CSCVI法快速制备C纤维增韧SiC基复合材料及其微观结构

采用一种改进的 CVI工艺 (CSCVI法 )制备连续炭纤维增韧 Si C基复合材料 ,使预制体的编织与 Si C基体的沉积同步复合进行。在不同的工艺条件下 ,制备了 C/Si C复合材料 ,观察了其微观结构。结果表明 :CSCVI- C/Si C中的残留孔隙很小且明显小于 ICVI- C/Si C中的残留孔隙 ;CSCVI具有快速制备孔隙率低、体积密度较高的 C/Si C复合材料的能力 ;纤维束缠绕转轴的线速度直接影响到 C/Si C的显气孔率、纤维束间 Si C基体墙的厚度和 C/Si C复合材料的最终体积密度。     

Effects of fibre content and relative fibre-orientation on the solid particle erosion of GF/PP composites

The erosive wear behaviour of glass fibre (GF) reinforced thermoplastic polypropylene (PP) composites was studied in a modified sandblasting apparatus as a function of the impact angle (30, 60 and 90°), relative fibre-orientation (parallel Pa and perpendicular Pe), fibre length (discontinuous, continuous) and fibre content (40–60 wt.%).The results showed a strong dependence of the erosive wear on the relative fibre-orientation at low impact angles (30°), but hardly any difference for 60 and 90° impact angles. In contrast, the fibre length did not affect the erosive wear behaviour especially at high impact angles.The inclusion of brittle GF led to higher erosive wear rates (ER) of the GF/PP composites; the higher the fibre content, the higher was the ER. Nevertheless, the composites still failed in a ductile manner. Different approaches proposed to describe the relationship between ER and fibre content were applied. Best results were generally delivered with the inverse rule of mixture. The modified rule of mixtures proposed for abrasive wear do not seem to apply for erosive wear.     

Effect of the Graphite Content on the Tribological Behavior of Al/Gr and Al/30SiC/Gr Composites Processed by In Situ Powder Metallurgy (IPM) Method

The influence of graphite content on the dry sliding wear characteristics of Al6061/Gr composites along with Al6061/30SiC/Gr hybrid composites has been assessed using a pin-on-disc wear test. The composites with different volume fraction of graphite particles up to 13% were processed by in situ powder metallurgy (IPM) technique. The porosity and hardness of the resultant composites were also examined. It was found that an increase in the graphite content reduced the porosity, hardness, and friction coefficient of both types of composites. The hybrid composites were more porous and exhibited higher hardness and lower coefficient of friction at identical graphite contents. The increased graphite content in the range of 0–13 vol.% resulted in increased wear rate of Al/Gr composites. The Al/30SiC composite exhibited a lower wear rate as compared with the base alloy and graphite addition up to 9 vol.% improved the wear resistance of these hybrid composites. However, more graphite particles addition resulted in increased wear rate. SEM micrographs revealed that the wear mechanism was changed from mostly adhesive in the base alloy sample (Al/0Gr) to the prominently abrasive and delamination wear for Al/Gr and Al/SiC/Gr/composites.     

Abrasive wear behaviour of laser sintered iron–SiC composites

Direct metal laser sintering (DMLS) is one of the popular rapid prototyping technologies for producing metal prototypes and tooling of complex geometry in a short time. However, processing of metal matrix composites (MMCs) by laser sintering is still in infant stage. Thermal cracks and de-bonding of reinforcements are reported while processing MMCs by laser sintering process. There are reports on use of metallic-coated ceramic reinforcements to overcome these problems. The present investigation is aimed at using nickel-coated SiC in developing iron composites by DMLS technique and to characterize its abrasive wear behaviour.Microstructure, microhardness, and abrasive wear tests have been carried out on both DMLS iron and its composites sintered at a laser scan speed of 100 mm/s. Abrasion wear tests have been carried out using a pin-on-disc type machine. SiC abrasive papers of grit size 60, 80, and 150 having an average particle size of 268, 192, and 93 μm, respectively, have been used. Load was varied between 5 and 25 N in steps of 5, while the sliding distance and sliding velocity of 540 m and 2.5 m/s, respectively was adopted for all the tests. Optical, scanning electron micrograph and surface roughness observation of worn surfaces have been undertaken.An increase in microhardness and a decrease in density of the laser sintered iron–SiC composites was observed with increase in SiC content. The abrasive wear resistance of composites increases with increased content of SiC in iron matrix. For a given grit size of SiC abrasive paper, at all the loads studied, iron–SiC composites exhibit excellent abrasive wear resistance. Increase in abrasive wear was observed with the increase in abrasive particle size.     

Microstructural investigations in Cf–SiC composites in as-sintered state and after creep experiments

The high interest in ceramic matrix composites during the last decade has led to a considerable number of studies devoted to their thermomechanical properties and damage processes. Despite their sensitivity to oxygen partial pressure, carbon fibres appear to possess higher stability and better mechanical properties if they are treated under protective atmospheres than other ceramic fibres (especially classical silicon carbide fibres). The aim of this investigation is to characterize at the nanoscale the main microstructural parameters of C_f–SiC composites provided by the SEP (Division of SNECMA, Bordeaux, France). This material was fabricated from a 2.5D preform made of high strength polyacrylonitrile (PAN)-based carbon fibres densified according to the chemical vapour infiltration process. A pyrocarbon (PyC) interphase was deposited on the fibre prior to the β-SiC matrix infiltration. A careful high resolution electron microscopy (HREM) microstructural investigation focused on the fibre microstructure as well as on the different interfaces in the material: pyrocarbon/fibre and matrix/pyrocarbon interfaces. All these observations have been realized in longitudinal and transverse sections of the specimen. These observations are found in good agreement with Guigon's model for high strength ex-PAN carbon fibres. The PyC interphase texture was strongly anisotropic at the fibre/interphase and interphase/matrix interfaces over a mean thickness of 8–15 nm. Tensile creep tests were performed under partial pressure of argon between 1273 and 1673 K for stress levels ranging from 110 to 220 MPa. Scanning electron microscopy and high resolution electron microscopy were used to study the microstructural modifications inside the fibres and at the different interfaces. A discussion of the possible creep mechanisms based on the microstructural investigation and the creep results is presented.     

Parametric study of the dry sliding wear behaviour of AA6082-T6/SiC and AA6082-T6/B<Subscript>4</Subscript>C composites using RSM

In this paper a parametric study of the wear behaviour of Aluminum matrix composites has been carried out. AA6082-T6/SiC and AA6082-T6/B₄C composites were fabricated using stir casting technique. The percentage of reinforcement was taken as 5, 10, 15 and 20 wt.% for both SiC and B₄C particulates. Dry sliding wear tests were conducted using pin-on-disc apparatus at room temperature and process optimization was done using Response surface methodology (RSM). Weight percentage (wt.%) of reinforcement, sliding speed, load and sliding distance were the four process parameters considered to analyse these composites wear behaviour. Analysis of variance (ANOVA) showed that sliding distance exerted the highest contribution (60.24 %) to AA6082-T6/SiC wear, followed by sliding speed (14.28 %), load (11.88 %) and reinforcement content (4.31 %). The same trend was found in AA6082-T6/B₄C composites with slightly different contribution values, namely sliding distance (63.28 %), sliding speed (14.02 %), load (10.10 %) and reinforcement content (4.05 %). RSM analysis revealed that increases in the reinforcement content and sliding speed reduce the wear rate in both composites. On the other hand, increases in load and sliding distance led to higher AA6082-T6/SiC and AA6082-T6/B₄C composites wear. The two predictive models were validated by conducting confirmation tests and certified that the developed wear predictive models are accurate and can be used as predictive tools for wear apllications.     

The friction and wear of electroless Ni–P matrix with PTFE and/or SiC particles composite

In this paper, the friction behaviour and wear mechanism of electroless Ni–P matrix with PTFE and/or SiC particles composite coating are investigated by virtue of ring-on-disk wear machine at a high load of 150 N. The worn surface, wear debris and the composition changes after wear were characterized using scanning electron microscopy (SEM) and energy-dispersive analysis of X-ray (EDAX). By comparison with Ni–P and Ni–P–SiC coatings, the results indicated that the combination of a PTFE-rich mechanical mixed layer (PRMML) formed on the worn surface and hard SiC were responsible for the good tribological properties of the hybrid Ni–P–PTFE–SiC composites at high load. After heat treatment at 400 °C for 1 h, the wear rate of Ni–P matrix composites decreased with corresponding increase in microhardness. During sliding, an obvious decrease in the temperature rise with PTFE addition was attributed to the good anti-friction of PTFE.     

Friction and Wear Behavior of Copper Matrix Composites Reinforced with SiC and Graphite Particles

The objective of this paper is to investigate the friction behavior and wear mechanism of copper matrix composites reinforced with SiC and graphite particles. The results indicate that a graphite-rich mechanically mixed layer (MML) formed on the tribo-surface was responsible for the good tribological properties of the hybrid composites at low normal loads. When graphite content was high enough for delamination wear to take place at high load, wear resistance deteriorated. A continuous supply of graphite to the tribo-surface is an important precondition for the formation of a graphite-rich MML and the benefit of its anti-friction properties for the copper hybrid composites.     

Wear properties of Saffil/Al,Saffil/Al2O3/Al and Saffil/SiC/Al hybrid metal matrix composites

The purpose of this study is to investigate the wear properties of Saffil/Al, Saffil/Al₂O₃/Al and Saffil/SiC/Al hybrid metal matrix composites (MMCs) fabricated by squeeze casting method. Wear tests were done on a pin-on-disk friction and wear tester under both dry and lubricated conditions. The wear properties of the three composites were evaluated in many respects. The effects of Saffil fibers, Al₂O₃ particles and SiC particles on the wear behavior of the composites were elucidated. Wear mechanisms were analyzed by observing the worn surfaces of the composites. The variation of coefficient of friction (COF) during the wear process was recorded by using a computer. Under dry sliding condition, Saffil/SiC/Al showed the best wear resistance under high temperature and high load, while the wear resistances of Saffil/Al and Saffil/Al₂O₃/Al were very similar. Under dry sliding condition, the dominant wear mechanism was abrasive wear under mild load and room temperature, and the dominant wear mechanism changed to adhesive wear as load or temperature increased. Molten wear occurred at high temperature. Compared with the dry sliding condition, all three composites showed excellent wear resistance when lubricated by liquid paraffin. Under lubricated condition, Saffil/Al showed the best wear resistance among them, and its COF value was the smallest. The dominant wear mechanism of the composites under lubricated condition was microploughing, but microcracking also occurred to them to different extents.     

Wear behavior of Al-Mg-Cu-based composites containing SiC particles

The friction and wear behavior of Al-Mg-Cu alloys and Al-Mg-Cu-based composites containing SiC particles were investigated at room conditions at a pressure of 3.18 MPa and a sliding speed of 0.393 m/s using a pin-on-disk wear testing machine. This study is an attempt to investigate the effects of adding copper as alloying element and silicon carbide as reinforcement particles to Al-4 wt% Mg metal matrix. The wear loss of the copper containing alloys was less than that for the copper free alloys. It was observed that the volume losses in wear test of Al-Mg-Cu alloy decrease continuously up to 5%. Also it was found that the silicon carbide particles play a significant role in improving wear resistance of the Al-Mg-Cu alloying system. The formation of mechanically mixed layer (MML) due to the transfer of Fe from counterface disk to the pin was observed in both Al-Mg-Cu alloys and Al-Mg-Cu/SiC composites.     

Unlubricated wear of Si/SiC and its composite with nickel Si/SiC-Ni

Using a pin-on-disk tribometer, dry friction and wear properties at different temperatures were investigated for reaction-sintered silicon carbide Si/SiC and its composites with nickel Si/SiC-Ni. The friction and wear properties of the composites are improved by the addition of nickel. The analysis on the worn surfaces and sub-surfaces by SEM suggest that shallow grooves are the main wear feature at 15°C. At 600°C, surface cracking and fracture is the predominating wear mechanism for Si/SiC, and the formation of flake pits on the surface due to crack propagation at subsurface is the main wear mechanism for Si/SiC-Ni. Finally the relationships between wear resistance and mechanical properties are discussed.     

