Influence of the CMAS on the aging of titanium alloy β21s

The interaction of CMAS (an acronym for a mixture of oxides including CaO, MgO, Al2O3, SiO2) with aerospace materials has been studied as part of the degradation of protective coatings on turbine blades, since the presence of these mixture oxides can also be found in exhaust gasses. To restrict this degradation phenomenon, the material used in gas extraction cone can be improved.This study examines the aging of titanium alloy β21s (metastable alloy β) in relation to the presence of CMAS on the surface.CMAS depositions were made by plasma torch (laboratory SPCTS Limoges). Two coverage rates, 50 and 100% were achieved. The samples were then aged in a thermal cycle comprising various times and temperatures and exhaust nozzles may face at long and medium haul flights.Reference samples were not coated and followed the same aging cycle. Analysis by glow discharge optical emission spectroscopy (GDOES) of the CMAS layer is made difficult by the low conductivity of materials, resulting in vaporization of the surface which is not homogeneous.The XRD analysis showed that the content of the alpha phase is the same when the sample is bare or coated at 50%. The presence of TiO2 and TiN was only revealed on these samples. On the other hand, the rate of the alpha phase created by the heat treatment is lower in the case of the coating at 100%. Without completely blocking the diffusion of oxygen, the CMAS coating appears to play a protective role, not allowing the alpha phase to appear with quick rate.