Evaluation of Microhardness and
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Ž . Surfac e and Coa tings Techno logy 135 2001 166172 Evaluation of microhardness and elastic modulus of thermally sprayed nanostructured zirconia coatings R.S. Lima, A. Kucuk, C.C. Berndt Department of Materials Science and Engineering, State Uni ersity of New York at Stony Brook, 306 Old Engineering Building, Stony Brook, NY 11794-2275, USA Received 8 February 2000; accepted in revised form 2 August 2000 Abstract Ž . Results concerning microhardness and roughness R of plasma spraye d coatings fabricat ed from nano struct ured partiall y a Ž . Ž . stabil ized zirco nia PSZ feed stock are presen ted. Nano structu red zirconi a particle s were plasma spray ed Ar H at three power 2 lev els, with two argon flow rates at two spr ay dis tan ces . The resul ts indica te tha t the mic rohardness, ela sti c mod ulu s and roughn ess of the nanos tructu red zircon ia coatings exhibit the following trends : the smoother the rough ness, the high er the microhardness and elastic modulus. It was found that roughness is an indicator of the coating state that reflects the intrinsic mic rostructure of the coa tin gs. It was asc ertained tha t a surface profilo met er could be used to det ermine the lev el of microhardness and elastic modulus as a non-destructive and in situ test by simple comparison with standard samples. 2001 Elsevier Science B.V. All rights reserved. Keywords: Thermal spray; Microhardness; Elastic modulus; Roughness; Nanostructured zirconia-yttria; Thermal barrier coatings 1. Introduction Ž Na nocr ys tall ine ma terials also referred to as nano structures, nano phase materials, or nano mete r- . sized crys tall ine solids are single- phas e or multi- phase polycrystals. The crystal size is typically approximately 1 100 nm in at lea st one dimension 1,2 . Nan ost ruc - Ž . tured mate rial s come in two gene ral morphologies: i nano laye red materials deposited by phys ical vapo ur Ž . dep ositio n or ele ctr odeposition pro cesses and ; ii nanograined materials, which are usually consolidated fro m nanostruc tur ed pow der s 1,2 . As the gra in size Corresponding author. Tel.: 1-631-632-8507; fax: 1-631-632- 8525. Ž . E-mail addres s: cberndt @notes .cc.s unysb.ed u C.C. Berndt . becomes sma lle r, the re are an inc rea sin g number of atoms associated with grain boundary sites compared to cr ys tal la tt ice sites. Th e un ique pr op er ti es of nanograined materials are associated with the fineness of str uc ture as well as the enh anc ed sol ubi lit y and increasing atomic mobility associated with grain boun- da ri es 1,2 . It has also be en de mo nstrat ed that nanostructured ceramics can be sinte red at relat ively low temperatures, exhibit improved ductility, and even pote ntial supe rpla stici ty, in the nano cryst alli ne state 1 . Ž . Thermal barrier coatin gs TBCs consist of a bond coat and a zirconia coating overlay. They are primarily used for aerospace applications. TBCs, due to their low thermal conductivity and thermal diffusivity combined with proper chemical stability at high temperatures, Ž . prov ide a means fo r i raisi ng the ope ratin g temp era- 0257-897201$ - see front matter 2001 Elsevier Science B.V. All rights reserved. Ž . PI I: S 0 2 5 7 - 8 9 7 2 0 0 0 0 9 9 7 - X
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