Assessment of convergence effects in weak-beam transmission electron microscopy in partial spacing measurements in Ni3Al

Abstract

ABSTRACT Recently, Schaublin, Meng and Stobbs have taken a new approach to the weak-beam technique for the measurement of dissociated dislocation spacings in the evaluation of stacking fault energies. They have demonstrated, through image simulations, both the importance and usefulness of using convergence values above those traditionally considered to be appropriate. An experimental exploration of the new convergent weak-beam technique is presented here in the case of Ni3Al for a g(4g) condition at 200 kV. It appears that the influence of the 3 convergence in weak-beam transmission electron microscopy (WB TEM) as depicted by Schäublin et al. is confirmed experimentally for the conditions used here. Owing to the depth oscillations being smeared out, the accuracy in partial dislocation spacing measurement is increased when the beam convergence is increased. A further study of the influence of the convergence in relation to the WB TEM condition is presented here and shows that the higher the deviation parameter, the lower the variation in average apparent spacing with convergence.