Study On The Microstructure Evolution And Mechanic Properties Of Superalloy Hastelloy C-276after Long-term Aging

The nickel-based superalloy Hastelloy C-276had been determined to be one of thealternative materials in simulation loop of thorium molten salt reactor nuclear powersystem(TMSR) in the strategy guide research project “Future advanced nuclear fissionenergy” started in2011by Chinese Academy of Sciences. The research on mechanicalproperties and their attenuation laws of the C-276superalloy has important theoreticaland practical significance for TMSR Safe and reliable operation, because the circuit andrelated equipment of TMSR will be working under high temperature, and the materialstrength and plasticity will decay under high temperature for a long time.This study simulate working environment of C-276by aging treatment. Withoptical microscopy, scanning electron microscopy and transmission electronmicroscopy, the microstructure of the C-276after long-term aging was observed. Themechanical properties was tested. Then the relationship between microstructure andmechanical properties was analysis.The results show:1.M6C was found after long-term aging at650℃,M6C and μ phase were foundafter long-term aging at700and750℃.2. The aging temperature and aging time have a great impact on the microstructureof the C-276alloy. At the same temperature, as the increasing of aging time, thenumber and size of precipitated phase increases, precipitated transition from the blockto the alkyl group, and gradually form needle-like phase of the μ; after aging the sametime,as the increasing of temperature the number size of precipitates in the alloybecame large in precipitation the phase precipitates rate proportional to the agingtemperature. The precipitation rate of precipitation phase is proportional to the agingtemperature.3.Tensile strength and yield strength of C-276alloy after long-term aging lessaffected by the aging temperature and aging time, the intensity remained stable; whenstretched at room temperature, the alloy elongation decreases as the aging temperatureand aging time increases. When stretched at high-temperature, elongation increases withincreasing aging time. In the same aging time, elongation of alloy was highest at700°C and elongation decreased at750℃.4. Deformation temperature and strain rate have significant influence on the flow stress. The flow stress decreases with the increase of deformation temperature, whileincreases with the increase of strain rate. The deformation mechanism of C-276superalloy exhibit dynamic recovery feature in the case of deformation temperature700℃.However, when the deformation temperature increases to750℃, dynamicrecrystallization behavior may be occurred.