Rapid Solidification Research Articles

Precipitation behaviour and strengthening mechanisms of Nb-Ti microalloyed HSLA steel produced by CSP process

Compact strip production promotes the uniform and sufficient precipitation of the second phase particles in the steel by means of rapid solidification rate and large depressions, and improves the utilisation of microalloying elements. In this article, the Nb content in compact strip production hot-rolled strip was slightly increased, resulting in a significant improvement in mechanical properties. The results showed that two types of (Ti, Nb)(C, N) were observed in the investigated steels, in particular, coarse (Ti, Nb)(C, N) precipitated in austenite, relying on the K-S orientation relationships and fine (Ti, Nb)C precipitated in ferrite, relying on the B-N orientation relationships. Combined with the thermodynamic and kinetic analyses of Ti-Nb composite precipitation, the increase of Nb content could improve Gibbs free energy, increase the precipitated nucleation rate, and promote precipitation in austenite. Thereby, more precipitation precipitated in the process of rolling, which pinned grain boundaries, and then refined the ferrite grain size from 4.9 ± 0.37 μm to 3.9 ± 0.25 μm, resulting in stronger grain strengthening. As the temperature range decreases from austenite to ferrite, the main influence on nucleation shifts from Gibbs free energy to diffusion of solute elements, and therefore, the precipitation-temperature-time curve of ferrite is C-shaped. The increase of Nb not only raises the temperature at the nose point from 630 °C to 660 °C, but also improves the relative nucleation rate by 4 times within the coiling temperature. Thereby, more and finer precipitation precipitated in the process of coiling, which improved the precipitation strengthening from 45.92 to 86.29 MPa. The combined improvement of the two strengthening mechanisms increased the yield and tensile strengths of the investigated steels from 458 and 518 MPa to 517 and 592 MPa, respectively.

Microstructure, Hardness and Tribological Characteristics of High-Entropy Coating Obtained by Detonation Spraying

In this study, powders based on a high-entropy AlCoCrFeNi alloy obtained by mechanical alloying were successfully applied to a 316L stainless steel substrate by detonation spraying under various conditions. Their microstructural features, phase composition, hardness, and wear resistance were studied. A comparative analysis between the initial powder and the coatings was performed, including phase transformation modeling using Thermo-Calc under non-equilibrium conditions. The results showed that the phase composition of the powder and coatings includes body-centered cubic lattice (BCC), its ordered modification (B2), and face-centered cubic lattice FCC phases, which is consistent with the predictions of the Scheil solidification model, describing the process of non-equilibrium solidification, assuming no diffusion in the solid phase and complete mixing in the liquid phase. Rapid solidification and high-speed impact deformation of the powder led to significant grain refinement in the detonation spraying coating, which ultimately improved the mechanical properties at the micro level. The data obtained demonstrate the high efficiency of the AlCoCrFeNi coating applied by detonation spraying and confirm its potential for use in conditions of increased wear and mechanical stress. AlCoCrFeNi coatings may be promising for use as structural materials in the future.

The Effects of Heat Treatment Temperatures on the Properties of 316L Stainless Steel Produced via Laser Powder Bed Fusion.

316L stainless steel (316L SS) exhibits excellent corrosion resistance, mechanical properties, and biocompatibility, but the rapid melting and solidification of the laser powder bed fusion (PBF-LB/M) process reduce the properties of the newly formed parts. This study aims to enhance the mechanical properties of PBF-LB/M PBF-LB/M-formed 316L SS parts by investigating the effects of various heat treatment temperatures. The results show that an appropriate heat treatment temperature can improve the microstructure and mechanical properties of the formed parts. Lower temperatures have minimal effects on performance; however, at 1100 °C, recrystallization occurs, resulting in more uniform grain structures, improved densification, and substantial stress relief. The residual stress is reduced by 85.59% compared to the untreated PBF-LB/M samples, while the ferrite content is significantly decreased, making the phase structure more homogeneous. Although both yield strength and tensile strength decrease, plasticity improves by 21.11%.

