0.31-0.81 were resolved. The database developed in the present study can contribute to the development of a large CALPHAD database containing tramp elements.

Thermodynamic Simulation of Solidification of Ti-Containing Steels with Consideration for Possibility of Peritectic Transformation and Second Phase Precipitation

An algorithm is proposed for predicting the phase composition of titanium-containing steels after solidification. The approach is based on thermodynamic calculations and provides for crystallization through the formation of ferrite and austenite, as well as a peritectic reaction. The algorithm takes into account the possibility of precipitation of TiN, TiS, MnS and TiC0.5S0.5 from the liquid phase upon crystallization. Two possible behaviors of ferrite upon crystallization are considered: frozen and fast diffusion of elements in the metal sublattice of this phase. Calculations illustrating the operation of the proposed algorithm have been performed.

Grain refinement and abnormal peritectic solidification in WxNbTiZr high-entropy alloys

The microstructures of many high-entropy alloys (HEAs) can be understood or controlled based on traditional phase formation mechanisms. In this study, peritectic solidification was introduced to HEAs by designing novel WxNbTiZr peritectic high-entropy alloys (PHEAs). The phase constitutions and solidification microstructure evolutions of WxNbTiZr were clarified by combining experiments and thermodynamic simulations. Grain refinements were achieved in WxNbTiZr, which should attribute to the high growth restriction factors introduced by W solute and the segmentations of the primary phase during peritectic transformation. The significantly refined grains can simultaneously enhance the strength and ductility of the alloy. High fractions of peritectic phases and special pearl chain structures that are highly likely the products of peritectic solidification are seen in WxNbTiZr but not in the typical binary W-Zr peritectic alloy, highlighting that the compositional complexity featured by PHEAs could heavily influence peritectic reaction. The PHEAs idea is also generalized by developing WxMoTiZr alloys.

The influence of the main alloying elements on the formation of the initial grain structure, on phase transformations and on structural changes that occur during superplastic deformation of alloys Al - 4.1 wt.% Mg - 0.5 wt.% Zr, 1420T, 1421, 1423

The article presents the results of research aimed at revealing the influence of the main alloying elements on the formation of the initial grain structure, on phase transformations and on structural changes that occur during superplastic deformation of several aluminum alloys. It was possible to form a homogeneous ultrafine-grained structure in samples of alloys Al - 4.1 wt.% Mg - 0.5 wt.% Zr and 1423 due to dynamic recrystallization during their superplastic deformation. It is revealed that the initial microstructure of the 1420T alloy samples is bimodal. The average grain size is approximately 5 μm, in some areas of the working part of the samples there are large elongated grains, the average size of which is approximately equal to 25 μm. The initial structure of alloy 1421 samples is fine-grained, and the initial structure of alloy 1423 samples is multi-grained and coarse-grained. Metallographic studies showed that the grain structure of samples of alloys 1420T, 1421 and 1423 increases slightly during superplastic deformation at high homologous temperatures. Cavitation accumulates in the samples and structural changes occur, which are probably associated with local melting at grain boundaries and at interphase boundaries. It was established that the presence of zirconium and scandium additions in the composition of the samples ensures the formation of an ultrafine-grained structure in them and counteracts the grain growth during superplastic flow. Magnesium and lithium, which are included in the samples of the studied alloys 1420T, 1421 and 1423, form several intermetallic phases with aluminum. These phases are part of mixtures of crystals of peritectic origin, which are localized in the form of layers between some grains. The occurrence of peritectic reactions at high homologous temperatures can be one of the reasons for the partial melting of samples of alloys 1420T, 1421, and 1423 during their superplastic deformation. Partial melting of samples of alloys 1420T, 1421 and 1423 can probably be carried out due to the presence of segregations of magnesium and lithium at the grain boundaries, which lower the melting temperature of the aluminum-based solid solution. Partial melting of samples of alloys 1420T, 1421, and 1423 during their superplastic deformation, which is performed at high homologous temperatures, leads to the formation of cells of a metastable liquid-solid phase at the grain boundaries, the viscous flow of which leads to the formation of fibrous structures due to the development of grain boundary sliding.

Phase transformation mechanism and mechanical properties of Ti-45Al-8Nb alloy prepared by directed laser deposition

In this work, the Ti-45Al-8Nb alloy was fabricated by directed laser deposition. The phase transformation mechanism and mechanical properties were analyzed. The results show that different solidification paths were found. In the dendritic stem, the path is L → L + β → β → β + αβ → β + αβ + γ → α2 + γ + B2. At the periphery of the dendrite, the path is changed to L → L + β → αp → αp + γ → α2 + γ. The different solidification paths are due to elemental segregation, with Nb segregation in the dendritic stem leading to the formation of the B2 phase in α2 + γ lamellar. The decrease in Nb at the periphery of the dendrites leads to an L + β → αp peritectic reaction. The tensile strength and elongation are 365 ± 11 MPa and 0.36 ± 0.08%, respectively. Strength was higher than the methods of electromagnetic levitation cold crucible (EMLCC) and vacuum consumable arc melting (VCAM). The crack propagation model was analyzed, which was along the lamellar fracture and through the lamellar fracture.

