2001 · 18 citations · 0 references
Natural SciencesMaterials EngineeringMaterials ScienceMaterials ChemistryMechanical Behavior Of MaterialsMetallurgyAlloysCreep BehaviorCreep DeformationFracture MechanicsMetalsNucleationAlloy Creep BehaviorCrack PropagationCreep Crack GrowthCreep TestingCreep-resistant AlloysFatigue-creep InteractionPrecipitatesThermal Exposure Assessment
Structure stability study on Alloy 71 8 disks with four different forginglheat treatment process combinations, i.e. Standard7 18, Super I 7 18,Super I1 7 1 8 and DA7 1 8, has been conducted with long time thermal exposure at 593 "C (1 1 00F),649 "C (1 200F ) and 677 "C (1 250F ) till 2000hrs. A b.c.c chromiunl enriched phase a -Cr has been identified by XRD,SEM,TEM and SAD methods. The existence of a -Cr in Alloy 718 is also confirmed by Thermo-Calc method. The weight fraction o f a -Cr has been determined by special designed electrolytic isolation and micro-chemical analyses. a -Cr precipitates are often in small globular particles (-0.3 P m) and form at the vicinity of 6 -Ni,Nb phase. More a -Cr particles will precipitate in Alloy 71 8 at higher exposure temperatures and longer times. Retained stress can promote a -Cr precipitation . The fractions of a -Cr in 4 different processed Alloy 7 18 disks are not very high.