Autogenous laser welded joint of Inconel 625 and AISI 316L steel: Microstructure and mechanical properties

The study focused on a dissimilar laser-welded joint between heat-resistant AISI 316L stainless steel and Inconel 625. It included optical and scanning electron microscopy (SEM) analysis of the weld metal, heat affected zone, and fusion interface, along with microhardness measurements, Charpy impact toughness tests, and tensile property evaluations at room and elevated temperatures. Microstructural examination revealed an asymmetric solidification behavior across the weld metal of the dissimilar welded joint. On AISI 316L side, weld metal near the fusion boundary predominantly exhibited cellular and columnar solidification structure. In contrast, Inconel 625 side showed the formation of columnar dendritic structures, indicating directional solidification driven by thermal gradients and compositional differences between the base metals. Within the inter-dendritic regions and along cellular grain boundaries of the weld metal, the precipitation of Laves phases and NbC was evident in various morphologies including spherical, chain-like, and rectangular, suggesting non-equilibrium segregation during rapid solidification. The tensile strength of the dissimilar weld metal was significantly lower than that of Inconel 625 base metals and close to AISI 316L steel base metal, with an average ultimate tensile strength of 600 MPa and elongation of 46%. The tensile strength of the welded joint was measured to be 336 MPa at 650 °C and 280 MPa at 700 °C. Similarly, Charpy impact testing at room temperature revealed lower energy absorption in weld metal compared to the base metals, with an average toughness value of 72 J.

Microstructural Control of Zn Alloy by Melt Spinning - A Novel Approach Towards Fabrication of Advanced Biodegradable Biomedical Materials.

Microstructural Control of Zn Alloy by Melt Spinning - A Novel Approach Towards Fabrication of Advanced Biodegradable Biomedical Materials.

Computational design of additively manufacturable, cost-effective, high-strength aluminum alloys exploiting rapid solidification

Computational design of additively manufacturable, cost-effective, high-strength aluminum alloys exploiting rapid solidification

Quantitative phase-field modeling of nonequilibrium microstructural evolution in rapid solidification for additive manufacturing

Quantitative phase-field modeling of nonequilibrium microstructural evolution in rapid solidification for additive manufacturing

Enhancement of mechanical properties in AZ91D magnesium alloy via wire arc additive manufacturing: influence of rapid solidification and solute segregation on microstructure and deformation behavior

Enhancement of mechanical properties in AZ91D magnesium alloy via wire arc additive manufacturing: influence of rapid solidification and solute segregation on microstructure and deformation behavior

Microstructure and Mechanical Properties of Functionally Graded Materials on a Ti-6Al-4V Titanium Alloy by Laser Cladding.

Functionally graded materials (FGMs) are fabricated on Ti-6Al-4V alloy surfaces to improve insufficient surface hardness and wear resistance. Microstructure and mechanical properties and strengthening-toughening mechanisms of FGMs were investigated. The FGM cladding layer exhibits distinct gradient differentiation, demonstrating gradient variations in the nanoindentation hardness, wear resistance, and Al/V elemental composition. Molten pool dynamics analysis reveals that Marangoni convection drives Al/V elements toward the molten pool surface, forming compositional gradients. TiN-AlN eutectic structures generated on the FGM surface enhance wear resistance. Rapid solidification enables heterogeneous nucleation for grain refinement. The irregular wavy interface morphology strengthens interfacial bonding through mechanical interlocking, dispersing impact loads and suppressing crack propagation. FGMs exhibit excellent wear resistance and impact toughness compared with Ti-6Al-4V titanium alloy. The specific wear rate is 1.17 × 10-2 mm3/(N·m), dynamic compressive strength reaches 1701.6 MPa, and impact absorption energy achieves 189.6 MJ/m3. This work provides theoretical guidance for the design of FGM strengthening of Ti-6Al-4V surfaces.

Exploring the Influence of Composition and Microstructure on High-Strain-Rate Properties in Fe-Cu Alloys Made by Laser Powder Bed Fusion

Abstract Laser-powder bed fusion (L-PBF)-based additive manufacturing (AM) of pure Fe and two alloys in the Fe-Cu system (FeCu2.5 and FeCu5 wt.%) was used to understand the role of Cu in the microstructure and resulting mechanical properties at strain rates between 10−3 s−1 and 103 s−1. Small amounts of Cu were found to significantly increase yield strength at all strain rates because of a combination of grain refinement and the presence of nanoscale Cu precipitates within the Fe grains. The strengthening increments are interpreted in terms of Hall–Petch strengthening from Fe grain boundaries, strengthening from dislocations introduced via processing, and precipitation hardening from Cu precipitates. Enhancements in yield strength were accompanied by slight reductions in strain rate sensitivity and tensile ductility. Fracture surface analysis revealed that Fe and FeCu2.5 showed similar ductile fracture features at all strain rates, whereas FeCu5 exhibited a shear-dominated slanted fracture surface. The absence of solidification defects in these alloys can be rationalized in terms of CALPHAD-based Scheil and Clyne–Davies solidification simulations. The simulations show that the propensity for solidification cracking is expected to increase rapidly for Cu contents exceeding ~ 8%. This demonstrates the potential of rapid solidification simulations in aiding alloy design.

