Hydride Precipitation Behavior and Fracture Morphology of Ti-6Al-4V Alloy

Abstract

The relation between hydride precipitation behavior and fracture morphology was investigated on Ti-6Al-4V alloy by means of fractography and internal friction measurement.
When the specimen hydrogenated thermally at 1273K for 7.2ks was furnace-cooled (β annealed specimen), fine particles of hydride precipitated from the β phase during cooling. The fracture morphology showed the occurance of fracture at the interface between the β phase and the hydride or inside the hydrides.
The strength of the hydride was 0.5GPa and smaller than that of the matrix, and the elongation was hardly present. The hydride acted as the fracture initiation site.
When the same hydrogenated specimen was water-quenched (β quenched specimen), the hydride hardly precipitated and hydrogen was solutionized compulsorily in the β phase. When the β quenched specimen was plastic-deformed, the hydride precipitated from the β phase. At a high tensile strain rate, the fracture morphology was similar to that of the β annealed specimen. This means that the hydride precipitated finely from the β phase by plastic deformation and the fracture occurred at the interface between the hydride and the β phase or inside the β phase.
At a low tensile strain rate, the fracture morphology showed the terrace fracture inside the hydride. This means that the hydride precipitated from the β phase, grew to a large block independent of microstructure, and then fracture occurred inside the hydride.