Influence of the interaction between Si and Sc on the microstructure and tensile properties of as casted Al-Si-Sc alloys

Scandium (Sc) and silicon (Si) are effective for modifying Al based alloys, while their combined effect may be limited by some Si-Sc interaction, which was rarely reported. In this work, Al alloys with varying Si and Sc additions were prepared for microstructure characterization and tensile testing. The results show that Sc refines the α-Al grain via a heterogeneous nucleation induced by in-situ formed primary Al3Sc. A network AlSi2Sc2 phase was formed via a eutectic reaction and a bulk AlSi2Sc2 was generated from a peritectic reaction. Both AlSi2Sc2 competitively consumed the Sc solute in the same alloy, weakening the refining effectiveness of Al3Sc. The Sc also refined the eutectic Si to more ordered fiber/plate-like structure, and a proper ratio of Si to Sc could avoid the AlSi2Sc2 formation. When increasing Sc from 0.3 to 1.0 wt% in Al alloys containing 6 wt% Si, the ultimate tensile strength (UTS) and yield strength (YS) increased, but the EL decreased due to the presence of AlSi2Sc2 phase. The UTS and YS can increase along with a 41% raise in EL by a strategy combining higher Sc (>0.6 wt%) and a lower Si (<4 wt%) with Al3Sc in a dominant role in solidification reactions without AlSi2Sc2 formation. The mechanisms of microstructure modification with Si-Sc interaction are also discussed.

Nanostructured crystallization of casting alloys

Crystallization of casting alloys has been shown to be a nanostructured process. Microcrystals of phases in the temperature range of liquidus and solidus, during eutectic and peritectic reactions, are formed from nanocrystals of components A and B of alloys, their free atoms and atomic complexes. Microcrystals of primary austenite and austenite-graphite eutectics during crystallization of cast iron, microcrystals of austenite and δ-ferrite during crystallization of steel are formed as a result of nanostructural reactions from elementary nanocrystals of iron and graphite, free atoms of iron and graphite, iron-carbon complexes. Primary and eutectic microcrystals of silumin are formed from elementary nanocrystals of aluminum and silicon, free atoms of aluminum and silicon, aluminum-silicon complexes.

Phase field modeling of partial remelting during reheating of a multiphase peritectic solidification microstructure

While they are known for years to be the main source of equiaxed grains in metallurgical processes such as casting, melting and remelting phenomena currently receive an increasing attention owing to the developments of additive manufacturing. In multiphase alloys, i.e. having a eutectic or peritectic microstructure, these phenomena still remain poorly documented. In this work, the solidification and subsequent remelting of peritectic alloys have been studied using phase field simulations, with emphasis on the influence of the peritectic equilibrium, that yields the peritectic reaction L+β→α below the peritectic temperature and the reverse peritectic reaction α→L+β above. During solidification, the growth of the peritectic α phase has little influence on the growth of the pro-peritectic β phase. On the other hand, the evolution during remelting of a previously solidified peritectic microstructure is more complex and involves temperature gradient zone melting and liquid film migration phenomena. Close to the peritectic temperature, the reverse peritectic reaction is driven by liquid film migration, and some scenarii are evidenced depending on whether the growth takes place without triple junction from a pure α phase or with a triple junction along the α/β interface. At the scale of the mushy zone, the Temperature Gradient Zone Melting phenomenon also occurs but remains incomplete at the time scale investigated here. Finally, a new mechanism for fragmentation, induced by the reverse peritectic reaction during remelting, has been identified.

A high-withdrawing-rate method to control the orientation of (γ+α2) lamellar structure in a β-solidifying γ-TiAl-based alloy

β-solidifying γ-TiAl-based alloys with well-controlled lamellar orientation possess excellent mechanical properties, and low withdrawing rates are usually used to control the lamellar orientation by directional solidification. Herein, a high-withdrawing-rate method to control the lamellar orientation in a β-solidifying γ-TiAl-based alloy, TNM alloy (Ti-43.5Al–4Nb–1Mo-0.1B at.%), is proposed by Bridgeman directional solidification. Using this method, polysynthetic twinned (PST) single crystal of TNM alloy with a good lamellar controlling result is obtained. The mechanism of lamellar orientation controlling lies in the process of solidification and β/α transformation, which are governed by thermal stabilization treatment and withdrawing rate. Thermal stabilization treatment for 60 min can make the sample maintain stable interfaces of liquid/solid and β/α phase with a high temperature gradient before the withdrawing process starts, and it also leads to the incline of β dendrites; a high withdrawing rate of 100 μm/s can accomplish the grain selection of α phase during β/α transformation and make complete peritectic reaction occur. Compared with as-cast one, PST single crystal specimen has its room-temperature tensile property enhanced greatly, and presents an ultimate tensile strength/strain of 476 MPa/1.75% with a trans-lamellar fracture morphology.

