The Ti-51 at.% Ni shape memory alloy solution treated at 1123 K for 1 h followed by 5% cold rolling and annealing at 573 K for 1 h was studied by transmission electron microscopy, including high-resolution and in situ observations at cooling. The applied treatment suppressed the B19' martensitic transformation and thus the studied transformation was the R-phase transition. It was found that the transformation starts by the incommensurate modulations occurring along <110> directions. The incommensurability exists in a wide temperature range and it decreases with lowering the temperature. The lock-in R-phase observed at liquid nitrogen temperature occurred in the form of relatively small domains. Additionally, another transformation was also observed at low temperatures that gave extra 1/2 <110> spots at the diffraction patterns. (C) 2003 Elsevier Science B.V. All rights reserved.