Advancing fracture toughness in high-strength TC18 alloy by optimizing the forging process

Abstract

Optimizing performance and reducing costs often exhibit a trade-off relationship, thereby limiting the broader application of Ti alloys. To address the above challenge, this study involves comparative analyses of strength and fracture toughness, for TC18 alloy processed through distinct forging methods—long-period forging (M1) and short-period forging (M2). The results shows that both M1 and M2 present analogous content and dimensions of equiaxed primary α phase (αp) and secondary α phase (αs), as well as comparable values for yield stress (∼1050 MPa), and plasticity (∼7 %). Nevertheless, fracture toughness of the latter (M2) exhibits a notable increase (74.3 MPa∙m1/2) than that of the former (55.1 MPa∙m1/2). This phenomenon is primarily attributed to the heightened compatibility of mechanical properties and superior orientation relationship between αp and βt in M2 as opposed to M1. These characteristics give rise to a homogeneous deformation and an augmentation in void nucleation within the αp phase in the larger plastic deformation zone in M2. Additionally, the translocation of dislocations from αp/βt interfaces into the βt matrix in M2 is also verified by the tensile test at 3 % strain. The findings provide a promising insight for the design of low-cost Ti alloys with attractive strength and damage tolerance.