Preparation of Zirconium Phosphate Bonded Silicon Nitride Ceramic Coatings by Cold Spray and Presureless Sintering

In the present study, a new method for preparing zirconium phosphate bonded silicon nitride (Si3N4) ceramic coatings with low porosity was developed using cold spray and pressureless sintering technique. Zirconium phosphate (ZrP2O7) was used as a binder material instead of the traditional organic materials, in order to prevent the residual carbon which was severe to the dielectric properties of the Si3N4ceramics. Firstly, aqueous Si3N4slurries with 0~40 wt.% solid loading were prepared, using deionized water as the liquid medium. Then the Si3N4slurries were cold sprayed on the Si3N4porous ceramic substrates and finally the samples were presurelessly sintered at 1000oC to achieve the Si3N4ceramic coatings. The rheological properties and viscosity of Si3N4slurries were investigated in detail, as a function of solid loading. The optimum cold spray parameters were spray distance 21 cm and spray time 20 s. The porosity of the obtained Si3N4ceramic coating was ~5 % and the interface between the coating and substrate was well bonded, without microcracks, indicating a good thermal physical match between the coating and substrate.