Ti3SiC2-SiC复合材料的耐磨擦磨损性能

以商用硅粉、碳粉、钛粉以及少量的铝粉为原料, 利用放电等离子烧结技术原位反应制备了Ti₃SiC₂-SiC复合材料. 利用盘销式摩擦磨损实验机测试了Ti₃SiC₂-SiC复合材料的耐摩擦磨损性能. 结果表明: 随着SiC含量的增加, 材料相对于硬化钢的摩擦系数和磨损系数均呈下降趋势, 这表明SiC的引入提高了复合材料的抗摩擦磨损性能. Ti₃SiC₂单相材料摩擦系数在0.8～1.0之间, 而Ti₃SiC₂-40vol% SiC复合材料在稳态下的摩擦系数达到了0.5, Ti₃SiC₂-40vol% SiC复合材料相对于Ti₃SiC₂单相材料的磨损系数下降了一个数量级. Ti₃SiC₂-SiC复合材料的高抗磨损性归因于磨损类型的改变以及SiC良好的抗氧化性能.     

Laser processing of an aluminium AA6061 alloy involving injection of SiC particulate

In the present laser processing work, the powder injection technique was investigated as a method for producing a surface metal matrix composite (MMC) containing large SiC particulates (SiC_p) (105–150 m). This size is known to enhance the wear resistance of bulk aluminium-based composites. The effects of the laser-processing conditions, the powder feeding rate and the surface situations necessary to produce a well incorporated MMC on the surface were studied, and the microstructure examined. In previous work, laser processing involving the preplacement of SiC_p was developed to create an AI-SiC_p (45 m) MMC layer on aluminium alloy surfaces. Some of these ideas were used in conjunction with the injection process in the present work to enhance the surface-wear resistance. The wear resistance of an MMC obtained by a single laser track with the injection technique was determined and compared with the base alloy and the MMC layer produced by the preplacement technique.     

Refining SiCp in reinforced Al–SiC composites using equal-channel angular pressing

Aluminum–silicon carbide composite (Al–SiC_p) is one of the most promising metal matrix composites for their enhanced mechanical properties and wear resistance. In the present study, Al–SiC (average size 55 μm) composites with 5% and 10% by volume were fabricated by stir casting technique. The equal-channel angular pressing (ECAP) was then applied on the cast composites at room temperature in order to study the effect of ECAP passes on the SiC_p size and distribution. The ECAP process was successfully carried out up to 12(8) passes for Al–5%(10%)SiC samples. Microstructure study revealed that the highest refinement by breakage of SiC_p was achieved after the first ECAP pass and that further refinement took place in the next passes. More breakage of the SiC_p was found in the composite richer in reinforcing particles so that the SiC_p reached approximately 1 μm in the Al–10%SiC after 8 passes and 4 μm in Al–5%SiC after 12 ECAP passes. The distribution of SiC reinforcement particles also improved after applying ECAP. The factors including decrease in reinforcing particle size, improvement in their distribution, decrease in porosity in addition to strain hardening and grain refining of the matrix resulted in enhancement of tensile and compressive strengths as well as hardness by more than threefold for the Al–5%SiC after 12 passes and for Al–10%SiC after 8 passes compared to the cast composites. Additionally, the composite remained ductile after the ECAP process. The fracture surface indicated good bond between the matrix and the reinforcement.     

Al-Ti合金钎焊SiC陶瓷接头界面微观结构与力学性能

SiC陶瓷具有优异的综合性能, 通过钎焊获得高强度接头是其获得广泛应用的重要前提。研究采用Al-(10, 20, 30, 40)Ti(Ti的名义原子含量10%、20%、30%、40%)系列合金, 在1550 ℃条件下, 对SiC陶瓷进行钎焊30 min。当中间层厚度为~50 μm时, SiC钎焊接头的平均剪切强度处于100~260 MPa范围内。当采用Al-20Ti合金作为钎料时, 随着中间层厚度从~100 μm减小至25 μm, 钎焊接头的平均强度逐渐提高, 且最大强度~315 MPa。同时, 钎焊中间层中(Al)相逐渐减少直至消失, 只留下Al₄C₃、TiC和(Al,Si)₃Ti相。SiC/Al-20Ti/SiC钎焊接头的断裂主要发生在靠近中间层/陶瓷界面位置的陶瓷基体内。     

