A self-consistent model was applied to predict the plastic flow behavior during hot working of alpha/beta titanium alloys with wrought (equiaxed alpha) microstructures as a function of the flow behavior and volume fractions of the individual phases. For this purpose, constitutive relations that incorporated composition-dependent strength coefficients were determined for the alpha and beta phases. With these constitutive relations and measurements of the specific compositions and volume fractions of the two phases at hot-working temperatures, the flow stress dependence on temperature under nominally isothermal conditions and the (average) strain rates in the individual phases were predicted for Ti-6Al-4V. The effect of temperature transients during hot deformation on the flow stress under nonisothermal (conventional) forging conditions and under nominally isothermal, high strain-rate conditions was also established using the self-consistent modeling approach. In these instances, the effect of a rapid temperature drop or rise, respectively, on the retention of a metastable microstructure was quantified. The predicted flow behaviors showed good agreement with experimental measurements.

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The development of an affordable nickel disc alloy that shows the required combination of strength, damage tolerance and creep resistance continues to challenge materials engineers. RollsRoyce has developed the alloy known as RR1000, which when processed to produce a fine grain microstructure, shows at least a 25ºC increase in temperature capability over the current disc alloy, 720Li, and has an equivalent crack growth resistance to coarse grain Waspaloy. This paper discusses the steps that were taken to attain these mechanical properties, and also examines the potential to increase temperature capability by a further 30ºC through the development of a coarse microstructure in selected areas of disc forgings.

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