Modelling the optimum hot workability of TiB reinforced Ti-6Al-4 V alloy by stability maps

摘要

Hot workability of Ti-6Al-4V and two whisker discontinuously reinforced materials, Ti-6Al-4V/1.2TiB and Ti-6Al-4V/8.9TiB, have been investigated. Hot uniaxial compression tests were carried out using a computer controlled thermomechanical simulator Gleeble machine at temperatures in the range 850 A degrees C to 950 A degrees C and strain rates ranging from 1 to 50 s(-1). The microstructures and the compression test results were compared among the three materials. The Ti-6Al-4V/8.9TiB material presented extensive cracking after deformation. In contrast, the Ti-6Al-4V/1.2TiB material showed an interesting compromise between flow stress and workability. The parameters of the Garofalo equation were calculated for the three materials revealing apparent activation energies that increased with increasing TiB content. The modelling is carried out by stability maps that gives the temperature at a given strain rate to obtain optimal workability and the stresses that has to bear the equipment. Taken 5 s(-1) as a reference strain rate, the temperature required to obtain a quality product increased from about 1143 K (870 A degrees C) for the Ti-6-4 alloy without TiB to 1228 K (955 A degrees C) for the 1.2TiB and to 1283 K (1010 A degrees C) for the 8.9TiB material. Therefore, the production of parts of the TiB composites should be conducted at a higher forming temperature to avoid the presence of cracks.