Modification of chemical and mechanical properties of p-W-O coating after Magnum-PSI D2-N2 plasma exposure and its consequences for the analysis of LIBS spectra

The present study investigated the effect of D2-N2 (7%) plasma exposure in Magnum-PSI on the D retention and chemical and mechanical properties of a porous W-O (p-W-O) coating. The variation of the chemical composition, crystalline phase and mechanical properties along the sample surface were determined by Nuclear Reaction Analysis (NRA), Rutherford Backscattering Spectroscopy (RBS), nanoindentation and Raman spectroscopy. These changes were compared to the Laser-Induced Breakdown Spectroscopy (LIBS) measurements. LIBS depth profiles of W and Mo were consistent with the profiles determined by NRA and RBS, showing a W-O layer, a thin W adhesion layer and a Mo substrate. Typically, the high D intensity was determined only during the first LIBS laser shot on a measurement spot, while the spatial distribution of D intensity determined by LIBS along the coating surface followed the D concentration determined by NRA. According to the Raman spectra, the investigated p-W-O coating corresponded to nanograins of W-O and the phase composition was relatively uniform along the coating surface. The elastic modulus of p-W-O coating was considerably lower than the modulus of Mo coating or bulk W coating and corresponded to the values found in other studies carried out with W-O mixtures. The elastic modulus of p-W-O coating decreased towards the edge of the coating. The study revealed that the modulus and the background intensity of the LIBS spectra had a negative correlation, suggesting that LIBS may be a suitable method for the estimation of the stiffness of tungsten co-deposits as a similar correlation is shown for other types of W coatings.