EUROPEAN CONCERTED ACTION - COST 50 - MATERIALS FOR GAS TURBINES. EC-2 - THE INFLUENCE OF GRAIN BOUNDARY CHEMISTRY AND SEGREGATION PHENOMENA ON THE CREEP FRACTURE OF IN 738-LC
Intergranular creep cavitation and wedge cracking in IN 738 LC, at 850 degrees C, is frequently associated with accumulations of second phase precipitates, formed either by segregation of reactive elements from adjacent grains, or by decomposition of carbide phases sited in the alloy grain boundaries. Fracture is initiated by propagation of cracks from surface sites of intergranular oxidation along the grain boundary to link these defects, followed by ductile shear when the alloy cross-section area reduces to a critical value. The exclusion of surface oxidation by application of ductile corrosion - resistant coatings do not significantly alter this fracture pattern, nor extend creep lives in the range 500 to 5,000 hours. In an attempt to evaluate the influence on alloy fracture of intergranular phases and segregants originating from both within the bulk alloy and by inward diffusion from applied coatings, the present study examines the morphology and chemistry of fracture surfaces of the alloy, ruptured in creep at 850 degrees C, in high vacuum, using Auger and X-ray microprobe spectroscopy. Differences in fracture morphology between the coated and the uncoated alloy are discussed in terms of intergranular gamma' precipitate distribution.
Bibliographic Reference: EUR 9124 EN (1984) FS, 80 P., BFR 300, EUROFFICE, LUXEMBOURG, POB 1003
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Record Number: 1989122072000 / Last updated on: 1987-01-01
Available languages: en