I have a black oxide bit and a titanium bit but do not understand what the difference, if any, is between them. Is it how long they last or how they cut the wood? Anything on this would be great!
Bits coated with black oxide should be cheaper than titanium ones. They have decent heat resistance. Most sites that talk about the breakdown between the types rate these for better water, rust and corrosion resistance.
Titanium is a little ambiguous as there are multiple coating that use titanium. For the most part though they should outlast black oxide bits and are better rated for heat resistance. so you should be able to run them faster for longer.
What does this mean for a woodworker?
Both bits are rated for more or less the same materials. It is true that titanium coated should outlast a black oxide coated bit. However, for a wood worker, they should both be just fine and provide the same results in relatively comparative times (This largely depends on each bits size and pitch as well as some other factors).
Between Black Oxide and Titanium coatings, bits with a Titanium based coat will generally fare better when drilling through soft steels and other metals (~A36 hardness). The greatest contributing factor, however, is the base material used to make the bit, and how it was formed (forged vs. ground). A soft, ground bit will not fare as well with the same coating as a harder, forged bit.
Strictly between same material bits, those with Ti coats will outlast those with Black Oxide in denser materials. This is due to Ti bits having greater surface hardness, which allows the structure to hold up against the longer duration drill times needed to bore the denser materials. Even with the increased ‘lubricity’ (or reduction of friction due to surface texture) Black Oxide bits boring in metals are slowed; such that friction resilience can not compensate for lack of competitive surface hardness.
TL;DR: Friction wears soft bit surfaces faster. Titanium coated bits generally have greater hardness, and thus last longer.
For wood working it makes no difference at all. Titanium coating is an exceptionally thin layer of titanium nitride on HSS or other steel ; produces a gold color. Claimed to be an advantage cutting high strength steels (not wood). black oxide is the normal oxides that are on HSS ( high speed steels ) when tempered at the usual tempering temperatures of 950 to 1100 F. Again adding a very thin hard layer , and saving the manufacturer the cost of removing it.If a bit is ever resharpened these coating are gone. Searching the internet , I find "black oxide" is more of a decorative finish with very marginal corrosion protection ( my evaluation as a corrosion professional).