MECHANISMS-BASED CONSTITUTIVE-EQUATIONS FOR THE SUPERPLASTIC BEHAVIOROF A TITANIUM-ALLOY

Mechanisms-based constitutive equations are proposed for the high-temp erature behaviour of a class of titanium alloys, for which the deforma tion mechanisms include diffusional creep, grain boundary sliding disl ocation creep and grain growth. A computational procedure has been dev eloped for the determination of the constitutive equations from a mate rial database. The constitutive equations and the procedure for their determination have been validated by modelling the behaviour of the ti tanium alloy Ti-6Al-4V at 927 degrees C. It is shown that the procedur e developed for the determination of the mechanisms-based constitutive equations can be used to identify the important deformation mechanism s in operation for particular stress, temperature and strain rate cond itions. For the case of the Ti-6Al-4V material, the procedure develope d correctly predicts the material hardening due to grain growth and in dicates that an additional hardening mechanism operates. In addition, the procedure is able to identify grain boundary sliding as a predomin ant deformation mechanism. The constitutive equations, which are gener ic in nature, and the procedure for their determination are applicable over a range of materials and are suitable for modelling the macrosco pic and the important microscopic aspects of material behaviour during processing. The equations may be readily determined using the procedu re presented, which is highly suitable for development as an expert sy stem, to completely automate the process.