Your profile indicates you are in zone 7a. Pretty cold for Bermuda.

How long is your Bermuda dormant each year? When the Bermuda isn't actively growing, it can have trouble competing with cool season grasses. One thing you could do is spray the fescue with glyphosate when the Bermuda is dormant. If you are careful, the glyphosate shouldn't harm the Bermuda.

This is a crazy thought but do you have a way to source "Santa Ana" bermudagrass? Santa Ana supposedly has a very long active growing period. In fact it doesn't become dormant until soil temperatures drop below 50 degrees or so. You could try introducing one pallet into your lawn as an experiment.

We actually have about 4 Bermuda cultivars growing in our 20,000 square foot lawn. We expect the most adapted Bermuda to take over (hopefully just not the common!).

Your profile indicates you are in zone 7a. Pretty cold for Bermuda.

Really? It does very well here, that's one reason why I decided to keep it, and get rid of the fescue. Mainly I've been depriving fescue of water, and keeping it cut very low to get rid of it. But some of the the tall fescue seems to hang on a bit. I would say I have about 25% to get rid of. My bermuda goes dormant around November, and starts greening back up around March. I don't mind the dormancy. I like my grass to be full and green during the months I actually enjoy being outside. Don't get me wrong. I'm sure I would enjoy fescue if I lived further north. It's a beautiful grass, just not that I have found here in the transition zone. The fescues in my neighborhood are terrible right now, mainly because people don't want to spend money aerating, overseeding every year, and refuse to go broke paying for their high water bills. And also tired of the fungus issues. The problem in my neighborhood is that it was built on top of bermuda that was already here before they developed the land, and everyone has it. But for some reason, we ended up with two different builders in the neighborhood, and one sodded fescue in the front, and seeded in the back, while the other sodded bermuda in the front, and seeded fescue mix in the back.

I've never heard of Santa Ana bermuda. I'll check it out, but I'm happy with what I have, just want to remove the rest of the fescue. I don't want to go down the glysophate road, even if it means my only choice is digging the clumps up with a shovel.

Believe it or not, Bermudagrass typically performs best in temperatures between 85 degrees and 117 degrees! Here in Dallas Bermuda is just revving up when average temperatures climb into the 80's. It is growing full-tilt in August when we're in the 100's. Bermuda is an incredibly adaptable grass so it will grow fairly far north. In the transition zone though, Bermuda will have more difficulty competing with other cool season grasses.

It seems Tall Fescue is a tough grass to kill with selective herbicides. If you aren't interested in using Glyphosate, a shovel might be a better route. In some ways Image is arguably more harmful to mammals than Glyphosate.
Celcius has the same signal word as Glyphosate- "warning". Glyphosate is inactivated moments after it touches soil. Many other herbicides are active in the soil for longer periods.

If you can use a small bit of Glyphosate instead of repeated sprays of other herbicides, the environment is probably better off. Just my 2 cents.