Effect of Re on the precipitation behavior of μ phase in several single crystal superalloys

Three single crystal superalloys were designed based on the composition of superalloy CMSX-4 and effect of Re on the thermo-stability of these designed alloys has been investigated. Addition of the Re increased the phase instability of the alloys but did not change the type of the precipitation. All the topologically close packed (TCP) precipitation found in the three alloys was characterized as mu phase. Addition of the Re increased the formation temperature of mu phase, accelerated the precipitation of mu phase near the nose temperature of the temperature-time-transformation (TTT) curve and at low temperature (850 degrees C), but relatively depressed the precipitation of mu phase between these temperatures. It is also found that the Re could stabilize or increase the segregation abilities of other alloying elements in the gamma/gamma' phases. With the addition of Re, the W content increased in the gamma phase, while the Cr content decreased, which is the reason of that addition of the Re can enhance the phase instability of mu phase in superalloys. (C) 2012 Elsevier B.V. All rights reserved.