The Influence of Thermomechanical Processing on the Microstructure of Particulate Reinforced Titanium Metal Matrix Composites

摘要

Ti and Ti-6A1-4V matrix composites reinforced with 5%,10%,15% and 20%vol. particulate TiC were prepared using two powder metallurgy routes. The composites were either sintered at 1375°C or hot pressed at 920°C under argon atmosphere. Both methods were followed by hot deformation with strain rates ranging from 0. 001s~(-1) to 0. 1s~(-1) and temperature varying from 850°C to 1050°C. The microstructures of the composites were examined by scanning electron microscopy (SEM) coupled with electron backscattering diffraction (EBSD). The density,grain size and volume fractions of the phases were measured from these observations. Complete densification of this type of composite cannot be achieved by sintering alone. Furthermore, at high temperatures, TiC reacts with metal Ti and transforms progressively into TiC_(0.5). However, by hot pressing the composite powder,it was possible to obtain fully dense composites with a finer microstructure and to limit the reaction between TiC and Ti. The objective of the forging step is to suppress the remaining porosity and refine the microstructure to increase the mechanical properties of the composites. This study proposes a method to identify the best forging parameters for various configurations (grain size, reinforcement volume fraction,matrix nature) of titanium matrix reinforced with particulate TiC.