Mechanism of accelerating creep rupture under high stress level of pack cementation aluminide coatings deposited onto T92 steel tube

An aluminide coating was deposited on commercial T92 steel by pack cementation. The coating exhibits bilayer structure composed of an outer FeAl layer and an inner interdiffusion layer. The creep rupture coated and uncoated T92 was investigated. Results show that the rupture life of the coated T92 significantly, i.e., decreases by 46 % at the creep stress of 110 MPa compared with the uncoated examining the microstructure and fractography of the coated specimen, the mechanism of aluminide deteriorating creep rupture life is clarified. The main fracture mode of T92 substrate with and without microvoid accumulation fracture. The characteristic microstructure of the aluminide coating is responsible the premature creep rupture. The formation of columnar grains and brittle nature of FeAl phase make crack during creep. The phase transformation and needle-like AlN precipitates in the inner interdiffusion contribute to the inward propagation of cracks and accumulation of creep damage.

Automated summary

An aluminide coating was applied to T92 steel using pack cementation, resulting in a bilayer structure with an outer FeAl layer and an inner interdiffusion layer. Creep rupture behavior of the coated and uncoated T92 was investigated, revealing a significant decrease in rupture life for the coated samples. The microstructure and fractography analysis of the coated specimen provided insights into the mechanism behind the aluminide-induced deterioration of creep rupture. The formation of columnar grains and the brittle nature of FeAl phase were found to contribute to crack formation during creep, while the phase transformation and needle-like AlN precipitates in the interdiffusion layer promoted crack propagation and creep damage accumulation.