Phase transformation mechanism and mechanical properties of Ti-45Al-8Nb alloy prepared by directed laser deposition

Abstract

In this work, the Ti-45Al-8Nb alloy was fabricated by directed laser deposition. The phase transformation mechanism and mechanical properties were analyzed. The results show that different solidification paths were found. In the dendritic stem, the path is L → L + β → β → β + αβ → β + αβ + γ → α2 + γ + B2. At the periphery of the dendrite, the path is changed to L → L + β → αp → αp + γ → α2 + γ. The different solidification paths are due to elemental segregation, with Nb segregation in the dendritic stem leading to the formation of the B2 phase in α2 + γ lamellar. The decrease in Nb at the periphery of the dendrites leads to an L + β → αp peritectic reaction. The tensile strength and elongation are 365 ± 11 MPa and 0.36 ± 0.08%, respectively. Strength was higher than the methods of electromagnetic levitation cold crucible (EMLCC) and vacuum consumable arc melting (VCAM). The crack propagation model was analyzed, which was along the lamellar fracture and through the lamellar fracture.