Stress-corrosion resistant ultrahigh-strength steels. Semiannual Progress report, 1 June-30 November 1993
Based on the Rice-Wang thermodynamic model of intergranular embrittlement, total energy calculations employing the FLAPW, DMol and DVM techniques address the electronic basis of the segregation energy difference between grain boundaries (GB) and free surfaces (FS) controlling the embrittlement potency of a segregating solute. Precise FLAPW calculations employing large supercells with structural relaxations determined by DMol predict the embrittling effect of P in Fe, and indicate that B is neutral or weakly cohesion enhancing in Fe. The embrittlers P and S are found to behave as embedded atoms with negligible hybridization with Fe, while B hybridizes to form directional sigma bonds which significantly raise its relative energy on the free surface. Magnetic contributions are found to decrease both the embrittling potency of P and the cohesion enhancing ability of B. Toward greater precision of segregation energy calculations, DMol calculations have been initiated with modified boundary conditions to allow for GB free volume. DVM cluster calculations are applied to explore the third-element interaction with substitutional Mo at the GB core. A cohesion enhancing effect of Mo more than compensates the embrittling effect of P. GB fracture strength is measured in UFIS steels and correlated with segregation of P and S.
- Research Organization:
- Northwestern Univ., Evanston, IL (United States). Materials Research Center
- OSTI ID:
- 189840
- Report Number(s):
- AD-A--299205/5/XAB; CNN: Contract N00014-90-J-1363
- Country of Publication:
- United States
- Language:
- English
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