Improving hot corrosion resistance of aluminized TiAl alloy by anodization and pre-oxidation

To shield TiAl alloy from hot corrosion attack,a compact protective coating was fabricated by the combination of aluminizing,anodization and pre-oxidation.The hot corrosion behavior of the coated-TiAl specimen was investigated in the mixture salt consisting of 75 wt.%Na2SO4 and 25 wt.%NaCl at 700°C.Results indicated that the anodization and pre-oxidation were beneficial to the generation of Al2O3 layer,which could act as a diffusion barrier to prevent the molten salts and oxygen from diffusing into the alloy during exposure to a hot corrosion environment while the aluminizing coating could provide sufficient aluminum source to support the continuous formation of Al2O3 layer.Moreover,the internal stress of the coating was reduced due to the formation of a gradient coating consisting of TiAl3 and TiAl2.

Comparison of bulk snow density measurements using different methods

Snow density is one of the basic properties used to describe snow cover characteristics,and it is critical for remote sensing retrieval,water resources assessment and modeling inputs.There are many instruments available to measure snow density in situ.However,there are mea-surement errors of snow density for bulk and layers or gravimetric and electronic instruments,which may affect the accuracy of remote sensing retrieval and model simulation.Especially in China,due to the noticeable heterogeneity of snowpacks,it is necessary to evaluate in detail the performance and applicability of snow density instruments in different snowpack conditions.This study evaluated the performance of different snow density instruments:the Federal Sampler,the model VS-43 snow density cylinder(VS-43),the wedge snow density cutter(WC1000 and WC25O),and the Snow Fork.The average bulk snow density of all instrument measurements was set as the reference value for evaluation.The results showed that as compared with the reference,the VS-43 cylinder presented the best performance for bulk snow density measurement in the measured range with the lowest RMSE(11 kg m^(-3)),BIAS(3 kg m^(-3)),and MRE(1.6%).For layer observation,bulk snow density was overestimated by 8.1%with WC1000 and underestimated by 11.4%with Snow Fork which was the worst performance compared with the reference value,and there were greater measurement errors of snow density in the depth hoar than other snow layers.Compared with grassland,the uncertainty of snow density measurements was slightly lower in forests.Overall,the Federal Sampler and VS-43 cylinder are more suitable for bulk snow density measurement in deep snowpack regions across China,and it is recommended to use WC1000,WC250 and Snow Fork to measure the snow density of snow layers in the snow stratigraphy.