Formation mechanism of Si-Y-C ceramic matrix by reactive melt infiltration using Si-Y alloy and properties of C/Si-Y-C composites

Herein, Si-Y eutectic alloy were introduced into porous C/C preform by reactive melt infiltration (RMI) to prepare C/Si-Y-C composite. Phase compositions and their distributions in the as-prepared composites were investigated. Result indicated that four main regions were found in the typical zone in Si-Y-C matrix, i.e., amorphous carbon, polycrystalline SiC doped with YSi2, amorphous SiC and single crystal YSi2. Based on the reaction between Si-Y alloy and C/C preform and microstructural observations, a model regarding to microstructure formation mechanism was proposed to reveal reaction process. Moreover, improved flexural strength, fracture toughness, thermal diffusivity and thermal conductivity of C/Si-Y-C composite were achieved compared to C/C-SiC.     

Si/(Yb1-xYx)2Si2O7/LaMgAl11O19热/环境障涂层的高温性能研究

采用等离子喷涂法在碳化硅纤维增强碳化硅陶瓷基复合材料(SiC_f/SiC-CMCs)表面制备了Si/(Yb_1-xY_x)₂Si₂O₇/LaMgAl₁₁O₁₉(x=0、0.5)热/环境障涂层(T/EBCs)体系。通过SEM、EDS和XRD等测试方法研究了不同组成的T/EBCs体系在1 300 ℃下的热循环性能和抗水氧腐蚀性能,进而探讨了热循环失效和水氧腐蚀失效机理。结果表明,在T/EBCs体系中,Si/Yb₂Si₂O₇/LMA涂层体系的热循环寿命为403次,抗水氧腐蚀性能为50 h,Si/YbYSi₂O₇/LMA体系的热循环寿命降低至277次,而水氧腐蚀性能提高至80 h。YbYSi₂O₇与LMA之间较大的热失配应力以及层间含Al化合物或固溶体的生成是Si/YbYSi₂O₇/LMA热循环寿命降低的主要原因;YbYSi₂O₇-EBCs层较少的杂质氧化物减少了与水反应生成挥发性物质的几率,提高了Si/YbYSi₂O₇/LMA的抗水氧腐蚀能力。     

Biodegradable magnesium alloy coated with TiO2/MgO two-layer composite via magnetic sputtering for orthopedic applications: A study on the surface characterization,corrosion, and biocompatibility

In this study, a coating of thin TiO₂ layer and a TiO₂/MgO double layer were created on the surface of AZ91D alloy by magnetic sputtering method in order to improve the corrosion and biocompatibility properties of this alloy. The microstructural studies by field-emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD) showed that coatings were formed continuously and homogeneously on the alloy surface. In the double-layer coating, MgTiO₃ and Mg₂TiO₄ compounds were formed at the coating/substrate interface in addition to TiO₂ and MgO phases as the main phases in the coating structure. The results of corrosion test showed that in general, coating improves the corrosion of AZ91D alloy in simulated-body fluid (SBF). The double-layer coating showed the best corrosion resistance at a corrosion current of 5.743 × 10^?7 μA/cm² and a corrosion potential of ?1.513 V due to its cathodic protection of the substrate and blockage of the path of the corrosive solution towards the substrate. In vitro tests showed that considering the good match between the used materials as the coating and body, no toxic material exits which results in improvement in biocompatibility, adhesion, and bone-cell multiplication.     

