well, boron carbide (B4C) is the third hardest material on earth. just behind diamond and boron nitride.
B4C finish is toughest finish there is, but applying it comes at the cost. it takes a jet of super-heated gas (plasma) to thermal-spray it and allow it to adhere B4C powder to some substrate.
since this method is fairly labor involved and pretty cost prohibitive for every day applications, people settle for next best thing - Nickel-Boron Carbide.
Nickel substrate and solution suspended B4C powder can be applied by means of electrolysis more cheaply, although not much more.
So yes, it is tougher than a lot of other types of finishes, but still not quite as tough as gas-jet fused B4C powder.
at one point 5-6 years ago there was this business offering B2C finish on guns. they called it 'diamond black' i believe, but it seemed like they either quickly went under or stopped offering service because of some technical difficulties.
Boron nitride (BN) has two common structures, one is very hard and has a diamond structure (cubic boron nitride or cBN). The other is very soft is used as a dry lubricant and has a graphite structure.