Low temperature effects on the fracture behaviour of a nickel base superalloy

The mechanical properties of a solution treated and double aged nickel - 18% iron - 18% chromium alloy (Inconel 718) were studied to assess its utility at temperatures in the ambient-to-cryogenic range. Uniaxial tensile property measurements using unnotched specimens at decreasing temperatures between 295 and 4 K show that yield and ultimate strengths increase by 20% and 29%, respectively, while ductility remains virtually constant. Fracture mechanics tests using 2.54 cm thick compact specimens revealed that the fatigue crack growth resistance of this alloy improves slightly at extreme cryogenic temperatures, and its plane strain fracture toughness, K_lc, increases from 96.3 MPa m^{$\text{1}\text{2}$} at 295 K to 112.3 MPa m^{$\text{1}\text{2}$} at 4 K. These results are compared with similar data for Inconel 750 alloys