Si Phase Research Articles

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.

First-principles study on the lithiation process of amorphous SiO anode for Li-ion batteries with Bayesian optimization.

Amorphous silicon monoxide (a-SiO), which contains Si atoms with various valence states, has attracted much attention as a high-performance anode material for lithium (Li) ion batteries (LIBs). Although current experiments have provided some information during charge/discharge cycles, further investigation of structural changes at the atomic scale is needed. To investigate the lithiation process of a-SiO using first-principles simulations and machine learning techniques, we developed a computational code employing Bayesian optimization to efficiently identify stable sites for Li insertion in the large search-space of amorphous models to reproduce the actual lithiation process and compared this approach to the conventional random scheme by applying it to an a-SiO model previously generated with neural network potentials. The lithiation process based on Bayesian optimization resulted in lower formation energies compared to the conventional random scheme, indicating a more stable structure. During lithiation, Li atoms tended to enter the silicon (Si) phase after the SiO2 phase, in agreement with experimental results. We analyzed the structural changes and observed significant differences in the structural evolution between the conventional and new schemes. Our study highlights the significant influence of the lithiation process on the structural transformation of a-SiO materials, which in turn affects the reversible capacity of the material. These findings will provide a framework for improving the performance and lifetime of a-SiO materials.

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.

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.

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.

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.

Effect of Casting Process and Thermal Exposure on Microstructure and Mechanical Properties of Al-Si-Cu-Ni Alloy.

This paper employed squeeze-casting (SC) technology to develop a novel Al-7Si-1.5Cu-1.2Ni-0.4Mg-0.3Mn-0.15Ti heat-resistant alloy, addressing the issue of low room/high temperature elongation in traditional gravity casting (GC). Initially, the effects of SC and GC processes on the microstructure and properties of the alloy were investigated, followed by an examination of the evolution of the microstructure and properties of the SC samples over thermal exposure time. The results indicate that the SC process significantly improves the alloy's microstructure. Compared to the GC alloy, the secondary dendrite arm spacing of the as-cast SC alloy is refined from 50.5 μm to 18.5 μm. Meanwhile, the size and roundness of the eutectic Si phase in the T6-treated SC alloy are optimized from 11.7 μm and 0.75 μm to 9.5 μm and 0.85 μm, respectively, and casting defects such as porosity are reduced. Consequently, the ultimate tensile strengths (UTSs) at room temperature and at 250 °C of the SC alloy are 5% and 4.9% higher than that of GC alloy, respectively, and its elongation at both temperatures shows significant improvement. After thermal exposure at 250 °C for 120 h, the morphology of the residual second phase at the grain boundaries in the SC alloy becomes more rounded, but the eutectic Si and nano-precipitates undergo significant coarsening, resulting in a 49% decrease in UTS.

Microstructural refinement in a high elastic modulus Al-18Si-8Ni casting alloy

A new Al-Si-based casting alloy with high elastic modulus in the range of 90‐100 GPa and low density, less than 3 g/cm3, was developed by alloy design and microstructural refinement approaches. The addition of 8 wt.% Ni to a hypereutectic Al-18Si alloy introduces large volume fractions (∼40 vol.%) of hard primary Si and primary Al3Ni phases. Coarse primary Si and primary Al3Ni formed in the early stage of solidification, however, can interfere with the melt flow, reducing the castability, and also were deleterious to elongation. By the assessments of the crystallographic misfit between a nucleant substrate and a nucleated solid, we discovered key inoculants, AlP and TiB2, which can successfully refine such coarse and brittle primary phases, Si and Al3Ni, respectively. More importantly, along with the improved elastic modulus, the combined addition of AlP and TiB2 results in a significant increase in the elongation up to 1% with an advantageous yield strength of over 230 MPa. The important role of an inoculant, particularly TiB2 in nucleating the Al3Ni phase is also discussed based on the theoretical lattice misfit calculations and experimental characterization, further confirming their orientation relationship between the Al3Ni and the TiB2 as (110)[11¯0]Al3Ni∥ (0001)[12¯10]TiB2.

