Etude du comportement élastique et plastique de revêtements élaborés par projection plasma : Mise au point d'une méthode de caractérisation des propriétés mécaniques par perforation et comparaison avec les propriétés obtenues par indentation

Abstract : Thermal sprayed ceramic coatings are highly used in application where high performance regarding to mechanical properties are required. Thus it is essential to determine the coatings’ mechanical properties (hardness, Young modulus and fracture toughness), which is made by classical indentation methods using Vickers, Knoop and Berkovich indenters. Those methods use sophisticated devices, rigorous sample preparation and demanding time processes in execution and data analysis that make them expensive and complicated in implementation. This research is focused tostudy the drilling resistance as an alternative method to measure the mechanical properties of atmospheric plasma spray ceramic coatings. For these purpose powders of six chemical compositions most widely used in industrial applications were employed as feedstock powders to manufacture coatings by atmospheric plasma spraying: Al2O3, TiO2, Al2O3-15wt % TiO2, Al2O3-43wt % TiO2, YSZ and Al2O3-YSZ. Physical, chemical and mechanical properties have been determined. Macro and micro hardnesses were determined by Vickers indentations, the Young’s modules werecalculated from Knoop micro hardness measurements and fracture toughness from Vickers micro hardness. Static drilling resistance tests were carried out with commercial drill bits used to perforate glass plotting the applied force (P). against the drill bit depth (h). Relationships between the applied force and the bit’s contact or cross sectional areas (P/Ac and P/At respectively) corresponding to the drilled depth (h) were used to set the Static Drilling Hardness (HDs).Furthermore, the slopes in the unloading stage corresponding to ΔP/ΔAc or ΔP/ΔAt were used to calculate the Static Drilling Elastic Modulus (Es). The HDs and Es results exhibit both well fit with the micro-hardness and Young modulus measurements made by classical methods and high reproducibility in the results. It was observed that cracks and spalling produced on the coatings surfaces during loading reduce the slope of the P vs h plot which could be used in future studies to correlate to the toughness of coatings. Dynamic drilling tests using bits to perforate metals (HSS) andmasonry were also carried out. The ratios between applied load and contact or cross sectional areas (P/Ac and P/At respectively) corresponding to the depth (h) of the hole drilled on each coating were used to calculate the Dynamic Drilling Hardness HDD which shows a good fit with the measured hardness on the surface of coatings realized by micro-indentation Vickers but lower reproducibility than those obtained with static drilling hardness results.
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Claudia Palacio Espinosa. Etude du comportement élastique et plastique de revêtements élaborés par projection plasma : Mise au point d'une méthode de caractérisation des propriétés mécaniques par perforation et comparaison avec les propriétés obtenues par indentation. Matériaux. Université de Limoges, 2016. Français. ⟨NNT : 2016LIMO0129⟩. ⟨tel-01522635⟩

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