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.
Positron confinement in ultrafine embedded particles: Quantum-dot-like state in an Fe-Cu alloy
A quantum-dot-like positron state is demonstrated in the ``defect-free'' particles using coincidence Doppler broadening of positron annihilation radiation. The wave functions of all positrons are entirely confined spatially in all three directions within the embedded nanosize and subnanosize Cu particles in a dilute Fe-Cu alloy. With use of this probe, the ultrafine particles are revealed to have nearly the same electron momentum distribution as bulk Cu, to be free from Fe atoms and defects, three dimensional, and to have no open-volume defects at the interfaces which can trap the positron. These successes indicate that this positron state promises to be a powerful tool for the studies of mesoscopic systems in metals and semiconductors.
APFIM investigation of clustering in neutron-irradiated FeCu alloys and pressure vessel steels
Abstract Pressure vessel steels used in PWRs are known to be prone to hardening and embrittlement under neutron irradiation. The changes in mechanical properties are commonly supposed to result from the formation of point defects, dislocation loops, voids and copper-rich precipitates. However, the real nature of the irradiation induced damage, in these particularly low copper steels ( A new experimental work has been carried out thanks to atom probe and field ion microscopy (APFIM) facilities and, more particularly with a new generation of atom probe recently developed, namely the tomographic atom probe (TAP), in order to improve: - the understanding of the complex behavior of copper precipitation which occurs when low-alloyed Fe Cu model alloys are irradiated with neutrons; - the microstructural characterization of the pressure vessel steel of the CHOOZ A reactor under various fluences (French Surveillance Programme). The investigations clearly reveal the precipitation of copper-rich clusters in irradiated Fe Cu alloys while more complicated Si, Ni, Mn and Cu-solute ‘clouds’ were observed to develop in the low-copper ferritic solid solution of the pressure vessel steel.