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Plate-type heat exchangers are anticipated to be used in the next-generation nuclear industry, and solid-state diffusion welding is a critical technology for building plate-type heat exchangers with high integrity. In this study, we manufactured a diffusion weldment and evaluated its creep behavior. Microscopic analysis revealed that Al-rich oxides were developed along the interface, significantly impeding grain-boundary movement across the interface. Oxide-containing planar grain boundaries resulted in premature brittle fracture at the interface with less than 9% creep strain under all test conditions. The time to rupture and time to 1% creep strain of the diffusion weldment were less than those of the as-received alloy, while the slopes in double-logarithmic plots were almost identical for both alloys. In a Larson–Miller parameter study, the stress to rupture of the diffusion weldment reached 95.59% of that of the as-received alloy, whereas the stress to 1% creep strain steeply decreased in the low-stress range. [ABSTRACT FROM AUTHOR]

The Ni-Cr-Mo-Co material Alloy 617 is the leading candidate for VHTR intermediate heat exchangers operating above 750 °C. Time-dependent properties are an important consideration in qualifying the alloy for construction of nuclear components. Creep behavior of several different heats of Alloy 617 has been evaluated in the temperature range of 800–1000 °C. Power law creep behavior was observed for the minimum creep rate, with a stress exponent of 5.6 and activation energy of approximately 400 kcal/Mol. The Monkman-Grant approach relating minimum creep rate to time to rupture gave a reasonable representation of the data for all of the testing with a slope of −0.84. Similarly, a modified Monkman-Grant fit the strain to failure data reasonably well. A Larson-Miller analysis was carried out to compare rupture behavior determined in the current experiments and historical data with well-known provenance over a wide range of conditions. It appears that the properties of modern heats of material are near the lower bound of rupture behavior when all of the data are considered in the same analysis. [ABSTRACT FROM AUTHOR]