Metal Vapor Vacuum Arc (MEVVA) ion source (IS) is a unique tool for production of high intensity metal ion beam that can be used for material surface modification. From the other hand, the duoplasmatron ion source provides the high intensity gas ion beams. The MEVVA and duoplasmatron IS developed in Institute for Theoretical and Experimental Physics were used for the reactor steel surface modification experiments. Response of ferritic-martensitic steel specimens on titanium and nitrogen ions implantation and consequent vacuum annealing was investigated. Increase in microhardness of near surface region of irradiated specimens was observed. Local chemical analysis shows atom mixing and redistribution in the implanted layer followed with formation of ultrafine precipitates after annealing.
It is shown that simulation experiments on the heavy-ion irradiation of structural materials used in nuclear power facilities can be used for tomographic atomic-stand studies. Experiments have been performed on irradiation of samples of advanced steel used in nuclear and fusion reactors EK-181 and ODS Eurofer by iron ions to damaging dose 10 dpa. The steel is characterized by the presence of a large number of nanosize (2-3 nm) clusters, dispersion-hardening these materials. Irradiation was performed on the TIPr-1 heavyion linear accelerator. Atomic-probe studies of irradiated samples reveal a change in the composition of nanosize clusters under irradiation.The determination of the service life of steel operating in radiation fields is the most important stage in the development of new reactor materials. The most difficult stage is studying the radiation resistance of core materials, since this requires prolonged irradiation in a reactor. A high dose (>100 dpa) of neutron irradiation is reached over months-years even in fast reactors. In addition, strong activation considerably complicates subsequent studies, especially microscope studies.It is known that the quickest method of producing radiation damage is irradiation with heavy ions. It reproduces cascade creation of defects, which is also the main damage occurring when fast neutrons pass through a material. Heavyion irradiation makes it possible to study the role of cascades of atomic displacements in radiation degradation processes in materials. It is important to note that when materials are irradiated by heavy ions radiation defects are formed nonuniformly, and for this reason in simulation experiments samples for microscope studies are irradiated. The first direction in such experiments was irradiation of samples for transmission electron microscopy and subsequent study of their microstructure. Another direction of such studies is irradiation and study of samples for tomographic atomic-probe microscopy. The unique possibilities of an atomic probe with respect to local resolution of the chemical composition of a material on atomic scales are used in these experiments. A change in the macroscopic properties is predicted on the basis of data on the change in the microstructure of materials in simulation experiments.In the present work, it is shown that simulation experiments with heavy-ion irradiation of samples can be used for tomographic atomic-probe studies. These studies were performed at the Institute for Theoretical and Experimental Physics using as a base a complex for studying the radiation resistance of materials that includes a TIPr-1 heavy-ion linear accelerator (heavy-ion prototype) with spatially uniform quadrupole focusing and ultramicrosopy methods -tomographic atomic probe, transmission electron microscopy and others [1,2].
INTRODUCTIONReduced activation ferritic/martensitic chromium steels are promising candidates as structural materials for new generation fusion and fission reactors [1,2]. Of known foreign materials of this class are 9% chro mium Eurofer 97, JLF 1, F82H, CLAM, and 9Cr 2WVTa steels [3][4][5][6][7]. Such materials are developed in Russia, as well, which are capable of withstanding high radiation doses and capable of working at tempera tures of up to 700°C. Special attention is paid to 12% chromium ferritic martensitic EK 181 steel with increased heat resistance that is considerably higher than that of foreign ones at such temperatures [8,9]. An improvement of mechanical properties can be accomplished selecting regimes of alloying and heat treatment. As a result, this steel suffers precipitation hardening [8][9][10].It was shown by transmission electron microscopy technique [8,9], different types of heat treatment of EK 181 steel result in formation of various hardening phases in the material. For example, after conven tional normalizing and tempering (N&T) heat treat ment including quenching at 1070-1100°C and tem pering at 720°C, the size of carbide phases is in the range of 10-200 nm, with the average size of these phases being 75 nm [9]. As follows from the results of atom probe tomography studies of ferritic martensitic EK 181 steel [11], clusters enriched in V, Cr, and N with dimensions ~3 nm are also formed in a matrix after conventional heat treatment.Further improvement of the properties of EK 181 steel is associated with a decrease in the dimension of disperse particles and homogeneity of their distribu tion. In turn, this requires clarification of heat treat ment for a particular material. For optimizing regimes of heat treatment, one needs information on the nanoscale state of EK 181 steel that is formed after different stages of heat treatment.The aim of this work is to study the nanoscale state of EK 181 steel after various heat treatments using atom probe tomography.
MATERIALThe chemical composition of EK 181 steel is shown in the table below. A high level of high temper ature strength and radiation resistance of EK 181 steel are known to depend considerably on the regime of heat treatment [9]. Conventional normalizing and tempering (N&T) heat treatment is used to increase the tensile strain up to 700°C. To decrease ductile to brittle temperature transition shift caused by irradia tion, to increase impact strength and tensile strain within brittle region combined heat treatment is used, including termocycling near the onset point of the phase transition α γ [9]. The content of δ ferrite does not exceed 5% after both heat treatments. The microstructure of steel after quenching at 1070-1100°C comprises a martensite phase which is formed as a result of polymorphic transition γ α. A ferrite Abstract-Reduced activation ferritic/martensitic 12% Cr EK 181 steel (Fe-12Cr-2W-V-Ta-B-0.16C) was investigated using atom probe tomography after various regimes of heat treatment: annealing at 800-850°C, conventional n...
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