An additively manufactured near-eutectic Al–Ce–Ni–Ti–Zr alloy: microstructure, mechanical properties and heat resistance

ABSTRACT Nowadays, heat resistance of additively manufactured aluminum alloys is highly in demand to meet the high-temperature strength requirements for lightweight components. However, existing commercially-available alloys exhibit severe strength degradation at elevated temperatures due to coarsening of strengthening phases. In this study, an additively manufactured near-eutectic Al–Ce–Ni–Ti–Zr alloy with superior heat resistance was developed based on the thermodynamic calculations. The new alloy possesses good printability thanks to the combination of the near-eutectic Al–Ce–Ni composition and inoculation treatment provided by Ti and Zr micro-additions. The eutectic solidification microstructure comprises a high volume of coarsening-resistant Al11Ce3 and Al3Ni phases and presents a typical hierarchical microstructure where refined equiaxed grains decorates melt boundaries. Such microstructure characteristics determine excellent heat resistance and good mechanical properties at ambient and elevated temperatures with 400°C. The alloy possesses a yield strength of 427 MPa and an elongation of 4.7% at ambient temperature. Even at 400°C, the alloy still retains a superb tensile yield strength of 104 MPa and an elongation of 17.86%. This work provides an effective pathway for heat-resistant aluminum alloy design via additive manufacturing and other rapid solidification processes.

The Origins of Spinodal Decomposition and Ductile-to-Brittle Transition in Fe-P Metallic Glass: MD Simulations, DFT Calculations and CALYPSO Searches.

The existence of the spinodal decomposition phenomenon in the Fe-P metallic glasses (MGs) has long been debated, and the fundamental physical mechanism underlying the ductile-to-brittle transition, which is closely related to the chemical composition of Fe-P MGs, has remained unresolved. In this study, we employ molecular dynamics (MD) simulations based on empirical potentials, ab initio molecular dynamics (AIMD) based on density functional theory (DFT), and the CALYPSO structure search software, which utilizes a particle swarm optimization algorithm, to systematically investigate the rapid solidification, tensile fracture behavior, and geometric configurations of ground-state atomic clusters in Fe-P MGs with six different chemical compositions (Fe84P16, Fe73P27, Fe64P36, Fe50P50, Fe36P64, Fe14P86). Our results demonstrate that spinodal decomposition is an intrinsic atomic structural feature of the Fe-P MGs, rather than an artifact of empirical potential functions. This unique atomic structure arises from the strong electronic interactions between Fe atoms, which are governed by a mix of metallic and ionic bonding. Additionally, microcracks are found to preferentially propagate along P-enriched regions, owing to the high energy, reduced structural stability, and extremely weak electronic interactions between P atoms within these clusters. These factors collectively promote crack initiation and growth, fundamentally contributing to the ductile-to-brittle transition in Fe-P MGs. This work establishes a robust theoretical framework for understanding the intrinsic mechanical behavior of Fe-P MGs and provides valuable guidance for future research.

Effect of Fe content on tensile properties of TA15 alloy with equiaxed microstructure produced by laser directed energy deposition

ABSTRACT The thermal gradient during laser directed energy deposition (LDED) makes avoiding columnar grains difficult. Columnar grains result in solidification defects and mechanical property anisotropy, which has become a significant challenge during additive manufacturing. Recently, various strategies have been explored to achieve the columnar-to-equiaxed transition (CET) process, including heat treatment, control of energy input, optimisation of processing parameters, incorporation of inoculants, and addition of solutes. This study explored the effect of Fe solute with low cost on the microstructure and tensile properties of LDEDed Ti-6.5Al-2Zr-Mo-V (TA15) alloys. The LDEDed TA15-xFe alloy from mixed powder widened the freezing temperature range by Fe addition and rapid solidification, achieving equiaxed β grain. Fe-modified TA15 alloy achieved higher strength (YS∼921 MPa, UTS∼1015 MPa) and better ductility (uniform elongation∼8.9%) than TA15, which enabled strength-ductility synergy. Compared with TA15 alloy, the strength and ductility of TA15-3Fe were improved by 27% and 37%, respectively, which mitigated the trade-off of strength and ductility. The strengthening mechanism and deformation mechanism of TA15-3Fe were systematically investigated. The findings provided a new insight for overcoming the strength-ductility trade-off in additively manufactured titanium alloys with equiaxed microstructure by alloy design.

