· 94 · IMP & HIRFL Annual Report 2018

Fig. 3 (color online) (a) and (b) S parameter of samples irradiated at 1×1016 ions/cm2 500 ℃ and 1×1017 ions/cm2 500 ℃ as

a function of depth. (c) and (d) S-W plots for samples irradiated at 1×1016 ions/cm2 500 ℃ and 1×1017 ions/cm2 500 ℃.

References

[1] Z. M. Sun, Int. Mater. Rev. 56(2011)143.

[2] D. W. Clark, S. J. Zinkle, M. K. Patel, C. M. Parish, Acta Materialia., 105(2016)130.

[3] Q. Huang, R. D. Liu, L. Yan, J. Nucl. Mater., 465(2015)640.

[4] Z. J. Zhu, M. Y. Yao, J. J. Shi, J. Nucl. Mater., 508(2018)12.

[5] F. Wang, Q. Su, M. Nastasi, Ceramics International, 44(2018)14686.

5 - 9 Investigation on Microstructure and Surface Morphology of

Tungsten Carbide Irradiated with He Ions

Tai Pengfei, Sun Jianrong and Wang Zhiguang

According to the present design of ITER, the divertor armor is consisted predominantly of carbon fiber com-

posites and tungsten (W) with carbon coatings in the areas subject to the highest heat load[1]. Due to sputtering

and subsequent re-deposition, mixing of these materials will occur. Studying radiation damage in tungsten carbide

(WC) is of importance both due to its applications of plasma facing materials and due to the presence of WC in

the divertor of fusion reactors[2].

In this work, WC samples with the purity of 99.9 % and 10 mm×10 mm×1.0 mm in size were implanted by

500 keV He+ ions from 320 kV Multi-discipline Research Platform for Highly Charged Ions (IMP, Lanzhou). The

irradiation doses were from 1×1015 to 1×1018 ions/cm2 at room temperature, and from 1×1015 to 1×1017 ions/cm2

at 800 ℃. After the irradiation, the lattice structure and surface morphology of the samples have been investigated

by grazing incident XRD and AFM.

As is shown in Fig. 1, the XRD results indicated that at room temperature, the characteristic peak intensity

of two phases (W1C1 and W2C1) were decreasing meanwhile the FWHMs were broadened with the increasing of

implanted He+ dose, which means the increasing of lattice damage. At the implantation temperature of 800 ℃,

2018 IMP & HIRFL Annual Report · 95 ·

there were no significant changing of the peak intensity and FWHM, but at the implanted dose of 1×1017 ions/cm2,

the peak of W appeared. The XRD results indicated that the metallic tungsten will be precipitated under long-term

irradiation at 800℃. As is reported in many simulation results[3], the irradiation of WC can lead to major elemental

asymmetries in the defect production, especially in the fraction of isolated point defect. This effect is explained by

the much higher formation energies of W than of C defects, and can thus be expected to occur that W rich layer

could be formed in the irradiated layer, combine with the long term high temperature effect, which may lead to the

precipitation of W particles.

Fig. 1 (color online)XRD patterns of WC samples irradiated with various doses at a) RT and b) 800 ℃.

AFM observation was carried out in order to study the changes on the surface of WC samples induced by the

irradiation, as shown in Fig. 2. As the result of RT irradiation, the roughness values were increasing with the

irradiation doses, the higher value is mainly caused by the helium bubble aggregation and irradiation swelling.

One sample with the dose of 1×1017 ion/cm2 at 800 ℃, the value is much higher than the sample with the same

irradiation dose at RT, but is lower than the sample of 1×1018 ion/cm2. This might be caused by the precipitation

of W presents at WC surface.

Fig. 2 (color online) Surface modifications of WC samples characterized by AFM.

References

[1] H. Maier, ASDEX Upgrade Team, J. Nucl. