Effect of Silicon Carbide Whisker and Titanium Carbide Particulate Additions on the Friction and Wear Behavior of Silicon Nitride

A Si₃N₄/TiC composite was previously demonstrated to exhibit improved wear resistance compared to a monolithic Si₃N₄ because of the formation of a lubricious oxide film containing Ti and Si at 900°C. Further improvements of the composite have been made in this study through additions of SiC whiskers and improved processing. Four materials—Si₃N₄, Si₃N₄/TiC, Si₃N₄/SiC_wh, and Si₃N₄/TiC/SiC_wh— were processed to further optimize the wear resistance of Si₃N₄ through improvements in strength, hardness, fracture toughness, and the coefficient of friction. Oscillatory pin on flat wear tests showed a decrease in the coefficient of friction from ∼0.7 (Si₃N₄) to ∼0.4 with the addition of TiC at temperatures reaching 900°C. Wear track profiles illustrated the absence of appreciable wear on the TiC-containing composites at temperatures above 700°C. Microscopic (SEM) and chemical (AES) characterization of the wear tracks is also included to deduce respective wear and lubricating mechanisms.     

Effect of Composition on Properties of Alumina/Titanium Silicon Carbide Composites

In the present study, the room-temperature properties of Al₂O₃-Ti₃SiC₂ composites with different Ti₃SiC₂ contents are determined. The composites are prepared by attrition milling Al₂O₃ and Ti₃SiC₂ mixture powders followed by spark plasma sintering (SPS) under vacuum. From a closer examination of the dependencies of the electrical conductivity on compositions in this system, we determined the percolation threshold at which an interconnected network of electrically conductive phase arises. Since the hardness of Ti₃SiC₂ is lower than that of Al₂O₃, the Vickers hardness decreased with the increasing of Ti₃SiC₂ content while the fracture toughness and the strength increased. The maximum strength (673 MPa) and the maximum toughness (9.3 MPa·m^1/2) were reached in the pure Ti₃SiC₂ material.     

Processing and Microstructure Development in Alumina–Silicon Carbide Intragranular Particulate Composites

Al₂O₃–SiC particulate composites were fabricated by hot-pressing mixtures of 5–30 vol% SiC with either α-Al₂O₃, γ-Al₂O₃, or boehmite (γ-AlOOH) to determine whether grain growth or the α-alumina phase transformation could be used to fabricate intragranular particulate composites. Samples starting with α-alumina resulted in primarily intergranular SiC of 0.3 μ and an alumina grain size of 1.5–4.1 μm. Heat treatments resulted in SiC coarsening but no entrapment of SiC by grain boundary breakaway. The α-alumina transformation in the samples starting with γ-alumina resulted in the entrapment of ∼48% of the 5 vol% of SiC added whereas 79% of the SiC was entrapped in the α-alumina grains in samples starting with boehmite. Only SiC particles ≤0.2 SmUm were entrapped in the α-alumina grains during the phase transformation. With increasing SiC content, the relative volume of intragranular SiC decreased, but the amount of intragranular SiC was constant and independent of the amount of SiC added before transformation. The formation of intragranular composites from γ-alumina and boehmite samples was explained with a model that attributes particle entrapment to the vermicular growth of α-alumina into the transition alumina matrix during the α-alumina phase transformation. Seeding the boehmite-based samples did not affect the concentration of entrapped SiC, but did lower the hot-pressing densification temperature by as much as 150°C.     

Microstructure, Phase and Thermoelastic Properties of Laminated Liquid-Phase-Sintered Silicon Carbide–Titanium Carbide Ceramic Composites

Hot-pressed silicon carbide–titanium carbide (SiC—TiC) composites sintered with liquid-phase forming Al₂O₃ and Y₂O₃ mixtures have been studied. Samples were fabricated by successively stacking tape-cast sheets of a single composition, resulting in a laminated body of uniform composition. This approach required the development of a technology easily transferable into the production of functionally graded SiC–TiC materials. The effects of this processing route on the resultant microstructures and phases were explored in detail. Additionally, because of the consequences for graded materials, the effects of TiC proportion on the thermal expansion coefficients, Young's modulus, and Poisson's ratios for several SiC–TiC composites were also determined.     

R-Curve Behavior of Silicon Nitride–Titanium Nitride Composites

The R –curve for Si₃N₄−40 wt% TiN composites was estimated by the indentation-strength method and compared to that of monolithic Si3N4 with duplex microstructure. Both materials exhibited rising R -curve behavior. The Si3N4-TiN composites, however, displayed better damage tolerance and higher resistance to crack growth. From TEM observation, it was inferred that this superior performance of Si₃N₄-TiN composites can be attributed mainly to stress-induced microcracking at hete rophase (Si₃N₄/TiN) boundaries.     

Microstructure and Mechanical Properties of Mullite–Silicon Carbide Composites

Mullite-SiC-whisker composites were prepared by powder processing using two commercial SiC whiskers. These composites were prepared by sintering rather than hot-pressing. A mulliteSlC-powder composite and a base line mallite material were also prepared for comparison with the two whisker composite materials. Fracture toughness measurements showed significant enhancement in only one of the whisker composite materials. The microstructure of the four materials was examined by scanning electron microscopy and transmission electron microscopy to assist in the explanation of the mechanical behavior of these composites. The examinations suggested that most of the toughening results from second-phase particles, with only limited toughening from effects associated with whiskers per se. In one case, higher toughness was partially associated with the formation of sialon phase by reaction with the whiskers and the furnace environment.     

Properties of Silicon Nitride–Molybdenum Disilicide Particulate Ceramic Composites

The physical and mechanical properties of hot-pressed Si₃N₄–MoSi₂ particulate composites containing 15 and 30 vol% MoSi₂ were studied. The average room-temperature four-point bend strength, fracture toughness, and electrical resistivity are 522 MPa, 3.6 MPa·√m, and 6.3 × 10⁵Χ·cm for the 15 vol% MoSi₂ composite, and 487 MPa, 5.3 MPa·√m, and 0.31 Ω·cm for the 30 vol% MoSi₂ composite. The mechanical properties of the composites are very close to those of hot-pressed Si₃N₄ ceramics. The high electrical conductivity of the 30 vol% MoSi₂ composite was attributed to the percolation effect of MoSi₂ particles. Parabolic oxidation behaviors were observed for the 30 vol% MoSi₂ composite during the 1200°C long-term oxidation experiments.     

Zirconia Transport by Liquid Convection during Oxidation of Zirconium Diboride–Silicon Carbide

During high-temperature oxidation of ZrB₂–SiC composites, a multi-layer oxide scale forms with a silica-rich borosilicate liquid as the surface oxide layer. Here, a recently proposed novel mechanism for the high-temperature oxidation of ZrB₂–SiC composites is further investigated and verified. This mechanism involves the formation of convection cells in the oxide surface layer during high-temperature oxidation of the composite. The formation of zirconia deposits found in the center of the convection cells is proposed here to be the consequence of liquid transport. The nature and deposition mechanism of the zirconia is reported in detail, using calculated phase equilibrium diagrams and microstructure observations of a ZrB₂-15 vol% SiC composite tested at 1550° and 1700°C in ambient air for various times. The calculated phase equilibrium diagrams for the binary ZrO₂–B₂O₃ system as well as the ternary B₂O₃–SiO₂–ZrO₂ system at 1500°C are reported here to interpret these results.     

Silicon Carbide Platelet/Silicon Carbide Composites

α-silicon carbide platelet/β-silicon carbide composites have been produced in which the individual platelets were coated with an aluminum oxide layer. Hot-pressed composites showed a fracture toughness as high as 7.2 MPa·m^1/2. The experiments indicated that the significant increase in fracture toughness is mainly the result of crack deflection and accompanying platelet pullout. The coating on the platelets also served to prevent the platelets from acting as nucleation sites for the α- to β-phase transformation, so that the advantageous microstructure remains preserved during high-temperature processing.     

Thermo-Mechanical Properties and Abrasive Wear Behavior of Silicon Carbide Filled Woven Glass Fiber Composites

A study was done to determine the effect of physical, mechanical, thermal and three body abrasive wear response of Silicon Carbide (SiC) filled Glass Fiber Reinforced Epoxy (GFRE) composites. The main purpose was to study the influence of different weight percentages (wt.%) of SiC filler in addition to that of glass fiber. A three body abrasive wear analysis was conducted by varying different factors such as fiber/filler reinforcement, abrasive particle size, normal load, sliding distance and sliding velocity. An attempt was made to find out the dominant factor and the effect of each factor on specific wear rate analysis. Physical and mechanical properties, i.e. density, hardness, tensile strength, flexural strength, inter laminar shear strength and impact strength, were determined for each weight percent of filler reinforcement to determine the behavior of mechanical properties with varying SiC filler loading. Thermo – mechanical properties of the material, i.e. storage modulus, loss modulus and tan delta with temperature were measured using a Dynamic Mechanical Analyzer (DMA). The result shows the increasing / decreasing trend and critical points of each analysis. The trend and major factors responsible for reducing the specific wear rate were determined. Mechanical properties, i.e. hardness and impact strength, increase with the increase in SiC content, whereas tensile strength, flexural strength and inter laminar shear strength decrease. Worn surfaces were studied using scanning electron microscopy (SEM) to give an insight into the wear mechanisms.     

Elastic Properties of Laminated Calcium Aluminosilicate/Silicon Carbide Composites Determined by Resonant Ultrasound Spectroscopy

The elastic properties of unidirectional and 0°/90° crossply Nicalon-SiC-fiber-reinforced calcium aluminosilicate (CAS/SiC) ceramic-matrix composites have been measured using a resonant ultrasound spectroscopy (RUS) technique. This approach has allowed the nondestructive determination of the complete set of independent second-order elastic stiffness constants of these ceramic composites. These stiffness data have been used to obtain the orientation dependence of Young's modulus and the shear modulus. The results are in reasonably good agreement with the limited experimental data obtained from mechanical testing. The RUS measurements reveal that the unidirectional CAS/SiC composite is well modeled by transverse isotropic symmetry, indicating relatively isotropic fiber spacing in the transverse plane. The analysis indicates that the overall elastic anisotropy is also small for unidirectional and 0°/90° laminated CAS ceramic-matrix composites, a result that can be attributed to the relatively low modulus ratio of the Nicalon SiC fiber to the CAS matrix and to the moderate fiber volume fraction.     

碳化硅/氟橡胶复合材料的制备与性能研究

采用机械共混法制备碳化硅（SiC）/氟橡胶（FKM）复合材料,SiC添加前用偶联剂KH-560进行表面改性,研究改性SiC用量对SiC/FKM复合材料性能的影响。结果表明：随着改性SiC用量的增大,SiC/FKM复合材料的硬度增大,拉伸强度在一定范围内得到有效提升,阻尼性能和耐液体介质性能略有降低;当改性SiC用量为15份时,SiC/FKM复合材料具有良好的加工性能、物理性能、阻尼性能、热稳定性和耐液体介质性能,综合性能较优异。     

Silicon Carbide Monofilament-Reinforced Silicon Nitride or Silicon Carbide Matrix Composites

SiC-monofilament-reinforced SiC or Si₃N₄ matrix composites were fabricated by hot-pressing, and their mechanical properties and effects of filaments and filament coating layers were studied. Relationships between frictional stress of filament/matrix interface and fracture toughness of SiC monofilament/Si₃N₄ matrix composites were also investigated. As a result, it was confirmed experimentally that in the case of composites fractured with filament pullout, the fracture toughness increased as the frictional stress increased. On the other hand, when frictional stress was too large (>about 80 MPa) for the filament to be pulled out, fracture toughnesses of the composites were almost the same and not so much improved over that of Si₃N₄ monolithic ceramics. The filament coating layers were found to have a significant effect on the frictional stress of the SiC monofilament/Si₃N₄ matrix interface and consequently the fracture toughness of the composites. Also the crack propagation behavior in the SiC monofilament/Si₃N₄ matrix composites was observed during flexural loading and cyclic loading tests by an in situ observation apparatus consisting of an SEM and a bending machine. The filament effect which obstructed crack propagation was clearly observed. Fatigue crack growth was not detected after 300 cyclic load applications.     

Mechanical Properties of Alumina/Silicon Carbide Whisker Composites

The improvement of mechanical properties of Al₂O₃/SiC whisker composites has been studied with emphasis on the effects of the whisker content and of the hot-pressing temperature. Mechanical properties such as fracture toughness and fracture strength increased with increasing whisker content up to 40 wt%. In the case of the high SiC whisker content of 40 wt%, fracture toughness of the sample hot-pressed at 1900° decreased significantly, in spite of densification, compared with one hot-pressed at 1850°. Fracture toughness strongly depended on the microstructure, especially the distribution of SiC whiskers rather than the grain size of the Al₂O₃ matrix.     

Machine Learning-Based Erosion Behavior of Silicon Carbide Reinforced Polymer Composites

Silicon - The machine learning methodology is gaining immense exposure as a potential methodology for solving and modelling the machining behaviour of advanced materials. The present paper deals...     

Synthesis of Titanium Silicon Carbide

Synthesis of bulk titanium silicon carbide (Ti₃SiC₂) from the elemental Ti, Si, and C powders has been accomplished for the first time, using the arc-melting and annealing route. The effects of various parameters on the phase purity of the Ti₃SiC₂ have been examined, including the starting composition of the powders, compaction technique, arc-melting of the samples, and temperature and time of anneal. The best bulk samples, containing about 2 vol% TiC as the second phase, were made from Si-deficient and C-rich starting compositions. Based on electron probe microanalysis data from a number of bulk samples, it appears that Ti₃SiC₂ exists over a range of compositions; the Ti-Si-C ternary section has been modified to reflect this. The purest samples of the ternary phase were obtained by leaching powders of silicide-containing samples in diluted HF, and contained over99vol%Ti₃SiC₂.     

Silicon Carbide/Silicon and Silicon Carbide/Silicon Carbide Composites Produced by Chemical Vapor Infiltration

Composites of SiC/Si and SiC/SiC were prepared from single yarns of SiC. The use of carbon coatings on SiC yarn prevented the degradation normally observed when chemically vapor deposited Si is applied to SiC yarn. The strength, however, was not retained when the composite was heated at elevated temperatures in air. In contrast, the strength of a SiC/C/SiC composite was not reduced after this composite was heated at elevated temperatures, even when the fiber ends were exposed.     

Oxidation Resistance of Alumina–Titanium Nitride and Alumina–Titanium Carbide Composites

The presence of TiC or TiN paritcles in an Al₂O₃ matrix affects the thermal stability of the composites in oxidizing environments. In isothermic oxidation tests at 700°, 800°, 900°, 1000°, and 1100°C for up to 20 h, two different oxidation regimes have been observed at T < 900°C and at 900°C ≤ T ≤ 1100°C. At low temperatures ( T < 900°C), the oxidation follows a phase-boundary reaction; the reaction product initially consists of aggregates of submicrometer needlelike TiO₂ rutile crystals that subsequently grow and coalesce. When a continuous TiO₂ rutile layer is formed ( T ≥ 900°C), the oxidation kinetics change to parabolic, and the diffusion of O₂ through a thick TiO₂ layer is proposed as the governing step.     

碳化钛复合材料的制备及性能研究

采用真空烧结工艺和热压烧结工艺制备了碳化钛复合材料。凭借场发射扫描电镜（SEM）对试样的表观形貌与断口形貌进行了观察,检测了其力学性能并分析了抗氧化性能。结果显示：采用不同烧结工艺制备的碳化钛复合材料的力学性能及微观结构有较大差别,热压烧结工艺制备的试样各项性能较优,且试样的断裂面显微组织细密、晶界分布明显、裂纹扩张路线多样变化且走向清晰。力学性能分别为：弯曲强度1139 MPa,断裂韧性9.8 MPa·m1/2,维氏硬度21.7 GPa,相对密度99.2%。在设定的条件氧化2 h后,900℃时热压烧结制备的试样表面生成了对基体没有保护效用的非保护性氧化膜;而1150℃时试样表面形成了一层致密的对基体具有保护效果的保护性氧化膜。