The interfacial bonding between SiC and matrix in magnesium matrix composites (MMCs) has a crucial influence on their properties. In this work, SiC/AZ91 composites were prepared by stir casting and hot extruded. It was found that SiC refines grain size and decrease texture strength. The nano-state interfacial products Mg2Si and MgO adhered to the SiC surface, facilitating load transfer. The Al4C3 and Mg32(Al,Zn)49 are present near SiC, the brittleness of Al4C3 reduces the composite plasticity. After adding 1 wt% SiC, the yield strength (YS), ultimate tensile strength (UTS) and elongation (El) of AZ91 alloy increased to 250 MPa, 350 MPa and 15.1 %, respectively. El increased by more than 20 %. Higher SiC content increased YS, but UTS and El decreased significantly. The addition of few SiC can improve the properties, while high SiC content can bring excessive interfacial reaction and lead to degradation of composite properties.

Heat treatment is commonly employed after fabrication of metal matrix composites to enhance their physical and mechanical properties. Different heat treatment methods exert a significant impact on the mechanical behavior of composites. Using molecular dynamics simulations, we investigate the tensile loading behavior of SiCp/Al composites under various heat treatment conditions. We found that the accumulated residual stresses and microdefects introduced by heat treatment play a critical role on the yield strength and plastic evolution of the composites. Higher temperature differences and increased heat treatment cycles lead to more residual stresses and microdefects accumulation, resulting in decreased ultimate yield strength and earlier onset of yielding. Insufficient relaxation during heat treatment can lead to a lower ultimate tensile strength but a higher flow stress. At strain rates below a threshold (approximately 1 x109 s-1), strain rate sensitivity is reduced from 0.0295 to 0.0009 after heat treatment, evidenced by less pronounced variations in yield stress with strain rate at relatively low strain rates. The accumulation of microdefects and residual stress concentration near the reinforcement-matrix interfaces after heat treatment can serve as the initiation sites for plastic deformation and partly alleviate the mechanical loading.

The phenomenon of coalescence-induced droplet jumping on superhydrophobic surfaces has gained significant attention owing to its broad potential applications in self-cleaning, anti-icing, and phase-change heat transfer. In this study, molecular dynamics simulations were employed to investigate the coalescence-induced jumping behavior of nanodroplets on superhydrophobic surfaces with protruding, limitation, and combination structures. The simulations cover a broad range of parameters, including the dimensionless height of protruding structure (Hb* = 0–0.82), the dimensionless width (L* = 0.78–1.28), and the height (H* = 0–5) of the limitation structure, contact angles (100°–180°), and droplet radius ratios (0.6–1.3). The results reveal that all three patterned surfaces significantly influence droplet jumping behavior, with the specific effects depending on both structural parameters and droplet characteristics. Notably, the combination structure achieves the highest dimensionless droplet jumping velocity of 0.58 under specific conditions, corresponding to an energy conversion efficiency of 28.9%. This enhancement is attributed to the earlier impact of the expanding liquid bridge on the protruding structure and the increased asymmetry of the droplet morphology, along with the associated capillary force induced by the limitation structure during deformation. Additionally, the critical contact angles for coalescence-induced droplet jumping on superhydrophobic surfaces with flat, protruding, and combination structures are 162°, 117°, and 117°, respectively. It is also observed that the enhancement of droplet jumping is more pronounced for droplets of similar size.

Investigating the infiltration mechanism of molten metal in ceramic particle porous preforms provides critical theoretical guidance for optimizing the casting infiltration process and improving the quality of castings. In this study, the microstructural model of the zirconia-toughened alumina ceramic porous preform was precisely reconstructed using high-resolution X-ray computed tomography. Based on the lattice Boltzmann method, the infiltration process of the high-chromium cast iron molten metal in the porous preform of ceramic particles was simulated at the pore scale. The effects of molten metal viscosity (0.00175–17.5 Pa·s), injection velocity (0.005–0.1 m/s), surface tension (0.072–5 N/m), contact angle (20–80°), and preform placement positions on the infiltration behavior of the molten metal in the preform were investigated. The results indicate that increased molten metal viscosity enhances flow front stability by mitigating pore heterogeneity effects, thereby achieving higher steady-state saturation. However, it also increases flow resistance, which reduces steady-state saturation when the driving pressure is insufficient. Increasing the injection velocity or reducing the surface tension significantly improves steady-state saturation. The steady-state saturation distribution diagram of capillary number (Ca) and viscosity ratio (M) yields the empirical relation defining the boundary between high and low saturation regions: LogCac − 0.93LogM = −6.79. Moreover, reducing the contact angle of the preform wall significantly enhances steady-state saturation. Furthermore, positioning the preform in the top or middle regions of the cavity improves steady-state saturation under low injection velocities.

