DEUTERIUM SURFACE SEGREGATION IN TITANIUM-ALLOYS

Deuterium surface segregation has been investigated in α, α+β, and β-phase titanium that were deuterium charged over the range of 2 to approximately 300 wppm. Surface segregation was observed in samples that were essentially α-phase materials, i.e., high-purity commercial α-Ti, Ti-6Al, and Ti-3Al-2.5V, whereas Ti-6Al-4V had slight enrichment and β-Ti-13Mn had no detectable segregation. Nuclear reaction analysis (NRA) techniques were used to measure the near-surface deuterium concentration, and the segregation has been localized to within 50 nm of the surface. The time-dependent increase of deuterium at the surface is consistent with deuterium diffusion from the bulk to the surface and a room-temperature diffusivity of approximately 3×10-9 cm2/s. Surface enrichment in excess of 30 times the bulk concentration was observed in charged samples and in excess of 60 times for samples that had been charged and then vacuum annealed. Polishing was found to be of importance in causing segregation. The presence of deuterides or a surface defect state is suggested to explain the deuterium surface enrichment.