ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.441

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractApplications for metal matrix composites (MMCs) have not emerged at the rate needed to justify the development costs. A reason for this may be that material developments have not been adequately linked to identified commercial needs. It is certainly true that some of the expectations raised about the potential offered by MMCs have been misguided. As the MMC business contracts, there is an ever greater need for a systematic method of linking material properties to the needs of engineering designers. This paper presents a methodology for evaluating materials in design, with the aim of linking MMCs to applications. The methodology has two main components: first, the use of performance indices and materials selection charts for specific design goals, to compare existing MMCs with competing materials; and secondly, the conceptual design of new MMC systems guided by those design goals. A selection of case studies illustrates that in mechanical applications the gains in using MMCs are frequently marginal, whereas in design for thermal management and vibration control, the materials can show very substantial improvements in performance. The methodology is general, and could be applied to other material systems.MST/3094

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.443

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractAcceptance of metal matrix composites for industrial applications depends upon improving properties using an economic production route, which includes the processing design. Two powder metallurgical routes have been used in the manufacture of Al 6061 metal matrix composites. The first involves blending, vacuum canning, and hot pressing from prealloyed powders and the second involves blending of elemental powders, liquid phase sintering, and subsequent hot rolling. These composites comprise 7·5 or 15 vol.-% of 7, 23, or 45μm SiC particles. In this paper, the composite microstructure at each stage of the different processing routes has been examined and the aging behaviour investigated. Effects on the tensile properties of fabrication techniques, SiC particle size, and volume fraction are presented and discussed.MST/3020

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.452

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA sound, mechanics based approach, using the reference stress concept, has been provided to allow the effects of volume ratio, fibre aspect ratio, and fibre spacing on the creep behaviour of uniaxial metal matrix composites to be quickly assessed. It is shown that fibres are much more effective than particles in reducing creep deformations. In addition, volume ratio and fibre aspect ratio have a large effect on creep properties, while fibre spacing has a relatively small effect. The existence of cracks at the ends of fibres is shown to reduce seriously the effectiveness of the reinforcement. The creep properties for loading in transverse directions are much lower than for loading in longitudinal directions.MST/2059

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.460

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe effect of test temperature and reinforcement shape on cavitation is investigated for commercial purity Al–Al2O3composite produced via either a powder route or squeeze infiltrationfollowed by extrusion. At room temperature, voids form at the reinforcement/matrix interface. Voids are favoured by reinforcement elongation and planar surfaces normal to the applied stress. Angularities themselves are not favoured sites for cavitation. Increasing the test temperature delays the onset of cavitation and angularities become favoured void nucleation sites. At higher temperature, necking begins to occur at much lower plastic strains, resulting in lower strains to failure, suggesting that void stability is reduced by increasing the temperature. Finite element calculations have been performed to investigate the component of the matrix stress which is responsible for the onset of cavitation in these materials. Results suggest that cavitation is stimulated by the attainment of a critical value of the hydrostatic stress at the interface, rather than of the interfacial normal stress.MST/3029

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.468

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThermomechanical processing has been employed to control the grain and subgrain structure of a powder produced SiC particle reinforced (3μm; 17 vol.-%) Al–Cu–Mg alloy. The present research investigates the effect of grain structure on fracture toughness. Variation in grain size and structure was accompanied by significant changes (up to 50%) in plane stress fracture toughness; toughness was observed to decrease with decreasing grain size. No pronounced modification in fracture path/mode was observed to explain this behaviour. However, a dependency of fracture toughness on work hardening rate was observed. A detailed analysis was performed to interpret the flow properties of the materials studied, particularly the effect of grain structure on work hardening–relaxation mechanisms. The lower work hardening rate and hence toughness exhibited by the fine grained composite is postulated to emanate from stress relaxation by grain boundary sliding in the highly stressed SiC particle/matrix interface region.MST/3002

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.475

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe microstructural and technological characteristics of metal matrix composites can be tailored if the role played by typical reinforcement parameters (type, shape, and volume fraction) is correctly evaluated. The present work used commercially pure Al reinforced with ceramic particles (Al2O3, SiC), manufactured via powder metallurgy and hot extruded. The volume fraction of reinforcement ranged from 5 to 15%. Dry sliding tests were performed on the composites using a fiat on cylinder tribometer and the friction coefficient versus sliding distance was recorded. The counterface was a carbon steel cylinder treated up to a Rockwell hardness of 60 HRC. The microstructure of the worn surfaces of the composites was evaluated via light microscopy, scanning electron microscopy, and transmission electron microscopy. The wear behaviour and microstructural evolution of all materials including the unreinforced matrix, were related to both reinforcement variables and testing conditions. Using wear mechanism mapping, some guidelines for designing and selecting wear resistant composites are suggested.MST/3006

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.481

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractHot working and microstructural behaviour of a 15 vol.-%SiC particle reinforced Al 6061 composite is discussed in this paper. The average size of the SiC particles is 18μm. The hot torsion test temperatures range from 200 to 500°C with strain rates of 0·1, 1·0, and 4 s−1. The equivalent stress versus strain curves show that the Al 6061–SiCpcomposite has great strengthening behaviour compared with the Al–Mg–Si bulk alloy below 500°C. It is mainly due to the high dislocation density from differential thermal contraction between SiCpand the matrix during cooling and to geometrical constraints around SiC particles during theplastic deformation. The logarithmic maximum stress and reciprocal temperature relationship is non-linear in the temperature range 200–500°C which indicates a complex mechanism. Transmission electron microscopy confirms that the dislocation densityis increased and subgrain size is decreased with an increase in strain rate and decrease of the test temperature. Transmissionelectron microscopy reveals that a number of grains in the matrix of approximately 2–3μm are highly misoriented, indicatingthat dynamic recrystallisation occurred during deformation. Highly misoriented 200–600 nm crystallites have also beenfound atvarious test temperatures. These are dynamic recrystallisation nuclei. The dynamic recrystallised grains nucleate both in the Almatrix between the SiC particles and at the SiCp/matrix interfaces. Experimental investigations are performed to examine astrain hardening model. The distribution of dynamic recrystallised grains in metal matrix composites fits the computer simulationresults well.MST/2095

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.487

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe microstructure and the mechanical properties of A357 aluminium alloys reinforced with Ni and NiP coated SiC particles produced via addition of particles into liquid metal are described. Ingots solidified under pressure and subsequently extruded, and centrifugally cast parts were used in this investigation. Microstructural observations show that the coating is dissolved during fabrication of the composites leading to NiAl3phase formation. For the NiP coated particles, AlP phases are also observed together with some Mg segregation around the particles. Mechanical property evaluation shows the materials to be age hardenable, leading to good mechanical properties in the T6 condition. Strain to failure, however, is much smaller than that oft he unreinforced alloy. In situ tensile tests carried out via scanning electron microscopy show that fracture of the SiC particles isthe main failure mechanism and that the NiAl3phases have a weak influence.MST/2094

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.497

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe manufacture of solid diamond fibres by chemical vapour deposition onto various wire and ceramic cores and the production of hollow diamond fibres by removal of the cores is described. The values for Young's modulus of diamond fibres and diamond fibre–Ti alloy metal matrix composites calculated via the rule of mixtures are predicted to be substantially higher than for the corresponding values for the commerical SiC fibre products. It is concluded that chemical vapour deposition diamond fibres offer, for the first time, the possibility of exploiting the properties of diamond in engineering structures.MST/3007

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.505

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor