There are some titanium framed guns out there, like the older pre-lock S&W lightweight j-frames with titanium cylinders, S&W 1911 (that's scandium I guess), Taurus j-frames, Taurus 915T .41 mag, think they also make a titanium .357 not sure though, Beretta made a titanium Tomcat, Caspian makes titanium 1911 frames, S&W lightweight .44mags (I think scandium again), there's quite a few others that I'm not thinking of off the top of my head.
I don't think a titanium barrel is doable, as far as I'm aware it doesn't have the combo of mostly strength and to some extent elasticity of steel. Like when you bend aluminum it just never goes back to its original form, I think titanium is sort of the same way, just a bit stronger. It would probably just bow out in time after firing shots through it and you'd have to melt it back down to get it back to its original shape.
I'm not a metallurgist and don't claim to be, maybe someone so qualified can step in and speak on this..