Irradiation Assisted Grain Boundary Segregation in Steels
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0981-JJ05-09
Irradiation Assisted Grain Boundary Segregation in Steels Zheng Lu and Roy G. Faulkner IPTME, Loughborough University, Ashby Road, Loughborough, LE11 3TU, United Kingdom
ABSTRACT This paper reviews the major methods used currently for radiation-induced grain boundary segregation (RIS) prediction: namely, Rate Theory, Inverse Kirkendall, and Solute Drag approaches. RIS of phosphorus in different reactor pressure vessel (RPV) steels is summarized and discussed in the light of the predictions of the various models in an effort to show which models are the most reliable and easy to use for forecasting P segregation behaviour in steels. A consequence of RIS in RPV steels is a radiation-induced shift in the ductile to brittle transition temperature (DBTT). It will be shown how it is possible to relate radiationinduced P segregation levels to DBTT shift. Examples of this exercise will be given for RPV steels and for ferritic steels being considered for first wall fusion applications. RIS of chromium in high alloy ferritic stainless steels is also briefly discussed. INTRODUCTION The understanding of radiation-induced grain boundary segregation (RIS) has considerably improved over the past decade. New models have been introduced and much effort has been devoted to obtaining comprehensive information on segregation from the literature. Analytical techniques have also improved so that chemical analysis of layers 1 nm thick is almost routine. This invited paper will review the major methods used currently for RIS prediction: namely, Inverse Kirkendall [1], Rate Theory[2-4], and Solute Drag approaches [5,6]. A summary is made of the available data on phosphorus RIS in reactor pressure vessel (RPV) steels. This will be discussed in the light of the predictions of the various models in an effort to show which models are the most reliable and easy to use for forecasting P segregation behaviour in steels. A consequence of RIS in RPV steels is a radiation induced shift in the ductile to brittle transition temperature (DBTT). It will be shown how it is possible to relate radiation-induced P segregation levels to DBTT shift. Examples of this exercise will be given for RPV steels and for ferritic steels being considered for first wall fusion applications. Cr RIS in high alloy stainless steels and associated irradiation-assisted stress corrosion cracking (IASCC) will be briefly discussed.
MODELLING Inverse Kirkendall[1], Rate Theory[2-4] and Solute Drag [5,6]models have been applied to modelling radiation-induced inter-granular segregation of impurities and solute atoms in dilute and concentrated alloys; These models are summarized and compared below. Radiation-induced segregation Inverse Kirkendall Model Inverse Kirkendall model [1] assumes that the preferential exchange of an alloying element with the vacancy flux results in a net solute flux toward or away from the boundary. If the diffusion rate of solute A is faster than the average diffusion rate of all solutes, there is the depletion of solute A at sinks, e.g. gra
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