Eutectic Cells Research Articles

Investigation on effect of different types of inoculants on the solidification of ductile cast iron using thermal analysis

PurposeProducing superior-quality ductile cast iron demands the use of various intricate inoculants. In addition to iron and silicon, these materials also include alloying elements like calcium, barium, cerium, bismuth and zirconium. These elements are effective in minimizing carbide solidification and enhancing the formation of eutectic cells, thereby resulting in improved cast iron quality.Design/methodology/approachThis article discusses the findings of an investigation on how various inoculants impact critical thermal analysis parameters such as undercooling, recalescence and their correlation with the nucleation of graphite nodules and shrinkage tendency.FindingsFor the study, five distinct inoculants with varying active components in their chemical composition were utilized. The particular formulation of the inoculant has a notable impact on the extent of undercooling during the solidifying process of ductile cast iron. Investigation indicates that incorporating inoculant reduces the temperature at which austenite dendrites form and raises the eutectic freezing temperature. Upon analyzing the microstructure, it is found that the inclusion of inoculation led to a rise in the nodule count from 103 to 272 nodules.Originality/valueAn increased graphite factor, which denotes the growth of graphite nodules during the subsequent stage of the eutectic reaction, supports the benefits of inoculation. Ce and Bi-inoculation have increased the growth of graphite nodules in the cast area during solidification compared to other inoculant formulations. This enhanced production helps in decreasing the size of macroporosity.

Influence of heat treatment on the microstructure evolution and corrosion performance of biodegradable Zn-Mg alloys

Zinc and zinc-based alloys have garnered increasing attention as biodegradable materials due to their excellent mechanical properties, lower degradation rates compared to magnesium, and favorable biocompatibility. This study investigates the impact of homogenization treatment on the microstructure and corrosion behavior of Zn-Mg alloys using scanning electron microscopy, X-ray diffraction, hardness testing, and accelerated corrosion immersion tests. The results reveal that homogenization treatment induces the fusion of eutectic cells within the alloys, causing significant morphological alternations in the eutectic structure and varying proportions of the Mg2Zn11 phase, These changes notably affect material properties. The raised content of Mg2Zn11 phase in the eutectic structure correlates with higher hardness but reduced corrosion resistance, whereas the reduced Mg2Zn11 phase content leads to enhanced corrosion resistance. Furthermore, in-situ corrosion observations demonstrate that corrosion initiates at the eutectic phase, with corrosion pits forming due to the ion release as corrosion progresses, leading to gradual enlargement of the corrosion pits. In summary, this study provides comprehensive insights into the microstructural changes in Zn-Mg alloys and their impact on corrosion resistance, offering valuable references for their engineering applications.

The influence of trace vanadium on the solidification process, microstructure, and mechanical properties of gray cast iron

This study employed optical microscopy (OM), scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS) to investigate the impact of vanadium (V) on the microstructure and mechanical properties of gray cast iron (GCI) HT250. Additionally, Thermo-Calc software was employed to explore the influence of V on the solidification process. The results indicate that adding trace amounts of V in GCI forms a face-centered cubic VC phase, with the precipitation temperature of the VC phase gradually increasing. When the V content reaches 0.28 wt%, the VC phase begins to precipitate during the eutectic reaction. The incorporation of V consumes carbon, reducing the graphite content and promoting the formation of type D graphite. As the V content increases, there is an enlargement in the pearlite area ratio, a decrease in the pearlite layer spacing, and a reduction in the size of eutectic cells. These microstructural alterations lead to enhanced mechanical properties. The tensile strength peaks at 336 MPa with a V content of 0.77 wt%, representing a 29% increase compared to samples without added V. Similarly, the Vickers hardness increases with increasing V content, reaching a peak of 373 HV at 0.92 wt% V, a 27% increase compared to samples without V addition. However, at this point, the tensile strength decreases to 322 MPa.

