Massive α precipitation selectivity and tensile fracture behavior of TC18 alloy

Abstract

Near β titanium alloys have been widely used for preparing the aerospace structure. However, the microstructure and mechanical properties are highly sensitive to the processing process. In the large size alloy bar, especially, the massive α phases precipitate in some β grain (black spot defects), which is not beneficial for improving the mechanical properties. In this paper, the analysis of β recrystallization and local α precipitation in TC18 alloy (near β alloy) has been carried out during the annealing. It is found that the massive α phases precipitate in β grains with stable-deformation orientations. The local massive α phases are responsible for forming the “black spots”. Compared with the alloy containing non-massive α, the strength of the alloy with the massive α apparently increases by the α precipitation strengthening, while the plasticity decreases greatly due to the crack propagation along the textured β grain or α lath/β interfaces within the normal grains. Based on the analysis of the relationship between the massive α and β orientations, the deformation dislocation storage energy induced α precipitation and tensile fracture mode have been further discussed.