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The carbide gradation related to geometry size and local stress concentration sensitivity significantly impacts the performance of the carburized 16Cr3NiWMoVNbE steel. The conventional metallurgical graphic comparison method by manual comparison is not capable of grading the carbide gradation automatically. A novel method is thus introduced to automatically evaluate the carbide grade by using a new shape factor φsc with stress distribution analysis instead of using the circularity or roundness shape factor which only considers the geometry shape of carbide particles. The logarithm of the stress concentration factor ln(K) is linearly related to the logarithm of the shape factor ln(φsc). The gradient b of the fitted straight line shows sensitivity to the carbide grade. The gradients are b1 = 0.039, b3 = 0.049, and b5 = 0.055 for the three carbide classes from low to high. Furthermore, there is also a linear relationship between hardness in different grades of carbide microstructure and the gradient b. [ABSTRACT FROM AUTHOR]

The hot salt corrosion behavior of TiAlTaN coating and TiAlTaN/CrAlN multilayer coatings with different modulation periods under external stress condition were studied. The complex stress distribution on the specimen surface was obtained by designing a double-sided notched tensile specimen, and then the hot salt stress corrosion test was carried out at 500 °C for 120 h. The TiAlTaN monolayer coating had obvious stress cracking under stress loading, while the TiAlTaN/CrAlN multilayer coatings showed good resistance to hot salt stress corrosion crack even under high stress. The performance improvement was attributed to the role of multilayer interfaces in inhibiting microcrack growth and diffusion of the corrosion medium into the coating. In particular, the TiAlTaN/CrAlN-10 multilayer coating with smaller modulation period not only had better hot salt corrosion resistance, but also showed excellent resistance to crack propagation under stress loading, forming effective protection for the titanium alloy substrate. • The double-sided tensile model was designed to explain the hot salt stress corrosion behavior of TiAlTaN/CrAlN coating. • External stress is easy to produce stress concentration at the inherent defects of the coating and accelerate crack growth. • The multilayer coating exhibits excellent crack propagation resistance compared with the monolayer coating under stress loading. [ABSTRACT FROM AUTHOR]