Preparation of SiC/SiC composites with high toughness by reaction of the SiCP+C double-cladding layer with liquid silicon

SiC/SiC composites prepared by liquid silicon infiltration (LSI) have the advantages of high densification, matrix cracking stress and ultimate tensile strength, but the toughness is usually insufficient. Relieving the residual microstress in fiber and interphase, dissipating crack propagation energy, and improving the crystallization degree of interphase can effectively increase the toughness of the composites. In this work, a special SiC particles and C (SiC_P +C) double-cladding layer is designed and prepared via the infiltration of SiC_P slurry and chemical vapor infiltration (CVI) of C in the porous SiC/SiC composites prepared by CVI. After LSI, the SiC generated by the reaction of C with molten Si combines with the SiC_P to form a layered structure matrix, which can effectually relieve residual microstress in fiber and interphase and dissipate crack propagation energy. The crystallization degree of BN interphase is increased under the effects of C-Si reaction exotherm. The as-received SiC/SiC composites possess a density of 2.64 g/cm³ and a porosity of 6.1%. The flexural strength of the SiC/SiC composites with layered structure matrix and highly crystalline BN interphase is 577 MPa, and the fracture toughness reaches up to 37 MPa·m^1/2. The microstructure and properties of four groups of SiC/SiC composites prepared by different processes are also investigated and compared to demonstrate the effectiveness of the SiC_P +C double-cladding layer design, which offers a strategy for developing the SiC/SiC composites with high performance.     

Effect of interface oxidation treatment on the interfacial reactions and wear properties of co-continuous SiC3D/Cu composites

Co-continuous SiC_3D/Cu composites are interesting wear-resistant materials with a unique structure. However, their interface reaction limits their practical applications. In this study, co-continuous SiC_3D/Cu composites were fabricated by pressureless infiltration, and their interfaces were modified with different interface oxidation states by high-temperature oxidisation and atmospheric treatment. The effects of the different interface oxidation treatments on the interfacial reaction and wear behaviour of the co-continuous composites were investigated. The results revealed that the surface oxidisation of the three-dimensional SiC skeleton by high-temperature oxidisation prevented the interface reaction between the SiC strengthening phase and the Cu alloy matrix phase, thus improving the interface bonding and wear properties of the composites. In addition, the surface oxidisation of the Cu alloy matrix phase prevented the occurrence of the interface reaction and improved the interface bonding of the composites. However, the Cu alloy was oxidised and the hardness of the matrix phase in the composites decreased when the infiltration atmosphere was changed into an air environment. Finally, the co-continuous SiC_3D/Cu composite with oxidised SiC and unoxidised Cu showed the best wear-resistance performance (approximately 9.77 × 10^-7 cm³·m^?1·N^?1).     

Novel approach using EIS to study flow accelerated pitting corrosion of AA5083-H321 aluminum–magnesium alloy in NaCl solution

EIS was utilized as a novel approach to study the role of mechanical and electrochemical processes in flow accelerated pitting corrosion behaviour of AA5083-H321 aluminum–magnesium alloy in 3.5% NaCl solution. This alloy is a suitable material for manufacturing of high speed boats, submarines, desalination systems etc. Impedance spectra were obtained during 24 h of exposure of the samples to the test solution at different rotation speeds. The surface and cross section of the samples were studied by scanning electron microscopy (SEM) and EDAX analysis. The results indicated that increasing the rotation speed causes the depth of pits to increase. By further increasing the rotation speed to 5 and 7 m s⁻¹, the flow condition causes the passive layer inside the pits to breakdown. Simultaneously, the thickness of the passive layer on the areas other than the pits becomes thinner. Shear stresses at 10 m s⁻¹ are so severe that the passive layer on the entire surface breaks down and leads to micropitting corrosion.     

The ablation behavior and mechanical property of C/C-SiC-ZrB2 composites fabricated by reactive melt infiltration

In order to improve the ablation resistance of carbon/carbon (C/C) composites, SiC-ZrB₂ di-phase ceramic were introduced by reactive melt infiltration. The ablation properties of these composites were evaluated by oxyacetylene torch with a heat flux of 2.38 MW/m² for 60 s. Compared with the pure C/C composites, the C/C-SiC-ZrB₂ composites show a significant improvement in the ablation resistance, and the linear and mass ablation rates decreased from 10.28×10⁻³ mm/s to 6.72×10⁻³ mm/s and from 3.08×10⁻³ g/s to 0.61×10⁻³ g/s, respectively. After ablation test, the flexural strength retentions of the C/C and C/C-SiC-ZrB₂ composites near the ablated center region are 39.7% and 81.6%, respectively. The higher strength retention rate of C/C-SiC-ZrB₂ composites was attributed to the introduction of SiC-ZrB₂ ceramic phases, which have excellent ablation resistant property. During ablation test, an ‘embedding structure’ of Zr-O-Si glass layer was formed, which could act as an effective barrier for oxygen and heat. The oxide ceramic coating could protect the C/C-SiC-ZrB₂ composites from further ablation, and thus contribute to retaining the mechanical property of C/C-SiC-ZrB₂ composites after ablation.     

Microstructures and tribological behaviors of Cf/C-SiC composites tailored by Cu and Fe-Si matrices

Ternary Cu-Fe-Si alloy were applied to modify tribological behavior of carbon fiber/carbon-silicon carbide (C_f/C-SiC) composites by reactive melt infiltration. Microstructures, physical properties and tribological properties on a full-scale train brake test rig of the modified composites were studied. Results indicate that both Cu and Fe-Si alloy as matrices lead to significantly enhanced thermal conductivity and compressive strength for C_f/C-SiC composites. Moreover, the average friction coefficient of the modified composites is between 0.25 and 0.55, which is higher than that of copper metal matrix composites. In addition, the average volume wear rate of the modified composites is only 0.168 cm³/MJ. The C_f/C-SiC composites modified by Cu and Fe-Si alloy with improved physical properties and tribological properties meet the technical requirement and show high application potential in express train brake systems.     

Reactive infiltration processing of SiC/Fe–Si composites using preforms made of coked rice husks and SiC powder

A reactive infiltration processing of SiC/Fe–Si composites using preforms made of coked rice husks (RHs) and SiC powder in different ratios is reported, in which FeSi₂ alloy was used as infiltrant. The preforms were heat-treated at 1550 °C for 6 h prior to the infiltration. The coked RHs, which are composed of SiO₂ and C, were converted to SiC and poorly crystallized C by carbothermal reduction during the heat treatment. The study of the microstructure and mechanical properties of the composites shows that molten Fe–Si alloy had good wetting of the heat-treated preforms and adequate infiltration properties. Free carbon in the preform reacted with Si in the molten FeSi₂ during infiltration forming new SiC, the composition of the intermetallic liquid being moved towards that of FeSi. As a result, the infiltrated composites are composed of SiC, FeSi₂ and FeSi phases. Vickers hardness, elastic modulus, three-point flexural strength and indentation fracture toughness of the composites are found to increase with SiC additions up to 30% w/w in the preforms, reaching the values of 18.2 GPa, 290 GPa, 213 MPa and 4.9 MPa m^1/2, respectively. With the SiC addition further raised to 45% w/w, the elastic modulus, flexural strength and fracture toughness of the composite turned down probably due to high residual stress and hence the more intense induction of microcracks in the composite. De-bonding of SiC particles pulled out of the Fe–Si matrix, transgranular fracture of part of the SiC particles and in the Fe–Si matrix, and crack bridging all exist in the fracture process of the composites.     

Corrosion resistance of calcium zirconate crucible to titanium-copper melts

The corrosion resistance of refractory materials to the titanium alloy melts is vital for the production of titanium alloys by vacuum induction melting. In this study, the corrosion behavior of calcia-stabilized zirconia, solid state synthesized calcium zirconate, and fused calcium zirconate refractory suffering Ti-5 wt% Cu melts were investigated at 1680 ℃ for 15 min of soaking time by the cup test method. It was found that the three crucibles directly dissolved into the titanium melt, then generated Ti (Zr, O) and CaZrO₃ in the infiltration layer, and eventually developed a porous Ti₃O layer in the lining. Besides, the contamination of Ti-5 wt% Cu alloy (oxygen: 5.3 wt%; zirconium: 6.01 wt%; calcium: 0.42 wt%) by fused calcium zirconate crucible was significantly less than the solid state synthesized one (oxygen: 5.83 wt%; zirconium: 6.14 wt%; calcium: 0.43 wt%), implying that the production method of calcium zirconate notably affected the impurity of titanium alloys.     