A Model for the Effect of Microstructure on the Ultimate Tensile Strength of Cast Irons

AbstractThe aim of the present study is to elucidate the influence of individual microstructural parameters, such as pearlite fraction, nodularity, and eutectic cell size, on the tensile strength (UTS) of cast irons. The UTS model was built by integrating the rule of mixtures for each microstructural component, and the UTS was described as a function of the aforementioned factors. The UTS and the required microstructure parameters for the model calculation were obtained experimentally. In the model, two coefficients were introduced to quantify the influence of the eutectic cell size and the interaction terms for the mixed two components. These coefficients were determined through fitting the experimental data, and the model's accuracy was validated using data not included in the fitting process. The results exhibited reasonable agreement, confirming the model's reliability. The model, thus, offers insights into the influence of each microstructural factor on UTS and serves as a guide for designing alloys to achieve the desired UTS through microstructure modifications.

Microstructure evolution of dendrite and eutectic in undercooled Al70Ge30 alloy

Al-Ge eutectic alloy, as a desirable bonding material, has been widely used in microelectromechanical systems (MEMS) packaging. The bonding property of Al-Ge eutectic alloy is closely related to their microstructures. However, the microstructure evolution and underlying mechanisms in undercooled eutectic Al-Ge alloy remain unclear. In this work, Al70Ge30 alloy was prepared and subjected to undercooling using a cycled superheating purification technology. The maximum undercooling can reach 90 K (0.13TL). The solidified Al70Ge30 alloy exhibits concomitant dendrites and eutectic microstructures. The dendrites undergo rapid refinement at low undercooling and subsequently maintain nearly constant size as undercooling increases. Intriguingly, undercooling has a significant influence on eutectic microstructures. The eutectic microstructure transformed from feather structures to fishbone structures as undercooling increases then transformed into a line-like structure in eutectic cells. The evolution mechanisms of dendrites and eutectic structures are further elucidated based on several classical thermodynamic models. This study can provide theoretical and experimental guidance for the microstructure evolution of undercooled eutectic alloys with similar eutectic structures.

Relationships Between Macrostructure and Microstructure in Lamellar Graphite Iron Castings

AbstractSpherical sheet steel molds filled with gray iron melts of varying chemical compositions and metallurgical conditions were air-cooled until solid, followed directly by austempering to preserve the austenite grain structure. The castings were studied using a combination of cooling curves and quantitative metallography, in order to clarify control of the austenite grain structure and its impact on the local microstructure. A novel method utilizing fast Fourier transform provided visual overview of macroscopic trends in the scale of the flake graphite structure. Castings inoculated with Sr-containing ferrosilicon featured finer eutectic cell structure but coarser equiaxed structure of austenite, emphasizing that melt treatments applied to control the graphite structure may have unintended effects on the austenite grain structure. In most non-inoculated castings, the microstructure was banded, with alternating layers of coarse and fine flake graphite with distance from the casting surface. The extent of the columnar zone of austenite grains showed no correlation with the graphite structure nor the volume fraction of dendrites. The volume-to-surface ratio of dendrites was more uniform in the columnar zone, but increased toward the center in the equiaxed zone. The casting with the highest carbon equivalent (4.34), featured zones containing finer dendrites and graphite. These zones appear to be gaps in the early solidification structure which filled later by secondary dendritic growth from surrounding austenite. This highlights that high carbon equivalent may lead to poor dendrite coherency which can make the microstructure less uniform and less predictable.

Near Net Shape Manufacturing of Sheets from Al-Cu-Li-Mg-Sc-Zr Alloy.

Thin twin-roll cast strips from a model Al-Cu-Mg-Li-Zr alloy with a small addition of Sc were prepared. A combination of a fast solidification rate and a favorable effect of Sc microalloying refines the grain size and the size of primary phase particles and reduces eutectic cell dimensions to 10-15 μm. Long-term homogenization annealings used in conventionally cast materials lasting several tens of hours followed by a necessary dimension reduction through rolling/extruding could be substituted by energy and material-saving procedure. It consists of two-step short annealings at 300 °C/30 min and 450 °C/30 min, followed by the refinement and hardening of the structure using constrained groove pressing. A dense dispersion of 10-20 nm spherical Al3(Sc,Zr) precipitates intensively forms during this treatment and effectively stabilizes the structure and inhibits the grain growth during subsequent solution treatment at 530 °C/30 min. Small (3%) pre-straining after quenching assures more uniform precipitation of strengthening Al2Cu (θ'), Al2CuMg (S'), and Al2CuLi (T1) particles during subsequent age-hardening annealing at 180 °C/14 h. The material does not contain a directional and anisotropic structure unavoidable in rolled or extruded sheets. The proposed procedure thus represents a model near net shape processing strategy for manufacturing lightweight high-strength sheets for cryogenic applications in aeronautics.

