Spray Dried

FIGURE 15: THERMAL CYCLE PERFORMANCE OF COATINGS MADE FROM VENDOR 'H' CAST, CRUSHED AND SPRAY DRIED POWDERS

cially manufactured cast, crushed and spray dried powder was obtained from vendor 'H' which closely fit the distribution of the best performing sintered 'B' powder, sprayed and tested. The thermal cycle test performance observed was substantially less than the original powder, and less than the best of the spray dried powders tested (Figure 15).

Further demonstration of the effect of powder size is shown in Figure 16. Source 'D1 powders having size ranges from 56 to 110 v™ were erosion and thermal cycle tested. The thermal cycle performance generally increased and erosion resistance decreased with increasing powder size. At the largest size, the mode of failure in thermal cycle testing changed from normal spallation process to an attrition of the coating near the edges of the specimen. This mode appears to be indicative of incomplete melting of the powder during application .

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