Polymer-metal slurry reactive melt infiltration: A flexible and controllable ceramic modification strategy for irregular C/C components

Herein, we investigate the applicability of the polycarbosilane (PCS)–metal slurry reactive melt infiltration (RMI) process to various metals. The slurry exhibiting the best ceramized ability was used to examine the relationship between the ceramic thickness and reactive time, ceramic thickness and reactive temperature, and infiltration depth and slurry-coating thickness. The results show that the thickness of the ceramic layer increases with reactive time and temperature and the infiltration depth increases with the coating thickness. PCS–Si₉₀Zr₁₀ slurry RMI was selected to modify cylindrical nozzle C/C preforms, and dense C/C–SiC–ZrC composites with a density of ~2.05 g cm⁻³ were obtained. Owing to the good control of the PCS–Si₉₀Zr₁₀ slurry RMI on the interface, matrix, and carbon fiber of the as-received cylindrical composites, the bending strength of the C/C–SiC–ZrC composites was as high as 306.4 MPa, which is considerably higher than that of a C/C preforms (70.4 MPa). Considering the ablation resistance, the mass and linear ablation rates of the C/C–SiC–ZrC composite (~0.29 mg s⁻¹ and ~2.48 × 10⁻³ mm s⁻¹, respectively) were similar to those of the composites prepared using traditional RMI (~0.23 mg s⁻¹ and ~2.29 × 10⁻³ mm s⁻¹). The proposed polymer–metal RMI is more suitable for the modification of C/C preforms with thin-wall structures owing to its advantages including precise control of infiltration dose and flexible operation of slurry coating. Furthermore, it is suitable for the local modification of C/C components.     

Application of SiO2-coated SiC powder in stereolithography and sintering densification of SiC ceramic composites

Stereolithography additive manufacturing of SiC ceramic composites has received much attention. However, the forming efficiency and mechanical properties of their products need to be improved. This study aimed to prepare SiC ceramic composites with complex shapes and high flexural strength using a combination of digital light processing (DLP) and reactive solution infiltration process (RMI). A low-absorbance SiO₂ cladding layer was formed on the surface of SiC powder through a non-homogeneous precipitation process. With the densification of the cladding layer at high temperatures, SiO₂-coated SiC composite powder was used to formulate a photosensitive ceramic slurry with a solid content of 44 vol%. The resulting slurry exhibited a considerable improvement in curing thickness and rate and was used to mold ceramic green body with a single-layer slicing thickness of 100 μm using DLP. The ceramic blanks were then sintered and densified using a carbon thermal reduction combined with liquid silica infiltration (LSI) process, resulting in SiC ceramic composites with a density of 2.87 g/cm³ and an average flexural strength of 267.52 ± 2.5 MPa. Therefore, the proposed approach can reduce the manufacturing cycle and cost of SiC ceramic composites.     

Effect of PyC interphase thickness on mechanical behaviors of SiBC matrix modified C/SiC composites fabricated by reactive melt infiltration

A dense carbon fiber reinforced silicon carbide matrix composites modified by SiBC matrix (C/SiC-SiBC) was prepared by a joint process of chemical vapor infiltration, slurry infiltration and liquid silicon infiltration. The effects of pyrolytic carbon (PyC) interphase thickness on mechanical properties and oxidation behaviors of C/SiC-SiBC composites were evaluated. The results showed that C/SiC-SiBC composites with an optimal PyC interphase thickness of 450 nm exhibited flexural strength of 412 MPa and fracture toughness of 24 MPa m^1/2, which obtained 235% and 300% improvement compared with the one with 50 nm-thick PyC interphase. The enhanced mechanical properties of C/SiC-SiBC composites with the increase of interphase thickness was due to the weakened interfacial bonding strength and the decrease of matrix micro-crack amount associated with the reduction of thermal residual stress. With the decrease in matrix porosity and micro-crack density, C/SiC-SiBC composites with 450 nm-thick interphase exhibited excellent oxidation resistance. The residual flexural strength after oxidized at 800, 1000 and 1200 °C in air for 10 h was 490, 500 and 480 MPa, which increased by 206%, 130% and 108% compared with those of C/SiC composites.     

