Titanium carbide / nitride is very hard: ~9 on the Mohs scale. This is approximately equal to sapphire. Diamond is 10 for reference. This is also much harder than most steels when hardened. This is why Carbides / nitrides are used in cutting tools for working hard metals such as steel. Most knife blades will have a Rockwell hardness between 50-60, this is about equal to 3-3.5 on the Mohs scale.
When one side of the is carbidized / nitrided, the soft side of the metal is continually worn down, exposing more and more carbides, forming what is essentially micro-serrations. In this sense it is self sharpening. I'm not sure any of these knives are treated this way however, and it is not a cheap process.
Because of the "micro-serrations" it may not seem like a sharp blade if you were to just touch it, but it functions as a sharp blade when slicing. For example, these knives would work well for slicing food, but not for whittling wood.