|About this Abstract
||2017 TMS Annual Meeting & Exhibition
||Gamma (FCC)/Gamma-Prime (L12) Co-Based Superalloys II
||The Grain Boundary Pinning Effect of the μ-phase in Polycrystalline L1<sub>2</sub> Hardened Co-base Superalloys
||Lisa Freund, Steffen Neumeier, Mathias Göken
|On-Site Speaker (Planned)
In polycrystalline Ni-base superalloys, the pinning of grain boundaries by precipitates during recrystallization is used to obtain a homogeneous grain structure with fine grains. Such a microstructure provides good low cycle fatigue properties and high temperature strength. In order to use this effect for γ/γʹ Co-base superalloys, a polycrystalline cast-and-wrought alloy was produced, containing a significant amount of Mo to intentionally introduce a grain boundary pinning third phase. Diffraction results and TEM-EDS identified this phase as μ-phase (Co,Ni,Cr)<sub>7</sub>(W,Mo)<sub>6</sub>. Since the μ-phase and the γʹ-phase are competing for W, a lower γ’-volume fraction is formed in comparison to Mo-free alloys. In-situ high energy X-ray diffraction experiments confirm the stability of the grain structure up to 1050°C and therefore the grain boundary pinning effect of this phase. The homogeneous distribution of small grains results in a higher strength compared to a polycrystalline γ/γʹ Co-base superalloy without grain boundary pinning phases.