Originally Posted by CrystalSong

I've studied both.
Ti Chi was more of a soft martial art - it is based on Chi energy, but focuses solely on the sacral chakra or dantien. After years of practice it moves more into self defense and more forceful martial arts form but comes at it from an energy point of view. Most martial arts never get to the actual usage of energy until the upper degrees of black belt - if they get there.

Qi Gong deliberately bases its move on stretching and activating energy centers and moving the energy through them and up and out through the auric field and back in.
Ti Chi does get to that eventually I think, but it never focuses beyond the sacral chakra
Qi Gong does defiantly have some martial arts moves in it and some are even named the same, quite a few I recall from Kung Fu and Ti Chi.