Instrumented spherical micro-indentation of plasma-sprayed coatings

Abstract

The mechanical response of plasma-sprayed coatings is studied by recourse to instrumented spherical micro-indentation. It is shown that the elastic moduli of the coatings can be determined in a more reliable and reproducible manner with instrumented spherical indentation than prior (Knoop) indentation methods, while at the same time minimizing damage to the coating during indentation. The results show that the values of the elastic moduli, E, of air plasma-sprayed (APS) materials are much lower than those of vacuum plasma-sprayed (VPS) materials. The VPS deposits are more homogeneous at a microstructural level as splat formation, microcracking and the development of oxide scales are suppressed. Such homogenization increases the value of E to the point where it becomes similar to that of fully dense materials. Larger amounts of inelastic flow occur in APS deposits as compared with VPS deposits. This flow is associated with fracture and sliding of splats.

Erosion Behavior of Plasma Sprayed Alumina and Calcia-Stabilized Zirconia Coatings on Cast Iron Substrate

“…The hardness of Al 2 O 3 coating is lower than that of bulk alumina (HV-2045) which is mainly due to the intrinsically lower hardness of γ-Al 2 O 3 than α-Al 2 O 3. The indentation response of a plasma sprayed material is governed not only by the intrinsic hardness of the material, but also by the lamellar microstructure, with splat boundaries giving off under load to facilitate the indenter accommodation [25]. Table 4.…”

Effect of spraying distance on the microstructure and mechanical properties of a Colmonoy 88 alloy deposited by HVOF thermal spraying

“…In the case of thermal spray coatings, the precise determination of the above properties is a difficult task since these materials possess oriented microstructures characterized by the presence of pores, cracks, lamella boundaries and unmelted particles, exhibiting an anisotropic mechanical behavior [5][6][7]. These microstructural features are intimately associated with the deposition conditions, particularly with speed and temperature of in-flight particles projected unto the substrate, which in turn depend of the spray distance employed in the deposition process.…”

Preparation of plasma sprayed mullite coating on stainless steel substrate and investigation of its environmental dependence of friction and wear behavior

“…Due to the lamellar structure, sliding between splats under normal load facilitates the indenter going deeper into the tested material. Hence, the measured hardness value is a little lower than actual hardness [19,20].…”