摘要
A single crystal Ni-base superalloy was processed with withdrawal rates between 2 and 7 mm/min.The ascast microstructures,heat treatment response and creep property have been characterized as a function of the withdrawal rate.As expected,the primary and secondary dendrite arm spacing decreased with increasing withdrawal rate; microsegregation degree and porosity distribution were also varied with different withdrawal rates.The withdrawal rate of 2 mm/min resulted in a noticeable residual microsegregation even after full heat treatment.The samples solidified at 7 mm/min exhibited a high density of cast porosities,and this led to a dramatical decline of the creep strain.4 or 6 mm/min appeared to be the optimum withdrawal rate in the present study,which resulted in a uniform microstructure and an optimum density of cast porosity.
A single crystal Ni-base superalloy was processed with withdrawal rates between 2 and 7 mm/min.The ascast microstructures,heat treatment response and creep property have been characterized as a function of the withdrawal rate.As expected,the primary and secondary dendrite arm spacing decreased with increasing withdrawal rate; microsegregation degree and porosity distribution were also varied with different withdrawal rates.The withdrawal rate of 2 mm/min resulted in a noticeable residual microsegregation even after full heat treatment.The samples solidified at 7 mm/min exhibited a high density of cast porosities,and this led to a dramatical decline of the creep strain.4 or 6 mm/min appeared to be the optimum withdrawal rate in the present study,which resulted in a uniform microstructure and an optimum density of cast porosity.
基金
supported by the National Basic Research Program(973 Program) of China under Grant No.2010CB631200
the National Natural Science Foundation of China(NSFC) under Grant No.50931004 and 50971124
