Guoding Zhang

Interface microstructure and reaction in Gr/Al metal matrix composites

The interface structure in Gr/Al composites fabricated with liquid metal infiltration has been studied using transmission electron microscopy (TEM). Morphologies of interfacial reaction product, aluminium carbide Al4C3, formed at different manufacturing parameters were compared and, the growth mechanism of the carbide was studied by means of high resolution electron microscopy (HREM). It has been shown that the morphology of the carbide is intimately related to the processing parameters with which the composites were produced. There are two kinds of interfaces between the carbide and the aluminium matrix. They have different growth mechanisms and relative growth rates under different growth driving forces. Several crystal orientation relationships between the carbide and the aluminium matrix have been observed.

Study on the interfacial reaction product in Gr/A1 composites

The interfacial reaction product Al4C3 in Gr/A1 composites was shown preferentially nucleated on graphite surface where attachments or amorphous carbon exist. No definite orientation relationship of Al4C3 with base graphite fiber was found in the present investigation. On the other hand, three different orientation relationships were established between Al4C3 and the surrounding aluminum matrix. The morphology of Al4C3, which was found to be controlled by processing conditions, is interpreted in terms of the extent and nature of two different growth control mechanisms. The concentration gradient of carbon in the aluminum matrix near graphite fiber surface was found. The carbon atoms for the growth of Al4C3 are considered to be supplied through the aluminum matrix along this concentration gradient.

Quantitative analysis of interfacial chemistry in TiC/Ti composite using electron-energy-loss spectroscopy

Due to titanium carbide`s physical and elastic properties, titanium carbide particles are widely used as a reinforcement in titanium-alloy-based composites. Previous studies have shown that no obvious reaction products were detected on the interface region in TiC/Ti alloy systems; instead, a nonstoichiometric region in the TiC particle between the Ti{sub 6}Al{sub 4}V alloy and the stoichiometric TiC was found. However, the nature and the extent of the nonstoichiometric zone have not been quantitatively described. The present communication reports some results of a parallel electron-energy-loss spectroscopy (PEELS) study on a 10 vol pct TiC-particle-reinforced IMI-829 metal-matrix composite.

Analyses on fracture characteristics of SiCp-6061Al/6061Al composites extruded by different ratios

Two 6061 Al alloy matrix composites reinforced with rods that are themselves composites of the same Al alloy reinforced with a high volume fraction of SiC particles were studied. After vacuum pressure infiltration, one was hot extruded at a ratio of 10 : 1 and the other at a ratio of 60 : 1. The fracture characteristics of the two SiCp-6061Al/6061Al composites were examined in detail. It was found that increasing the hot extrusion ratio of this kind of composite can improve the bonding between the SiCp-6061Al bars and the 6061Al matrix. The strengths of the SiCp-6061Al bars and the 6061Al matrix were considered to increase with increasing extrusion ratio. Thus, the SiCp-6061Al/6061Al composite extruded at a ratio of 60 : 1 shows fracture characteristics which are different from the composite extruded at a ratio of 10 : 1. The former has a higher fracture toughness, and its crack opening displacement versus load curve indicates a higher elastic modulus and maximum load. After application of the maximum external load, there is a slow decrease with increasing crack opening displacement in the case of the 60 : 1 extruded composite, but the load can be maintained for wide crack opening displacement in the case of the 10 : 1 extruded composite.

Effect of alumina coating and extrusion deformation on microstructures and thermal properties of short carbon fibre–Al composites

Short carbon fibres were coated with alumina by sol–gel process. Uncoated and alumina-coated short carbon fibre–Al composites were fabricated by gas pressure infiltration process. The effects of alumina coating and extrusion deformation on microstructures and thermal properties of the composites were studied. The results show that alumina coating is effective to improve the quality of the short carbon fibre preform as well as act as diffusion barrier to impede interfacial harmful chemical reactions between aluminium and short carbon fibres, which would increase the thermal properties of the composites. Extrusion deformation can orient the carbon fibres to the extrusion direction to improve their degree of orientation, meanwhile decreasing their aspect ratio. Extrusion deformation has a beneficial effect on the thermal conductivity of the composites. However, its effect on coefficient of thermal expansion of the composites is small because the effects of the improvement in degree of orientation and the decrease of aspect ratio tend to cancel each other somewhat.

Effect of aluminum on the microstructure of graphite fiber in Gr/Al composite materials

The atomic structure of a graphite fiber in a graphite/aluminum composite was compared with that of the uncomposited fiber. The radial distribution functions of the atoms of carbon fibers before and after compositing were obtained through the analysis of the extended fine structure of the energy loss spectra. The position of the first peak in the radial distribution functions is determined as 0.143 nm in both cases, which is in good agreement with the distance between the nearest atoms of 0.142 nm. However, the ratios of the atomic density in the nearest radius to that in the second nearest radius, p1/p2, are different in the two cases. In the case of uncomposited fiber p1, /p2 equals 2.27± 0.05 independent of the detection position. However, after it was composited with aluminum, p1/p2 was shown to vary with distance away from the fiber/matrix interface. p1/p2 increases from 2.26 at the point of 40 nm away from the interface to 2.94 at the interface. It is evident that the surrounding aluminum atoms have...