Mechanical and tribological properties of short-fiber-reinforced SiC composites

The short-carbon-fiber-reinforced SiC (C_sf/SiC) composites were prepared by hot-pressing sintering with Si, Al and B as sintering additives. The effects of fiber volume fraction on the mechanical and tribological properties of the C_sf/SiC composites were investigated. The results show that the bending strength values of the composites containing a certain content of the short carbon fibers are higher than that of the monolithic SiC. The friction coefficients of the composites decrease with increasing short carbon fibers content. Except of the composite containing 53 vol% short carbon fibers, the wear rates of the composites decrease with increasing short carbon fibers content, and are lower than that of the monolithic SiC drastically.     

Effect of SiC Particle Size on Wear Properties of Al2O3·SiO2/SiC/Mg Hybrid Metal Matrix Composites

The aim of this study was to investigate the effect of SiC particle size on the wear properties of magnesium-based hybrid metal matrix composites (MMCs) reinforced with Saffil short fibers and SiC particles. Hybrid MMCs with different SiC particle sizes of 1, 7, and 20 μm, respectively, were fabricated by the squeeze infiltration process. The volume fractions of Saffil short fibers and SiC particles in the hybrid composites were 15 and 5%, respectively. Wear tests were carried out using a ball-on-disk against a steel ball under the dry sliding condition. The test results showed that the composite with large-sized SiC particles had an improved wear resistance compared with the smaller sized particles.     

Investigation of wear mechanism of SiC particulate-reinforced Al-20Si-3Cu-1Mg aluminium matrix composites under dry sliding and water lubrication

Unreinforced Al-20Si-3Cu-1Mg (ASCM) aluminium alloy and SiC particle reinforced Al-20Si-3Cu-1Mg (ASCM-SiC) aluminium matrix composites were fabricated by powder metallurgy (). The samples were slid against 4Cr13 stainless steel in a reciprocal friction tester under a load of 25 N to 175 N and sliding velocity of 0.3 to 1.2 m s⁻¹ at ambient conditions. The results show that SiC particulate-reinforced aluminium matrix composites possess good wear resistance at dry sliding and less wear resistance under water lubrication. Ploughing wear is the dominant wear mechanism at dry sliding and tribochemical wear is dominant under water lubrication. SEM, AES and XPS were used to examine the wear morphology and surface chemistry.     

载荷对激光选区烧结Cf/SiC复合材料摩擦磨损性能的影响

通过激光选区烧结技术和液相渗硅工艺制备了碳纤维增强碳化硅（Cf/SiC）复合材料。试样组织由C、SiC和Si三相组成,其密度和弯曲强度分别为2.89±0.01 g/cm3和237±9.8 MPa。采用UMT TriboLab多功能摩擦磨损试验机研究了Cf/SiC复合材料在不同载荷(10 N, 30 N, 50 N和70 N)条件下的摩擦学特性。研究结果表明：载荷较小(10 N)时,Cf/SiC复合材料的磨损由微凸起和SiC硬质点造成,磨损机制为磨粒磨损;载荷为30 N时,复合材料的摩擦磨损综合性能最好,其平均摩擦因数为0.564,磨损率低(5.24×10-7 cm3/（N·m）),主要磨损机制为犁削形成的磨粒磨损和黏结磨损。载荷增大到70N时,材料磨损严重,磨粒脱落形成凹坑,产生裂纹,其磨损率(8.68×10-7 cm3/（N·m）)高,磨损机制主要为脆性剥落。     

The tribological properties of bronze–SiC–graphite composites under sea water condition

Bronze–SiC–nickel coated graphite composites were fabricated by powder metallurgy technique (P/M). The tribological properties of composites sliding against AISI321 stainless steel pin were studied under sea water condition. The graphite is an effective solid lubricant in sea water environment. The SiC improved the hardness and tribological properties of composites. The friction coefficient of bronze–SiC–graphite composites increased with the increase of SiC. However, the specific wear rate of bronze–SiC–graphite composites decreased with increasing SiC. Bronze-2 wt% SiC-11.7 wt% nickel coated graphite composite showed the best tribological properties due to the synergistic effects of reinforcements.     

