Search Results (31)

As a third-generation advanced high-strength steel (AHSS), δ-TRIP steel exhibits the characteristics of high strength, high plasticity, and low density. However, the addition of Al to steel will affect solidification and segregation, which may impact the final microstructure and mechanical properties of the product. In this study, thermodynamic calculations and microsegregation model analysis were employed to investigate the effects of Al addition on the solidification path, peritectic reaction range, equilibrium partition coefficients, and microsegregation behavior of δ-TRIP steel. The results show that with an increase in the Al content, the carbon content range in which δ ferrite is retained without complete transformation during the solid-state phase transition becomes broader. Simultaneously, the carbon concentration range of the peritectic zone expands. The segregation of the C, Si, Mn, P, and S elements increases with increasing Al content, whereas the segregation of Al decreases as the Al content increases. Under non-equilibrium solidification conditions, unlike equilibrium solidification, the temperature difference between the solid and liquid phases initially increases, then decreases, and subsequently levels off with further Al addition. This study provides information for the composition design and production process optimization of δ-TRIP steel, and the research results can provide a reference for similar high-aluminum, low-density steels. Full article

The self-foaming method offers a promising approach for producing AlCuFe metallic foams without the need for external foaming agents. Although it is well established that both alloy composition and heat treatment play a fundamental role in pore formation, the specific influence of annealing time on the resulting microstructure and physical properties remains insufficiently explored. In the present study, the effects of annealing time on the microstructure, phase evolution, and magnetic properties of self-foaming Al₅₈Cu₂₇Fe₁₅ alloys are investigated. Metallic foams were synthesized using the self-foaming method, heat-treating the samples at 850 °C for 6, 9, 15, and 24 h. X-ray diffraction (XRD), differential thermal analysis (DTA), and scanning electron microscopy (SEM) reveal that prolonged annealing increases porosity, reaching 64% and 61% after 15 and 24 h, respectively. The porosity formation mechanism was attributed to a peritectic reaction involving the liquid metastable τ phase and the solid λ and β phases. Magnetic measurements indicated complex behavior consistent with the Curie–Weiss law, influenced by phase composition and interactions between Coulomb forces, Hund’s rule exchange, and Fe 3d–Al s, p orbital hybridization. Full article

To investigate the relationship between microstructure, chemical composition, and thermoelectric properties, we have applied graded temperature heat treatments to recently developed τ₁-Al₂Fe₃Si₃-based thermoelectric (FAST) materials formed by a peritectic reaction. We investigated microstructures, chemical compositions, and Seebeck coefficients as continuous functions of heat treatment temperature. The τ1 phase can become p- and n-type semiconductors without doping by changing the Al/Si ratio. The Seebeck coefficient was maximized, exceeding |S| > 140 μVK⁻¹ for both p- and n-type materials, by heat treatment at 1173 K for 24 h through microstructural optimization. These results show that combining the graded temperature heat treatments and spatial mapping measurements of thermoelectric properties gives effective routes to determine the suitable heat treatment temperature for materials with multiphase microstructure. Full article

Al–Zn–Mg–Si alloy coatings have been developed to inhibit the corrosion of cold-rolled steel sheets by offering galvanic and barrier protection to the substrate steel. It is known that Fe deposited from the steel strip modifies the microstructure of the alloy. We cast samples of Al–Zn–Mg–Si coating alloys containing 0.4 wt% Fe and directionally solidified them using a Bridgman furnace to quantify the effect of this Fe addition between $600 °\mathrm{C}$ and $240 °\mathrm{C}$. By applying a temperature gradient, growth is encouraged, and by then quenching the sample in coolant, the microstructure may be frozen. These samples were analysed using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) to determine the morphological effects of the Fe distribution across the experimental temperature range. However, due to the sub 1 wt% concentration of Fe, synchrotron X-ray fluorescence microscopy (XFM) was applied to quantitatively confirm the Fe distribution. Directionally solidified samples were scanned at 7.05 keV and 18.5 keV using X-ray fluorescence at the Australian Synchrotron using the Maia array detector. It was found that a mass nucleation event of the Fe-based τ₆ phase occurred at $495 °\mathrm{C}$ following the nucleation of the primary α-Al phase as a result of a peritectic reaction with remaining liquid. Full article

