A method for evaluating the creep properties of overlay coatings

A new method is described for the evaluation of the creep properties of as- deposited overlay coatings. The method uses a composite tensile specimen co nsisting of a core alloy of well-characterised creep properties onto which the overlay coating is deposited. The overall strain/time response of this specimen, tested under constant stress conditions, can then be deconvoluted to obtain the creep characteristics of the coating. The method has the adv antage that the coatings are evaluated for the same microstructural conditi ons as they will be used under, i.e. having the same porosity levels and mi crostructure. A limited demonstration of the method has been made for an ai r plasma-sprayed Ni25Cr6AlY coating deposited onto an austenitic steel core and creep tested at 900 degrees C. The creep strength of this coating was surmised to be higher than that of equivalent monolithic samples produced b y low pressure plasma spraying. (C) 2000 Elsevier Science S.A. All rights r eserved.