Use of the hole-drilling method for measuring residual stresses in highly stressed shot-peened surfaces

Abstract The same shot-peening treatment was applied to five steels with different mechanical properties. The induced residual stress profiles were analyzed using X-ray diffraction and incremental hole drilling (IHD). The results of both techniques showed that IHD can still be successfully used for measuring shot-peening residual stresses, even if these exceed the yield strength of the bulk material. Expected errors due to the plasticity effect are reduced by the strain hardening of the surface. For an assessment of the reliability of IHD data, strain-hardening variation was quantified by microhardness measurements to estimate the yield strength of the plastified layer. All the main calculation methods for IHD were applied. The results were compared and discussed with respect to the characteristics of each method

Importance of Non-uniform Boundary Migration for Recrystallization Kinetics

Recrystallization kinetics is studied by three characterization methods: post-mortem electron microscopy, in situ three-dimensional X-ray diffraction (3DXRD), and ex situ electron microscopy. Cold-rolled copper is used as a model material. The post-mortem analysis shows that the average migration velocity of unimpinged recrystallizing boundaries decreases strongly with annealing time, leading to a low Avrami exponent. For individual grains, the in situ 3DXRD measurement reveals that the growth rates decrease significantly shortly after nucleation. This is explained by the ex situ characterizations, which show that different segments of the recrystallizing boundaries migrate with significantly different velocities, and some boundaries, although unimpinged, remain stationary. This non-uniform migration of recrystallizing boundaries leads to an amoeba-like growth, and is proposed to be responsible for the decrease of the average boundary migration velocity, because the fraction of slowly moving/stationary boundaries increases during the recrystallization. Reasons for stationary boundaries are discussed based on a quantitative analysis of the local deformed microstructure. It is concluded that non-uniform boundary migration has a significant influence on recrystallization kinetics and needs to be included in recrystallization models