There are a number of different abradable coating types
Abradable coatings are designed to preferentially abrade when contact is made with a mating part. Thermal spray abradable coatings have low structural integrity so they are readily abraded when they come into contact with a moving surface with higher structural integrity. The coatings are designed not to damage the mating surface.
There are a number of different abradable coating types, to cater for different operating temperatures, corrosive environments and mating materials. The coating structure can be either:
1.Very porous with many unreacted or unmelted particles (which would by normal standards be considered as a very poor coating) produced by very careful selection of spraying parameters to achieve the right degree of abradability. These coatings can be difficult to reproduce accurately and need strict monitoring.
2.Dense and uniform structured coatings with additives such as polymers, graphite, bentonite and boron nitride. These additives weaken the matrix material of the coating and can provide some degree of dry lubrication. Abradability is controlled mainly by the concentration of additives and not by changes to the spraying parameters, which aids in providing more consistent coatings.