Tailoring lamellar orientation and tensile properties of TNM alloy via extrusion

Abstract

The rectangular billet of TNM alloy with oriented lamellar microstructure was obtained by extrusion above its α transus temperature. The as-extruded TNM alloy exhibits a nearly lamellar microstructure with an average colony size of approximately 60 μm, and the proportion of lamellar colonies with an angle between the interface and the extrusion direction less than 30° exceeds 70 %. EBSD results show that strong basal texture of α phase with basal planes parallel to the extrusion direction was formed during the extrusion process in the (α+β) two-phase field. During the subsequent cooling process, the γ lamellae precipitates along the (0001) plane of α phase according to the Blackburn orientation relationship, allowing the lamellar structure to inherit the orientation of the parent phase. Tensile test results indicate that the strength and fracture elongation of the as-extruded TNM alloy along the extrusion direction (ED) increased simultaneously, which were 1100 MPa and 1.26 %, respectively. The hindrance effect of interfaces on dislocations and stacking faults in lamellar colonies parallel to the extrusion direction helps to improve strength, while the activation of the prismatic slip and pyramidal slip systems in the α2 lamellae is beneficial to the plasticity. This study shows that it is feasible to control the lamellar orientation and improve the mechanical properties of TNM alloy by extrusion above its α transus temperature.