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

Abstract

In the present study, a new method for preparing zirconium phosphate bonded silicon nitride (Si 3 N 4 ) ceramic coatings with low porosity was developed using cold spray and pressureless sintering technique. Zirconium phosphate (ZrP 2 O 7 ) 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 Si 3 N 4 ceramics. Firstly, aqueous Si 3 N 4 slurries with 0~40 wt.% solid loading were prepared, using deionized water as the liquid medium. Then the Si 3 N 4 slurries were cold sprayed on the Si 3 N 4 porous ceramic substrates and finally the samples were presurelessly sintered at 1000 o C to achieve the Si 3 N 4 ceramic coatings. The rheological properties and viscosity of Si 3 N 4 slurries 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 Si 3 N 4 ceramic 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.