FORMATION OF INTERFACE PHASES IN THE TITANIUM-ALLOY IMI-834

A variety of different preparation techniques have been used in order to identify the experimental conditions under which interface phases a re formed in the near-alpha alloy, IMI 834. In particular, a Ni plated surface examined in cross-section in the TEM produced a gradation in hydrogen content from high at the surface to low levels in the bulk. T wo transformation products have been identified, one was a monolithic fee phase with a lattice parameter of a = 0.434 +/- 0.004 nm, which fo rms along alpha-platelet boundaries, and the second was an acicular fe ature which formed between alpha-platelet boundaries which was tentati vely identified as an hcp phase twin related to the alpha-titanium. Th e monolithic interface phase was found to form at both low and high hy drogen levels while the alpha twins were only seen at high hydrogen co ntents. In all cases, the transformations were shown to be artefactual and induced solely by hydrogen absorption. No evidence of mechanical strain induced interface phase formation was found. In conflict with t he literature, the monolithic fcc phase was found to occur during ion- beam milling and was attributed to water contamination of the milling gas. Formation of the interface phase was suppressed by electropolishi ng at temperatures less than or equal to - 50 degrees C.