Filters
Availability
Publication Year
Resource Type
Faculty
School/Institute
Publication Search Results
Sort
Results per page
1 - 10 of 1579
-
(1995)Journal ArticleThis paper examines changes to the abrasive wear resistance of aluminium-based composites when heat-treated to different ageing conditions. The composites studied were the age-hardenable aluminium alloys 2014 Al or 6061 Al reinforced with 3 μm or 20 μm SiC particles. The materials were aged at temperatures between 50°C and 250°C, and changes to the wear resistance were measured using a pin-on-drum machine. When aged at the lowest temperatures (between ≈50–150°C), transmission electron microscopy revealed the presence of the solute clusters (e.g. GP zones) and small coherent precipitates in the aluminium alloy matrices, and these were easily sheared by mobile dislocations. Consequently, the hardness and abrasive wear resistance of these under-aged composites were measured to be relatively low. Raising the ageing temperature to ≈200°C increased the hardness and abrasion resistance of the composites to the peak-aged condition, and this was associated with the precipitation of small intermetallic compounds which were incoherent with the crystal structures of the aluminium alloy matrices. At 250°C the composites were over-aged, and this resulted in a reduction in hardness and wear resistance due to the coarsening of the intermetallic precipitates. The composites containing 20 μm SiC particles were slightly more wear resistant than those containing 3 μm SiC.
-
(1996)Journal ArticleThe effect of angular and spherical shaped Al2O3 particulates on the precipitation behaviour of 6061 aluminium-matrix composites has been studied using microhardness testing, differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The evolution of precipitates at each stage of precipitation corresponding to the DSC-peak was monitored through careful TEM observations. Both the formation and dissolution behaviour of the precipitates in the ageing process in the composites were compared with the unreinforced 6061 matrix alloy. Although an overall accelerated ageing response in the composites was reported, not all stages in the ageing process were influenced by the addition of particulates. However, the precipitation sequence was not altered by the presence of the particulates. The degree of acceleration and the relative proportion of the phase/phases was found to depend on reinforcement parameters such as size, shape and volume fraction. In the composites, higher dislocation densities were observed in the immediate vicinity of the ceramic particles which may have formed due to the large difference in the coefficients of thermal expansion (CTE) between the ceramic particles and the matrix. These CTE-dislocation effects influence the kinetics of precipitation.
-
(1996)Journal ArticleThe microstructural development during annealing of a cold-deformed 6061Al metal matrix composite (MMC) reinforced with either 3 or 20 mgrm diameter SiC particles has been investigated. The composites were compressed to low (< 10%) levels of strain and then annealed at either 350 or 450°C for different times. Microstructure examination was carried out by transmission electron microscopy and optical microscopy. The results reveal that prior grain boundaries and constituent particles are the dominant sites for recrystallization in both composites, although some nucleation was observed adjacent to the larger SiC particles. The concurrent presence of Mg2Si precipitates affected the progress of recrystallization.
-
-
(1997)Journal ArticleClose-to-theoretical-density compacts of Fe3Al intermetallic and its composite with 4 vol% A12O3 were made by mechanical smearing of powders, followed by Hot Isostatic Pressing. Mechanical characterisation of the compacts were carried out, predominantly, by ultramicro-indentation technique. The materials exhibited very high mechanical properties, and in particular, the composite compact appeared to possess 50% more strength than, and the same modulus of elasticity as, ultra high strength steels. The A12O3 in the composite preferentially occupied the grain boundary positions giving rise to a grain boundary hardness of 9 GPa. The hardness decreased to 6 GPa in the interior, and a functionally graded zone, 0.6-1.0 μm in thickness was observed. Electron probe microanalysis profiles showed good correlation with the results of the mechanical study.
-
-
-
-
-