The assembly of Ga alloys with Ni or Ni alloy has been widely developed for various low-temperature applications in recent years. In the constituent Ni-Ga binary system, however, the phase equilibrium with the phase “NiGa₅” and its stability has scarcely been investigated. The present study used the diffusion couple technique combined with SEM-EPMA and XRD analysis to examine the phase stability and the homogeneity range of the phase. The results show that “NiGa₅” is a stable phase in the binary system with little homogeneity range and suggest that the peritectic reaction $\mathrm{L}+{\mathrm{Ni}}_3{\mathrm{Ga}}_7\to {\mathrm{NiGa}}_5$ lies between 112.0 and 115.5 °C. This work provides new information for the modification of the Ga-rich low-T region of the Ni-Ga phase diagram. Full article

Extensive research has been conducted on Ti–Fe–Sn ultrafine eutectic composites due to their high yield strength, compared to conventional microcrystalline alloys. The unique microstructure of ultrafine eutectic composites, which consists of the ultrafine-grained lamella matrix with the formation of primary dendrites, leads to high strength and desirable plasticity. A lamellar structure is known for its high strength with limited plasticity, owing to its interface-strengthening effect. Thus, extensive efforts have been conducted to induce the lamellar structure and control the volume fraction of primary dendrites to enhance plasticity by tailoring the compositions. In this study, however, it was found that not only the volume fraction of primary dendrites but also the morphology of dendrites constitute key factors in inducing excellent ductility. We selected three compositions of Ti–Fe–Sn ultrafine eutectic composites, considering the distinct volume fractions and morphologies of $\beta$-Ti dendrites based on the Ti–Fe–Sn ternary phase diagram. As these compositions approach quasi-peritectic reaction points, the $\alpha$${}^{″}$-Ti martensitic phase forms within the primary $\beta$-Ti dendrites due to under-cooling effects. This pre-formation of the $\alpha$${}^{″}$-Ti martensitic phase effectively governs the growth direction of $\beta$-Ti dendrites, resulting in the development of round-shaped primary dendrites during the quenching process. These microstructural evolutions of $\beta$-Ti dendrites, in turn, lead to an improvement in ductility without a significant compromise in strength. Hence, we propose that fine-tuning the composition to control the primary dendrite morphology can be a highly effective alloy design strategy, enabling the attainment of greater macroscopic plasticity without the typical ductility and strength trade-off. Full article

Grain refinement in Al-Si alloys is crucial for enhancing material castability and mechanical properties. Industrial practice involves adding inoculants, composed of TiB₂ particles coated with metastable Al₃Ti via adsorption, to the melt. This introduces essential free titanium for metastable phase formation and subsequent growth restriction. The superstoichiometric grain refiner Al-5Ti-1B, with 2.2 wt.% free titanium, is applied for this purpose. A peritectic reaction forms α-aluminium from this layer. However, when silicon content exceeds 3.5 wt.%, grain coarsening occurs due to silicon’s detrimental effect. This study quantified silicon poisoning in an Al-10Si alloy using stoichiometric and superstoichiometric grain refiners through ASTM-standardized TP1 tests. Adding 0.02 wt.% tantalum acted as an antidote to the τ₁ phase, resulting in a finer microstructure. This was attributed to the formation of a Ta-rich layer on TiB₂ particles, which causes α-aluminium formation via a peritectic reaction without generating ternary phases with Ti or Si. Correlating to the increasing particle size curves from the TP1 tests, phases were collected in the filter cake with the help of a PoDFA apparatus. These could be examined more closely on the SEM and identified as needle- or plate-shaped. By using an EDS unit, the phases found were assigned to the poisoning phase and further investigated. After the addition of tantalum, a solubility of tantalum could be detected in former poisoning phases. In combination with the gradients of the grain size, it can thus be assumed that tantalum is both an antidote for silicon poisoning in the Al-Si-Ti system and can itself have a grain-refining effect in this system. Full article

The cooling paths and kinetics in the system Cu-Fe-O are investigated by the empirical micro- and nanoscale analysis of slags from the flash furnace smelter at Olympic Dam, South Australia. We aim to constrain the exsolution mechanism of delafossite (Cu¹⁺Fe³⁺O₂) from a spinel solid solution (magnetite, Fe₃O₄) and understand why cuprospinel (CuFe₂O₄) is never observed, even though, as a species isostructural with magnetite, it might be expected to form. Flash furnace slags produced in the direct-to-blister copper smelter at Olympic Dam contain four Cu-bearing phases: Cu-bearing magnetite, delafossite, metallic copper, and cuprite. Delafossite coexists with magnetite as rims and lamellar exsolutions, as well as bladed aggregates, associated with cuprite within Si-rich glass. The empirical compositions of magnetite and rim delafossite are (Fe²⁺_6.89Cu²⁺_0.86Co_0.13Mg_0.15Si_0.02)_8.05 (Fe³⁺_15.52Al_0.41Ti_0.01Cr_0.01)_15.95O₃₂, and (Cu¹⁺_0.993Co_0.002Mg_0.002)_0.997(Fe³⁺_0.957Al_0.027Ti_0.005Si_0.004)_0.993O₂, respectively. The measured Cu content of magnetite represents a combination of a solid solution (~6 mol.% cuprospinel endmember) and exsolved delafossite lamellae. Atomic-resolution high-angle annular dark field scanning transmission electron microscope (HAADF STEM) imaging shows epitaxial relationships between delafossite lamellae and host magnetite. Defects promoting the formation of copper nanoparticles towards the lamellae margins suggest rapid kinetics. Dynamic crystallization under locally induced stress in a supercooled system (glass) is recognized from misorientation lamellae in delafossite formed outside magnetite grains. The observations are concordant with crystallization during the cooling of molten slag from 1300 °C to <1080 °C. Melt separation through an immiscibility gap below the solvus in the system Cu-Fe-O is invoked to form the two distinct delafossite associations: (i) melt-1 from which magnetite + delafossite form; and (ii) melt-2 from which delafossite + cuprite form. Such a path also corroborates the published data explaining the lack of cuprospinel as a discrete phase in the slag. Delafossite rims form on magnetite at a peritectic temperature of ~1150 °C via a reaction between the magnetite and copper incorporated in the oxide/Si-rich melt. The confirmation of such a reaction is supported by the observed misfit orientation (~10°) between the rim delafossite and magnetite. HAADF STEM imaging represents a hitherto underutilized tool for understanding pyrometallurgical processes, and offers a direct visualization of phase relationships at the smallest scale that can complement both experimental approaches and theoretical studies based on thermodynamic modelling. Full article

Investigating the effect of Fe and Si is essential for any new Al-based composition, as these impurities can be easily found both after primary production and recycling. This study is dedicated to filling the gap in revealing the phase composition of an Al-6%Mg-2%Ca-2%Zn alloy after the combined and separate addition of Fe and Si. This was addressed by permanent mold casting and solid solution heat treatment. The investigation of slowly solidified samples also contributed to understanding potential phase transitions. It was found that the alloy containing 0.5%Fe can have nearly spherical intermetallics after heat treatment, whereas a higher Fe content brought the formation of a needle-shaped Al₃Fe intermetallic. We explain this by the formation of a ternary α-Al + Al₁₀CaFe₂ + Al₄Ca eutectic, which is more compact in as-cast condition compared to divorced binary α-Al + Al₄Ca and α-Al + Al₃Fe eutectics. Similarly, 0.5%Si readily incurred the formation of a needle-shaped Al₂CaSi₂ intermetallic, probably also by a binary reaction L → α-Al + Al₂CaSi₂. In the solidified samples, no Mg₂Si phase was found, even in slowly solidified samples. This is contrary to the thermodynamic calculation, which suggests a peritectic reaction L + Al₂CaSi₂ Mg₂Si. Interestingly, the addition of 0.5%Si caused an even coarser microstructure compared to the addition of 1%Fe, which caused the appearance of a primary Al₃Fe phase. We conclude that the new alloy is more tolerable to Fe rather than Si. Specifically, the addition of 0.5%Fe can be added while maintaining a fine morphology of the eutectic network. It was suggested that the morphology of eutectic and solid solution hardening governed the mechanical properties. The strength of the alloys containing separate 0.5%Fe (UTS = 215 ± 8 MPa and YS 146 ± 4 = MPa) and the combined 0.5%Fe and 0.5%Si additions (UTS = 195 ± 14 MPa and YS ± 1 = 139 MPa) was not compromised compared to the alloy containing 0.5%Si (UTS 201 ± 24 = MPa and YS = 131 ± 1 MPa). Full article

Melting phase relations of the diamond-forming olivine (Ol)–jadeite (Jd)–diopside (Di)–(Mg, Fe, Ca, Na)-carbonates (Carb)–(C-O-H-fluid) system are studied in experiments at 6.0 GPa in the polythermal Ol₇₄Carb_18.5(C-O-H)_7.5-Omp₇₄Carb_18.5(C-O-H)_7.5 section, where Ol = Fo₈₀Fa₂₀, Omp (omphacite) = Jd₆₂Di₃₈ and Carb = (MgCO₃)₂₅(FeCO₃)₂₅(CaCO₃)₂₅(Na₂CO₃)₂₅. The peritectic reaction of olivine and jadeite-bearing melts with formation of garnet has been determined as a physico-chemical mechanism of the ultrabasic–basic evolution of the diamond-forming system. During the process, the CO₂ component of the supercritical C-O-H-fluid can react with silicate components to form additional carbonates of Mg, Fe, Ca and Na. The solidus temperature of the diamond-forming system is lowered to 1000–1020 °C by the joint effect of the H₂O fluid and its carbonate constituents. The experimentally recognized peritectic mechanism of the ultrabasic–basic evolution of the diamond-forming system explains the origin of associated paragenetic inclusions of peridotite and eclogite minerals in diamonds, as well as the xenoliths of diamond-bearing peridotites and eclogites of kimberlitic deposits of diamond. Diamond-forming systems have formed with the use of material from upper mantle native peridotite rocks. In this case, the capacity of the rocks to initiate the peritectic reaction of olivine was transmitted with silicate components to diamond-forming systems. Full article