Effect of Vanadium Addition on Solidification Microstructure and Mechanical Properties of Al-4Ni Alloy.

The effects of vanadium addition on the solidification microstructure and mechanical properties of Al-4Ni alloy were investigated via thermodynamic computation, thermal analysis, microstructural observations, and mechanical properties testing. The results show that the nucleation temperature of primary α-Al increased with increased vanadium addition. A transition from columnar to equiaxed growth took place when adding vanadium to Al-4Ni alloys, and the average grain size of primary α-Al was reduced from 1105 μm to 252 μm. When the vanadium addition was 0.2 wt%, the eutectic nucleation temperature increased from 636.2 °C for the Al-4Ni alloy to 640.5 °C, and the eutectic solidification time decreased from 310 s to 282 s. The average diameter of the eutectic Al3Ni phases in the Al-4Ni-0.2V alloy reduced to 0.14 μm from 0.26 μm for the Al-4Ni alloy. As the vanadium additions exceeded 0.2 wt%, the eutectic nucleation temperature had no obvious change and the eutectic solidification time increased. The eutectic Al3Ni phases began to coarsen, and the number of lamellar eutectic boundaries increased. The mechanical properties of Al-4Ni alloys gradually increased with vanadium addition (0-0.4 wt%). The Al-4Ni-0.4V alloy obtained the maximum tensile strength and elongation values, which were 136.4 MPa and 23.5%, respectively. As the vanadium addition exceeded 0.4 wt%, the strength and elongation decreased, while the hardness continued to increase. Fracture in the Al-4Ni-0.4V alloy exhibited ductile fracture, while fracture in the Al-4Ni-0.6V alloy was composed of dimples, tear edges, and cleavage planes, demonstrating mixed ductile-brittle fracture. The cleavage planes were caused by the primary Al10V and coarse Al3Ni phases at the boundary of eutectic cells.

Study on Dissolution of Ba-Containing Inoculant in Ductile Cast Iron Melt and Nucleation of Graphite

The production of high quality ductile cast iron requires different and complex inoculants. Besides iron and silicon, they also contain alloying elements such as zirconium, strontium, barium, calcium and rare earth metals. The addition of these elements reduces carbide solidification and increases the number of eutectic cells, which improves the quality of the cast iron produced. This study investigates the process of incipient melting of a complex barium inoculant and its effects on graphite nucleation. In the study, the sample was prepared by introducing the inoculant grain into the melt of the ductile iron. The region between the inoculant grain and the less inoculated matrix was examined metallographically using light and scanning electron microscopy. We used energy dispersion spectroscopy to determine the phases in the microstructure formed. It was found that graphite particles can already nucleate and grow in solid particles when the inoculant is still dissolving and also from the melt where the Ba and Ca concentrations are high and form BaO·CaO phases that serve as nuclei for graphite growth.

Transmission electron microscopy of the rapid solidification microstructure evolution and solidification interface velocity determination in hypereutectic Al-20at.%Cu after laser melting

