THERMODYNAMICS OF THE BAINITIC TRANSFORMATION IN A CU-ZN-AL ALLOY

The driving forces of two possible bainitic reactions within the bainitic transformation temperature range have been calculated for a Cu-Zn-Al alloy. The results show that DELTA-G-beta'--> alpha' and DELTA-G-beta'--> beta'1 + alpha < 0 in this transformation temperature range. Accordingly, the bainitic transformation can only proceed by the diffusional reaction beta'--> beta', + alpha. Furthermore, the driving force of 9R ordering transition of alpha has also been calculated. On account of DELTA-G-alpha --> alpha' < 0, the disordered alpha-phase produced after the diffusional bainitic transformation may further transform into the ordered one with 9R structure.