The role of grain boundary chemistry and structure in the environmentally-assisted intergranular cracking of nickel-base alloys. Progress report, [December 1, 1990--November 31, 1993]
Progress focused on (1) determination of the role of C and Cr on deformation and IG cracking behavior of Ni-(5--30)Cr-9Fe, (2) determination of the effect of grain boundary misorientation on IG cracking behavior, (3) construction of an electron backscattering pattern (EBSP) imaging system, (4) determination of effect of the environment on creep and cracking, and (5) characterization of the surface film. Results showed that both C and Cr are potent solid solution strengtheners which can reduce the steady state creep rate at 360{degree}C by several orders of magnitude. Intergranular cracking of 100 {mu}m grain samples of high purity Ni-16Cr-9Fe at 360{degree}C occurs by formation of grain boundary voids and interlinkage, driven by dislocation creep in the matrix. Creep experiments in primary water at 360{degree}C and an applied cathodic potential show that the creep rate is increased by an order of magnitude over that in Ar and the percent IG fracture increases as well. Oxide film composition and thickness is a sensitive function of the C content, increasing in thickness and Ni(OH){sub 2} content with increase in C or decrease in Cr to 5 wt%. Thermomechanical treatments along with electron channeling pattern (ECP) analysis wee used to create and index, samples with enhanced fractions of coincident site lattice boundaries (CSLBs). Constant extension rate tensile (CERT) experiments on samples with a high percentage of CSLBs showed IG cracking compared with general high angle boundaries. However, these experiments were conducted on grain sizes of 300 {mu}m, while commercial material is an order of magnitude smaller. An electron backscattering pattern imaging system has been constructed for an environmental scanning electron microscope which can image grains below {mu}m. The system has been successfully benchmarked against results from ECP analysis.
- Research Organization:
- Michigan Univ., Ann Arbor, MI (United States). Dept. of Nuclear Engineering
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-85ER45184
- OSTI ID:
- 10104654
- Report Number(s):
- DOE/ER/45184-9; ON: DE94003159; BR: KC0201020
- Resource Relation:
- Other Information: PBD: [1993]
- Country of Publication:
- United States
- Language:
- English
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