Effect of PBF-LB/M Processing on the Microstructural Evolution and Local Mechanical Properties of Novel Al-Fe-Si-Cr-Ni Alloy

The present study aims to investigate the microstructural evolution and local mechanical properties of an AlFe18Si8Cr5Ni2 alloy processed via Powder Bed Fusion–Laser-Based Manufacturing (PBF-LB/M). Designed with a focus on sustainability, this alloy was produced by deriving the necessary elements from AlSi10Mg and 304L steel, two of the most widely used alloys and, consequently, among the easiest materials to source from machining scrap. By leveraging iron, chromium, and nickel from these widespread standard compositions, the alloy mitigates the detrimental effects of Fe contamination in Al-based alloys while simultaneously enhancing mechanical performance. A comprehensive investigation of the impact of rapid solidification and thermal cycling offered novel insights into phase stability, elemental distribution, and local mechanical behavior. In particular, microstructural analyses using scanning electron microscopy (SEM), field emission SEM, energy-dispersive X-ray spectroscopy, X-ray diffraction, and differential scanning calorimetry revealed significant phase modifications post PBF-LB/M processing, including Fe-rich acicular phase segregation at melt pool boundaries and enhanced strengthening phase formation. In addition, nanoindentation mapping was used to demonstrate the correlation between microstructural heterogeneity and local mechanical properties. The findings contribute to a deeper understanding of Al-Fe-Si-Cr-Ni alloy changes after the interaction with the laser, supporting the development of high-performance, sustainable Al-based materials for PBF-LB/M applications.

A Novel Method to Predict Phase Fraction Based on the Solidification Time on the Cooling Curve

The phase fraction plays a critical role in determining the solidification characteristics of metallic alloys. In this study, we propose a novel method (fs = (t − tl)/(ts − tl)) for estimating the phase fraction based on the solidification time in cooling curves. This method was validated through an experimental analysis of Al-18 wt%Cu and Fe42Ni42B16 alloys, where the phase fractions derived from cooling curves were compared with quantitative microstructure evaluations using computer-aided image analysis and the box-counting method. Then, a comparison between the analysis using the present novel method and Newtonian thermal analysis demonstrates good agreement between the results. The present method is easier to operate, since it does not need derivative and integral operations as in Newtonian thermal analysis. In addition, based on the characteristics of the cooling curve, we also found two other relationships—V/Rc = D/ΔTc and RΔt = constant, where V is the solidification rate, Rc is the recalescence rate, D is the diameter of the focal area of the pyrometer, ΔTc is the recalescence height, R is the cooling rate, and Δt is the solidification plateau time. These findings establish an operational framework for quantifying phase fractions and solidification rates in rapid solidification.

Study on the Effect of EICP Combined with Nano-SiO2 and Soil Stabilizer on Improving Loess Surface Strength

Loess, predominantly distributed in arid and semi-arid regions of central and western China, exhibits low shear strength and structural instability, rendering it prone to geological hazards such as landslides and collapses, which pose significant threats to local infrastructure and safety. This study evaluated the urease activity of soybean and sword bean at different temperatures to screen the optimal enzyme source for enzyme-induced carbonate precipitation (EICP). Methods including single EICP, EICP combined with nano-SiO2, and EICP combined with both nano-SiO2 and soil stabilizer (SS) were adopted to enhance the surface strength of loess. The results showed that the EICP technique significantly improved the surface strength of loess, especially with the addition of nano-SiO2 and soil stabilizer. This study confirmed that using sword bean urease treated at −20 °C for 24 h in combination with 1.5% nano-SiO2 was both cost-effective and efficient in reinforcement. The incorporation of 5% soil stabilizer further enhanced the surface strength, and the accuracy was further verified by combining the results of SEM and XRD. Future research will focus on optimizing the material ratio to maximize the improvement of surface strength, providing an economical and feasible solution for rapid loess solidification, and evaluating the long-term durability under cyclic wet and dry conditions.

