Imagine that inside a turbine blade there are tiny little channels. These channels transport a fluid that solidifies in contact with air or water, depending on where the blade operates. This fluid is is the same material that is used to coat the blade in the first place. When the blade is damaged, the channels are exposed and the fluid leaks, covering the damage part and restoring it. 

Now, I don't think that other types of blades, sharped blades, would actually retain their sharpness if such channels were used there, but I honestly don't know.