Hot deformation studies on discontinuously reinforced Ti-Alloys

Titanium alloys exhibit high specific strength and stiffness that fit structural applications demanding lightweight. The microstructure of the alpha-beta titanium alloys can be changed by thermomechanical processes such as heat treatments and pre-forging to achieve a certain ductility. Ceramic reinforcements can improve specific strength and stiffness, and also the wear resistance. In Situ particle reinforcement introduces neither further anisotropy to titanium alloys nor large internal stresses. The particulate reinforced titanium alloys (PRTi) are cheaper than the fiber reinforced materials and can be hot deformed. The present work-studies the effect of thermomechanical processes on the microstructure of the PRTi produced in-situ by powder metallurgy from Ti-6Al-4V-powders with additions of 1.0%wt of B and 0.1%wt of C. In the as received material TiB is precipitated as needle like reinforcement in the Ti-6Al-4V-0.1C matrix. Hot compression tests on this PRTi and on conventional Ti64 (pre-deformed) were carried out between 850 and 1100°C at strain rates between 0.001 and 10/s using a servohydraulic Gleeble® device. The stability of the alpha and beta phases and of the TiB precipitates was studied by heat treatments before deformation. The beta transus temperature of the composite increases with respect to that of the Ti64 matrix indicating changes in composition. The microstructures before and after deformation were studied by SEM and light microscopy. Some broken particles are found in the deformed samples at lower and some porosity in the matrix at higher temperatures, respectively. These results are compared with those of TiC-particle reinforced Ti64 produced by Cold-Hot Isostatic Pressing (CHIP).