Quantitative Non-Destructive Detection of Residual Stresses of the 2 nd and 3 rd Order by Using Micro Magnetic Methods
Micro residual stresses (MRS) of the 2 and 3 order play an important role in the lifetime analysis of thermally-cycled materials. The coherent residual stresses (MRS of 3 order) appear when the lattice parameter of the second phase particles (coherently embedded in the matrix) and the lattice parameter of the matrix are different from each other. Such differences in case of the Fe-Cu alloys between the lattice parameters of coherent Cu precipitates and the lattice parameters of the αFe matrix lead to distortion of the lattice around the Cu particles causing coherent tensile MRS of 3 order. Thermally induced MRS of the 2 order appear when individual material phases exhibit different thermal expansion coefficients. Such differences in temperature-related expansion coefficients of copper precipitates and the α-Fe matrix promote the development of thermally induced compressive MRS of the 2 order. The main objective of the presented research project is to develop an integral, economical and fast micro-magnetic non-destructive method for quantitative characterisation of MRS of the 2 and 3 order in Fe-Cu and Fe-Cu-Ni alloys. For this purpose Fe-Cu and Fe-Cu-Ni alloy samples with different Cu and Ni contents were prepared.
A comparison of the effect of electron irradiation and of thermal aging on the hardness of FeCu binary alloys
The hardening of binary FeCu alloys under 2.5 MeV electron irradiation between 175°C and 360°C was investigated. We show that an extra-hardening component which cannot be ascribed to copper precipitation is induced during irradiation with electrons. We discuss the possible nature of the objects responsible for this extra-hardening component. They have to be very small since they are not visible by transmission electron microscopy. We come to the conclusion that they most likely are very small interstitial clusters nucleated by random encounter of interstitials. An important issue from the technological point of view raised by this work is to know whether it is reasonable to totally ignore any hardening component of the pressure vessel steels attributed to the clustering of freely migrating point defect escaping from the core of the displacement cascades or created between them.
Experimental study and modelling of copper precipitation under electron irradiation in dilute FeCu binary alloys
In order to study the effect of the supersaturation of freely migrating defects on the precipitation of copper in high residual copper pressure vessel steels under neutron irradiation, FeCu (1.34, 0.30 and 0.11 at.% Cu) model alloys were irradiated between 175 and 360°C with high energy electrons. On-line electrical resistivity measurements and small angle neutron scattering (SANS) under magnetic field experiments were carried out. The use of the latter method to get the chemical composition of the precipitates is discussed. We show that the mechanisms of precipitation are identical under electron irradiation and under thermal aging. The sole effect of electron irradiation on the precipitation is to enhance the kinetics. A modelling of copper precipitation based on cluster dynamics is proposed. A comparison between our SANS results obtained under electron irradiation and those under neutron irradiation published in the literature shows that the mechanisms of precipitation are very likely different with both kinds of particles.