Anisotropic corrosion behavior of laser-based direct energy deposited H13 steel in molten ADC12 aluminum alloy

The immersion corrosion experiment of laser-based direct energy deposited H13 steel in ADC12 aluminum alloy melt was conducted to evaluate the demands for corrosion resistance after mold repair. The effect of the anisotropic microstructure of the deposited H13 steel on corrosion behavior was elucidated by characterizing the microstructure before and after corrosion. The results show that the microstructural heterogeneity affects the initiation, development and stabilization process of corrosion. Corrosion tends to initiate near the heat-affected zone due to the heterogeneous distribution of grain size, carbides, and dislocation density. Planes with weak microstructural heterogeneity are less likely to develop cracks in the intermetallic compounds (IMCs) layer during the corrosion development stage, thus exhibiting a slower corrosion rate. The IMCs layer of plane with weak microstructural heterogeneity stabilizes more quickly during the corrosion stabilization stage. The plane perpendicular to the build direction exhibits the highest corrosion resistance due to fewer corrosion initiation locations and the weakest microstructural heterogeneity. Furthermore, the composite structure of carbide core + Si phase shell, generated during corrosion, contributes to improving localized corrosion resistance. This study provides insights into understanding the influence of the heterogeneous microstructure from additive manufacturing on the reaction-diffusion process and offers guidance on direction selection when preparing components for applications in contact with aluminum melts using additive manufacturing techniques.

Effect of cooling rates and heat treatment time on Si phase of AlSi10Mg alloy manufactured by selective laser melting: Microstructure evolution and strengthening mechanism

As a processing technique to change the organization and properties of materials, heat treatment was widely used to strengthen metallic materials. This study examines the impact of varying cooling rates and heat treatment durations on the mechanical properties and microstructure of AlSi10Mg alloys produced through Selective laser melting (SLM). The heat treatment process was Solution Heat Treatment (SHT, 525 °C), and the heat treatment time includes 1 h, 2 h, and 3 h. Cooling methods consist of Refrigerant Cooling (RC), Water Cooling (WC), Air Cooling (AC), Oil Cooling (OC), and Furnace Cooling (FC). As the cooling rate decreases and the heat treatment time increases, the size of the formed Si phase particles varies from small to large, and the distribution deviates from inhomogeneous to homogeneous. In addition, the number of precipitated particles increases and then decreases. To investigate the impact of cooling rates and heat treatment time on the mechanical properties of AlSi10Mg alloys, quasi-static tensile and compression tests were performed. On the other hand, the tensile strength of the heat-treatment samples decreases while the ductility increases, and the Vickers hardness of the samples also decreases with decreasing cooling rate and increasing heat treatment time. The results of the study showed that the cooling rate and heat treatment time of the material had a greater effect on its tensile properties than on its compressive properties. The samples treated at 525 °C - 2 h - AC exhibited the highest tensile and compressive properties. Finally, the analysis of the strengthening mechanism of AlSi10Mg alloys through the presence of Si phase particles of varying sizes was conducted using transmission electron microscopy.

The aging-hardening behavior of short-time in high pressure die casting AlSi9MgMnZn alloy

Short-time aging is an effective industrial technique for enhancing the mechanical properties of high pressure die cast (HPDC) aluminum alloy components. However, the evolution of precipitation behavior during short-time aging of HPDC alloys remains unclear. In this study, the short-time aging behavior of HPDC AlSi9MgMnZn alloy was investigated. The results show that the AlSi9MgMnZn alloy exhibits effective aging-hardening, with an increment in hardness of approximately 30 HV through the optimal short-time aging treatment (aged at 180 °C for 120 minutes). Higher aging temperatures led to reduced peak hardness and rapid over-aging above 220 °C. The microstructure observation indicates that the peak short-time aging promotes the simultaneous precipitation of β″ precipitates, GP zones and nano Si phases. The contribution of different strengthening mechanisms to hardness was estimated, implying that the coexistence of β″ precipitates and GP zones can provide a positive contribution to aging-hardening during short-time aging. Moreover, as the aging temperature increases, the appearance of β′ precipitates reduces the strengthening effect, leading to a decrease in hardness.

