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Nucleation behaviour of to ! phase transformations in -type Ti alloys has been investigated using electron microscopy in four cases; (1) along the f112gh11 " 1 1i twin boundary, at which compressive stress occurs, (2) by means of aging under tensile stressing, (3) on the effects on the amounts of quenched-in vacancy in specimens quenched-in from two different temperatures, and (4) due to cooling to 131 K. Results show that the formation of nucleation-sites is enhanced by both compressive-stress along the twin boundary and tensile-stress during aging. In a specimen quenched from a higher temperature, the formation of nucleation-sites increases. It is considered that quenched-in vacancies and their clusters become nucleation-sites of to ! phase transformations. The phase transformation occurs due to cooling to 131 K. It is also found that the formation of new nucleation-sites cannot be reproduced and that they moved randomly.

In this paper we present a new method of generating a relativistic basis set for atomic Dirac-Fock (DF) orbitals. Here, all the occupied and a few low-lying unoccupied DF orbital wavefunctions of atoms obtained from the finite basis set expansion approach are replaced by orbital wavefunctions obtained from numerical solutions. We compare this with the Gaussian basis set generation by employing orbitals obtained from both the approaches in a coupled cluster method and computing the ionization potential and oscillator strengths for Mg + and Ca + using the above two different bases. The new method is found to be more appropriate for high-precision calculations.