Modification of pore size distribution in plasma sprayed coatings after hot isostatic pressing

This paper reports the modifications made in the pore size distribution of plasma sprayed yttria-stabilized zirconia (YSZ) and Ti-6Al-4V/hydroxyapatite (HA) composite coatings following hot isostatic pressing (HIP). The pore size distribution was measured by a mercury intrusion porosimeter (MIP). The results indicated that the YSZ coatings which were HIPped in the temperature range 1000° to 1200°C and approx. 185 MPa showed a small decrease in the average porosity (approx.2.5%). However, the hardness increased approx.39%, and there was a corresponding increase in the coating density. This was due to reduction of the average pore size in the HIPped coatings. In the Ti-6Al-4V/HA composite coatings, the reduction of pores is most significant amongst the small pores. The porosity of the as-sprayed 20 wt% HA composite was approx.19%. This value was reduced to 17% for the sample HIPped at 1000°C for 1 hour. Although the reduction was relatively minor the interesting aspect was the drastic reduction of small pores less than 0.3 μm. The average pore diameter was observed to increase from 0.1676 μm in the as-sprayed coating to 0.787 μm in the sample HIPped at 1000°C, as a result of the elimination of the micro-pores.