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M: Metallphysik
M 48: Mechanische Eigenschaften IV
M 48.1: Talk
Tuesday, March 8, 2005, 16:30–16:45, TU H111
Dislocation processes in a peak to overaged γ’-strengthened nickel base alloy studied by in situ TEM tensile tests — •Dietmar Baither1, Volker Mohles2 und Eckhard Nembach1 — 1Institut für Materialphysik, Universität Münster, Wilhelm-Klemm-Strasse 10, 48149 Münster — 2Institut für Metallkunde und Metallphysik, Rheinisch-Westfälische Technische Hochschule, 52056 Aachen
The commercial nickel base alloy NIMONIC PE16 is strengthened by nanoscale spherical coherent precipitates of the γ’-intermetallic phase Ni3(Al, Ti). Maximum strength is attained in the peak-aged state. In the transition range to the overaged state, the strength is reduced as the interaction process between dislocations and precipitates changes.
Thin foils of NIMONIC PE16 were stretched inside a TEM and the dislocation processes were observed under full load. It was found that dislocations overcome the γ’-precipitates by a combination of bypassing and shearing. Due to the L12-long range order of the γ’-precipitates two dislocations with identical Burgers vectors form a pair and glide together. The leading dislocation bypasses the γ’-precipitates and leaves Orowan loops behind. The trailing dislocation first forces the loops to shear the γ’-precipitates before it shears the precipitates itself. The dislocation configurations observed in situ in the TEM are compared with those obtained in computer simulations.