EPITAXIAL FORMATION OF NITRIDES IN A TI-6AL-4V ALLOY IMPLANTED WITH N

Samples of a Ti-6Al-4V alloy implanted with N+ ions have been studied by plan view transmission electron microscopy. Both single (90 keV Nions, 9x10(17) cm(-2)) and triple (25 keV n(+), 2.5x10(17) cm-(2), 60 keV N+, 4.5x10(17) cm(-2) and 125 keV N+, 10.5x10(17) cm(-2)) implants were examined. Single implant specimens were found to transform to ep silon-Ti2N or to two twin related variants of Tin from alpha-Ti was fo llowed by electron diffraction; close-packed planes and close-packed d irections in the two lattices were observed to be parallel to each oth er in the majority of alpha-grains. The transformation appears to have some similar characteristics to those reported for displacive reactio ns involving hydrides in Zr and Ti alloys, although a true invariant l ine or plane does not exist in the Ti --> TiN phase change. The format ion of two twin-related variants of TiN is thought to minimize the sha pe change associated with the transformation.