Si Phase Research Articles

Waste control by waste: Metals recovery from electroplating sludge via a chlorination roasting followed by silicothermic reduction using solar-grade silicon cutting waste.

Electroplating sludge (ES) is a hazardous waste, because it contains heavy metals. It poses severe environmental and health risk if not properly disposed. This study proposed a combined pyro-metallurgical process to separate and recover copper, nickel, chromium and iron from it. A chlorination roasting was firstly used to selectively recover copper and nickel, in which they were chlorinated and volatilized while chromium and iron retained in the residue in the forms of FeCr2O4 and Fe2O3. A certain FeS2 promoted the conversion of the chlorinating agent of NaClO to Cl2 (g), increasing the copper and nickel chlorination. Though Cr2S3 could be chlorinated and volatilized, a high O2 partial pressure oxidized it to Cr2O3 and reduced it chlorination. Under the optimal condition, the chlorination of copper and nickel obtained 99.1% and 92.6% respectively, while that of chromium was only 5.7%. In the followed silicothermic reduction, a silicon cutting waste (Si-CW) was employed as reductant to recover chromium and iron from the roasted residue, due to the reduction capacity of Si and SiC phases in it. The chromium and iron oxides were reduced and recycled in an Fe-Cr alloy ingot, and Si and SiC changed to a refractory SiO2 and entered into the slag. CaO could be slagged with SiO2 and converted to a slag-liquid phase, which accelerated the separation between alloy and slag. The chromium and iron yields could obtain 97.6% and 98.9%, respectively. This study supplied a new method to co-treat two wastes for recovering nickel, iron, copper and chromium.

Compositional heterogeneity of secondary minerals in mine waste rock: Origins and implications for water quality.

Secondary minerals in mine waste materials impose strong controls on water quality by scavenging solutes of concern. This study investigates the mineralogical and compositional characteristics of secondary Fe(oxy)hydroxides and Ca-sulfates, two globally ubiquitous secondary precipitates, in weathered mine waste rock. Bulk analyses show that Si, Ca, Fe, Al, and S-bearing primary phases were the most abundant in the entire samples, but up to a few wt% of secondary Fe(oxy)hydroxides and Ca-sulfates were present as well. In these secondary phases, trace metal impurities like V (37 mg/kg in Ca-sulfates), Cr (23 mg/kg in Fe-oxides and 21 mg/kg in Ca-sulfates), and Cd (up to 15 mg/kg in Fe-oxides and Ca-sulfates) could not be detected by bulk techniques (XRF and XRD), but their deportment to some extent characterized by automated mineralogy, and their spatial distribution assessed at high-resolution through microscale LA-ICP-MS analysis. Element mapping revealed that metal(loid)s were generally enriched at grain rims, reflective of peripheral sequestration through surface adsorption. An exception was V, which was uniformly distributed in the studied secondary Fe-oxides, suggestive of isomorphic substitution during co-precipitation. Factor analysis revealed distinct groups of elements co-associated within each secondary mineral (e.g., divalent transition metal cations versus oxyanionic metalloids), likely caused by similar primary mineral sourcing or a comparable sequestration mechanism. Our results demonstrate the importance of secondary mineral precipitates for scavenging (trace) elements and the insights that can be gained from complementary mineralogical and element analyses for the interpretation of trace element dynamics in waste rock.

A new SLM-manufactured Al[sbnd]Si alloy with excellent room and elevated-temperature mechanical properties

The synergistic strengthening of multiple phases has long been an effective method of enhancing conventional metallic structural materials. However, the assembly of solute atoms with high solubility and low diffusion rate into highly stable and high-volume fraction nano-precipitates using the selective laser melting (SLM) technique is challenging. In this study, a new Al-9.0Si-2.8Fe-2.1Mn-1.1Ni (in wt%) alloy was fabricated using the SLM. The melt pool structure of the alloy exhibits equiaxed grain characteristics under optimum parameters, with large volume fractions of in-situ precipitated IMC-Al15(Fe,Mn,Ni)3Si2 and Si phases within the grains. The alloy demonstrates commendable tensile properties at room temperature (YS 373 ± 8 MPa, UTS 602 ± 12 MPa, El 4.2 ± 0.5 %) and retains excellent strength and ductility as well as creep resistance at elevated temperatures of 400 °C (YS 92 ± 3 MPa, UTS 100 ± 5 MPa, El 24 ± 0.7 %, steady-state creep rate ~ 10−5 s−1 under 60 MPa). Lamellar nano-Si phases can induce strain delocalization effects and grain boundary relaxation through partial dislocation twinning behavior, thereby coordinating high-temperature deformation. Under large deformations and prolonged creep processes, the transmission of external loads and the evolution of defects (The edge dislocation at interfaces, the stacking faults and deformation twins within the Si phase) effectively transfer stress to low-load-bearing regions, promoting the delocalization of deformation. The abundant second phases within the alloy (IMC and Si phases) hinder dislocation movement and promote dislocation multiplication, maintaining ultra-high deformation resistance and low steady-state creep rate. Due to the absence of heat treatment and the addition of expensive elements, the alloy has wide industrial application potential.

