Which porcelain materials are you using? Because there are quite hard ceramics such as ZrO2, SiC.. If the as deposited coating is not as hard as you expected had you tried sintering in oxygen atmosphere? Sintering would cause cracking in non optimized conditions, but you could manage it usually controlling the thermal cycles.

Among the materials that have high hardness are carbides such as WC and SiC.

Thank you so much. I used porcelain with composition as mixture of metal oxides and I deposited it by electrophoretic method and then carried out sintering up to 300oC for 1h, but its stayed unhardened. 

Probably you must increase the tempersture, for example ZrO2 and TiO 2 are usually sintered up to 700-800 oC to get rutile phase

Thanks for your answers.