Polypyrrole electropolymerized on aluminum alloy 1100 doped with oxalate and tungstate anions

Polypyrrole films doped with oxalic acid and tungstate were potentiostatically electropolymerized on aluminum alloy 1100. Two statistical factorial designs (fractional and complete) were used to study the influence of the synthesis variables on the film performance against corrosion. Corrosion protection of the polypyrrole films doped with oxalate and tungstate anions (PPy/OXA/W) on the aluminum alloy was evaluated by potentiometric and electrochemical impedance spectroscopy (EIS) measurements in a 0.05 mol L⁻¹ NaCl solution. The results obtained showed that the best performance against corrosion was detected with the PPy/OXA/W film synthesized at 1.0 V, 1.5 C in 0.2 mol L⁻¹ pyrrole, 0.1 mol L⁻¹ oxalic acid and 0.05 mol L⁻¹ sodium tungstate solutions provide a protective effect against corrosion.     

Tuning ceramic content,mechanical and ablative properties of C/C–ZrC-ZrxCuy composites via using various C/C skeletons

C/C–ZrC-Zr_xCu_y composites were prepared by pressure-assisted reactive melt infiltration with Zr₂Cu alloy as an infiltrator. The mechanical and ablation properties of C/C–ZrC-Zr_xCu_y composites were tuned by applying various C/C skeletons (1.28, 1.40, 1.58, and 1.73 g/cm³). When the C/C skeleton density increased from 1.28 to 1.73 g/cm³, the density of the composites decreased gradually. Additionally, due to the higher ceramic content, composites with low skeleton density (1.28, 1.40 g/cm³) exhibit a higher compressive and flexural strength. The fabricated composites with a skeleton density of 1.28 g/cm³ possess better mechanical properties and ablative properties at 2800 °C. After plasma flame ablation for 54 s, the linear and mass ablation rates of the composites are 33.70 ± 1.33 μm/s and 22.39 ± 2.99 mg/s, respectively.     

Thermal conductivity of ceramic/metal composites from preforms produced by freeze casting

Porous alumina and zirconia preforms, processed by ice templating, have been used to manufacture ceramic/metal composites by aluminium alloy infiltration. The aim of the present work is to study the influence of the ceramic material nature and of the initial porous structure on the thermal conductivity anisotropy of the composite in order to assess potential applications in the field of thermal management. The materials are characterised in terms of pore volume fraction and pore size before and after metal infiltration. The freeze casted preforms exhibit anisotropic lamellar structures with ellipsoidal pores ranging from 35 µm to 40 µm and porosity fractions from 64 to 67%. After metal infiltration, composite parts present the same anisotropic morphology, which correspond to alternating ceramic and metal layers. Thermal conductivities have been determined, with an average of 80 W m⁻¹ K⁻¹ and 13 W m⁻¹ K⁻¹ parallel and perpendicular to the freezing direction respectively, for zirconia/metal composites. Theoretical values of thermal conductivity can be calculated using the Maxwell-Eucken relation, to handle the residual porosity, in combination with series and parallel resistance models to describe the overall anisotropic character. These give good agreement to experiment.     