Effects of particle size on fatigue crack initiation and small crack growth in SiC particulate-reinforced aluminium alloy composites

Fatigue crack initiation and small crack growth were studied under axial loading using powder metallurgy 2024 aluminum-matrix composites reinforced with SiC particles of three different sizes of 5, 20 and 60 μm. The 5 and 20 μm SiC_p/Al composites exhibited nearly the same fatigue strength as the unreinforced alloy, while the 60 μm SiC_p/Al composite showed a significantly lower fatigue strength due to its inferior crack initiation resistance that could be attributed to interface debonding between particles and the matrix. Small crack growth behaviour was different depending on stress level. At a low applied stress, the addition of SiC particles enhanced the growth resistance, particularly in the composites reinforced with coarser particles, while at a high applied stress, the 60 μm SiC_p/Al composite showed a considerably low growth resistance, which could be attributed to interaction and coalescence of multiple cracks. In the 5 μm SiC_p/Al composite, small cracks grew avoiding particles and thus few particles appearing on the fracture surfaces were seen, particularly in small crack size region. In the 20 and 60 μm SiC_p/Al composites, they grew along interfaces between particles and the matrix and the number of particles appearing on the fracture surfaces increased with increasing crack size or maximum stress intensity factor.     

Fabrication and mechanical properties of in situ formed carbide particulate reinforced aluminium composite

Stable carbide particles of TiC, ZrC and TaC were in situ synthesized in liquid aluminium by the reaction between Al-Ti, Al-Zr or Al-Ta systems liquid alloy and SiC or Al₄C₃ particles. It was possible to generate TiC particles of nearly 1 m diameter, even utilizing SiC of 14 m. However, the dispersion behaviour of TiC particles in the matrix depended on the size of the raw carbide. Finer SiC made the dispersion of TiC particles more uniform, resulting in a greater improvement of the mechanical properties. Furthermore, although Al-Ti-Si system intermetallic compound was detected in a TiC_p/Al-Si composite fabricated by the melt-stirring method, those compounds considerably decreased in the composite fabricated by the in situ method. The mechanical properties of in situ formed TiC_p/Al-5 wt% Mg and TiC_p/Al-5 wt% Cu composites were better than those fabricated by the melt-stirring method and by T6 heat treatment, the properties of in situ formed TiC_p/Al-5 wt% Cu composite were further improved. The experimental results were analysed by the reaction model based on the assumption that the overall reaction rate was controlled by both the reaction and the diffusion.     

Mechanical properties of Cu/SiCp composites fabricated by composite electroforming

The silicon carbide particles (SiC_p) dispersion-strengthened copper matrix composites (Cu/SiC_p) were fabricated by composite electroforming technology. The microstructure, tensile property and wear behavior of Cu/SiC_p composites were investigated. The results showed that composites with different SiC_p contents were obtained. The microstructure of the composite presented a uniform distribution of SiC_p in the matrix and good interfacial integrity. The hardness, yield strength and rigidity of the composites increased with increasing SiC_p content, but at the cost of ductility. Increasing SiC_p content in the composite was not always beneficial to the ultimate tensile strength and wear resistance. The ultimate tensile strength increased with SiC_p content increasing up to 16 vol.% and decreased as exceeding 16 vol.%, and the wear mass loss decreased with SiC_p content increasing up to 21 vol.% and increased again as exceeding 21 vol.%.     