Additive manufacturing of sustainable and heat-resistant Al-Fe-Mo-Si-Zr alloys

Improving the sustainability of metals and alloys is essential for slowing down global warming. The reason is that their extraction and production stand for about 40% of all greenhouse gas emissions in the industrial sector. This motivates new alloy design and processing criteria such as the (1) preferred use of abundant and sustainable alloying elements and (2) improved material tolerance against impurity intrusion from recycling. In this context, additive manufacturing (AM) is attractive, through rapid solidification, capable of quenching impurities into a solid solution state, avoiding formation of large intermetallics and introduction of metastable phases. Here, by using this approach we show how iron, an important scrap-related contaminant in aluminum alloys, can be turned from a harmful into a valuable ingredient. Specifically, the addition of Mo and Si facilitates the formation of beneficial metastable body-centred cubic (BCC) Al12(Fe, Mo)3Si phase, instead of more stable but detrimental intermetallic variants commonly observed in Al-Fe alloys. The as-built microstructures have excellent thermal stability, tested up to 200hours at 300 °C, because of low diffusivity of Fe and the formation of Zr shell. We find that for such supersaturated alloys, two issues are important, namely (a) the heterogeneous microstructures in the as-built condition, (b) the evolution of metastable precipitates during heating. We suggest that this type of approach help to guide sustainable alloy design via AM and other rapid solidification processes.

Phase selection mechanism and eutectic growth kinetics of refractory Nb<sub>81.7</sub>Si<sub>17.3</sub>Hf alloy under electrostatic levitation condition

The phase selection mechanism and eutectic growth kinetics of Nb<sub>81.7</sub>Si<sub>17.3</sub>Hf alloy are investigated by electrostatic levitation technique. The maximum undercooling of this alloy reaches 404 K(0.19<i>T</i><sub>L</sub>). By analyzing the cooling curves, its hypercooling limit is obtained to be 527 K (0.24 <i>T</i><sub>L</sub>). A critical undercooling of 194 K is determined for the transition of solidification path. Below this undercooling threshold, (Nb) phase firstly nucleates and grows into primary dendrites, resulting in the enrichment of Si and Hf in the residual melt, which is conducive to the formation of the (Nb)+<i>α</i>Nb<sub>5</sub>Si<sub>3</sub> eutectics. Therefore, (Nb)+<i>α</i>Nb<sub>5</sub>Si<sub>3</sub> lamellar eutectics form in interdendritic space. With the increase of undercooling, the growth velocity of primary (Nb) dendritic follows a power function, while the eutectic growth velocity increases slowly. The maximum values of (Nb) dendritic reaches 89.4 mm/s. A modified LKT/BCT model is used to calculate the growth velocity of (Nb) dendrites. The results are in good agreement with the experimental values, indicating that after the LKT model is modified slightly, it can be used to describe the rapid dendrite growth behavior of the (Nb) phase in the Nb<sub>81.7</sub>Si<sub>17.3</sub>Hf alloy melt. Meanwhile, the lamellar spacing of (Nb)+<i>α</i>Nb<sub>5</sub>Si<sub>3</sub> eutectics notably decreases to 360 nm at 194 K undercooling. Above the critical threshold, the primary (Nb) dendrites disappear, whereas (Nb) phase and Nb<sub>3</sub>Si phase nucleate independently in the undercooled liquid and grow into anomalous eutectics. The growth velocity of anomalous eutectic exhibits a power function relationship with the increase of undercooling, with a maximum value of 115.9 mm/s. The interphase spacing of (Nb)+Nb<sub>3</sub>Si anomalous eutectics is larger than that of (Nb)+<i>α</i>Nb<sub>5</sub>Si<sub>3</sub> lamellar eutectics. Owing to the formation of nanosized eutectics and the increase of volume fraction of (Nb) phase, the alloy fracture toughness at 194 K reaches 21.9 MPa·m<sup>1/2</sup>, which is 3.4 times as large as that under small undercooling condition.