The evolution of rapid solidification (RS) microstructure and solidification interface velocity has been studied experimentally by in-situ transmission electron microscopy and postmortem characterization for hypereutectic Al-20at.%Cu (37 wt.%Cu) after laser melting. Four morphologically distinct regions formed via growth modes changing from θ-Al2Cu phase dendrites to eutectic cell growth, possibly α-Al dendrite growth (α-cell), banded growth, and α-Al plane front growth. Tendency for faceting and low capacity for solute trapping limited the θ-phase dendrite growth to solidification interface velocity v < 0.07 m/s. Consequently, formation of pro-eutectic micro-constituent was suppressed, and RS microstructure formation was dominated by eutectic, α-cell, and banded morphology grains for the Al-20at.%Cu alloy. Eutectic growth operated for interface velocity of 0.1 m/s ≤ v < 0.3 m/s, with a transition from regular lamellar, 2-λ and 1-λ mode to a dense irregular morphology dominated by α-phase at v = 0.3 m/s. Interface temperature calculations indicated feasibility of α-cell growth mode for 0.3 m/s ≤ v < 0.7 m/s. Banded growth occurred for 0.7 m/s ≤ v < 1.3 m/s. Plane front α-phase growth was evident for interface velocities v ≥ 1.3 m/s. Previous work on rapid solidification microstructure development in hypereutectic Al-Cu alloys reported a regime of α-cell growth subsequently to eutectic and prior to transition to banded growth for Al-19at.%Cu (36 wt.%Cu), while for Al-22at.%Cu (40 wt.%Cu) eutectic growth transitioned directly to α-plane front growth without emergence of a banded regime. Based on the current study the disappearance of the banded growth regime occurs for a composition larger than 20at.%Cu.

Effect of Er addition on microstructural and mechanical properties of Al-11%Mg2Si alloy

During the solidification of Al-Mg2Si alloy, the eutectic Mg2Si phase with large size and flake-like morphology forms in the structure of the alloy which results in deterioration of mechanical properties; hence, modification/refinement of eutectic Mg2Si phase using alloying elements is a prime concern. Since there is a need to investigate further the characteristics of Al-Mg2Si alloy treated by rare earth additions, this study aims to investigate the influence of different Er concentrations (0.0, 0.1, 0.3, 0.5, and 1.0 wt%) on microstructure and mechanical characteristics of hypoeutectic Al-11Mg2Si metal matrix composite. The composite materials were prepared using an in-situ casting procedure with high purity of the elements. Microstructure characterisation was carried out by optical microscopy, in which an image analyser measured the eutectic Mg2Si cell sizes. The mechanical properties of the fabricated composites were analysed using tensile and hardness tests. The findings demonstrated that the morphology of primary Mg2Si changed with 0.1 wt% Er addition from irregular or dendritic shape to a polyhedral shape and becams uniformly distributed. Microstructural observations also showed that in the Al-11Mg2Si phase, the structure of the eutectic Mg2Si phase was altered from a flake-like structure to a fibrous structure, and the size of the black embedded structures decreased from 188.7 µm in the base alloy to 168.9 µm in the alloy added with 0.1 wt% Er. Further studies on mechanical properties found that 0.1 wt% of Er addition was optimum for enhancing the hardness, UTS, and elongation values, in which the harness value increased from 67.9 to 77Hv, UTS increased from 126 to 131 MPa and elongation (%) from 1.53 to 1.60. The SEM micrographs of the composite fracture surface depicted that with the addition of Er, the brittle fracture mode changed to the ductile mode with fine dimples.

A Thermal Conductivity Model for Grey Iron

Thermal conductivity is an important property for many iron cast components, and the lack of widely accepted thermal conductivity model for cast iron, especially grey cast iron, motivates the efforts in this research area. The present study contributes to understanding the effects alloy microstructure has on thermal conductivity. A thermal conductivity model for a pearlitic cast iron has been proposed, based on the as-cast alloy composition and microstructural parameters obtained at different solidification rates. According to the model, available parallel heat transfer paths formed by connected graphite flakes across eutectic cells are determined by the space between dendrite arms. The uncertainties both for model inputs and for validation measurements have been estimated. Sensitivity analysis has been conducted to result in better understanding of the model behaviour. The agreement between modelled and measured thermal conductivities has been achieved within 5% on the average for the investigated samples.