SiC-nanoparticle-reinforced Si3N4 matrix composites

Hot-pressed nanosized SiC-particle (SiC_p-reinforced Si₃N₄ composites have been studied with respect to their microstructures, room temperature mechanical properties and thermal shock resistance. The experimental results indicate that the flexural strength, fracture toughness and thermal shock resistance are all increased by the addition of 5 vol% SiC_p. Further additions of SiC_p, however, have a detrimental effect on these properties. These changes are closely related to the effects of SiC_p on the matrix grain morphology. The mechanisms of nucleation and growth of -Si₃N₄ grains in the presence of SiC nano-particles are discussed.     

The effects of magnesium additions on the structure and properties of Al-7 Si-10 SiCp composites

The additions of magnesium to an aluminium alloy matrix, which contains insufficient magnesium, was found to be essential during the synthesis of composites by the stir-casting technique. Magnesium promotes interfacial wetting between the dispersoid surface and the matrix. Dispersion of SiC_p in Al-7 Si-0.3 Mg (356) alloy matrix without agglomeration and rejection was not possible. Hence, the addition of up to 3 wt% Mg was made to the alloy matrix during the dispersion of 10 wt% SiC_p (34 m), and the microstructure and mechanical properties of the composites were investigated with a view to optimize the magnesium content. With a magnesium content less than 1 wt% in the matrix, the SiC_p particles were essentially in agglomerated form. The highest UTS of 280–300 MPa was obtained with 1 wt% Mg content and SiC_p was uniformly distributed in the matrix. A higher magnesium content (>1.0 wt%) did not further improve the uniformity in the dispersion of SiC_p but the ultimate tensile strength properties deteriorated. This decrease in strength was attributed to the observed coarseness of the Mg₂Si phase, the precipitation of Mg₅Al₈ phase and the presence of a higher amount of porosity in the composites in the heat-treated condition. The aspect ratio (length/width) of precipitates changed from 1–3 for 1% Mg to 3–9 for 3.2% Mg in the matrix. Corresponding values for per cent porosity were 2% and 6%, respectively.     

Interface microstructures in Ti-based composites using TiB2/C-coated and uncoated SiCf after short-term thermal exposure

The extent of interfacial reaction after short-term thermal exposure during vacuum plasma spraying (vps) and vacuum hot-pressing (vhp) of Ti-based metal-matrix composites (mmcs) using TiB₂/C-coated and uncoated SiC fibres has been investigated by a combination of scanning and transmission electron microscopies. There is no interfacial reaction after short-term thermal exposure during vps manufacture of SiC_f/Ti mmcs using either TiB₂/C-coated or uncoated SiC_f. There is only limited interfacial reaction after short-term thermal exposure during vhp manufacture of SiC_f/Ti-6Al-4V mmcs using TiB₂/C-coated SiC_f. In the initial stage of the interfacial reaction, TiB needles are formed by preferential nucleation and growth at β particles and grain boundaries in the Ti-6Al-4V matrix.     

Wear behaviour of aluminium matrix TiB2 composite prepared by in situ processing

Abstract

The wear behaviour and microstructure of aluminium and Al-12Si alloy (A413) matrix composites containing 1 and 5 vol.-%TiB₂ particles have been investigated. The composites were prepared by an in situ reactive slag technique. The wear surfaces and wear products were studied after reciprocating and rolling - sliding tests. Wear resistance increased with increasing particle content, and the Al-12Si composites were more wear resistant than those with Al matrixes. The wear mechanisms are briefly discussed.     

Effect of the filament nature on fatigue crack growth in titanium based composites reinforced by boron,B(B4C) and SiC filaments

Crack propagation testing has been applied to synthetic metal matrix composites (MMC) in order to compare failure mechanisms in Ti-6Al-4V alloy reinforced by uncoated boron, B(B₄C) and chemical vapour deposition (CVD) SiC filaments. The impeding effect of the fibres leads to low crack growth rates, compared to those reported for the unreinforced Ti-6Al-4V alloy and to higher toughness despite the presence of the reinforcing brittle phases. After long isothermal exposures at 850° C, the MMC crack growth resistance is reduced mainly due to fibre degradation, fibre-matrix debonding and an increase in matrix brittleness. However, for short-time isothermal exposures (up to about 10 h for B/Ti-6Al-4V, 30 h for B (B₄C)/Ti-6Al-4V and 60 h for SiC/Ti-6Al-4V) the crack growth resistance is significantly increased. This improvement is related to the build up of an energy-dissipating mechanism by fibre microcracking in the vicinity of the crack tip. This damaging mechanism allowing matrix plastic deformation is already effective for boron and B(B₄C) in the as-fabricated state, but occurs only after 10 h of thermal exposure at 850° C in the case of SiC/Ti-6Al-4V composites.     

