Characterization of microstructure and precipitation behavior in Al-4Cu-xTiB_2 in-situ composite

摘要

Al-4Cu-xTiB_2 (x=0, 2.5, 5, 10 wt %) in-situ composites were prepared by a mixed salt route technique. The composites were characterized by X-ray diffraction techniques, to confirm that no Al_3Ti has formed, which is the advantage of mixed salt route technique. The scanning electron microscopy (SEM) analysis was carried out to determine the size distribution of TiB_2 particles in the matrix. The results showed that there was no agglomeration of TiB_2 particles throughout the matrix. The differential scanning calorimerty (DSC) studies were performed on the alloys as well as on composites to identify and characterize the precipitation sequence G.P.(I)->G.P.(II)/theta"-> theta' -> stable theta. To understand the precipitation kinetics of these precipitates in the presence of TiB_2, the solutionized samples were heat treated at different temperatures of precipitation as indicated by the DSC Thermogram and subsequently quenched to room temperature to retain the precipitates that form at corresponding high temperatures. The TEM analysis was carried out to characterize the crystal structure and morphology of the different precipitates. The analysis suggested that the precipitation occur primarily on the dislocations in the matrix as well as in the TiB_2 particle/ Al-Cu matrix interface dislocations. It is believed that these dislocations are generated to accommodate the strain due to the difference in the coefficient of thermal expansion (CTE) of the TiB_2 particles and the Al-Cu matrix. TEM results displayed that the interface contained large amount of dislocations which may possibly accelerate the precipitation sequence.