High resolution residual stress measurement on amorphous and crystalline plasma-sprayed single-splats

Residual stress was measured on plasma sprayed crystalline Ni\Al, Al2O3 and amorphous Al2O3\TiO2\ZrO2-CeO2 single splats, by using an incremental focused ion beam (FIB) micron-scale ring-core method (IμRCM).Tensile residual stress exists in polycrystalline Ni\Al splats, where the quenching stress is only partially relaxedby edge curling and through-thickness yielding. Significant compressive stress was observed for theamorphous Al2O3\TiO2\ZrO2\CeO2 splats, where viscous flow above the glass transition temperaturecompletely relaxed the quenching stresses without micro-cracking. Comparatively lower compressive stresswas measured on crystalline Al2O3 splats, where, in spite of extensive micro-cracking, not all of the tensilequenching stress was relaxed. Using stress data and micro-crack geometry, the intrinsic shear adhesionstrength of Al2O3 splats was calculated, giving insights into the role of (sub)micron-scale phenomena onadhesion/cohesion of thermally sprayed coatings. The proposed stress build-up mechanisms and relaxationphenomena are supported by a TEM microstructural analysis of the splats.The experimental methodology developed provided a unique way for the study of the residual stress buildupmechanisms in amorphous and crystalline single splats obtained by plasma spraying, and gave further insightsinto the actual micro-scale phenomena that give rise to adhesion and nano-mechanical behavior ofthermally sprayed coatings.The proposed approach is also expected to find a wide range of applications in materials science and engineering,as it allows for the residual stress measurement even on amorphous materials with micrometer spatialresolution.