K. N. Subramanian

The interface in Al2O3 particulate-reinforced aluminium alloy composite and its role on the tensile properties

The interface characterization of the aluminium alloy reinforced with Al2O3 particulates ((Al2O3)p/AI composite) was performed using X-ray diffractometry and energy dispersive X-ray spectroscopy. A layer of MgAl2O4 single crystals was observed at the (Al2O3)p/Al interface in the as-received extruded composites. Such MgAl2O4 crystals formed at the surface of (Al2O3)p are believed to grow by consuming a certain amount of (Al2O3)p. Upon loading, interfacial debonding was observed to occur at the boundary between MgAl2O4 and the aluminium alloy, or along the MgAl2O4 layer itself. These experimental observations are correlated with the tensile properties of such composites.

Failure behaviour of particulate-reinforced aluminium alloy composites under uniaxial tension

Tensile tests were carried out at room temperature on 6061-aluminium alloy reinforced with SiC and Al2O3 particulates. Although a significant increase in strength could be achieved by introducing ceramic reinforcements into the aluminium alloy matrix, it is associated with a substantial decrease in fracture strain. In order to understand the reason for the inferior ductility of such composites, analytical solutions were obtained using a simple composite model. SEM studies were carried out on the side surfaces of the fractured specimens to verify the proposed failure behaviour. Failure modes observed to operate in such composites under uniaxial tension are described.

Deformation of duplex crystals and two-phase bicrystals of alpha-beta brass

A two-phase transition zone of alpha-beta brass forms as a result of the melting of beta brass on alpha brass single crystal substrates. Specialized heat-treatments can convert this transition zone into a duplex crystal region of alpha-beta brass, or eliminate this region resulting in a sharp boundary between alpha and beta crystals. Specimens prepared by these treatments were deformed in uniaxial tension to study the initiation of plastic deformation and its propagation across the phase boundary. Although the phase boundary initially poses a resistance to the approaching slip, its effectiveness as a barrier depends on the crystallographic relationships between alpha and beta crystals. No void formation was observed at the boundaries.

Metallic glass ribbon-reinforced glass-ceramic matrix composites

The role of metallic glass ribbons in modifying the properties of glass-ceramics was investigated using specimens prepared by conventional pressing and sintering techniques. Even very low volume fractions of such reinforcements were found to provide significant improvements in the strength, elastic properties and fracture toughness of the glass-ceramic matrices. The observed improvement in the fracture toughness is explained on the basis of various metallic glass ribbon-related energy absorbing mechanisms.

Elevated temperature mechanical properties of continuous metallic glass ribbon-reinforced glass-ceramic matrix composites

Effect of temperature on the modulus of rupture of glass-ceramic matrix composites reinforced with very small volume fractions (∼1%) of continuous metallic glass ribbons was studied. The failure modes in such composites were found to significantly depend on the test temperature. Variations in the strength of the matrix, and the interfacial shear strength between the matrix and the ribbons due to changes in the test temperature, were found to control the elevated temperature strength and failure mode of these composites.

Young's modulus of cold- and hot-rolled (Al2O3)p-Al composite

The Youngs modulus of hot-rolled Al alloy reinforced with Al2O3 particulates, (Al2O3)p-Al composite, is measured using the dynamic sonic resonance test method. The variation in the moduli of cold- and hot-rolled composites, as a function of the reduction ratio, is compared. Although both cold and hot rolling result in more uniform distribution of the particulates, hot rolling causes less damage to the reinforcements, resulting in more isotropic composites possessing a higher Youngs modulus. These observed variations in the Youngs modulus with respect to reduction ratio are analysed on the basis of the microstructural changes due to the rolling and T6 heat-treating operations.

Role of strain-rate and phase boundary geometry on the deformation behaviour of two-phase bicrystals of alpha-beta brass

Tensile testing was carried out at various strain-rates using alpha-beta brass two-phase bicrystal specimens having two types of boundary geometries, currugated and flat. The corrugated boundary was more effective in blocking the propagation of slip from alpha to beta phase. A strain-rate sensitivity was found in all specimens regardless of boundary geometry. At low strain-rate, both boundary types were found to be ineffective barriers to the propagation of slip. At high strain-rates both boundaries fully resisted the passage of deformation. At low strain-rates coarse slip was observed, while at high strain-rates fine slip occurred in the alpha phase.

Interfacial effects in a metallic-glass ribbon reinforced glass-ceramic matrix composite

The effect of temperature on the interfacial effects in a metallic-glass ribbon reinforced glass-ceramic matrix composite was investigated. The metallic-glass ribbon present in this composite was found to be significantly affected at elevated temperatures, owing to the diffusion of lead and zinc from the matrix. The presence of the matrix in the vicinity of the ribbon enhanced the formation of an oxide layer on the ribbon surface. The oxide layer decreased the interfacial bond strength between the ribbon and the matrix, affecting the failure mode of such composites at elevated temperatures.

The load transfer mechanism in a glass ceramic composite reinforced with continuous metallic glass ribbons

Abstract The load transfer mechanism in a glass ceramic matrix composite reinforced with metallic glass ribbons has been investigated. The critical ribbon length required for effective load transfer between the matrix and the ribbon was found to be a function of the ribbon width. This dependence was attributed to the size of the long transverse side available for load transfer.

Discontinuous metallic-glass ribbon reinforced glass-ceramic matrix composites

Discontinuous metallic-glass ribbons of varying lengths and widths were used to reinforce a brittle glass-ceramic matrix. The fracture strength and toughness of such composites as a function of ribbon volume fraction and geometry were measured by three-point bending. The mechanical properties were found to be relatively isotropic in the plane of compaction (without significant loss of strengthening achieved with unidirectional reinforcement). The higher composite strength exhibited in a direction perpendicular to the plane of compaction was attributed to the higher percentage of ribbons oriented with their short transverse faces perpendicular to the opening crack front.