Complementary mapping techniques to characterize the wood finish of musical instruments

The wood finish of historical bowed string musical instruments made in Cremona (Italy) during the seventeenth and eighteenth century is a complex multi-layered coating system, where varnishes and other organic binders are variously mixed with inorganic fillers and pigments. It consists of several layers with reduced thickness (tens of microns or less), hard to be distinguished due to the similarity of the constituent materials. Nevertheless, the identification of chemical and morphological features (layering and boundaries) is strictly necessary to disclose the traditional manufacturing procedures. In this paper, we propose an innovative protocol to fully characterize such a multi-layered coating system by combining hyperspectral photoluminescence (PL) micro-imaging with μFTIR-ATR mapping and SEM-EDX analysis. The protocol has been employed to study three cross-sectional samples from violins made by Lorenzo Storioni (second half of eighteenth century), whereas a properly reproduced laboratory mock-up was used to set the analytical protocol. The obtained results demonstrate that the combination of these complementary spectroscopy mapping techniques in a high-resolution strategy allows one to clearly identify the morphology of a few microns thin layers, to assess the penetration depth of sizing treatments into the wood and to detect restoration areas.

Erosion Behavior of PS-PVD Thermal Barrier Coatings and the Effect of Composite Coating (PS-PVD + APS) Thickness

In this work, feather-column 7YSZ thermal barrier coatings (TBCs) were prepared by plasma spray-physical vapor deposition (PS-PVD). The anti-particle erosion test was carried out at room temperature to study the erosion behavior and failure mechanism of PS-PVD TBCs. The results showed that the particle erosion process of the PS-PVD TBCs experienced three stages of high-rate, medium-rate and slow-rate erosion. In order to improve the particle erosion resistance of the PS-PVD TBCs, different thicknesses of dense-layered coatings were prepared on the surface of the PS-PVD TBCs by air plasma spraying (APS). The effect of dense-layered thickness on the erosion behaviour of PS-PVD TBCs was discussed. Experimental results showed that, as the thickness of the dense-layered increased, the erosion resistance of the PS-PVD TBCs enhanced. When the thickness of the dense-layered coating was 5μm, it was not obvious upon the influence on the erosion failure behavior of the PS-PVD TBCs. In the case of a 10μm dense-layered coating, the erosion resistance performance of the PS-PVD TBCs improved by about 30%. While the erosion resistance performance of the PS-PVD TBCs increased almost 4 times when the thickness of the dense layer reached 20μm.

Kinetics of Phase Transformations in FeAl(Cr,Si) / Fe3Al(Cr,Si) / Fe(Al,Cr,Si) Laminated Coating on the Cr15Al5 Alloy

The influence of thermal action at 1150 °C on the kinetics of phase transformations in a layered coating FeAl (Cr,Si) / Fe3Al (Cr,Si) / Fe (Al,Cr,Si), obtained using a technology involving aluminizing of an Cr15Al5 alloy by hot dipping in silumin melt AK12M2 and heat treatment. It was shown that after 100 hours of exposure, the visually distinguishable boundary between the coating and the alloy disappears. The aluminum content in the Cr15Al5 alloy increased to 17 at. %, silicon up to 3 at. %, and chromium is reduced to 14 at. %. The microhardness of the alloy increases from 1.6 to 2.4 GPa and survivability at a test temperature of 1150 °C increases from 120 to at least 920 hours.

STUDY OF THE STRUCTURE AND PHASE COMPOSITION OF THE OXIDE FILM ON THE SURFACE OF A LAYERED COATING OF THE Al-Ni SYSTEM

This work is aimed to the study of the structure and phase composition of the oxide film formed on the surface of the layered coating of the Al-Ni system during high-temperature heating. It was experimentally established that at the initial stages of heat treatment, as a result of the interaction of the Al-Ni system layered coating with atmospheric oxygen, separate sections of Al2O3 oxide are formed on its surface, which are agglomerates of plate crystals of α-modification of nanometer thickness, which increase and grow together with increasing exposure time continuous protective oxide film. An increase in the heating temperature leads to an intensification of oxidation processes and the formation of a complex oxide film of AlO and spinel NiAlO.