Study of the Inert-Gas Arc Welding of Titanium and its Alloys (5th Report)

On the β→α Transformation Process in α+β Titanium Alloys

Abstract

As for the β→α transformation process in α+β titanium alloy there are little theories.
In this investigation, were studied on the process and the mechanism of the β→α transformation were made clear.
The β→α transformation in α+β titanium alloy progresses as following.
β0→ω+βγ→ω+α+βγ→α+βγ (βγ→α+βu)
where, β0, βγ, and βu, mean the change of density (composition) of alloying element in β according to the transformation process.
This ω is a methodical crystal structure (the structure is b.c.c. and has about three times as large lattice constant as that of original β) which is formed with travelling of the solute atoms so as to form the unit cell which is necessary to the β→α transformation. But this w was seen only in the earlier period of the bigining of a precipitates from β in the β→α transformation, and when a little of the transformation progressed on (or in α+β titanium alloys containing a small amount of β-stabilizer), something as ω could not be seen.