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Effect of ion irradiation on the mechanical properties of high and low copper
Hiwa Mohammad QADR1*
1Department of Physics, College of Science, University of Raparin, Sulaimanyah, Iraqi Kurdistan, Iraq
A R T I C L E I N F O A B S T R A C T AIJ use only:
Received date Revised date Accepted date Keywords:
irradiation, hardness, dpa, copper.
An investigation into the effects of proton beam exposure on various aspects of nuclear reactors as structural materials was used high and low copper. The aim of this work presented here is to investigate the impact of the radiation damage in the materials by the proton energy irradiation. The damage parameter used in the evaluation is displacement per atom dpa in material as a function of proton energy.
In addition, a TRIM programmer was used to identify the penetration depth when changes were administered to proton energy. The hardness variation with depth for irradiated and non-irradiated was then investigated. Based on the results, the study found that the hardness test for high copper is higher than low copper.
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INTRODUCTION
Ion irradiation experiments allow control of ion energy, dose, dose rate and temperature which enables very reproducible and specific results making them desirable for studying irradiated micro-structure and property changes of a material in a shorter time period.
However the evolution of irradiated microstructure is dependent upon a combination of damage rate and irradiation temperature and so damage cannot always be reproduced in a shortened time period just through increased displacement rate (dpa/s), although temperature shift relations have be created which allow for more correlation of one type of damage evolution from one irradiation environment to another using dose, dose rate and temperature . Ion beams are also generally cheaper to produce a given dose compared to neutron sources.
suggest copper precipitates that are rich in other impurities (Ni, Al and Mn) that form under proton irradiation, remain stable with further irradiation.
Clusters of these precipitates inhibit the movement of dislocations under stress, which causes a net increase in hardness after irradiation. suggest that
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the mechanism of irradiation hardening is similar to that of ageing except in this scenario proton radiation increases the free movement of vacancies, which encourages the diffusion of solutes. Another similarity to thermal ageing is that under irradiation, instead of dissolving the precipitates coarsen. This acts to soften the material to some degree. The conclusions that can be drawn from are that hardness increases with segregation of impurities in RPV steels, namely copper. Their binding to point defects in the matrix furthers the movement of these Cu-rich precipitate clusters. These clusters migrate to areas of low energy such as grain boundaries and sometimes act as ‘sinks’ to which point defects continue to migrate. This process means that these sinks can also act as recombination sites, where interstitials and vacancies can combine and
‘recover’ the hardness of the material by some fraction. This process can occur during irradiation and aid to improve the mechanical properties of the material.
Further study was conducted by . They also suggested hardening was due to copper clustering in the matrix and that nickel additions aided this mechanism. Their work agrees that Frenkel pairs increase hardening, however they also suggested that after annealing above 400C, microvoids were
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no longer a cause of hardening, as they disappeared above 200C .
Hardness is the capability of a substance to resist permanent shape change under applied strain.
Historically it has been measured as a materials ability to resist scratching from other materials.
Many different methods for measuring hardness have been developed over the years, all of which have their own intricacies. The Vickers hardness test was the technique employed in this paper.
Microhardness for high and low copper samples was measured using a Vickers hardness machine.
The indent is a diamond in the form of a square- based pyramid. The included angle of the indent is 136ᵒ. As known, Hardness is a measure of force per area. Hardness can be calculated by:
(1)
Additionally, it is possible to work out the indent depth:
(2)
Where HV is hardness value, d is intender diagonal, F is load and h is indenter depth
EXPERIMENTAL METHOD
Hardness tests were performed on the high and low copper samples irradiated at 380oC. it was not possible to continue with the hardness tests because the black layer on the surface had a brittle profile. The indents were causing cracks in the material so the result was not valid because Vickers Hardness test is not supposed to be performed in brittle surfaces. Fig.1 shows the photos of invalid specimens.
Different loads were used in order reach different indent depths in the sample. 3MeV protons can reach up to approximately 40μm in the samples.
