M DRX grain size Q def activation energy for deformation Q DRX activation energy associated with the rate of DRX Q M activation energy associated with dynamic grain nucleation Q SRX apparent activation energy for SRX Q e activation energy for e 2 r ˙recrystallisation rate R gas constant RXD recrystallised RXN recrystallisation SRX static recrystallisation t period of static dwell time Dt time increment T temperature dV change in volume fraction RXD V 1 volume fraction recrystallised at start of time increment V 2 volume fraction recrystallised at end of time increment V f(SRX) volume fraction statically recrystallised a material constant de change in effective strain e DRX critical strain required to drive DRX e SRX critical strain required to drive SRX e 2 strain at maximum stress e ˙strain rate e ˙CRIT critical strain rate for DRX s flow stress
A computer-based process modelling capability has been developed to simulate the evolution of microstructure during ingot-to-billet conversion of nickel-base superalloys. A unique feature of the model is the incorporation of rules describing the dynamic and static recrystallisation phenomena that govern microstructural development. Computational investigations consider the influence of process control parameters such as die velocity and displacement to obtain an optimal microstructure. Furthermore, a comparison is made of the effective strain profiles obtained by squeezing flat versus rounded sections of the workpiece.The details of the model are given with particular emphasis placed on the description of microstructural evolution. A comprehensive testing programme using a purpose built compression testing machine has been carried out to acquire the materials data required for the model. The analysis of the flow curves is described. The microstructural model has been implemented within the three-dimensional visco-plastic Forge3"t finite element software. In order to validate the methodology developed, interrupted cogging trials have been performed. The evolution of microstructure is explained in terms of the cogging model and a more optimal process procedure suggested.Nickel-base superallovs for disc annlications
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