Microstructures and mechanical behaviors of a directional lamellar Ti-48Al-2Cr-2Nb alloy produced by laser additive manufacturing

Extremely large thermal gradient is considered as a unique characteristic of additive manufacturing, which can be utilized to fabricate directionally solidified alloys. In this study, we successfully fabricated a bulk Ti-48Al-2Cr2Nb alloy with directional solidified features by the approach of direct laser deposition. The microstructural characterizations revealed that our additively manufactured (AMed) alloy was dominantly featured by a directional alpha 2/gamma lamellar microstructure. Moreover, there occurs an intriguing phenomenon that the orientation relationship between alpha 2 and gamma lamellae appears a slight deviation from the well-known Blackburn relationship, which was seldom observed in previous reports. Additionally, some amounts of beta o and C14-type laves phases also formed and dispersed in the lamellar microstructure. Mechanical investigations indicate that the AMed alloy achieved an improvement in yield strength at room temperature. Moreover, its yield strength can remain 630 MPa at 800 degrees C, comparable to the value at room temperature, and only a slight decrease occurred when the temperature was increased to 900 degrees C, which is superior to that of the cast one. Then, the related strengthening mechanisms were discussed based on the directional lamellar features and the particularity in orientation relationship.