Automatic Si phase extraction from microscopic images of Al-Si alloys by unsupervised machine learning and supervised deep learning

Automatic Si phase extraction from microscopic images of Al-Si alloys by unsupervised machine learning and supervised deep learning

Quantitative Chemical State Analysis of Silicon-Based Anodes for Lithium Ion Battery Using X-Ray Emission Spectroscopy

The advancement of lithium-ion batteries for electric vehicles has prompted the utilization of diverse materials, including substances like amorphous and sulphated materials, which may lack inherent stability. Consequently, employing various analytical techniques, spectral analysis, and in-operando cell testing becomes imperative for their characterization. We assess the potential of X-ray Emission Spectroscopy (XES) to integrate chemical state and quantitative analysis, capitalizing on its bulk analysis capabilities with large analytical area and deep analytical depth.Silicon-based anodes offer high theoretical capacities and hold promise for lithium-ion batteries in electric vehicles. However, their practical application is hindered by poor cycling performance and mechanical failure attributed to significant volume changes during lithiation. Understanding the formation of amorphous and crystalline lithium silicon alloy phases, crucial for capacity degradation analysis, underscores the importance of quantifying the x value in the Li x Si phase. SiO emerges as a compelling anode material with potential to enhance energy capacity and mitigate degradation. Demonstrating this property involves the complex conversion of SiO to amorphous Si and lithium silicates during charging.While electrochemical reaction mechanisms and structural changes in silicon-based anodes have been explored using various techniques such as 7Li and 29Si solid-state NMR, Si K XAS, and Si-L2,3 soft X-ray emission spectroscopy, accurately quantifying reacted components remains challenging.In this study, Si Kβ X-ray emission spectroscopy (XES) is employed to quantify the composition of lithium-silicon alloys and lithium silicates during charging and discharging processes. The Si Kβ spectrum evolves with the reaction progression, and linear combination fitting (LCF) proves instrumental in estimating material quantities based on the reaction formula. The quantitative results of the XES analysis are shown and the accuracy, validity and findings are discussed.

First-Principles Study on Lithiation Process of Sio Anode for Li-Ion Batteries

Lithium-ion secondary batteries (LIB) with a high energy density have been developed mainly for use in small mobile devices. In recent years, the high capacity of LIB has become important for automobile applications. One possible high-energy density solution is the use of high-capacity negative electrodes fabricated from tin, silicon, or other materials, and a-SiO materials have been already commercialized. However, a-SiO materials has the issue of capacity degradation during charge-discharge cycles. In particular, it is speculated that the structural change during charging process causes the capacity degradation, but the detail has not been clarified yet. Therefore, in this study, we clarify the local structural changes in a-SiO up to full charge using first-principles calculations.In our previous study [1], a-SiO models were generated using classical molecular dynamics (MD) simulations with neural network potentials.Using one of these models, we explore the lithiation process of a-SiO using first-principles calculations with SIESTA code [2]. The simplest method to obtain a-Li x SiO model is to melt an initial structure in which Li atoms are randomly arranged at high temperature and then cool it. But it was found that this process could not reproduce the actual charge process and Li atoms should be placed at stable sites. Therefore, we developed a computational code with which stable sites of Li atoms can be searched efficiently using Bayesian optimization.Fig. 1 shows Li-inserted models at (a) 0%, (b) 55% and (c) 100% SoC (State of Charge). Li atoms are gradually inserted into the SiOx phase in the initial state of charging, and inserted into the Si phase over 20% SoC. These results are consistent with previous experimental results [3]. One Li6O octahedron can be seen in the model at 55% SoC, and the number of Li6O octahedra increases to five in the model at 100% SoC. The formation of Li6O octahedra during charging is irreversible, which is considered to cause the capacity degradation. To prevent capacity degradation, it is necessary to suppress the formation of these structures.