Zn additions modifying microstructure, thermal parameters and cytotoxicity of Sn-0.7Cu eutectic solder alloys

Alloys from the SnCu systems have superior properties as compared to the SnPb alloys, such as mechanical and corrosion resistance. However, SnCu alloys still exhibit low oxidation resistance, poor wettability and low reliability. One way to optimize such properties is by adding alloying elements, such as zinc. Zn is generally used in Pb-free solder alloys to minimize intermetallic compound growth in soldered joints, refine the microstructure and increase mechanical strength, in addition to reducing the final cost. The addition of Zn is motivated by the effects it promotes such as microstructural refining, suppression of intermetallics in the substrate/alloy reaction layer, increase in fluidity and mechanical properties. Therefore, this study aims to understand the effects of Zn additions (0.2 and 0.5 in wt%) on solidification thermal parameters (growth rate-V and cooling rate-Ṫ), macrostructure, microstructure, phase transformation, macrosegregation and cytotoxicity in directionally solidified eutectic Sn-0.7wt.%Cu alloy under transient heat flow regime of solidification in copper sheet. Thus, the samples have been characterized by Optical Microscopy (OM), Scanning Electron Microscopy (SEM), X-Ray Fluorescence (XRF) and X-Ray Diffraction (XRD). The CALPHAD (CALculation of PHAse Diagrams) method by Thermo-calc software was used to generate property diagrams and isopleths. Cytotoxicity analysis was performed based on cell viability with incubation periods of 15 and 30 days for the alloys, with subsequent exposures of the extracts for 24 and 48 h. The Zn additions caused slight changes in the phase transformation temperatures of the Sn-Cu-Zn alloys. Macrostructures exhibiting columnar-to-equiaxed transition (CET) were observed for the Sn-Cu-Zn alloys. The microstructures of the Sn-Cu-Zn alloys were predominantly dendritic with a matrix rich in tin (β-Sn) surrounded by a eutectic mixture of the β-Sn + Cu6Sn5 + CuZn phases. After CET on Sn-Cu-Zn castings, low velocity eutectic cells have been observed. Moreover, Zn additions refined and did not change the dendritic arrangement of the Sn-Cu-Zn alloys, when compared to the Sn-0.7wt.%Cu alloy. However, increasing the Zn content did not affect the microstructural scale in the ternary alloys when compared to each other. The variations in the microstructural scale did not influence the toxicity of the examined alloys, but factors such as incubation time and chemical composition did. In general, Zn improved the cell viability of the Sn-Cu-Zn alloys, but still with moderate cytotoxic levels.

Effect of V-Mn-Cr inoculant on microstructure and mechanical properties of grey cast iron

ABSTRACT In this study, the effects of different composition V-Mn-Cr inoculants on the microstructure and mechanical properties of GCI were investigated through Optical microscope (OM), Scanning electron microscope (SEM), Energy-dispersive spectroscopy (EDS), X-ray diffraction (XRD), etc. The results showed that the optimum quantity of inoculant was 7% V, 1% Mn and 6% Cr, and compared with the commercial inoculant samples, the tensile strength, Brinell hardness, and elastic modulus of the V-Mn-Cr inoculant samples increased by 16.7%, 14.2%, and 12.8%, respectively. V-Mn-Cr inoculants were found to refine austenite, graphite, pearlite and eutectic cells size, reduce pearlite lamellar spacing, and increase pearlite and eutectic cells number, thus improving mechanical properties. In addition, graphite nucleation substance may consist of oxides (SiO2, FeO, Cr2O3), carbides (SiC, TiC), sulfides (MnS, FeS), and XO·SiO2 silicates (X: Mn, Fe, Ca).

Effect of hydrogen pressure on pore growth and microstructure of GASAR porous Mg–Ag eutectic alloys

In order to study the effect of hydrogen, as a third non-metallic component, on the macroscopic pore growth and eutectic solidification structure in the directional solidification process, GASAR porous Mg–Ag eutectic alloy ingots were prepared by mould casting technology at different hydrogen pressures. The results show that with an increasing hydrogen pressure, the increased temperature gradient promotes the nucleation and growth of pores; for the microstructure, the increased temperature gradient cause an increasing driving force for solidification structure growth, which leads to the instability of the eutectic cells, and the eutectic structure transitions from lamellar to rod-like.