A new synergy to overcome the strength-ductility dilemma in Al-Si-Cu alloy by adding AlZrNiTi master alloy

With the increase in lightweight components, Al-Si-Cu alloys are extensively applied in the automotive field. In this study, a multi-principal element alloy (MPEA) AlZrNiTi was designed to modify the Al-9Si-3Cu alloy, and the modification effects of individual additions of Zr, Ni, and Ti elements to the alloy were assessed. Moreover, the microstructure evolution, fracture behavior, and the mechanisms of strengthening and toughening during the modification process were investigated. Experimental results showed that when the addition amount of AlZrNiTi alloy was 0.8 wt%, significant refinements were made to the α-Al, eutectic Si, and Al2Cu in the Al-9Si-3Cu alloy, and the mechanical properties were significantly improved. In addition, the AlSiZr phase served as the heterogeneous nucleation core of α-Al was discovered. Furthermore, the AlZiTi phase was enriched at the front edge of the solid-liquid interface in solidification, hindering the growth of α-Al grains. It was also found that Al(Ni, Cu) particles with a size of 336 nm promoted the formation of high-density twins in Si crystal through the impurity-induced twin (IIT) mechanism, thereby modifying the Si phase. Comparative experiments reveal that the modification effect and mechanical properties of AlZrNiTi master adding to Al-9Si-3Cu alloy was obviously better than that of individual adding Zr, Ni, and Ti elements.

Predictive modeling of fatigue and rutting parameters for asphalt cement modified with pretreated oil palm clinker using artificial neural network algorithms to enhance pavement performance

Currently, the viscoelastic properties of standard asphalt cement cannot sustain the increasing demands resulting from heavier traffic loads, greater stress levels, and changing environmental conditions. Thus, the usage of modifiers is encouraged. Also, the Sustainable Development Goal (SDG) encourages the use of waste resources and emerging technologies in asphalt pavement technology. This study intends to harness this gap by examining the use of oil palm clinker (OPC) as an asphalt-cement modification to improve its viscoelastic properties using an innovative prediction approach. The modified asphalt-cement was produced by varying the acid-treated OPC powder (OPCP) content at 2%, 4%, 6%, and 8% and the rutting and fatigue performance was evaluated. This paper also presents an optimization approach and prediction comparison based on statistical modeling and artificial intelligence (AI) algorithms for the fatigue and rutting parameters of the modified asphalt cement. Model variables for the predictive models include OPCP content and test temperatures. The AI algorithms use 70% of the data for training, 15% for testing, and 15% for validation. The results showed that the incorporation of OPCP improves the properties of pure asphalt-cement by increasing stiffness and temperature susceptibility and that the crystalline phase of Si–O formed a novel structural group Si–OH. The RSM R2 for rutting for unaged and RTFO aged responses was (99.743 and 99.893), the RMSE was (436.210 and 954.945), and the MRE was 3.269 and 2.315) for the model statistical performance index, respectively. The ANN R2 for rutting for unaged and RTFO aged responses were (99.903 and 99.970) the RMSE (106.283 and 528.500) and MRE (1.759 and 1.039). PAV fatigue RSM R2 values were (99.984), RMSE (77979.750), and MRE (12.089), while ANN R2 values were (99.997), RMSE (53933.500), and MRE (5.262). The findings demonstrated that the generated model and algorithm could predict the fatigue and rutting performance of the OPCP-modified asphalt cement accurately with the AI algorithms model outperforming the statistical model. Also, the study aligns with SDG 9 by developing advanced modeling techniques and enhancing infrastructure durability through innovative use of modified materials as well as SDG 12 by incorporating recycled materials into sustainable production practices.

A Quantitative Phase Analysis by Neutron Diffraction of Conventional and Advanced Aluminum Alloys Thermally Conditioned for Elevated-Temperature Applications.

