Solute clusters hardening

The precipitate hardening efficiency iOyp/fp) vs fp for solute cluster hardening within the IVAR database, compared with trends derived from the Russell-Brown (RB) and Bacon and Osetsky (B-O) models. o ,p, irradiation-induced yield stress increment associated with precipitation fp, volume fraction of precipitates fp, average precipitate radius derived from SANS measurements. 

Fe or Ni ion irradiation with energies of a few MeV is mostly used for studies of radiation damage of RPV steels. Previous studies have provided information on the effects of Cu, Mn and other elements, carbides, dose rate and tensile stress on hardness, matrix damage evolution and solute cluster formation in model alloys and commercial steels (e.g. Fujii and Fukuya, 2005 Murakami et al., 2009). These data provide clear evidence of the effects of various metallurgical parameters on hardening and microstructural evolution in Fe-based alloys and RPV steels, although these data cannot be directly or quantitatively correlated to data from neutron-irradiated materials. 

There are two main candidate models which describe the effect of the solute clusters on hardness. The modulus hardening model by Russell and Brown" has been successfully employed for many years to link microstructural and mechanical properties. It predicts very little effect of particle size on hardening at a given volume fraction of precipitates, when particle diameters are in the range 2-4 nm. A more modern model based... 

The observation of P clusters in irradiated steels led to the conclusion that the deleterious effect of P was caused by precipitation hardening and the depletion of P in the solid solution. 

Positron annihilation spectroscopy (PAS) is an excellent technique for investigating vacancy clusters and vacancy—solute complexes behavior during irradiation since positrons are very sensitive to these types of defects. These defects are important for the formation of the feamres responsible for hardening. In this technique, positrons are applied as a probe and positrons are trapped by defects with electron densities different from the bulk materials. These defects can be vacancies, vacancy clusters, interfaces, second-phase particles, dislocations, etc. [69]. Positrons annihilate with a different probability in the defects as compared to the bulk material because of the difference in positron affinity to different atomic species [69]. The advantage of the technique lies in its nondestructiveness, self-seeking nature, and ability to find small defects (>0.1 nm) even in low concentrations (>1 ppm) [69]. PAS can provide information... 

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