Si-Based Composite Anodes with Long Cycle Life for Lithium-Ion Batteries Achieved By Synergistic Effects of Elastic and Stiff Silicides

A composite electrode comprising LaSi2 and pure Si exhibits good charge–discharge cycling performance, even with a degrading capacity after repeated cycles. Before cycling, a metallographic structure was formed in which the Si phase was finely dispersed in the LaSi2 matrix phase; hence, the elastic LaSi2 relieves the stress generated by Si and suppresses electrode disintegration.1 In contrast, prior to capacity degradation, the metallographic structure transformed into a form in which the LaSi2 phase was surrounded by the Si matrix phase; the positional relationship between the two phases was reversed, and LaSi2 could not relieve the stress from Si. In the case of a composite electrode with CrSi2, which possesses stiff mechanical properties to withstand the stress generated by Si, the metallographic structural changes after cycling were suppressed, resulting in good cycling stability. Herein, we considered that the addition of stiff silicides as a third phase to the LaSi2/Si composite could further improve the cycle life by suppressing microstructure inversion. Composite comprising elastic LaSi2, stiff MSi2 (where M = Cr, Mo, Nb, Ta, Ti, or W), and elemental Si were prepared by mechanical alloying method, and the composite electrodes fabricated using gas-deposition (GD) method. The prepared GD electrode was mounted in a coin-type cell as the working electrode. We used a Li metal sheet and glass fiber filter as the counter electrode and separator, respectively. Additionally, we used 1mol dm–3 lithium bis(fluorosulfonyl)amide dissolved in N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)amide as an ionic liquid electrolyte. Galvanostatic charge-discharge tests were conducted in constant current mode with a charge capacity limitation of 1000 mA h g(Si)–1. In this study, the capacity of the silicides was ignored: the silicide-alone and Si-alone electrodes stored Li, whereas the silicide in the silicide/Si electrodes did not exhibit the reversible capacity.2 Figure 1 shows the cycle life of the LaSi2/MSi2/Si electrodes with the Vickers hardness of MSi2. The cycle life was shortest when WSi2, with the stiffest mechanical properties (hardest Vickers hardness), was used. The cycle life improved as the stiffness of MSi2 lowered. When NbSi2 was added, superior cycling performance was achieved, maintaining a reversible capacity of 1000 mA h g(Si)–1 for approximately 1800 cycles. This exceptional performance was achieved based on the synergistic effects of stiff and elastic silicides. In contrast, the cycle life was adversely decreased when TiSi2, which possessed the lowest stiffness, was used. This trend was observed when LaSi2 was used as the elastic silicide, and the same trend may not be obtained when combined with other elastic silicides. This study provides new insights into the effects of silicide functions on the charge–discharge characteristics of composite electrodes.1) Y. Domi, H. Usui, K. Nishikawa, and H. Sakaguchi, ACS Appl. Nano Mater., 4, 8473 (2021).2) Y. Domi, H. Usui, K. Nishikawa, H. Sakaguchi, et al., Electrochemistry, 88, 548 (2020). Figure 1

Anode Properties of Si-Based Composite Electrodes Containing Two Silicides with Different Functions for Lithium-Ion Batteries

A LaSi2/Si composite electrode has longer charge-discharge cycle life than a pure Si electrode. However, the capacity of the composite electrode decreases gradually over repeated cycles. We identified the microstructure of the electrode to ascertain factor of capacity fading by transmission electron microscopy. Before cycling, the pure Si phase was highly dispersed in the LaSi2 matrix phase. In such microstructure, the elastic LaSi2 could alleviate the stress caused by Si volume change during lithiation and delithiation; and hence it suppressed electrode disintegration.1 On the other hand, prior to capacity decline, the positions of LaSi2 and pure Si were reversed. The LaSi2 phase was surrounded by the pure Si matrix phase and the LaSi2 could not relax the stress. Hence, we added stiff silicide which withstands the Si-generated stress into the LaSi2/Si. As a result, the LaSi2/NbSi2/Si exhibited superior cycle life. Herein, we investigated the effect of difference in elastic silicides on cycle life. The MSi2/CrSi2/Si (M = Ni, La, or Sm) powder was prepared by mechanical alloying method. The composite powder was deposited on the Cu substrate using a gas-deposition (GD) method. The fabricated GD electrode was mounted in a 2032-type coin-cell as the working electrode. Li metal foil and glass fiber filter were also used as the counter electrode and separator, respectively. In addition, we used 1 mol dm–3 lithium bis(fluorosulfonyl)amide dissolved in N-methyl-N-propylpyrrolidinium bis(fluorosulfonyl)amide as an ionic liquid electrolyte. We conducted galvanostatic charge-discharge tests in constant current mode with a charge capacity limitation of 1000 mA h g(Si)–1. In the present study, we did not consider the capacity of the silicides: the Si-alone and silicide-alone electrodes stored Li, while the silicide in the silicide/Si electrodes did not show the reversible capacity2. Figure 1 shows the cycle life of the MSi2/CrSi2/Si electrodes with the different indentation work rates of MSi2. The indentation work rate means an indicator of elasticity: it indicates that how much the MSi2 layer returns to its original shape after deformation. The cycle life was the shortest when NiSi2 with the lowest indentation work rate was used. In contrast, when SmSi2 was used, it achieved the longest cycle life with high reversible capacity of 1000 mA h g(Si)–1 over 1900 cycles. We predicted that the cycle life improved using a more elastic silicide. However, the cycle life adversely lowered when LaSi2 with the highest elasticity was used. Thus, the excellent performance should be achieved based on the synergistic effects of stiff and elastic silicides.1) Y. Domi, H. Usui, K. Nishikawa, and H. Sakaguchi, ACS Appl. Nano Mater., 4, 8473 (2021).2) Y. Domi, H. Usui, K. Nishikawa, H. Sakaguchi, et al., Electrochemistry, 88, 548 (2020). Figure 1