Interface formation in infiltrated Al(Si)/diamond composites

This study pertains to the investigation of interface formation in infiltrated Al-based composites with high-volume fractions of monocrystalline synthetic diamond particles. The interface characteristics are discussed with respect to process conditions and Al matrix chemistry. To this end, two infiltration techniques, i.e., squeeze-casting and gas pressure infiltration are compared and the effect of Si-addition to the Al matrix is addressed. Eventually, thermal properties of the composite materials are presented and are in turn related to the interface characteristics.Electron microscopy investigations reveal a distinct 50–200-nm-thick layer at the interface between the metal matrix and the diamond particle, regardless of process history and matrix chemistry. This layer is amorphous and consists of carbon, aluminium and oxygen. Additionally, nanocrystallites of Al₂OC and enrichment of Si are observed within this interface layer in the Si-free, squeeze-casted material and in the gas pressure-infiltrated material with 7 wt.% of Si, respectively. Despite the fact that no evidence of SiC is found in the Si-containing composites, the process conditions experienced in gas pressure infiltration are clearly more favourable than those experienced in squeeze casting with respect to interfacial bonding and thermal properties. Actually, between 25 and 50 °C, the gas pressure-infiltrated AlSi/diamond composite yields a thermal conductivity of 375 W/m K along with a coefficient of thermal expansion of 7 × 10^− 6/K.     

Effect of CVI SiC content on ablation and mechanism of C/C-SiC-ZrC-Cu composites

C/C-SiC-ZrC-Cu composites were fabricated by chemical vapor infiltration, precursor infiltration-pyrolysis and vacuum-pressure infiltration methods. During Cu infiltration, the Cu_6·69Si and Cu₃Si new phases are generated through reaction between SiC and molten Cu. The formed Cu_6·69Si, Cu₃Si, ZrC and SiC phases can improve the wettability and interface combination between Cu and the doped carbon matrix. The ablation tests demonstrate that the CVI SiC content significantly affects the structure of protective oxide layer, and induces inverse effects in ablation center at 2500 ^°C and 3000 ^°C. The relatively high CVI SiC content enhances the ablation resistance of composites at 2500 ^°C, but increases the linear ablation rate at 3000 ^°C due to the excessive evaporation and mechanical denudation. During ablation, the formed Si-Zr-C-O layer underneath ablation center and the Si-Cu-C-O layer on transition or marginal areas can prevent carbon matrix from serious oxidation. After ablation for 20 s, the C/C-SiC-ZrC-Cu composites with high CVI SiC content display the best anti-ablation property at 2500 ^°C, and the ablation rates are 3.5 ± 0.1 μm/s and 3.4 ± 0.1 mg/s.     

Microstructure and properties of ablative C/ZrC–SiC composites prepared by reactive melt infiltration of zirconium and vapour silicon infiltration

C/ZrC-SiC composites with a density of 3.09 g/cm³ and a porosity of 4.8% were prepared by reactive melt infiltration and vapour silicon infiltration. The flexural strength and modulus were 235 MPa and 18.3 GPa, respectively, and the fracture toughness was 7.0 MPa m^1/2. The formation of SiC and ZrSi₂ during vapour silicon infiltration, at the residual cracks and pores in the C/ZrC, enhanced the interface strength and its mechanical properties. The high flexural strength (223 MPa, c. 95% of the original value) after oxidation at 1600 °C for 10 min indicated the excellent oxidation resistance of the composites after vapour silicon infiltration. The mass loss and linear recession rate of the composites were 0.0071 g/s and 0.0047 mm/s, respectively and a fine ablation morphology was obtained.     

Fabrication of Cf/ZrC–SiC composites using Zr–8.8Si alloy by melt infiltration

Cf/ZrC–SiC composites were fabricated by melt infiltration at 1800 °C using Zr–8.8Si alloy and carbon felt preforms. Microstructural analysis showed the formation of both ZrC and SiC phases in the matrix, in which ZrC acted as a main composition of the resulting composites. The results showed that carbon matrix reacted preferentially with Si of Zr–8.8Si alloy, which caused the formation of SiC first and then ZrC. The designed carbon coating by pyrolysis prevented the severe reaction between fibers and the melt. The composites could be more dense and uniform with the bending strength of 53.3 MPa, when preforms had a high open porosity (47.2%) with small size pores (10–40 μm).