|About this Abstract
||2017 TMS Annual Meeting & Exhibition
||Gamma (FCC)/Gamma-Prime (L12) Co-Based Superalloys II
||Role of Two Phase Microstructure during Early Stages of High Temperature Oxidation of Co-base Superalloys
||Martin Weiser, Sannakaisa Virtanen
|On-Site Speaker (Planned)
Elementary mechanisms of scale formation on Co-base superalloys are relatively unexplored. Although this class of high temperature materials reveals a microstructure similar to Ni-base superalloys, the nature of base element changes the segregation behavior and the diffusion velocities of alloying elements. Since both properties are essential for the formation of protective scales the inferior oxidation performances become explainable.
A series of polycrystalline model alloys of the quaternary system Co-xAl-yW-zTa (x = 8.8-8.9 at%, y = 4.0-9.0 at%, z = 0.5-2.3 at%) with varying γ′ - volume fraction was chosen to systematically investigate the oxidation properties of the individual phases at temperatures up to 900°C. The composition of phases stayed unaltered. Besides classical thermogravimetry, the change of surface topography was monitored by in-situ experiments in a SEM equipped with a heating stage. The layering sequences of the scales were investigated and compared by SEM and further high resolution surface analysis methods.