Influence of Cooling Rate on Primary Silicon Size in Hypereutectic Al–Si Alloy Fabricated by Laser Powder Bed Fusion

Herein, the effects of cooling rate on primary silicon (Si) phases in laser powder bed fusion (PBF‐LB/M) processed hypereutectic Al–Si alloy are investigated. These alloys are particularly in demand for automotive and electronic applications, thanks to their excellent wear and thermal properties. Nevertheless, when processed by conventional methods like casting with comparatively lower cooling rates, the coarse primary Si phases are responsible for increasing brittleness and inducing crack propagation. The refinement of the primary silicon phases is aimed to be achieved through the PBF‐LB/M process, which offers a high cooling rate. The primary Si phases are observed under three different thermal substrate plate conditions—untempered, with cooling and heating, and additionally with varying volume energy density. Furthermore, the impact of primary Si size on the hardness of the fabricated samples is evaluated. The findings show that a faster cooling rate has a notable effect on refining the primary Si size. Then, hardness is directly affected by the primary Si size, with larger Si resulting in decreased hardness.

Machine learning driven design of high-performance Al alloys

Aluminum (Al) alloys with both high strength and thermal conductivity (TC) are promising structural materials for wide application across different industries. Yet, design of such alloys is challenging, since strength and TC often share a trade-off. In this paper, we build prediction models for TC and ultimate tensile strength (UTS) of Al alloys using eXtreme gradient boosting (XGBoost) and support vector machine (SVM) algorithms, respectively. The models take physical descriptors from the alloy composition into account. Lasso and Gini Impurity algorithms were adopted for feature engineering. Guided by the models, an Al-2.64Si-0.43Mg-0.10Zn-0.03Cu alloy with TC over 190 W·m-1·K-1 and UTS over 220 MPa was designed. The alloy was fabricated and tested by experiment, and its UTS and TC are close to the model prediction. Microstructure characterization suggests that the fragmented and spherical Si phase, along with a few non-spherical Si phases, may be a key reason for the improved properties.

Stress-relief annealing friendly Fe-based metallic glass-reinforced Al-Si-Mg-Zr alloy fabricated by laser powder bed fusion

ABSTRACT To enhance the thermal stability of L-PBF Al-Si-Mg alloy, Fe-based metallic glass powder was mixed with Al-Si-Mg-Zr powder to fabricate a novel alloy via L-PBF. The study systematically investigated the effects of process parameters on processability and the impact of stress-relief annealing (300 ∘ C–2h) on the microstructure and mechanical properties. Results showed that metallic glass addition improved surface quality. Plastic deformation was analysed using finite element and molecular dynamics methods. The as-built alloy had a cellular substructure with Al 3 Zr, Si, AlFeMgSi, and AlFeSi phases. Si nanoparticles and stacking faults were observed in α-Al cells. The as-built samples had yield strength (YS) of 249±4 MPa, ultimate tensile strength (UTS) of 434±6 MPa, and 6.3±0.3% elongation. Post-annealing, the alloy retained high strength and plasticity with YS of 255±3 MPa, UTS of 449±15 MPa, and 7.2±0.3% elongation, outperforming similar L-PBF Al-Si and Al-Si-Mg alloys.