Electrohydrodynamic Liquid Bridge Printing of Complex 3D Architectures Using Biopolymeric Inks.

Electrohydrodynamic direct writing (EHDDW) has demonstrated significant advantages in fabricating high-resolution structures for biomedical applications. However, the limited biopolymers for thick architectures and the low geometric complexity constrain the broader application of EHDDW. Here, an electrohydrodynamic liquid bridge (ELB) printing method is reported that expands the boundaries of available materials and structural complexities in EHDDW, while retaining its high-resolution capabilities. This method employs an ELB for stable and controllable deposition of tiny ink, coupled with in situ UV illumination for the rapid solidification of the ink. ELB printing allows to fabricate a variety of synthetic and natural biopolymers into solid or hydrogel architectures with heights of 5mm and a resolution of up to 20µm, while also facilitating the creation of complex geometries with intricate internal structures. The application of ELB printing in producing advanced scaffolds is further demonstrated, including 4D-printed anisotropic cylinders and highly porous, cartilage-biomimetic hydrogels. The ELB printing provides a versatile and high-resolution technique for scaffold fabrication in tissue engineering.

Microwire vs. Micro-Ribbon Magnetoelastic Sensors for Vibration-Based Structural Health Monitoring of Rectangular Concrete Beams

Two different magnetoelastic Metglas materials with distinct shapes were compared as sensing elements for the structural health monitoring of concrete beams. One had a ribbon shape, while the other had a microwire shape. The sensing elements were attached to different concrete beams, and a crack was introduced into each beam. The beams were subjected to flexural vibrations, and their deformations were recorded wirelessly by coils, detecting the magnetic signals emitted due to the magnetoelastic nature of the sensors. Fast Fourier Analysis of the received signal revealed the bending mode frequencies of the beams, which serve as a “signature” of their structural health. In these spectra, the ribbon-shaped sensor exhibited a 1.4-times stronger signal than the microwire sensor. However, the extracted mode frequencies were nearly identical, with differences of less than 1% both before and after damage. This indicates that both sensors can be used equivalently to monitor structural damage in concrete beams. The damage-related relative frequency shifts ranged from −0.01 to −0.03, with similar results for both sensors. Thermal annealing was also studied and appeared to significantly enhance the signal by 10–30%, likely due to the relaxation of internal stresses induced during the rapid solidification synthesis of these materials. This enhancement was more pronounced in the ribbon-shaped sensor. This study is the first to utilize a magnetoelastic microwire sensor for damage detection in concrete beams.

Liquid state properties and rapid solidification mechanisms of ternary Fe–Dy–B alloy

The thermophysical properties and rapid solidification kinetics of stable and metastable liquid Fe84Dy8B8 alloy were investigated by electromagnetic levitation and drop tube techniques, which achieved maximum undercoolings of 215 K (0.14 TL) and 386 K (0.25 TL), respectively. The surface tension, viscosity, and diffusivity of liquid alloy were measured, and their correlations with liquid undercooling were derived, through which the activation energies for viscous flow and atomic diffusion were determined. At small undercoolings, the primary γFe phase growth velocity rose continuously as a power function. The increase of bulk undercooling not only significantly promoted the formation of pseudobinary eutectics by involving Dy2Fe17(B) as the main phase but also raised the volume fraction of peri-eutectics to some extent. At the intermediate undercooling regime, the Dy2Fe17(B) phase grew as the leading phase and was significantly refined with undercooling, and the following peri-eutectic transition was greatly accelerated, rendering the τ1 (Dy2Fe14B) dominant phase of solidification microstructure. When substantial undercoolings were achieved in alloy droplets, the τ1 phase nucleated and grew directly from the undercooled alloy and underwent a faceted to nonfaceted growth mode transition, whose maximum volume fraction reached up to 81%. This indicates that high undercooling rapid solidification is an effective approach to modulate the volume fraction of the τ1 phase by accelerating its peri-eutectic transition or even inducing its direct formation in rare earth alloys.

Microstructural analysis and defect characterization of additively manufactured AA6061 aluminum alloy via laser powder bed fusion

Microstructural analysis and defect characterization of additively manufactured AA6061 aluminum alloy via laser powder bed fusion