Modified MAR-M-200 single crystals with various amounts of rhenium were
tested in tensile creep in <111>, <011> and <001>
orientations. With the addition of rhenium, a significant improvement in
creep resistance was attained. This is illustrated clearly in Figure 1. In
order to understand the effect of the rhenium addition on the creep strength
of Ni-base superalloy single crystals, transmission electron microscopy was
used to analyze the microstructures and dislocation behavior. Creep samples
with gauge length of 10 mm and diameter of 2.5 mm were tested at 900°C/380
MPa unless otherwise specified. The chemical composition of the alloy
studied is 5Al-2Ti-lNb-9Cr-12(W + Re) with the balance Ni (in weight
percentage). The rhenium contents were 0, 2, 1, or 6 wt. $ at the expense of
tungsten. The samples were fully heat treated (l290°C/4 hrs. + 1080°C/4 hrs.
+ 870° C/32 hrs.) before testing. The oriented crystals (with 0 and 6 wt. $
Re, respectively) were creep tested to a strain of ~ 0.2$. Their detailed
transmission microstructures are shown in Figures 2 and 3. In <111>
crystals, cube slip, {001} <110> was observed while in <011>
crystals, octahedral slip, {111}<101> was observed. Results similar to
the <011> case were found in <001> crystals tested at 980°C/220
MPa.
Ultra-large elongation and dislocation behavior of nano-sized tantalum single crystals