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In situ transmission electron microscopy tensile tests of a peak- to overaged γ′-strengthened nickel base alloy
The commercial nickel base alloy NIMONIC PE16 is strengthened by nano-scale spherical coherent precipitates of the intermetallic γ′-phase Ni3(Al,Ti). A bulk polycrystalline specimen of NIMONIC PE16 was aged such that it was in the transition range from the peak- to the overaged state. This transition limits the duration of technically useful aging treatments of structural particle strengthened materials. Thin foils prepared from this specimen were stretched inside a transmission electron microscope, and the dislocation processes were observed under full load. Two dislocations with identical Burgers vectors of the type 1/2〈110〉 form a pair and glide together. The leading 1/2〈110〉 dislocation bypasses the γ′-precipitates and the trailing one shears them. These dislocation processes are also discussed with reference to the results of computer simulations.