Refinement of Primary Si Phase in Hypereutectic Al–Si Alloy by Electrically Assisted Solidification with P Addition

Refinement of Primary Si Phase in Hypereutectic Al–Si Alloy by Electrically Assisted Solidification with P Addition

Grain refiner fabricated by spark plasma sintering for hypoeutectic Al–Si alloy cast and its refining ability

Grain refiner fabricated by spark plasma sintering (SPS) for an as-cast hypoeutectic Al–Si alloy were proposed. The proposed grain refiner contains Al3Ti and Na flux particles in an Al-11 mass%Si alloy matrix. Through SPS, the grain refiner were obtained without any reaction between the Al3Ti particles, Na flux particles, and Al-11 mass%Si alloy matrix. Casting tests were conducted using the proposed grain refiners, and the refiners reduced the dendrite cell size and the dendrite arm spacing of the primary α-Al phase, as well as the lamellar spacing of the eutectic structure. The eutectic Si phase changed to a granular shape upon the refinement of the eutectic structure. Furthermore, the tensile strength and ductility of the as-cast Al-11 mass%Si alloy were drastically improved by adding the proposed grain refiner. This improvement was attributed to the refinement and granulation of the eutectic Si phase.

Micromechanical properties of reaction-bonded silicon carbide using atomic force microscopy and nanoindentation

Reaction-bonded silicon carbide (RB-SiC) ceramics have been produced using advanced technology for the production of space mirrors. Changing the volume content of SiC (from 78 to 93 %) in the ceramic's composition allows for improved the mechanical properties, which is achieved by a combination of the SiC and Si phases properties. In this work, a thorough study of the structure and micromechanical properties of individual SiC and Si phases for RB-SiC ceramics (with a SiC content of 78–93 vol%) was carried out at the micro- and nanolevel using atomic force microscopy and nanoindentation. The studies have shown the crack resistance limit each phase (an important factor for RB-SiC space mirrors) under mechanical loads, after which microcracks appear (sources of further degradation and destruction). The surface morphology, deformation area and crack propagation in each phase after exposure to mechanical load during indentation were studied using atomic force microscopy. Nanomechanical mapping of elastic modulus and microhardness on the surface, analysis of boundaries between phases (SiC and Si), assessment of mutual influence of phases and determination of micromechanical properties were carried out using the nanoindentation method. The fracture toughness KIC was determined using an improved indentation method with visualization of the deformation areas using atomic force microscopy. The highest values of microhardness H, elastic modulus E and fracture toughness KIC on the SiC and Si phases were obtained on a ceramic sample with 93 vol % SiC: for the SiC phase – E=486 GPa, H=35.6 GPa, KIC=5.03 MPa m1/2, for the Si phase – E=205 GPa, H=12.2 GPa, KIC=2.73 MPa m1/2. This study demonstrated the efficiency and possibility of using the atomic force microscopy and nanoindentation to determine the micromechanical properties of ceramics at the micro- and nanolevel.

Angiogenesis-osteogenesis coupling and anti-osteoclastogenesis zoledronate intermixed calcium silicate metal-organic/inorganic hybrid coating on biodegradable zinc-based intramedullary nails for osteoporotic fracture healing

Osteoporotic (OP) fractures remain a tough clinical challenge owing to their impaired healing outcome, which requires novel biomaterials with osteogenicity for effective healing. Metallic zinc (Zn) is attracting increasing attention for biodegradable intramedullary nails (IMNs) for OP fracture healing thanks to their comprehensive mechanical properties, biosafety, and bioactivity. However, the multiple biofunctions required for OP fracture healing have not been fully met by Zn. Herein, a zoledronate (ZA)-mediated calcium-zinc silicate (Ca(Zn)Si) metal-organic/inorganic hybrid coating was fabricated on Zn-based IMN by coordination chemistry driven via interactions between ZA and Ca2+/Zn2+ as well as in-situ directional growth of Ca(Zn)Si phase. The ZA&Ca(Zn)Si hybrid coating exhibited a homogeneous micro/nanostructure with a granular morphology, which prevented premature fracture failure of IMN in rat femur by ameliorating corrosion mode and decreasing degradation rate of the Zn matrix. More importantly, this hybrid coating enabled sustained release of Zn2+/Ca2+/Si4+ and ZA in the long term, achieving a remarkable effect on vascularized bone regeneration. The coated IMN enhanced angiogenesis–osteogenesis coupling through autocrine and paracrine effects between endothelial cells and bone marrow mesenchymal stem cells. Osteoclastogenesis was repressed by Zn2+ and ZA. This approach offers a new strategy for surface-engineering of biodegradable metals for bone fracture healing.

