It has been shown that enhancement of creep resistance in advanced single crystal superalloys is achieved by increasing the amount of tantalum and rhenium [1, 2]. Tantalum dissolves preferentially in 0 (Ni3Al) and acts as a solid solution strengthener of the 0 precipitates, while rhenium dissolves preferentially in the matrix, and acts as a solid solution strengthener of the matrix [3, 4]. In a single phase Ni-20Cr polycrystalline alloy, it has been shown further that tantalum acts as the most effective solid solution strengthener [5, 6]. Solid solution strengthening effects are divided into two features: tantalum decreases the creep rate, and suppresses the onset of accelerating creep [6]. In comparison with reports concerning the effect of tantalum additions, reports of rhenium additions are somewhat limited. Because the effect of solute additions on the creep rate and the onset of accelerating creep becomes more prominent at the lower stresses, creep tests must be performed at lower stresses [6].