It is possible to measure hardness until 25μm and have a good simulation of neutron damage profile.
The indent depths for different loads were approximately 3μm, 8μm, 11μm and 16μm. Indents were 0.5mm apart from each other, which avoids interference in the measurements. Moreover, measurement started and ended far away from the edges of the specimens.
Fig. 1. A contamination in the vacuum system has invalided specimens irradiated at 380ᵒC RESULTS AND DISCUSSION
The Monte Carlo code TRIM was used to gain information about the displacement per atom into the surface of materials . DPA is a strong function to measure the amount of radiation damage in irradiated materials . The ion used was Hydrogen, with ions of energies of 1.0MeV, 3.0MeV and 9.0MeV H PKA into high copper and low copper for 5000 incident ion.
One of the greatest advantages of using proton beam is the easy variation of parameters. Accelerators, such as the cyclotron used in this work, offer a huge variety of irradiation environments. It is important to express the displacements in terms of ion/cm² due to the fact that this value can be easily changed for different irradiation conditions. The graphs for low and high copper compositions are shown in Fig.2.
The results were pretty satisfactory as the dpa (Displacement per atom) behaviour is clear. For higher energies, the dose at the surface decreases because they pass through the material easily, the scattering cross section is lower.
Fig. 2. Bragg peak in low copper, showing penetration depth change with increase dpa a 1, 3, 9
MeV proton
According to details of hardness results are possible to notice that it does not have the same number of
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points for each condition. This is because the work was held throughout the surface and the interface between non irradiated and irradiated sides was not exactly in the half of the row. Additionally, the indent depth was approximately the same for all specimens and conditions, so this value was also averaged in order to make comparisons easier. It is possible to notice the influence of Copper in the specimen. It is slighter than expected. The surface was pretty rough and doing polish was complex due to safety issues related to the residual activity of the samples. Images from different indents are shown in Fig. 3.
Fig. 3. Images from the High Copper hardness analysis. (a) Indent on the non-irradiated surface (b)
Indent on the irradiated surface (c) Example of invalid indent
Different depths on the material receive different damage accumulation due their different volumes.
The deeper, the greater is the dose received. The hardness profile through sample thickness can be seen in Fig.4 and Fig.5. The values are averages for the non-irradiated and irradiated parts for both samples and the error bars express the standard deviation.
Fig. 4. Vickers hardness values profile through sample thickness. For non-irradiated and irradiated
low copper
Fig. 5. Vickers hardness values profile through sample thickness. For non-irradiated and irradiated
High Copper
The profile was not the best expected, because hardness should increase with dose, namely depth.
However, it is possible to notice that the standard deviation is large and comprehends a great variation among the values for both samples. Also, the surfaces were not ideal to do hardness tests because they were rough.
CONCLUSION
TRIM calculation of proton penetration in low Copper. The proton penetration depth varies strongly with its energy, and no difference was observed between low and high copper compositions. The penetration depth was approximately 7μm for 1MeV protons, 38μm for 3MeV and 234μm for the 9MeV ones.
Moreover, Irradiated values for hardness were higher than non-irradiated ones as expected from radiation hardening. Furthermore, it was expected that high Copper samples had a higher increase in hardness. This Copper influence was not very perceptive in the results.
ACKNOWLEDGMENT
Acknowledgment is recommended to be given to persons or organizations helping the au- thors in many ways. Sponsor and financial support acknowledgments may be placed in this section. Use the singular heading even if you have many ac- knowledgments.
REFERENCES
1. Was, G. S. Fundamentals of radiation mate- rials science: metals and alloys, Springer, 2016.
2. Zhang, Z. et al., Effects of proton irradiation on nanocluster precipitation in ferritic steel con- taining fcc alloying additions, Acta Materialia, 2012; 60; 6-7; 3034-3046.
3. Shibamoto, H. et al., Effects of proton irradi-
ation on reactor pressure vessel steel and its
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