Grain boundary engineering was used to improve materials properties such as corrosion resistance and strength by optimizing the grain boundary character distribution. Two high-temperature alloys, designated Incoloy 800H and Inconel 617 were selected. The grain boundary engineering treatments on the alloys 800H and 617 were accomplished by a series of thermomechanical processing. The effect of the grain boundary engineering treatments on the corrosion resistance and mechanical properties of the materials were evaluated using supercritical water exposure tests, cyclic oxidation tests, impact tests, and tensile tests. The microstructures of the tested samples were analyzed by means of optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, electron back-scattering diffraction, X-ray photo-electron spectroscopy, and grazing incidence X-ray diffraction. The results indicated that grain boundary engineering treatments greatly mitigated oxide exfoliation of 800H and reduced the oxidation rate of 617. The grain boundary engineering treatment also greatly enhanced the strength of 800H at room temperature (impact tests) and high temperatures (tensile tests after neutron irradiation), but did not significantly impair the ductility.

Microstructure Tailoring for Property Improvements by Grain Boundary Engineering. L.Tan, K.Sridharan, T.R.Allen, R.K.Nanstad, D.A.McClintock: Journal of Nuclear Materials, 2008, 374[1-2], 270-80