连续SiC纤维增强钛基复合材料横向高温变形机理研究

针对连续SiC纤维增强钛基复合材料(SiC_f/Ti)成形的技术难题,利用沿垂直纤维方向基体具有大变形的能力,可以采用超塑成形/扩散连接技术(SPF/DB)成形出复合材料空心构件。在不同工艺参数条件下,测试了SiC_f/Ti复合材料的横向高温变形规律,并分析了变形温度、应变速率、纤维含量等工艺参数的影响规律,对不同参数条件下拉伸试件的微观组织和断口形貌进行了对比,分析了复合材料的高温变形机制。     

Microstructure and properties of burn-resistant Ti-Al-Cu alloys

Ti-Al-Cu series burn-resistant alloys are newly developed materials which have low density, low cost and are easy to process. The results show that Ti-Al-Cu alloys have good burn resistance due to their good thermal conductivity, low melting point, and the existence of Ti₂Cu phase which also has a very low melting point. Ti-Al-Cu alloys have excellent thermal processability and good room and high temperature tensile properties, but an increase in copper content harms their thermal stability. After thermal exposure for a long time, Ti₂Cu phase will coalesce and coarsen, but the addition of Si and Al will be useful for their thermal stability. The Ti-13Cu-1Al-0.2Si alloy has good thermal stability at 540°C and good creep resistance at 300°C and 100 MPa. The phases of Ti-Al-Cu alloys were found to be composed of phase and Ti₂Cu. The character of the Ti₂Cu phase changes with the increasing copper content.     

Composites of aluminium alloys: fabrication and wear behaviour

In this paper processes for fabrication of aluminium-alloy composites containing paniculate non-metals, the net shape forming of these composites, their microstructures, their friction and wear behaviours and their mechanical properties are described. Composites of two wrought (2014 and 2024) and one cast (201) aluminium alloys containing 2 to 30 wt% of Al₂O₃ and SiC particles in the size range of 1 to 142m were prepared. The non-metallic particles were added to a partially-solid vigorously-agitated matrix alloy. The particles were then retained in the matrix until interface interaction, for example, the formation of MgAl₂O₄ spinel in the case of Al₂O₃ particles, were faciliated. These composites were solidified and subsequently reheated to above their liquidus temperature and formed under high pressure in a closed-die forging type of apparatus. Composites with particulate additions of size larger than 5m possessed homogeneous structures; particles of size 1m, however, tended to cluster. The wear behaviour of the composites was studied using a pin-on-disc type machine. It was shown that composites containing large amounts of non-metals, 20 wt%, exhibit excellent wear resistance whilst those with small to moderate amounts of non-metals possess tensile properties comparable to the matrix alloy. Increasing the amount of particulate additions results in reduced ductility. Finally, a method was investigated of producing components with high weight-fractions of non-metals near their surface.     

The effect of fabrication processes on the mechanical and interfacial properties of SiCf/Cu–matrix composites

