The processing-microstructure-property relationship for a multicomponent Nb–Ti–Al alloy

Extrusion as a processing route for a multielement Nb–Ti–Al alloy is the basis for this study correlating the microstructure at a subsequent processing step with a particular mechanical property. An 8 cm diameter extrusion was produced from an industrial-scale ingot of this high strength, bcc-solid solution alloy. In the as extruded at 1100°C condition, the so-called van Gogh sky (VGS) microstructure is obtained as a result of plastic instabilities and the accompanying segregation which occurred during extrusion. The changes in its appearance, after a subsequent processing step (heat treatment) and the accompanying grain structure and precipitate (identified as TiC) provide the microstructure that is linked to a particular mechanical property. These are fatigue crack growth and fracture toughness, plane-strain fracture and tensile properties. Re-extruding the 8 cm diameter to 2.5 cm diameter and followed by additional processing to 1.6 cm diameter left only a small remnant of the VGS pattern in the primary extrusion. A more uniform, recrystallized grain size occurs and the nature and distribution of the carbides are shown with their identity confirmed as cubic MC. This microstructure from the complete processing is correlated with tensile test results.