Understanding the mechanisms behind the evolution of microstructure and residual stress during heat treatment is crucial for improving the properties of metal matrix composites (MMCs). This study employs the molecular dynamics (MD) method to conduct six distinct cyclic heat treatments on SiCp/Al composites. The synergistic mechanisms of local residual stresses and microscopic defects during different heat treatments were explored. We found that all heat treatments successfully alleviate residual stresses in the first few cycles, with the gradual cooling strategy being the most effective after the second cycle. The dimensions of SiCp/Al composites consistently reduce after each cycle with high-temperature treatment, however in the later cycles stress accumulation and microstructural transformation occur. In the cycles with cryogenic (liquid nitrogen temperature) treatment, a localized stress concentration occurs after a certain number of cycles and leads to periodic dislocation avalanches, as well as a dramatic increase in the dimension. After cyclic heat treatment, both the number and size of stacking faults increase, the dislocation type may undergo a transformation. The study provides atomistic insights into understanding the thermal stress and microstructural evolution in SiCp/Al during heat treatment.

The novel type of vapor chamber (VC) with combined superhydrophilic/superhydrophobic surface holds great potential in hot spot cooling. In this study, an improved VC was developed by implementing structured surfaces on both condenser and evaporator. The thermal resistance, condenser temperature uniformity, and gravity independence were discussed. It was found that sintering an appropriate copper mesh on condenser could reduce the thermal resistance but would cause a slight deterioration in the temperature uniformity of the condenser. On the evaporator, the thermal performance of VC was further improved by introducing micro grooves on the wick in order to enhance bubble discharge of the boiling working fluid. Moreover, to strengthen the liquid recirculation on the evaporator, pore size gradient was adopted in the evaporator wick. Compared to the axial gradient of pore size, the radial gradient of pore size was more efficient in accelerating the working fluid recirculation. Among all the results reported in this study, the combination of sintering copper mesh on the condenser and implementing micro-grooves and pore size gradient on the evaporator wick yields optimal results, with the minimum thermal resistance of the VC reaching 0.041 K/W and the critical heat flux exceeding 213.3 W/cm2, which shows excellent thermal performance.

The coalescence-induced droplet jumping is a self-propelled water removal phenomenon on superhydrophobic surfaces, which has attracted considerable attention due to its potential in a wide range of applications such as self-cleaning and anti-icing/frosting. Improving the energy conversion efficiency, from the excessive surface energy to the kinetic energy, is pivotal to facilitate droplet jumping. In this study, we numerically investigated the dynamics of droplet coalescence on superhydrophobic surfaces with macro-stepped structures, with particular interest in understanding the role of the stepped structure on the droplet jumping process. Three-dimensional simulations were performed by using the lattice Boltzmann method, with the pseudopotential multiphase model and the multiple-relaxation-time collision operator being adopted to achieve high liquid–gas density/viscosity ratios. A wide range of nondimensional height difference of the stepped structure (0–1.5) and droplet radius ratio (0.5–2) was covered. Results show that adding macro-stepped structures can significantly enhance the droplet-wall interaction, thus yielding increased droplet velocity. The enhancement of droplet jumping is more remarkable for droplets of similar sizes, and the dimensionless height difference of the stepped structure is required to exceed a threshold of approximately 0.5. Among the present simulations, the maximum dimensionless droplet jumping velocity reaches 0.66, corresponding to an energy conversion efficiency of 35%. The present findings are helpful for the development of novel superhydrophobic surfaces that pursue efficient droplet removal.

The viscous fingering phenomenon often occurs when a low-viscosity fluid displaces a high-viscosity fluid in a homogeneous porous media, which is an undesirable displacement process in many engineering applications. The influence of wetting gradient on this process has been studied over a wide range of capillary numbers (7.5 × 10−6 to 1.8 × 10−4), viscosity ratios (0.0025 to 0.04), and porosities (0.48 to 0.68), employing the lattice Boltzmann method. Our results demonstrate that the flow front stability can be improved by the gradual increase in wettability of the porous media. When the capillary number is less than 3.5 × 10−5, the viscous fingering can be successfully suppressed and the transition from unstable to stable displacement can be achieved by the wetting gradient. Moreover, under the conditions of high viscosity ratio (M > 0.01) and large porosity (Φ > 0.58), wetting gradient improves the stability of the flow front more significantly.

