Coupled Growth of the Properitectic α~- and the Peritectic γ-Phases in Binary Titanium Aluminides

摘要

In a Bridgman laboratory furnace, TiAl with 53.4 at.% Al was directionally solidified with a solidification rate v = 0.05 mm/min and a temperature gradient of 15 K/mm. The resulting microstructures, analyzed by using optical and scanning microscopy with EDX and WDX, consist of two phases parallel to the growth direction. These phases are properitectic α (which subsequently eutectoidally transforms to a substructure of α_2-Ti_3Al and γ-TiAl) and peritectic γ, (α + L → γ). The experimental results show coupled growth over macroscopic length, but indicate, however, metastable eutectic growth rather than a stationary peritectic reaction. The reasons are discussed with respect to existing theoretical models.