Enhanced mechanical properties by eutectic cells in AlSi10Mg - A promising paradigm for strengthening aluminum in additive manufacturing

AlSi10Mg, as-built by laser powder bed fusion, includes performance-enhancing refined eutectic cells invariably paired with performance-impairing melt pool boundaries, where the cell network coarsens and breaks down. Eliminating melt pool boundaries (and their associated anisotropy) is a motivation for conventional heat treatments but at the cost of removing the AM-specific eutectic cell strengthening. This work evaluates the advantages and disadvantages of retaining the AlSi10Mg cell network (with melt pool boundaries) via direct aging, in contrast to a conventional (T6) approach, which relies primarily upon precipitation strengthening. We compare both heat treatment approaches and their impacts on microstructure, tensile properties, fracture, strain-hardening, and thermal stability. Direct aging achieves superior thermal stability and performance by preserving the as-built cell network and its exceptional strain-hardening capacity, despite the retained melt pool boundaries. As-built eutectic cells (which closely depend on build parameters and do not require post-processing) offer unique promise as potential enablers of voxel-by-voxel AM property control.

An Insight into the Defects-Driven Plasticity in Ductile Cast Irons.

The microstructure and tensile behavior of two heavy section castings that had chemical compositions typical of GJS400 were investigated. Conventional metallography, fractography, and micro-Computer Tomography (μ-CT) were employed, enabling the quantification of the volume fractions of eutectic cells with degenerated Chunky Graphite (CHG), which was identified as the major defect in the castings. The Voce equation approach was exploited to evaluate the tensile behaviors of the defective castings for integrity assessment. The results demonstrated that the Defects-Driven Plasticity (DDP) phenomenon, which refers to an unexpected regular plastic behavior related to defects and metallurgical discontinuities, was consistent with the observed tensile behavior. This resulted in a linearity of Voce parameters in the Matrix Assessment Diagram (MAD), which contradicts the physical meaning of the Voce equation. The findings suggest that the defects, such as CHG, contribute to the linear distribution of Voce parameters in the MAD. Furthermore, it is reported that the linearity in the MAD of Voce parameters for a defective casting is equivalent to the existence of a pivotal point in the differential data of the tensile strain hardening data. This pivotal point was exploited to propose a new material quality index assessing the integrity of castings.

Influence of Strengthening Elements and Heat Treatment on Microstructure and Fracture Toughness of NiAl-Cr(Mo)-Based Eutectic Alloy.

Due to their potential improvement of high-temperature properties, the refractory metal hafnium (Hf) and the rare earth holmium (Ho) have attracted much attention. In the present research, NiAl-Cr(Mo) eutectic alloys with different Ho and Hf additions were fabricated by conventional smelting method and heat-treated to study the synergetic influence of strengthening elements and heat treatment. The samples were characterized using XRD, SEM, and TEM, and the three-point bending test was performed to obtain fracture toughness. The results demonstrate that Hf addition leads to the formation of Ni2AlHf Heusler phase and that Ho promoted the formation of Ni2Al3Ho phase. The microstructure of the alloy is affected by thermal treatment, with the coarsening of eutectic lamellae after heat treatment. The mechanical properties are improved by Hf and Ho additions, with increased fracture toughness. Overall, this study provides insights into the microstructure and properties of NiAl-Cr(Mo) eutectic alloys and highlights the potential of Hf and Ho addition to improve room-temperature properties. Specifically, the as-cast NiAl-Cr(Mo)-Hf eutectic alloy contains a relatively fine NiAl/Cr(Mo) eutectic lamella but coarse eutectic cell with Ni2AlHf phase embellished along the cell boundary. Minor Ho addition induces the formation of Ni2Al3Ho phase, which leads to the coarsening of the intercellular region but contributes to the refining of eutectic cell. In addition, the synergetic effect of Ho and Hf promotes the precipitation of Ni2Al3Ho and Ni2AlHf phases in the intercellular zone and increases the interface dislocations. Heat treatment benefits the solid solution of Ni2Al3Ho and Ni2AlHf phases, which improves their size and distribution by secondary precipitation. The Ni2AlHf phase in the NiAl-Cr(Mo)-Hf eutectic alloy becomes fine and uniformly distributed, but the NiAl/Cr(Mo) eutectic lamella in the eutectic cell becomes coarse. In comparison, heat treatment mainly optimizes the size and distribution of the Ni2Al3Ho and Ni2AlHf phases in the NiAl-Cr(Mo)-Hf-Ho eutectic alloy. Furthermore, heat treatment helps to eliminate the interface dislocations in the large NiAl precipitates and the NiAl/Cr(Mo) phase interfaces, which also contributes to fracture toughness by decreasing stress concentration. Minor Ho addition decreases the fracture toughness of as-cast NiAl-Cr(Mo)-Hf eutectic alloy from 6.7 to 6.1 MPa·m1/2, which should be ascribed to the coarsened intercellular region including aggregated Ni2Al3Ho and Ni2AlHf phases. However, minor Ho-doped NiAl-Cr(Mo)-Hf eutectic alloy obtained the highest fracture toughness of 8.2 MPa·m1/2 after heat treatment. This improved fracture toughness should be mainly attributed to the refined and well-distributed Ni2Al3Ho and Ni2AlHf phases in the heat-treated NiAl-Cr(Mo)-Hf-Ho eutectic alloy.