As the issue of climate change becomes more prevalent, engineers have focused on developing lightweight Al alloys capable of increasing the power density of powertrains. The characterization of these alloys has been focused on mechanical properties and less on the fundamental response of microstructures to achieve these properties. Therefore, this study assesses the quality of the microstructure of two high-temperature Al alloys (A356 + 3.5RE and Al-8Ce-10Mg), comparing them to T6 A356. These alloys underwent thermal conditioning at 250 and 300 °C for 200 h. Time-of-flight neutron diffraction experiments were performed before and after conditioning. The phase evolution was quantified using Rietveld refinement. It was found that the Si phase grows significantly (13-24%) in T6 A356, A356 + 3.5RE, and T6 A356 + 3.5RE alloys, which is typically correlated with a reduction in mechanical properties. Subjecting the A356 3.5RE alloy to a T6 heat treatment stabilizes the orthorhombic Al4Ce3Si6 and monoclinic β-Al5FeSi phases, making them resistant to thermal conditioning. These two phases are known for enhancing mechanical properties. Additionally, the T6 treatment reduced the vol.% of the cubic Al20CeTi2 and hexagonal ᴨ-Al9FeSi3Mg5 phases by 13% and 23%, respectively. These phases have detrimental mechanical properties. The Al-8Ce-10Mg alloy cubic β-Al3Mg2 phase showed significant growth (82-101%) in response to conditioning, while the orthorhombic Al11Ce3 phase remained stable. The growth of the beta phase is known to decrease the mechanical properties of this alloy. These efforts give valuable insight into how these alloys will perform and evolve in demanding high-temperature environments.

A Comparison of the Tribological Properties of SiC Coatings Prepared via Atmospheric Plasma Spraying and Chemical Vapor Deposition for Carbon/Carbon Composites

The microstructure, mechanical performance, and tribological properties of SiC ceramic coatings prepared via atmospheric plasma spraying (APS) and chemical vapor deposition (CVD) method were compared to provide good anti-wear protection for carbon/carbon composites. The surface morphology of the APS-SiC coating was characterized as having a porous structure, whilst the CVD-SiC coating presented with many pyramidal-shaped crystals constituting the surface. The APS-SiC coating consists of a dominating SiC phase and a small fraction of the Si phase, while the XRD pattern of the CVD-SiC coating mainly consists of the SiC phase. The dense crystalline microstructure of the CVD-SiC coating made it possess a higher hardness and Young’s modulus at 31.0 GPa and 275 GPa, respectively. The higher H/E and H3/E2 parameters of the CVD-SiC coating implied that it exhibited better plastic resistance, which is also beneficial for anti-wear properties. The scratch test reflected the critical loads of the spallation of the APS-SiC coating and CVD-SiC coating, which were evaluated to be 25.9 N and 36.4 N, respectively. In the tribological test, the friction coefficient of the APS-SiC coating showed obvious fluctuations at high load due to damage to the SiC coating. The wear mechanism of the APS-SiC coating was dominated by abrasive wear and fatigue wear, while CVD-SiC was mainly dominated by abrasive wear. The wear rate of the CVD-SiC coating was far below that of the APS-SiC coating, suggesting the better wear-resistance of the CVD-SiC coating.

Improving the Mechanical Properties of Al-Si Composites through the Synergistic Strengthening of TiB2 Particles and BN Nanosheets

The size and distribution of the silicon phase and intermetallic phase are important factors affecting the properties of Al11Si3Cu2NiMg alloy (M142). In this study, BNNS and micro-TiB2 were used to synergistically refine and reinforce M142 composites (M142-BNNS-TiB2). After T6 heat treatment, the comprehensive mechanical properties of M142-BN-TiB2 composites were excellent, with an ultimate tensile strength of 463 MPa and an elongation of 2.6%. In addition, the introduction of BNNS and micro-TiB2 changed the fracture mode of M142 from brittle fracture to quasi-cleavage fracture, and the introduction of BNNS and micro-TiB2 refined the Si phase and intermetallic phase, which could change the origin of the crack in the composite, thus improving the ductility of the composite.

Fracture failure analysis of traction transformer oil pump flange

A flange fracture occurred during the installation of a traction transformer oil pump. The causes of the flange fracture were analyzed using physical, chemical, and finite element methods. The fracture surface shows expanded edges and a linear fracture source, indicating an overload fracture. No significant defects such as pinholes, looseness, or cracks were found in the internal structure, which contains elongated Si phases. The Si, Ti, and Zn content in the failure part does not meet standard specifications. The hardness of the failure part is HBW107.8, meeting standards, but the elongation at break is at the lower limit, suggesting higher material brittleness. Finite element analysis revealed a maximum tensile stress of 241.5 MPa on the flange, close to the yield strength, indicating a small safety margin. The flange fracture is related to high material brittleness and potential assembly anomalies. To prevent similar incidents, strict control of raw material quality, regular inspection of mechanical properties, and finite element analysis for structural optimization are necessary.