Three groups of SiC_f/Ti/Cu composites were prepared under conditions of 650 °C + 105 min (sample 1#), 750 °C + 85 min (sample 2#) and 840 °C + 50 min (sample 3#), respectively, by foil-fiber-foil method (FFF), and their room temperature tensile strengths were established. The aim is to model the reactive bonding states between Ti and SiC fiber and between Ti and Cu when Ti is used as interfacial adhesion promoters in SiC_f/Cu–matrix composites. The fracture surfaces, SiC_f/Ti interfaces and Ti/Cu interfaces were investigated by scanning electron microscopy (SEM), optical microscopy and energy dispersive spectroscopy (EDS). The tensile tests show that the tensile strengths of samples 1# and 2# are not obviously enhanced due to the weak bonding strength between SiC fiber and Ti, while those of sample 3# are achieved above 90% of ROM (the rule of mixtures) strength because of excellent bonding between SiC fiber and Ti. However, there are distinct Ti/Cu interfacial reaction zones after the three processes, which are approximately 5.4, 9.0 and 13.3 μm thick, respectively. The Ti/Cu interfacial reaction products are mainly distributed in four layers. In samples 1# and 2#, the products are predicted to be Cu₄Ti, Cu₃Ti₂, CuTi and CuTi₂ according to their chemical compositions determined by EDS, while in sample 3#, the products are Cu₄Ti, Cu₄Ti₃, CuTi and CuTi₂. Additionally, the relationships between the thickness of Ti interlayer and its reaction with C and Cu are also discussed, and an optimal thickness of Ti is introduced.     

Reactive metallic layers produced on AlN, Si3N4 and SiC ceramics

The paper presents the results of studies on the joining of non-oxide ceramics with copper with the use of intermediary metallic layers. AlN ceramics was covered with Mo, Mn, FeSi, Ti intermediary layers, Si₃N₄ ceramics – with Cu, Mn, Ti layers, and SiC ceramics – with Cr, TiCu layers. Although the individual metallic layers were synthesized under different conditions, all the structures contained barrier layers formed during the synthesis process. With the AlN and Si₃N₄ ceramics, the barrier layer was composed of TiN, which was well wetted by the metallic and oxide phases. With the SiC ceramics, the role of the barrier layer was played by the Ti₃SiC₂ phase. The thickness of the barrier layers of both types (TiN, Ti₃SiC) was about 1 m. They were well wetted by the metallic solders, coherent with the ceramic surface, and, within the brazed multi-layer joints, they constituted a continuous microstructure.     

Fabrication of Monolithic Ti3SiC2 Ceramic Through Reactive Sintering of Ti/Si/2TiC

Fabrication of monolithic Ti₃SiC₂ has been investigated through the route of reactive sintering of Ti/Si/2TiC mixtures. Significant phase differences existed between the surface and the interior of as-synthesized products due to the evaporation of Si during the reaction process. The use of a 3Ti/SiC/C mixture as a powder bed could control the evaporation of Si and develop monolithic Ti₃SiC₂. A reaction model for the formation of Ti₃SiC₂ in the Ti/Si/2TiC system is discussed.On leave from     

Wet erosion behaviour of low SiC alumina-SiC nanocomposites

We have investigated the erosive wear behaviour of alumina and Al₂O₃-SiC nanocomposites with SiC content between 1 and 5%. Nanocomposites (grain sizes between 3.15 and 7.16 m) and alumina (grain size 4.43 m) were eroded with SiC particles using a custom-built erosive slurry wear tester. The erosion resistance of the nanocomposites increased slightly with decreasing grain size. Nanocomposites of all grain sizes showed better wear resistance than the alumina. Erosion resistance increases with SiC content, though this effect is not strong for SiC contents greater than 2%. These results are compared with related results from the literature.     

Laser Surface Modification of Ti-6Al-4V Alloy with Silicon Carbide

We show that surface laser modification through a coating containing SiC powder is an efficient method for enhancing the wear resistance of Ti-6Al-4V titanium alloy. The laser melting of SiC particles enriches the pool of substrate melt with silicon and carbon. In the course of crystallization, primary dendrites, which are identified as TiC, are formed at first. After fast cooling to room temperature, a multiphase structure consisting of Ti₅Si₃ and TiSi₂ silicides and ductile -martensite is formed in the interdendritic space. Such a composite structure of the surface layer has a microhardness of 5–6 GPa and guarantees a sharp enhancement of the wear resistance under conditions of dry sliding friction as compared with the hardened-and-aged structure of this alloy.