Ultrasounds induced eutectic structure transition and associated mechanical property enhancement of FeCoCrNi2.1Al high entropy alloy

One dimensional (1D) and three dimensional (3D) ultrasound sources were applied to modulate the solidification process of FeCoCrNi2.1Al high entropy alloy whose liquidus temperature is up to 1614 K with the acoustic signal in liquid alloy in-situ measured. It was found that 1D ultrasound significantly refined the lamellar eutectic structure by decreasing both the eutectic cell width and the aligned α(B2)/γ(FCC) phase spacing. If ultrasound amplitude and dimension were increased, lamellar eutectic gradually transformed into anomalous eutectic without synergetic orientation. Meanwhile, a metastable σ phase enriched with Cr precipitated from γ phase in anomalous eutectic under 3D ultrasounds. Based on the combined analysis of eutectic structural evolution and sound field characteristics, the ultrasonic solidification mechanism was further clarified. The promoted dependent nucleation by stable cavitation and the fast growth rate caused by acoustic streaming were the main reasons for the significantly refined eutectic structure under 1D ultrasound. The induced independent eutectic nucleation and growth by transient cavitation, together with the enhanced solute and thermal diffusion by the intensive acoustic streaming under 3D ultrasounds were responsible for the formation of anomalous eutectic and the precipitation of metastable σ phase. The maximum ultimate strength and total elongation under ultrasound were simultaneously increased by 28% and 93%, showing comprehensive mechanical performance superior to those prepared by conventional approaches. The prominent strain hardening in γ phase and increase in α/γ interfaces induced by refining effect were the strengthening mechanisms, and the improvement of ductility was attributed to the intensified strain hardening in γ phase.

Effects of process parameters on strengthening mechanisms of additively manufactured AlSi10Mg

Abstract In industries like automotive and aerospace, the demand for structures with a high strength-weight ratio is increasing. Additive manufacturing (AM) studies and applications of AlSi10Mg material have increased due to the improvement of mechanical properties when the production is performed at high cooling rates in the laser-powder bed fusion (L-PBF) method. The study aims to investigate the effect of the AM process parameters on the microstructure features, and determine the mathematical relationship between yield strength and process parameters to obtain better mechanical properties. In this study, AlSi10Mg specimens are manufactured using L-PBF method with different process parameters. Microstructure images of the manufactured specimens are obtained by scanning electron microscopy. Melt pool width, eutectic cell size and diameter of Si precipitates are measured using the microstructure images. Parametric equations are generated between the process parameters and microstructural features including eutectic cell size and Si precipitate diameter. Thus, relationships between strengthening mechanisms and process parameters are established by integrating the generated equations into the related strengthening mechanisms. Consequently, the yield strength model of AlSi10Mg material is developed as a function of the process parameters of L-PBF method. It is found that the developed model estimates close results to the nano-indentation results.