Unveiling the failure mechanism on creep response of a casting Ni-based superalloy in thin-wall thickness

With the improvement of thermal efficiency and the lightweight tendency of engine blades, Ni-based superalloy is widely used owing to its excellent performance in high-temperature atmospheres. This work studied the effects of surface oxidation, internal environmental attack, and matrix damage on the failure mechanism in a thin-walled casting Ni-based superalloy at 980 °C/160 Mpa. At the edge of the fracture, the sample suffered a severe environmental attack, resulting in the oxidation-affected zone forms. However, the loss of effective bear area induced by surface damage could not be the main reason for the sample's failure. At the interior of the matrix, voids were preferably initiated at the interface of MC carbides. As the increase of creep deformation, dynamic recrystallization (DRX) occurred at the tip of the voids, which increased the transverse grain boundaries and promoted crack propagation. Moreover, the DRX provided a short penetration path for the nitrogen, causing internal nitridation with AlN and Ti(Ta)N to precipitate. EBSD analysis confirmed that nitrides induced significant dislocations to accumulate at the boundaries of nitrides/γ, accelerating the failure of the sample

Nanostructure, Mechanical Properties, and Corrosion Resistance of Super Duplex Stainless Steel 2507 Aged at 500 °C

In order to investigate the effect of phase separation (PS) on the super duplex stainless steel SAF 2507, the evolution of the nanostructure, mechanical properties, and corrosion resistance of the alloy was studied after aging at 500 °C for 1, 10, 100, and 1000 h. The nanostructure of PS was quantitatively characterized by small-angle neutron scattering. The hardness, impact toughness, and pitting corrosion resistance were measured for different conditions. The results show that the early stage of PS had a more significant impact on the nanostructure and properties of SAF 2507. The fracture behavior of the alloy was likely determined by the mechanical properties of ferrite for aged conditions. The pitting corrosion resistance of SAF 2507 aged at 500 °C was closely related to the Cr depletion caused by PS, and the resistance became weaker with the progression of PS. The evolution of the passivation region with aging time correlated well with that of mechanical properties and characteristic parameters of PS, indicating that it is possible to develop a new nondestructive electrochemical method to quantify the evolution of PS in SAF 2507