The plate-like iron-rich intermetallic phases in recycled aluminum alloys significantly deteriorate the mechanical properties. In this paper, the effects of mechanical vibration on the microstructure and properties of the Al-7Si-3Fe alloy were systematically investigated. Simultaneously, the modification mechanism of the iron-rich phase was also discussed. The results indicated that the mechanical vibration was effective in refining the α-Al phase and modifying the iron-rich phase during solidification. The forcing convection and a high heat transfer inside the melt to the mold interface caused by mechanical vibration inhibited the quasi-peritectic reaction: L + α-Al₈Fe₂Si → (Al) + β-Al₅FeSi and eutectic reaction: L → (Al) + β-Al₅FeSi + Si. Thus, the plate-like β-Al₅FeSi phases in traditional gravity-casting were replaced by the polygonal bulk-like α-Al₈Fe₂Si. As a result, the ultimate tensile strength and elongation were increased to 220 MPa and 2.6%, respectively. Full article

Inclusions in mantle minerals and xenoliths from kimberlites worldwide derived from depths exceeding 100 km vary in composition from alkali-rich saline to carbonatitic. Despite the wide distribution of these melts and their geochemical importance as metasomatic agents that altered the mineralogy and geochemistry of mantle rocks, the P-T range of stability of these melts remains largely undefined. Here we report new experimental data on phase relations in the system KCl–CaCO₃–MgCO₃ at 3 GPa obtained using a multianvil press. We found that the KCl–CaCO₃ and KCl–MgCO₃ binaries have the eutectic type of T-X diagrams. The KCl-calcite eutectic is situated at K2# 56 and 1000 °C, while the KCl-magnesite eutectic is located at K2# 79 and 1100 °C, where K2# = 2KCl/(2KCl + CaCO₃ + MgCO₃) × 100 mol%. Just below solidus, the KCl–CaCO₃–MgCO₃ system is divided into two partial ternaries: KCl + magnesite + dolomite and KCl + calcite–dolomite solid solutions. Both ternaries start to melt near 1000 °C. The minimum on the liquidus/solidus surface corresponds to the KCl + Ca_0.73Mg_0.27CO₃ dolomite eutectic situated at K2#/Ca# 39/73, where Ca# = 100∙Ca/(Ca + Mg) × 100 mol%. At bulk Ca# ≤ 68, the melting is controlled by a ternary peritectic: KCl + dolomite = magnesite + liquid with K2#/Ca# 40/68. Based on our present and previous data, the KCl + dolomite melting reaction, expected to control solidus of KCl-bearing carbonated eclogite, passes through 1000 °C at 3 GPa and 1200 °C at 6 GPa and crossovers a 43-mW/m² geotherm at a depth of 120 km and 37-mW/m² geotherm at a depth of 190 km. Full article

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 TiC_0.5S_0.5 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. Full article

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. Full article

An ordered ω-Al₄Cr phase synthesized recently by a high-pressure sintering (HPS) approach was calculated to be stable by density function theory (DFT), implying that high pressure can accelerate the disorder-order phase transitions. The structural building units of the ω-Al₄Cr phase as well as the non-stoichiometric disordered ε-Al₄Cr and μ-Al₄Cr phases have been analyzed by the topological “nanocluster” method in order to explore the structural relations among these phases. Both the ε-and μ-Al₄Cr phases contain the typical Macky or pseudo-Macky cluster, and their centered positions were all occupied by Cr atoms, which all occupy the high-symmetry Wyckoff positions. The mechanism of the pressure-induced disorder-order phase transitions from the ε-/μ-Al₄Cr to the ω-Al₄Cr phase has been analyzed. and the related peritectic and eutectoid reactions have been re-evaluated. All results suggest that the stable ω-Al₄Cr phase are transformed from the μ-Al₄Cr phase by the eutectoid reaction that is accelerated by high-pressure conditions, whereas the ε-Al₄Cr phase should form by the peritectic reaction. Full article