Impact performance of plasma spray coatings is usually evaluated by means of surface observation after impact action. As a matter of fact, the dynamic response characteristics of coatings in the course of impact action are also very important. In this paper, a method of response frequency spectrum analysis is developed for the impact evaluation of plasma spray coatings. An impact test machine, in which the impact load is generated by a pivot-rod-lever system, is specially designed, allowing both single impact test and repeated impact test. The frequency spectra of Cr2O3 ceramic coating and WC-CoI7% alloy coating under single and repeated impact action are analyzed. The results show that there is an obvious relationship between the impact perfonnance and the impact response frequency spectrum. Abrupt changes in the coating, such as appearance of surface cracks and surface damage, correspond the sudden changes of the response frequency spectrum. Key words impact test machine plasma spray coating frequency spectrum impact evaluation

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