1. The selection and proportion of resin and curing agent, and the film forming system with high functionality shall be selected. The proper crosslinking degree is the best. If the crosslinking degree is too high, the coating will be brittle and the flexibility will be poor. The hardness of hydroxyl containing polyester also be considered. B1530 can react with a small amount of hydroxyl group in polyester by adding 1% to the carboxylic pure polyester (TGIC/HAA) system to increase crosslinking and hardness.   
3. As for the addition of additives, the conventional additives in this kind of powder can be reduced. For example, leveling agent and wetting agent can only increase the lower limit. Other fine powder PTFE/PE that can increase smoothness and fill the gap can be extruded internally or added externally. 
The hardness of the coating is mainly related to the type and curing degree of the powder coating. The hardness of the coating is usually about 1H-3H, and some coatings with special requirements can be above 3H. The hardness of common indoor powder is lower than that of outdoor powder, which is usually tested with a hardness tester.  
IOTA high hardness polysilazane, pls check below links, 
https://www.polysilazane.cn/product-organopolysilazane-iota-9150-.html