h-BN is a two-dimensional ceramic material with a lamellar structure, known for its typical orientation char-acteristics on mechanical and thermal properties. By optimizing the size and arrangement of h-BN grains in the matrix, the anisotropic characteristics of h-BN ceramics can be fully utilized to obtain ceramic materials with high thermal conductivity or high strength. In order to study the effect of grain orientation distribution on the mechanical and thermal properties of materials, the index of orientation distribution (IOP) was used to quan-titatively characterize the orientation degree of h-BN grains and analyzed the effect of h-BN grain size on ma-terial properties. The results show when the initial h-BN size is 13.50 mu m, the ceramic has the highest orientation degree/-507, and the mechanical and thermal properties show obvious anisotropy. While the related properties of BN-YAG ceramics varies significantly with the decrease of initial h-BN grain size.

铝基多孔复合材料由铝基体和空心微球复合而成,兼具轻质与吸能特性.本文采用放电等离子烧结(SPS)方法制备玻璃空心微球/铝基多孔复合材料,通过光学显微镜、SEM、准静态压缩原位观察和数字图像相关技术表征,分析了空心微球含量及尺寸对复合材料准静态压缩变形行为和吸能性能的影响.结果表明:两步升温SPS烧结制备所得的铝基多孔复合材料,其微球弥散均匀嵌于铝基体中,铝基体熔合致密.随空心微球含量增加,复合材料压缩应力整体降低,屈服平台区扩大但由平滑转变为锯齿状,压缩变形行为从较均匀的鼓状形变逐渐发展为脆性剪切,微球体积分数为 50vol%的多孔复合材料吸能能力为 23.6 J·cm-3,高于体积分数为 30vol%和 70vol%的多孔复合材料,复合材料吸能能力与微球含量间存在最优对应关系.小尺寸微球具有更好的抗压能力,随小尺寸微球占比的提高,复合材料微观上可承受更高的应力-应变集中,宏观上剪切形变的压缩应变增大,本文中小尺寸微球多孔复合材料的峰值应力和吸能能力分别为 89.4 MPa和29.0 J·cm-3,与大尺寸微球多孔复合材料相比分别提高23.5%和22.9%.

The solid-liquid mixing is an important operation unit in the preparation of composites by stirring casting. High quality composite materials need good homogeneity and stable liquid level. In this work, the performances of the Rotor-Stator agitator for solid suspension in stirred tank were investigated through CFD modeling, including the homogeneity, power consumption and liquid level stability. The Eulerian-Eulerian (E-E) multiphase model and the RNG k-ε turbulence model were adopted for modeling the multiphase flow and the turbulence effects, respectively. The effect of various important parameters such as stirring speed, particle size, solid loading and the use of baffles were examined. Adding a stator structure with array holes outside the rotor can optimize the flow pattern, thereby improving the mixing uniformity and liquid level stability. The homogeneity and liquid level stability attained by the Rotor-Stator agitator were better than those for the A200 (an axial-flow agitator) and the Rushton (a radial-flow agitator).

We used molecular dynamics to simulate the interface diffusion and reaction behavior of Al/SiC composite at temperatures above the melting of the Al. The interfacial evolution, surface polarity and the wettability were examined by different hybrids of potentials that widely used in the simulations of metal-ceramic system. We demonstrated that the results from hybrids of potentials for the Al/SiC system that commonly used are inconsistent with experiments of the interfacial properties at high temperatures. The hybrids of the embedded atom method (EAM) potentials for Al with Tersoff-type potentials or the modified embedded atom method (MEAM) potential for the SiC show that the interface almost inert at 1200 to 1500 K. The combinations of Al potentials with Vashishta potential for SiC appear to give a more realistic description of the diffusion and reaction at Al/SiC interface, but still has shortcomings as diffusion also occurs at temperatures well below the melting point of Al. For the wetting behavior, the hybrids of EAM potential developed by Mendelev et al. for Al exhibit the largest contact angle among the potentials. The influence of surface polarity of the SiC on the wettability is weakened after a long enough time. The reaction products (e.g., Al4C3) and the influence on wetting at the interface may not be well characterized since the interaction of Al-C and Al-Si are only described by a pair potential. Our study provides support for molecular dynamics study of the Al/SiC system involving high temperature conditions.

