Effects of solution temperature and cooling rate on α phases and mechanical properties of a forged Ti-55511 alloy

Abstract

The influences of solution temperature (ST), as well as the cooling rate, on α phases and mechanical properties of a forged Ti-55511 alloy are investigated. It is found that the morphology, size, content, and distribution of α phases are apparently affected by the ST. With the increase of ST, the content and size of discontinuous grain boundary α (α GB) phases, globular α (α g) phases and lamellar α (α l) phases decrease, while those of the secondary α phases (α s) increase. α GB phases preferentially transform into β phases, and the transition process basically finishes at about 800 C. These transformation induce the obviously-changed mechanical properties, i.e., the ultimate tensile strength (UTS) and yield strength (YS) firstly increase and then decrease with increasing the ST. However, the elongation decreases with the increased ST. In addition, the content and size of α phases and mechanical properties are greatly influenced by the cooling rate. When the cooling rate is reduced, the content and size of α g and α l phases increase while those of α s phases decrease, resulting in the decreased strengths and the increased elongation. It can be concluded that the suitable ST and cooling rate are about 780 C and water cooling, respectively.