Ti6Al4V-0.55Fe合金连续升温过程的相变研究

The dilatometry behavior and microstructure of the α+β→β phase transformation in the Ti6Al4V-0.55Fe alloy were investigated during continuous heating process. Four heating rates (1, 5, 10, 15 K/min) were applied for the dilatometry behavior research. The results show that for the α+β→β phase transformation curve, the S-shaped pattern under the different heating rates indicates that the α+β→β phase transformation is a nucleation-growth-controlled process. The mean phase transition activation energy E was obtained by the Kissinger-Akahira-Sunose (KAS) method which equals to 200 kJ/mol. By calculating the corresponding Avrami index n with the increase of the β phase volume under the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model, we can divide the Avrami index n into three stages which include the initial phase transformation stage (0<f<0.01), the middle phase transformation stage (0.01<f<0.95) and the phase transformation end stage (0.95<f<1). It indicates that α+β→β transformation mechanism in the Ti6Al4V-0.55Fe alloy varies at different stages. At the meantime, the back scattered electron (BSE) micrograph was applied for the microstructure analysis. The microstructural aspects perfectly match the previous dilatometry research, which validate our assumptions. Finally, a continuous heating transformation (CHT) diagram of α+β→β phase transition in the Ti6Al4V-0.55Fe alloy was obtained. It can be found that the Ti6Al4V-0.55Fe alloy has a lower α+β→β phase transition activation energy compared with Ti6Al4V alloy, which indicates that the α phase re-dissolution is easier in the Ti6Al4V-0.55Fe alloy.