The first principles method was utilized to study the interfacial properties of the TiB2 reinforced copper matrix materials. The interfacial stabilities were studied initially via the works of adhesion and interfacial energies. According to the results, TT-OT (Ti-terminated TiB2/Cu "OT" stacking) and BT-HCP (B-terminated TiB2/Cu "HCP" stacking) were confirmed to be the most stable interfaces. The charge density distribution, charge density difference, electronic localization function and partial density of state were analyzed for TiB2/Cu interfaces. The results indicate that Ti-terminated TiB2(0001)/Cu(111) interfaces were more inclined to form the metallic bond, while the B-terminated TiB2(0001)/Cu(111) interfaces were likely to form the ionic bond. Moreover, the interfacial elastic energy, interfacial fracture toughness and ultimate tensile tress were carried out to make clear of fracture mechanism of the TiB2(0001)/Cu(111) interfaces. The TT-OT and BT-HCP were confirmed to be the two most stable interfaces due to their largest interfacial elastic energies. The computational ultimate tensile tress for Ti-terminated TiB2(0001)/Cu(111) and B-terminated TiB2(0001)/Cu(111) interfacial models were 23 GPa and 25 GPa, respectively.

The coefficient of thermal expansion (CTE) mismatch between the reinforcement and the matrix results in thermal residual stresses and defects within metal-matrix composites (MMCs) upon cooling from the processing temperature to ambient temperature. The residual stresses and thermally induced defects play an important role in the mechanical properties of MMCs, it is critical to understand the mechanism of defect formation and evolution. This study provides atomistic simulations to reveal the generation of thermal residual stresses, dislocation and incomplete stacking fault tetrahedron (ISFT) during cooling in the idealized Cu/SiC composites. We found that dislocations are generated explosively in a certain tem-perature range during cooling, which results in a non-linear relationship between dislocation density and temperature. The combined effect of the stresses induced by CTE mismatch and the thermodynamic state of the metal leads to the rapid generation of dislocations. The Shockley partial and the highly stable stair rod are the two dominant dislocation structures. The immobile stair-rod dislocations and the highly stable ISFTs formed in the initial high temperature stage inhibit further development of plastic deforma-tion. The present results provide new insights into the defect formation mechanism and the dislocation strengthening mechanism of MMCs caused by thermal mismatch between constituents.

Good solid-liquid mixing homogeneity and liquid level stability are necessary conditions for the preparation of high-quality composite materials. In this study, two rotor-stator agitators were utilized, including the cross-structure rotor-stator (CSRS) agitator and the half-cross structure rotor-stator (HCSRS) agitator. The performances of the two types of rotor-stator agitators and the conventional A200 (an axial-flow agitator) and Rushton (a radial-flow agitator) in the solid-liquid mixing operations were compared through CFD modeling, including the homogeneity, power consumption and liquid level stability. The Eulerian–Eulerian multi-fluid model coupling with the RNG k–ε turbulence model were used to simulate the granular flow and the turbulence effects. When the optimum solid-liquid mixing homogeneity was achieved in both conventional agitators, further increasing stirring speed would worsen the homogeneity significantly, while the two rotor-stator agitators still achieving good mixing homogeneity at the stirring speed of 600 rpm. The CSRS agitator attained the minimum standard deviation of particle concentration σ of 0.15, which was 42% smaller than that achieved by the A200 agitators. Moreover, the average liquid level velocity corresponding to the minimum σ obtained by the CSRS agitator was 0.31 m/s, which was less than half of those of the other three mixers.

The thermal residual stresses and plastic deformation caused by the coefficient of thermal expansion (CTE) mismatch in the cooling process play an important role in the physical and mechanical properties of metal matrix composites (MMCs). In this study, the Cu/SiCp composites with and without cooling process are subjected to uniaxial tensile and compressive loadings through molecular dynamics (MD) simulation. We found that the cooling process leads to a decrease in strength and earlier yielding. The mechanical response depends on the temperature drop, and samples cooled from a higher temperature have a lower yield strength. The introduction of reinforcements and thermally induced defects reduce the tension/compression (C/T) asymmetry as compared with that of single crystal and defective Cu. These pre-existing defects can be the source for the initiation of plasticity in early stage of external loading, and the defect evolution shows a C/T asymmetry. For the density of two predominant dislocation types, the Shockley partial increases at the stress buildup stage, while the stair-rod dislocation decreases, regardless of tension and compression. The mechanisms for the dissociation of stair-rod dislocation and incomplete stacking fault tetrahedrons (ISFTs) at the stress buildup stage have been revealed. Our results provide an atomic-scale perspective to understand the influence of thermally residual stresses and defects on mechanical behavior of MMCs.

