Abstract
In this study phase transformations in metastable beta Ti-15Mo alloy were investigated by an in situ electrical resistance measurement in a wide range of temperatures from -196 degrees C to 850 degrees C. Different temperature ranges of the evolution of electrical resistance were correlated with underlying phase transformations.
In the low temperature range, stage I (from -196 degrees C to 220 degrees C) the decrease of electrical resistance with increasing temperature is caused by the dissolution of omega(ath) (formed during quenching by athermal shuffle transformation) which is accompanied by the relaxation of lattice strain, while the diffusional assisted growth of omega(iso) in the range from 220 degrees C to 380 degrees C (stage II) is the main mechanism causing the increase of resistance. Another decrease of the resistance in the range from 380 degrees C to 550 degrees C (stage III) is explained by the dissolution or transformation of omega(iso).
The increase of resistance above 550 degrees C (stage IV) is related to the growth of alpha-phase particles. The fully reversible character of omega(ath) growth and dissolution during heating and cooling in the stage I up to 100 degrees C was confirmed by temperature cycling during repeated in situ resistance runs from RT.
Pre-ageing of samples at 300 degrees C promotes the formation of omega(iso) particles. Subsequently, omega(ath) particles are not created, which is fully consistent with electrical resistance measurements.
The presence of omega(ath) and the orientation relationship between omega and beta were identified by the electron diffraction.