Microstrain evolution during creep of a high volume fraction superalloy

✍ Scribed by S. Ma; D. Brown; M.A.M. Bourke; M.R. Daymond; B.S. Majumdar

• Publisher: Elsevier Science
• Year: 2005
• Tongue: English
• Weight: 858 KB
• Volume: 399
• Category: Article
• ISSN: 0921-5093
• DOI: 10.1016/j.msea.2005.02.034

✦ Synopsis

The creep of superalloys containing a high volume fraction of ␥ phase is significantly influenced by initial misfit and by the evolution of internal stresses. An in situ neutron diffraction technique was used to monitor elastic microstrains in a polycrystalline superalloy, CM247 LC. The misfit was nearly zero at room temperature and it increased to -0.17% at 900 • C. These values are rationalized in terms of thermal mismatch using an eigenstrain formulation and a simple formula is derived to relate the thermal mismatch to the misfit strain. During creep at 425 MPa at 900 • C, the material exhibited primarily tertiary behavior. For grains with [0 0 1] axis close to the loading direction, the elastic microstrain in the loading direction increased with creep time for the ␥ phase, whereas the opposite occurred for the ␥ phase. These results are explained in terms of constrained deformation in the narrow ␥ channels and by an interface dislocation buildup. TEM analysis of the crept microstructure provides evidence of the interface dislocation network.