Experimental investigation and thermodynamic assessment of the Al–Er system

The phase equilibria of the Al–Er binary system have been investigated through both experiments and CALPHAD assessment. The phase relationship in the compositional range of 0–50 at. % Er was experimentally redetermined using scanning electron microscopy (SEM) with Energy Dispersive Spectroscopy (EDS), electron probe micro analysis (EPMA) with wavelength dispersive spectrometer (WDS), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The results confirmed the existence of the Al3Er phase (Al3Ho-type structure) with limited homogeneity range in the Al–Er system. It was formed through the peritectic reaction L + Al2Er ↔ Al3Er at 1105.3 ± 2.4 °C. While the Al17Er2 phase was proved to be metastable in the present work. A full thermodynamic optimization of the Al–Er binary system has been carried out by utilizing the current experimental data as well as all available results in the previous publications. A set of self-consistent thermodynamic parameters for the Al–Er system was established. The calculated phase diagram and thermodynamic properties agree well with the available data. The artificial inverted liquid-liquid miscibility gap at high temperature in the previous evaluation is removed.

Formation of late Miocene silicic volcanic rocks in the central Tibetan Plateau by crustal anatexis of granulites

Partial melting of granulites generates melts, which causes the modification of continental crust. However, the detailed mechanisms of this partial melting and related magmatic processes are debated. In this study, we investigated how crustal melting of granulites generated late Miocene (ca. 6.0 Ma) silicic volcanic rocks in the Chibuzhangcuo area of the Qiangtang Block, Tibet. Various peritectic textures (e.g., quartz inclusions in clinopyroxene and fluorhydroxyl phlogopite) suggest that the pyroxenes were derived from a residual granulite phase and peritectic reactions, and were then entrained into the partial melts. The F-rich mica, granulite mineral assemblages, and high titanomagnetite–ilmenite (811–975 °C) and zircon saturation (836–867 °C) temperatures indicate the silicic magmas were high-temperature and water-poor. The geochemical and isotopic compositions of the silicic volcanic rocks are similar to those of middle–lower crustal intermediate–mafic granulite xenoliths in Cenozoic volcanic rocks in the Qiangtang Block. We suggest that these volcanic rocks were generated by partial melting of hydrous mineral-bearing granulites, triggered by an underlying thermal anomaly associated with the high crustal heat-flow of the central Tibetan Plateau. This work indicates that the occurrence of restitic hydrous mineral and perturbation of thermal anomaly are the primary conditions to cause the partial melting of granulite. As the melting went on, the residual granulite phase and peritectic minerals were likely to be preferentially entrained into the melt due to the erosion effect caused by the continued melt flow at the sites of melting.

The production of in situ (Mo,Ti)(C,N)-based cermets without a core/rim structure by reaction hot pressing: Formation mechanism and mechanical properties

A novel reaction hot pressing process was developed for the fabrication of in situ (Mo,Ti)(C,N)-based cermets without a conventional core/rim structure. Moreover, the reaction mechanism of the Co–Mo–Ti–TiN–C system was investigated. The results indicate that the allotropic transformation of hexagonal εCo→cubic αCo occurred first. Then, solid-state reactions of powder mixtures were conducted, which contributed to the synthesis of Mo2C, CoTi2, and TiC. Continuous heating induced a peritectic reaction of CoTi2→CoTi + Co–Ti liquid. The presence of a Co–Ti liquid facilitated the dissolution of C, and the production of a Co–Ti–C melt. In the liquid, TiC was prepared. Then, in situ TiC was combined with ex situ TiN to synthesise Ti(C,N). As the temperature increased, Mo/Mo2C diffused into whole Ti(C,N) particles, resulting in the formation of micro coreless (Mo,Ti)(C,N) grains. Subsequently, residual Mo2C and part of (Mo,Ti)(C,N) dissolved into a Co–Ti–C liquid, resulting in the formation of a Co–Mo–Ti–N–C melt. Once the liquid became saturated, ultrafine (Mo,Ti)(C,N) particulates with a weak or non-existent core/rim structure were precipitated. (Mo,Ti)(C,N)-based cermets can be prepared at 1523 K. An increased sintering temperature enhanced the relative density and homogeneity of the cermets, eliminated the by-products Mo2C and Co3Mo, and promoted the formation of more ultrafine (Mo,Ti)(C,N) particles. These effects increased the hardness and fracture toughness of the prepared cermets. The results of this work provide valuable guidance for the development of in situ coreless Ti(C,N)-based cermets.

