Coupled growth behavior in the rapidly solidified Ti-Al peritectic alloys

Laser melting technology, an ultra-high-temperature gradient direction solidification process, has been, adopted on near equal atomic percent Ti+Al peritectic alloys with an effort to achieve the two-phase coupled growth structure. Both the alloy composition range and its local solidification parameters were determined by means of mathematical calculation of local solidification parameters in the melt pool. X-ray, SEM, TEM and optical microscopy techniques were carried out to investigate the microstructure and identify the phase composition. The two-phase (alpha and gamma) coupled growth morphology under conditions of high growth velocity and high-temperature gradient was first detected in the laser resolidified Ti-Al peritectic alloys. The aluminum composition range appearing in the coupled growth of alpha and gamma phases, lies in Ti-(51.0-54.0)at% Al, a little shift towards the left direction of the hypoperitectic plateau. Microstructural analysis showed that the coupled growth morphology changed from regular lamellar, irregular blocks and equiaxed structures in sequence, with the temperature gradient decreasing during growth. Energy spectrum analysis results showed that not only the solute diffusion but also the dissolution of phase gamma played an important role in the coupled structure evolution. Rapid eutectic growth KT model (Kurz, Trivedi, Metall Trans. A 22(1991) 3051) could be used effectively to predict the characteristic lamellar spacing of two-phase coupled, structures in TI-AI peritectic alloys. The transformation from a peritectic, L + alpha --> gamma, to metastable eutectic reaction, L --> alpha + gamma, of near equal atomic percent Ti-Al peritectic alloys, induced the formation of two-phase coupled growth morphologies. (C) 2001 Elsevier Science B.V. All rights reserved.