Building on successful development experience of transformation induced plasticity (TRIP) steels, an analogous concept was taken to design high performance titanium alloys. This article describes a computational design framework of novel near-α TRIP titanium alloys with both high yield strength and fracture toughness for naval structural applications using a systems design approach integrating processing/structure/properties/performance relations. Predictive models including a transformation stability model based on Olson-Cohen heterogeneous martensite nucleation theory for titanium alloys was proposed. Integration of the models with CALPHAD software and databases enables parametric design optimization to meet design objectives. The developed models were calibrated with experimental measurements.
By means of tensile and compression creep testing and SEM, TEM observation, an
investigation has been made into the microstructure evolution of a single crystal nickel base
superalloy during tensile / compression creep. Results show that the cubic γ′ phase in the superalloy is
transformed into the N-type meshlike structure along the direction vertical to stress axis during tensile
creep. The cubic γ′ phase is transformed into the P-type structure along the direction parallel to stress
axis during compression creep. An obvious asymmetry strain of the alloy occurs during tensile and
compression creep, the formation of the needle-like γ′ rafts during compression creep is a main reason
of the alloy displaying a smaller strain. During compressive creep, the deformation feature of the alloy
is the <110> and (1/3) <112> super dislocations shearing into the γ′ rafts. The deformation
mechanism of the alloy, in the stage state of tensile creep, is dislocation climb over the γ′ rafts.
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