Free Access
Microsc. Microanal. Microstruct.
Volume 7, Number 1, February 1996
Page(s) 65 - 84
Microsc. Microanal. Microstruct. 7, 65-84 (1996)
DOI: 10.1051/mmm:1996106

Local Order and Associated Deformation Mechanisms in the $\gamma$ Phase of Nickel Base Superalloys

Nicole Clement1, Armand Coujou1, Yvonne Calvayrac2, Francois Guillet2, Didier Blavette3 et Stéphane Duval3

1  CEMES-LOE/CNRS, 29 rue Jeanne Marvig, BP. 4347, 31055 Toulouse Cedex, France
2  CECM/CNRS, 15 rue Georges Urbain, 94407 Vitry Cedex, France
3  LMI, URA CNRS 808, UFR Sciences et Techniques, BP. 118, 76134 Mont Saint Aignan Cedex, France

Using X-ray diffraction, atom probe nanoanalysis, T.E.M. associated with in situ deformation, the presence of local order in the $\gamma$ matrix of a monocrystalline MC2 superalloy is demonstrated. In Ni2CoCr the model alloy of this phase, as well as in the $\gamma$ MC2 matrix, the existence at room temperature of a strong short range order of $\{1 ~1/2~ 0\}$ special point type is emphasized. It induces high friction stresses opposing the movement of dislocations which have to propagate in planar arrays in the corresponding materials. In addition, long range ordered $\rm L1_2$ hyperfine precipitates appear in the $\gamma$ MC1 samples annealed at $\rm 750~^\circ C$. They induce several pairs of dislocations at the head of the moving pile-ups in order to cut them.

8130B - Phase diagrams of metals and alloys.
6170J - Etch pits, decoration, transmission electron microscopy and other direct observations of dislocations.
6475 - Solubility, segregation, and mixing.
8130M - Precipitation.
6155H - Crystal structure of specific alloys.

Key words
chromium alloys -- cobalt alloys -- deformation -- dislocation arrays -- dislocation motion -- dislocation pile ups -- friction -- ion microprobe analysis -- long range order -- nickel alloys -- precipitation -- short range order -- superalloys -- transmission electron microscopy -- X ray diffraction -- TEM -- annealing -- dislocation movement -- dislocation planar arrays -- dislocation pile ups -- gamma phase -- X ray diffraction -- atom probe nanoanalysis -- deformation -- local order -- monocrystalline MC2 superalloy -- short range order -- high friction stresses -- long range ordered -- L1 sub 2 hyperfine precipitates -- 300 K -- 750 degC -- Ni sub 2 CoCr

© EDP Sciences 1996