DETERMINATION OF PROCESSING-INDUCED STRESSES AND PROPERTIES OF LAYERED AND GRADED COATINGS - EXPERIMENTAL-METHOD AND RESULTS FOR PLASMA-SPRAYED NI-AL2O3
O. Kesler et al., DETERMINATION OF PROCESSING-INDUCED STRESSES AND PROPERTIES OF LAYERED AND GRADED COATINGS - EXPERIMENTAL-METHOD AND RESULTS FOR PLASMA-SPRAYED NI-AL2O3, Acta materialia, 45(8), 1997, pp. 3123-3134
Citations number
48
Categorie Soggetti
Material Science","Metallurgy & Metallurigical Engineering
An experimental method is proposed which enables the determination of
processing-induced intrinsic stresses, elastic modulus, and coefficien
ts of thermal expansion of surface coatings of homogeneous and graded
compositions. In this method, a number of identical substrate specimen
s are coated simultaneously with surface layers of fixed or graded com
positions, and specimens with different layer thicknesses are periodic
ally removed from the deposition chamber. It is shown that the followi
ng results can be obtained from a knowledge of the strain or curvature
and thermal history of the coated specimens, in conjunction with simp
le four-point bend tests and thermal loading/cycling at different temp
eratures: (i) the magnitude of the processing-induced intrinsic stress
es through the thickness of the coating, (ii) the in-plane Young's mod
ulus, E, as a function of the coating thickness, (iii) the coefficient
of thermal expansion, alpha, as a function of the coating thickness,
(iv) the variation of E and alpha as a function of temperature at any
thickness location within the coating, and (v) the separation of inter
nal stresses arising From thermal expansion mismatch between different
constituent phases or layers from those arising from the deposition p
rocess (so-called ''intrinsic'' or ''quench'' stresses). The thermomec
hanical analyses underlying this method are discussed in detail, and i
ts significance and limitations are addressed. The proposed method is
used to determine the evolution of processing-induced stresses during
the successive build-up of plasma-sprayed Ni-Al2O3 coatings of homogen
eous and graded compositions. (C) 1997 Acta Metallurgica Inc.