The interfacial mechanics and electrical properties of SiC reinforced copper matrix composites were studied via the first principles method. The work of adhesion (Wad) and the interfacial energies were calculated to evaluate the stabilities of the SiC/Cu interfacial models. The carbon terminated (CT)-SiC/Cu interfaces were predicted to be more stable than those of the silicon terminated (ST)-SiC/Cu from the results of the Wad and interfacial energies. The interfacial electron properties of SiC/Cu were studied via charge density distribution, charge density difference, electron localized functions and partial density of the state. Covalent C–Cu bonds were formed based on the results of electron properties, which further explained the fact that the interfaces of the CT-SiC/Cu are more stable than those of the ST-SiC/Cu. The interfacial mechanics of the SiC/Cu were investigated via the interfacial fracture toughness and ultimate tensile stress, and the results indicate that both CT- and ST-SiC/Cu interfaces are hard to fracture. The ultimate tensile stress of the CT-SiC/Cu is nearly 23 GPa, which is smaller than those of the ST-SiC/Cu of 25 GPa. The strains corresponding to their ultimate tensile stresses of the CT- and ST-SiC/Cu are about 0.28 and 0.26, respectively. The higher strains of CT-SiC/Cu indicate their stronger plastic properties on the interfaces of the composites.

Molecular dynamics (MD) simulations are performed to study the near-surface deformation during nanoscratching on nanocrystalline Al. The influence of Si particle on wear behavior of nanocrystalline Al is also investigated by MD simulation. It is shown that the local deformation in nanocrystalline Al workpiece is associated with one or more mechanisms: (1) grain boundary (GB) migration, (2) GB sliding, (3) grain rotation, and (4) dislocations and deformation twin emitting from the indenter-workpiece interface and GBs. Moreover, the coarsening of Al grains is observed as the scratch proceeds. During grain coarsening, the low angle GB dissociates while the high angle GB migrates without dissociation. Interestingly, the GB motion is more active in nanocrystalline Al workpiece than that in Al/Si workpiece. The presence of Si particle changes the stress state of the adjacent Al grains, and therefore enhances the stability of GBs. Meanwhile, the specific wear rate in Al/Si workpiece is significant less than that in nanocrystalline Al workpiece, indicating that the Si particle enhances the wear resistance. In summary, this study sheds light on the interaction mechanism of second-phase and nanocrystalline matrix under sliding wear, which can provide theoretical support for the design of metal matrix composite with excellent wear resistance.

As-cast irons and aluminum alloys are used in various industrial fields and their phase and microstructure properties are strongly affected by the undercooling degree. However, existing studies regarding the undercooling degree are mostly limited to qualitative analyses. In this paper, a quantitative analysis of the undercooling degree is performed by collecting experimental data and employing machine learning. Nine machining learning models including Random Forest (RF), eXtreme Gradient Boosting (XGBOOST), Ridge Regression (RIDGE) and Gradient Boosting Regressor (GBDT) methods are used to predict the undercooling degree via six features, which include the cooling rate (CR), mean atomic covalence radius (MAR) and mismatch (MM). Four additional effective models of machine learning algorithms are then selected for a further analysis and cross-validation. Finally, the optimal machine learning model is selected for the dataset and the best combination of features is found by comparing the prediction accuracy of all possible feature combinations. It is found that RF model with CR and MAR features has the optimal performance results for predicting the undercooling degree.

The charge communications have been widely existed in the metal materials when they are under the processing, the modeling and the failing. We studied the interfacial charge transformation of the TiB 2 /Cu composites via the first principles method. The layer thickness was predicted by the interfacial charge communications performed on the regions of the TiB 2 /Cu interfaces. The layer thickness of the Ti-terminated (TT)TiB 2 /Cu were predicted longer than those of the B-terminated(BT) TiB 2 /Cu and contrasting with their average vales as 0.75 (nm) and 0.65 (nm), respectively. The Mulliken population was applied to investigate the bond length, bond population and charge transformation of the six TiB 2 /Cu models. The Ti-Cu bond was only detected in TT-HCP interfaces among the all TT-TiB 2 /Cu models, which was further confirmed that the metallic bond of the Ti-Cu with the bond length and population as 2.5 Å and 0.22, respectively. Nevertheless, the B-Cu bond were detected in all BT-TiB 2 /Cu models, and the bond length and population higher than those of B-Cu bond in chemical complexes. The 5 atomic layers were involved in quantitative analyses of the interfacial charge transformation. The results indicate that the charges lost by interfacial Ti atom were inequivalent obtained by Cu and B atoms which nearby the interfacial Ti atoms of the TT-TiB 2 /Cu. Comparing with the BT-TiB 2 /Cu models, the charges acquired by the interfacial B atom were most from the Ti and less from the Cu atoms surrounded the interfacial B atoms.