We studied the effect of sulfur addition on a Ni-base single-crystal superalloy, TMS-1700, by performing creep tests at 1100°C/137 MPa using specimens doped with 0, 10, 20, and 100 ppm sulfur. The creep rupture life was found to decrease with increasing sulfur concentration. The scanning electron microscopy (SEM) observation of creep-ruptured specimens revealed the coarsening of the raft structure with increasing sulfur concentration. Their transmission electron microscopy (TEM) observation showed the formation of coarser γ/γ′ interfacial dislocation networks with increasing sulfur concentration. These microstructural differences may be the cause of the shorter creep rupture life observed in alloys with higher sulfur addition.
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