Cutting performance of Si<Subscript>3</Subscript>N<Subscript>4</Subscript> based SiC ceramic cutting tools

Composites of Si₃N₄-SiC containing up to 30 wt% of dispersed SiC particles were fabricated via hot-pressing with an oxynitride glass. To determine the effect of sintering time and SiC content on the mechanical properties and the cutting performance, the composites with fixed 8 hr-sintering time and 20 wt% SiC content were fabricated and tested. Fracture toughness of the composites increased with increasing sintering time, while the hardness increased as the SiC content increased up to 20 wt%. The hardness of the composites was relatively independent of the grain size and the sintered density. For machining heat-treated AISI4140, the insert with 20 wt% SiC sintered for 8 hr showed the longest tool life while the insert with 20 wt% SiC sintered for 12 hr showed the longest tool life for machining gray cast iron. An effort was made to relate the mechanical properties, such as hardness, fracture toughness and wear resistance coefficient with the tool life. However, no apparent relationship was found between them. It may be stated that tool life is affected by not only the mechanical properties but also other properties such as surface roughness, density, grian size and the number of the inherent defects in the inserts.     

Wear mechanisms of the C/SiC brake materials

The C/SiC brake materials were fabricated by chemical vapor infiltration combined with liquid melt infiltration. The wear mechanisms of C/SiC brake materials were investigated. The main wear mechanisms were grain-abrasion, oxidation-abrasion, fatigue wear, and adhesive wear. These wear mechanisms always occurred simultaneously , and showed mutual enhancing effects between them. Grain-abrasion mainly was the result of hard SiC grain action. Adhesive wear could cause high wear rates and a large unstable friction coefficient. Si was the significant factor on the adhesive wear, so Si in the C/SiC brake materials must be removed.     

RETRACTED ARTICLE: Wear Mechanism for In Situ TiC Particle Reinforced AZ91 Magnesium Matrix Composites

TiC reinforced AZ91 magnesium matrix composites have been fabricated by a melt in situ reaction spray deposition. The microstructures of spray-deposited alloys were studied by using scanning electron microscopy (SEM) and X-ray diffraction (XRD). The dry sliding wear behavior of the alloys was investigated by using a pin-on-disc machine under five loads, namely 10, 20, 30, 40, and 50 N. The composites had much better wear-resistance than the matrix alloy. The wear behavior of the composites was dependent on the TiC content in the microstructure and the applied load. The improvement in the wear resistance of the composites became more prominent at larger normal load. At a lower load (10 N), with increasing TiC content, the wear rate of the composite was decreased, and the dominant wear mechanism was an oxidative mechanism. At a higher loads (50 N), a spray-deposited AZ91/TiC composites exhibited superior wear resistance to the AZ91 magnesium alloy, and the dominant wear mechanism was delamination.     

Wear and friction behavior of sand cast brake rotor made of A359-20 vol% SiC particle composites sliding against automobile friction material

The effect of load range of 30-100 N and speed range of 3-12 m/s on the wear and friction behavior of sand cast brake rotor made of A359-20 vol% SiC particle composites sliding against automobile friction material was investigated. Dry sliding frictional and wear behavior were investigated in a pin-on-disc type apparatus. Automobile friction material was used as pin, while the A359-20 vol% SiC particle composites formed the rotating disc. For comparison, the wear and friction behavior of commercially used cast iron brake rotor were studied. The results showed that the wear rate of the composite disc decreased with increasing the applied load from 30 to 50 N and increased with increasing the load from 50 to100 N. However, the wear rate of the composite disc decreased with increasing the sliding speed at all levels of load applied in the present work. For all sliding speeds, the friction coefficient of the composite disc decreased with applied load. The worn surfaces as well as wear debris were studied using scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analyzer and X-ray diffraction (XRD) technique. At load of 50 N and speed range of 3-12 m/s, the worn surface of the composite disc showed a dark adherent layer, which mostly consisted of constituents of the friction material. This layer acted as a protective coating and lubricant, resulting in an improvement in the wear resistance of the composite.