Influence of Rare-Earth Additions on Properties of Titanium Alloys. Effects of Yttrium and Erbium Additives on Rapid Solidification Processing, Superplastic Forming, Welding, and Strengthening of Titanium Alloys

摘要

Effects of 0.01-2.0 wt% yttrium and erbium additions on rapid solidification processing, superplastic forming, welding, and strengthening of titanium alloys were determined. Ti-8Al-Y and Ti-8Al-Er alloys were rapidly solidified by laser surface melting and electron beam melting and splat-quenching with the objective of simultaneously producing coherent Ti3Al precipitates and incoherent dispersoids. Rapid solidification at cooling rates > 10,000 K/s resulted in 10-100 nm incoherent dispersoids in Ti-8Al-1.5Y and in a nonequilibrium, supersaturated, solid solution Ti-8Al-1.5Si. Dispersoid formation and stability at 700-900 C were studied, and the annealing conditions for the production of a large volume-fraction of fine incoherent dispersoids and of coherent Ti3Al precipitates were determined. Metallic yttrium additions to Ti-6Al-2Nb-1Mo-0.8Ta improved the superplastic formability and increased the strength and ductility of laser weldments. The superposition of solid-solution strengthening, precipitation strengthening, and grain-size strengthening in ingot processed Ti-xAl (x = 4, 5.5, 7.0, 8.5, and 10.0) alloys was studied.