Measurement and Modeling of Hydrogen Environment-Assisted Cracking in a Ni-Cu-Al-Ti Superalloy

Strain Gradient Plasticity-Based Modeling of Damage and Fracture

“…The heat treatment and microstructure of the superalloy, Monel K-500 (Ni-28.6Cu-2.89Al-0.45Ti-0.166C by wt pct), are described elsewhere [102,174]: 0.2% offset yield strength (σ YS ) is 773 MPa, elastic modulus (E) is 183.9 GPa, and ultimate tensile strength (σ UT S ) is 1169 MPa from tensile testing; Ramberg-Osgood flow constants from compression testing (to 2% total strain) are n = 20, α=0.39, E = 185.7 GPa and σ 0 = σ YS = 773 MPa; and plane strain fracture toughness (K IC ) is 200 to 340 MPa √ m. The heat treatment and microstructure of two similar quenched and aged martensitic alloy steels, AerMet T M 100 (Fe-13.4Co-11.1Ni-3.0Cr-1.2-Mo-0.23C by wt pct) and Ferrium T M M54 (Fe-7.0Co-10.1Ni-1.0Cr-2.1Mo-1.3-W-0.1V-0.30C by wt pct), are described elsewhere [92,172,175] The kinetics of HEAC were measured for Monel K-500, AerMet T M 100, and Ferrium T M M54 using precracked fracture mechanics specimens stressed under slow-rising K I while immersed in an aqueous solution of 0.6 M NaCl, as detailed elsewhere [92,102,147,171,172]. The da/dt versus K I results for each alloy, characterized as a function of E APP , are typical of HEAC in high strength alloys [36].…”

“…Model assessment is based on detailed measurements of da/dt versus K I reported for HEAC in a Ni-Cu superalloy [102,171] and two ultra-high strength martensitic steels [92,172], each stressed in a chloride solution. Electrochemistry measurements and modeling yielded crack tip H concentration versus applied potential (E APP ) [102,173], as well as trap-affected effective hydrogen diffusivity (D H−EFF ) for each alloy [174][175][176].…”

“…Electrochemistry measurements and modeling yielded crack tip H concentration versus applied potential (E APP ) [102,173], as well as trap-affected effective hydrogen diffusivity (D H−EFF ) for each alloy [174][175][176]. The E APP dependencies of K T H and the hydrogen-diffusion limited Stage II crack growth rate (da/dt II ) were originally modeled [92,102,171,172] using crack tip stress from a continuum blunt-crack formulation [91]. This database and the HEDEmodeling approach are reanalyzed using crack tip stress distributions from new FE analyses that incorporate: (a) the finite strain framework for both PSGP and MSGP formulations [132], and (b) specific alloydependent properties and load levels that create H cracking.…”

“…K T H from (8.1) is predicted versus E APP for the PSGP and MSGP-model values of σ H /σ Y (the average of the 1 µm and 2 µm intervals of r, Table 1). Results in Figure 8.3a are compared to experimental data for Monel K-500 in 0.6M NaCl solution [102,171]. The 3-replicate measurements of K T H at E APP of -1.000 V SCE are used to determine α, which equals 6.…”

“…r(µm) MPa √ m for each steel, and the α and β are identical to those used for Monel K-500 [171] and steel [161]. This Griffith toughness was estimated based on maximum modeled γ S for a 100 surface of Fe (3.09 J/m 2 [59]) and Poison's ratio of 0.29.…”