DS nickel-base superalloy incorporates Hf and Re for high creep strength

摘要

Directionally solidified (DS) castings of rhenium-bearing columnar grain nickel-base superalloys have successfully replaced first generation (non-Re-bearing) single crystal (SX) alloys at a cost savings because of higher casting yields, according to Cannon-Muskegon, Muskegon, Mich. However, DS components are less advantageous than SX vanes because of grain boundaries in non-airfoil regions, particularly the inner and outer shrouds of multiple airfoil segments that endure high, complex stress conditions in gas turbine engines.CM 186 LC is a 3 percent rhenium-bearing, highly alloyed nickel-base superalloy developed for directionally solidified columnar grain turbine airfoils. CM 186 LC has 70 percent volume fraction of the coherent gamma prime precipitate strengthening phase. The alloy contains optimum amounts of carbon, boron, hafnium, and zirconium, which results in carbide and boride grain boundary strengthening phases. These alloy additions also provide good transverse creep-rupture strength, ductility, and Tow-cycle fatigue properties in directionally solidified (DS) columnar grain turbine airfoils. These same strengthening phases are beneficial in the single-crystal (SX) cast components to strengthen LAB /HAB grain detects. They also allow more generous grain acceptance criteria and improved casting yield.