On the microstructure of as-cast Zn-based ternary alloy

There are limited investigations of the alloys that involve peritectic reactions, due to its complexity. In the present study, casting experiments in a steel mold of square section were carried out in order to show a formal characterization of a zinc-based ternary alloy that has a complex microstructure. The results obtained confirm that instead of the typical structure of primary phase surrounded by peritectic phase on Zn-Ag peritectic systems, a AgZn dendritic phase, a mixture of two solid solutions (η-Zn and AgZn3), precipitates, and a eutectic-like lamellar structures with atomic ratio of Zn/Ag/Mg ~95/3/2 were observed.

Exploring Cu-Ge alloys as filler materials for high vacuum brazing application of W and CuCrZr

Cu-Ge system was evaluated for its application as a filler material in W-CuCrZr joints proposed as heat sink components of the future fusion power plants. The selected compositions were rich in Cu, with the aim of retaining the ductility that characterizes copper metal. Three compositions (Cu-13.5Ge, Cu-19.5Ge and Cu-33.2Ge) and two manufacturing routes (flexible and rigid tapes) were evaluated and characterized thermally, microstructurally and mechanically. The brazing temperature decreased as the Ge content increased, giving rise to less base material thermal affectation. The microstructure was dominated by several peritectic reactions that hinder the solid state diffusion control, and three main phases (Cu solid solution, ε and ζ) were detected both in the solidified filler drop and in the joint braze. In addition, the rigid filler manufacturing route seemed to produce more continuous joints due to its more homogeneous composition. The mechanical properties indicated that both lower and richer Ge compositions gave rise to joints with higher strength.

Relationship between Austenite‐Stabilizing Elements and Austenite Fraction in Near‐Rapidly Solidified Fe–Mn–Al–C Lightweight Steel

A peritectic reaction (liquid + δ‐ferrite → γ‐austenite) and eutectoid reaction (γ‐austenite → α‐ferrite + κ carbide) occur in the Fe–Mn–Al–C lightweight steel. Experimental results show that the main constituent phase of the near‐rapidly solidified Fe–Mn–Al–C lightweight steel is γ‐austenite and/or δ‐ferrite in this study, and the eutectoid reaction is restrained by the rapid cooling rate. With the increase of C content, the γ‐austenite fraction of near‐rapidly solidified medium‐Mn and high‐Mn Fe–Mn–Al–C lightweight steels increase significantly. However, in the early study, the increased Mn content had little effect on the γ‐austenite fraction of the near‐rapidly solidified Fe–(8/12/16)Mn–9Al–0.8C steel strips. This study attempts to reveal the reasons for the different effects of Mn and C on Fe–Mn–Al–C lightweight steel strip under near‐rapid solidification. It is found that the γ‐austenite fraction of the near‐rapidly solidified Fe–Mn–Al–C steel strip is closely related to the γ‐austenite fraction at the end of equilibrium solidification. This suggests that the main constituent phase of lightweight steel strip depends on its liquid–solid phase transformation under near‐rapid solidification and is seldom affected by solid phase transformation.

Study of Wettability and Solderability of SiC Ceramics with Ni by Use of Sn-Sb-Ti Solder by Heating with Electron Beam in Vacuum.

The aim of this research was to study the wettability and solderability of SiC ceramics by the use of an active solder of the type Sn5Sb3Ti in a vacuum by electron beam heating. This solder exerts a narrow melting interval, and only one thermal effect, a peritectic reaction, was observed. The liquidus temperature of the solder is approximately 243 °C. The solder consists of a tin matrix where the Ti6(Sb,Sn)5 and TiSbSn phases are precipitated. The solder wettability on a SiC substrate decreases with decreasing soldering temperature. The best wetting angle of 33° was obtained in a vacuum at the temperature of 950 °C. The bond between the SiC ceramics and the solder was formed due to the interaction of Ti and Ni with silicon contained in the SiC ceramics. The formation of new TiSi2 and Ti3Ni5Si6 phases, which form the reaction layer and thus ensure the bond formation, was observed. The bond with Ni is formed due to the solubility of Ni in the tin solder. Two phases, namely the Ni3Sn2 and Ni3Sn phases, were identified in the transition zone of the Ni/Sn5Sb3Ti joint. The highest shear strength, around 40 MPa, was attained at the soldering temperature of 850 °C.