摘要:

AbstractHigh wear resistance is an attribute frequently ascribed to metal matrix composites and is of clear importance to the designer is considering both the use of these materials in some applications and in selecting the machining processes which can be employed to fabricate components. Sliding wear of metal matrix composites is important wherever there is relative motion, either deliberate or unintentional. If hard particles are present in the system, for example, as contamination in a lubricant or intentionally in abrasive machining, then the abrasion resistance of the material may be relevant. This critical review considers the complex tribological behaviour of metal matrix composites with fibre, whisker, and particulate reinforcement. Under certain conditions, metal matrix composites show high wear resistance, but this is not always the case; an understanding of the fundamental mechanisms of wear is essential in order to use them more efficiently.MST/2057

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.513

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractResults are reported on the compositional and structural features of metal/ceramic interfacial reactions in a series of magnesium based composites containing Al2O3fibres (3μm diameter) produced via liquid metal infiltration of preforms. The composites employed a range of matrix compositions and fibres of different porosities and in some cases binders were used. The practical objective was to optimise the combination of matrix and fibre to reduce the extent to which alumina reacts with liquid magnesium. Detailed electron microscopy has shown that the dominant factor in minimising this reaction is reduction in the extent of interconnecting porosity in the fibres. The presence of alloying elements, such as aluminium in the matrix plays a more limited role in reducing the extent of interface reaction.MST/3021

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.518

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA stereometric method for digitising the fracture surface of unidirectional fibre composites is used to calculate the breaking height differences of each fibre to its six nearest neighbours. From this height distribution the overload profile along the fibres, the critical length, interfacial shear strength, and the characteristic strength of the fibres are derived. This method is applied to ceramic fibre reinforced aluminium matrix composites tested in three point bending.MST/3004

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.526

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractConsideration has been given to the possibility of graded laminates based on aluminium and titanium alloys and their composites. In addition to increased toughness, damping, and fatigue crack growth resistance, laminates produced by diffusion bonding may provide a cost effective route to the utilisation of advanced materials in lightweight high stiffness structures.MST/3008

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.531

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe creation of wear resistant surface metal matrix composites in both aluminium alloys and titanium via the incorporation of preplaced SiCphas been successfully undertaken by using a 5 kW CO2laser. The problems associated with the production of a metal matrix composite layer freefrom porosity, cavities, and cracks, with a satisfactory distribution of ceramic were considered. Optimum laser processing conditionsfor Al–SiCpgave a well distributed ceramic withfew defects, but limited to 35μm thickness. This was increased to 250μm using a preplaced mixture of Al powder and SiCp. A prep laced SiCplayer on commercially pure Ti resulted in a dissolution of SiCpand precipitation of TiC, or the partial dissolution of SiCpand agglomeration into a hard layer (1400 HV). Pin on disc wear tests indicated that surfaces could be produced via laser surface melting associated with preplaced SiCpwhich showed a similar wear resistance to bulk metal matrix composite Al alloy–SiCp, and an improvement of an order of magnitude for commercially pure Ti–SiCpsurface metal matrix composites, over a commercially pure Ti laser treated surface.MST/3003

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.536

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractA spiral test was used to evaluate the flowability of an AlSi7 Mg0·6 alloy reinforced via 10–30 vol.-%SiC particles having average diameters of 9, 13, and 23μm. The results show that the composite melt has the same ability to flow into long thin sections as unreinforced aluminium, when the particle content is20 vol.-% and approaching 30 vol.-% as a result of increased viscosity. At these higher levels of SiC, an increase in pouring temperature cannot compensate for the reduced flowability. The particle distribution in the solidified material depends on the length which the metal flows before solidification. After 150–200 mm of flow, dendritic grains growing in the composite melt push the particles so that the solidified microstructure consists of open areas without particles. The particle free areas increase in diameter with the flow distance.MST/3005

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.545

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe adhesion of carbon coatings to Sigma silicon carbide monofilament is primarily dependent on the electrical power used to heat the monofilament. The adherence of the coating can be detected by performing bend tests on the fibre. It is suggested that in order to bond the carbon to the surface, a chemical reaction involving the formation of SiCl4takes place on the surface of the silicon carbide. This etches the surface and provides a good key for the carbon. If there is too little power the chemical reaction is suppressed. Too much power results in over etching and fibre damage. An additional factor of importance is the coefficient of thermal expansion of the coating. As power increases the carbon coefficient of thermal expansion reduces. The increased compressive stresses in the coating can lead to debonding.MST/3000

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.552

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractFor the design and optimisation of advanced materials, the possibility of reliably testing very small amounts of material or laboratory scale simple shape specimens is particularly interesting. To satisfy such requirements, this work presents a new procedure for mechanical testing of metal matrix composites. The method is essentially a diametral compression test of cylindrical specimens and represents an improvement of the‘Brazilian’test. The mechanisms leading to fracture of composites have been investigated via the mechanical behaviour of different metal matrix composites (A354–SiCpA354–A12O3short fibres) and consideration given to the role of the major parameters involved (both test and material related). The results of the diametral compression test, in terms of rupture strength have been compared with those of conventional tensile tests and characterisation of the microstructure via light and electron microscopy has been carried out. Evaluation of the results led to the conclusion that the failure of the materials is due to a tensile mechanism, according to elasticity theory, and that under identical testing conditions, for all the composites examined, the ratio of ultimate tensile strength/rupture strength is constant. The method developed constitutes a useful and rapid tool for both the selection of raw materials and the optimisation of metal matrix composite manufacturing processes.MST/2060

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.558

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractReliable mechanical testing procedures for particulate metal matrix composites are essential for both alloy development and component design. The measurement of toughness properties in these materials presents particular difficulties. In this paper, Charpy impact and chevron notch fracture toughness testing of an Al2124–17%SiC alloy are described. Although impact testing is a relatively simple technique for grading alloy toughness, it has not been widely used for metal matrix composites. Here, the effects of notch type and specimen thickness are examined and recommendations are made regarding the optimum testing procedure. Conventional fracture toughness tests using prefatigued specimens are difficult to apply to particulate metal matrix composites because residual stresses give rise to bowed crack fronts. The short bar chevron notch test, in which a crack is initiated at the apex of the machined notch and the toughness is evaluated after the crack has grown to a critical length, is therefore particularly suitable for these materials.MST/2073

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.565

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor

摘要:

AbstractThe application of chemical vapour deposition and physical vapour deposition coatings, either singly or in combination, onto SiC fibres is discussed in terms of their ability to enhance the high temperature stability of Ti–SiC composites. The thermal stability and success of potential barrier layers was assessed by studying the fibre-matrix interdiffusion and measurement of the mechanical properties of individual fibres following coating and thermal exposure. Measurements of the level of strength retention have proved to be a reliable method of assessing the effectiveness of potential diffusion barriers. Failures may result from one of three sources. For high strength fibres failures are SiC–core reaction zone initiated, for intermediate strength fibres failures are surface defect (SiC) initiated and for low strength fibres, failures are fibre–matrix reaction zone or coating initiated. To ensure high strength (i.e. core failures) it is essential that a carbon layer is retained at the SiC surface. The most successful barriers have been shown to be TiB2and PtAl2coatings preventing outward diffusion of carbon and minimising the interaction with the titanium matrix. From these results a life prediction model has been developed based on the fibre–coating interaction, which will predict fibre strength as a function of time at a given temperature.MST/3001

ISSN:0267-0836    

DOI:10.1179/mst.1994.10.6.572

出版商:Taylor&Francis    

年代:1994

数据来源: Taylor