Influence of Sc on high temperature strengthening behavior of Ti-6Al-4V alloy

Abstract

Vacuum arc melting technique was used to prepare Ti-6Al-4V alloy containing Sc (0.3% and 0.5%, mass fraction). The ingots were melted twice by vacuum self-consumable electrode arc furnace. Forging of ingots was started in β-phase region and finished in high (α+β)-phase region. Annealing after forging was performed in low (α+β)-phase region for 30 min. Isothermal high temperature compression tests were conducted using thermal simulation machine under Ar atmosphere at 850 °C and 1 000 °C, and the strain rate were 0.001, 0.01, 0.1 and 1.0 s−1. Optical microscope(OM), scanning electron microscopy(SEM), energy dispersive spectrum(EDS) and transmission electron microscope(TEM) were used to study the microstructure evolution during high temperature deformation. The results show that, the peak stress value of alloys increases with increasing Sc content after deformation at 850 °C, however, there is no obvious strengthening of Sc when the alloys are deformed at 1 000 °C. Sc exists as Sc2O3 forms by internal oxidation during forging procedure, only minor Sc solutes in matrix. At 850 °C, the interaction between dislocation and participated particles and twinning mechanism controls the deformation procedure accompanied recrystallization. At 1 000 °C, the deformation of alloys containing Sc is mainly controlled by twinning, while the deformation of alloy without Sc is not only controlled by twinning, but also the interaction between dislocation and precipitated particles inside the twinning lamellar.