Sl. Semiatin et al., PHASE-TRANSFORMATION BEHAVIOR OF GAMMA-TITANIUM ALUMINIDE ALLOYS DURING SUPERTRANSUS HEAT-TREATMENT, Metallurgical and materials transactions. A, Physical metallurgy andmaterials science, 29(1), 1998, pp. 7-18
Microstructure evolution in a wrought near-gamma titanium alloy, Ti-45
Al-2Cr-2Nb, was investigated by a series of heat treatments comprised
of initial heating high in the alpha-plus-gamma phase field followed b
y short-time heating in the single-phase alpha field. The initial heat
ing step led to a dispersion of gamma particles which pinned the alpha
grain boundaries. The kinetics of the gamma grain dissolution during
subsequent heating in the single-phase field were interpreted in terms
of models for both interface reaction-controlled and diffusion-contro
lled processes. The model for diffusion-controlled dissolution yielded
predictions comparable to the observed times, whereas the model for i
nterface reaction-controlled behavior predicted dissolution kinetics o
ver an order of magnitude slower than observed. The growth of the alph
a grains, both before and after the dissolution of the gamma phase, wa
s also modeled. Section size limitations to the ability to use supertr
ansus heating to obtain uniform and moderately fine alpha grain sizes
were examined using the transformation models and a simple heat transf
er analysis approach. The results were validated through the heat trea
tment of subscale and full-scale forgings.