Orientation and temperature dependence of some mechanical properties of the single-crystal nickel-base superalloy René N4: Part III. Tension-compression anisotropy

Abstract

Single crystal superalloy specimens with various crystallographic orientations were tested in compression at room temperature, 650, 760, 870, and 980 °C. These results are compared with the tensile behavior studied previously. The alloy, René* N4, was developed for gas turbine engine blades and has the nominal composition 3.7 Al, 4.2 Ti, 4 Ta, 0.5 Nb, 6 W, 1.5 Mo, 9 Cr, 7.5 Co, balance Ni, in weight percent. Slip trace analysis showed that primary cube slip had occurred even at room temperature for the [111] specimens. With increasing test temperature more orientations exhibited primary cube slip, until at 870 °C only the orientations near [001] and [011] exhibited normal octahedral slip. The yield strength for octahedral slip was numerically analyzed using a model proposed by Lall, Chin, and Pope to explain deviations from Schmid’s law in the yielding behavior of a single phase γ’ alloy, Ni₃(Al,Nb). The Schmid’s law deviations in René N4 were found to be largely due to a tension-compression anisotropy. This is one of the sources of the Schmid’s law violations observed in Ni₃(Al, Nb) which are rationalized by the model. A second effect, which increases the strength of orientations away from [001], was found to be small in René N4. Analysis of recently published data on the single crystal superalloy PWA 1480 yielded the same result.