Joint formation mechanism and mechanical properties of laser brazed Zn coated steel under different defocusing conditions

Laser brazing, producing a class-A joint surface in automotive, relies on the defocus control to manage laser heating mode and braze performance. This work demonstrates that the laser interaction mechanism transitioned from keyhole welding to conduction brazing as defocus distances increased from −20 to ≥18 mm while keeping other parameters consistent. Uniform brazed joints were achieved at defocuses of +22, +25 and + 30 mm. Increased defocus distance resulted in a wider bead, with a larger laser irradiation area and expanded heat affected zone (HAZ), leading to increased steel melting and more Fe-rich precipitates within the Cu braze. The interfacial reaction layers remained Fe(Si) with increasing thickness as defocus changed from +22 to +30 mm, and two distinct Fe(Si) phases were initially identified. The steel Zn coating evaporated upon direct laser irradiation at upper two regions while participated in interfacial reactions at the weld root. At the weld root, a dramatic phase transition from Zn–Cu to Cu was observed, with liquid Zn(Cu) phases particularly forming in joints with a +30 mm defocus, led to solidification cracks that acted as failure initiation sites during tensile testing. Cracks propagated along the interfacial reaction layer/bead interface, or along large Fe-rich precipitates within the bead. A +30 mm defocus produced a lower hardness HAZ than with a +22 mm defocus, due to the higher content of bainite and tempered martensite resulting from a slower cooling rate. This work provides insights into optimizing laser brazing parameters for Zn-coated steel.

Cutting mechanism of reaction-bonded silicon carbide in laser-assisted ultra-precision machining

Reaction-bonded silicon carbide (RB-SiC) is an important material used in aerospace optical systems. Due to the property mismatch between Si and SiC phases, the underlying cutting mechanism in ultra-precision machining of RB-SiC remains relatively unclear. Recently, laser-assisted machining (LAM) has emerged as an effective technique to improve the machinability of hard and brittle materials, which brings the question that how the high temperature affects the machining mechanism of RB-SiC. To elucidate these aspects, a series of grooving experiments and MD simulations were conducted in this study. The interaction mechanism between phases on material removal and subsurface damage was revealed and the effect of cutting temperature on Si-SiC interaction was explored. The results indicate that in conventional ultra-precision machining, SiC grains could affect the deformation of Si phase, whereas the influence of Si phase on SiC deformation is limited. As the cutting temperature increases, the Si-SiC interaction is less apparent and the deformation of Si and SiC becomes more independent. Meanwhile, the prominence of phase property mismatch on subsurface damage are reduced while the extension of disordered phases into boundaries merges as an important mechanism in subsurface damage formation. This research helps to understand the thermal effect on material interaction between phases during machining and aid to improve the performance of LAM on RB-SiC.

Mechanism of homogenization temperature and time on Fe-containing phase transition in AA8014 aluminum alloy

The presence of coarse Fe-containing phases detrimentally affects the fracture toughness of 8xxx aluminum alloys, and their complete dissolution during homogenization is unattainable. Therefore, it is essential to determine the optimal homogenization temperature and time to facilitate particle breakup during hot rolling, necessitating the development of effective homogenization processes. This study systematically examines the effect of homogenization temperature and time on the transition of Fe-containing phases in AA8014 aluminum alloy using scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The transition mechanisms of Fe-containing phases during homogenization were elucidated through first-principles calculations, thermodynamics, and kinetics calculations. Under homogenization conditions of 610–650 ℃/12 h and 630 ℃/1–20 h, the Al6(Fe,Mn) phase initially transforms into the α-Al12(Fe,Mn)3Si phase with a “micropore structure” via the reaction. Subsequently, the α-Al12(Fe,Mn)3Si phase transforms into the Al3(Fe,Mn) phase. First-principles calculations confirm the sequential stability enhancement of the Al6(Fe,Mn), α-Al12(Fe,Mn)3Si+6Al, and Al3(Fe,Mn) phases. Homogenization kinetics indicate an optimal homogenization time of 11.5 h at 630 ℃, rationalizing the observed phase transitions and homogenization treatment. This study provides a foundation for the manufacture of 8xxx series aluminum alloys.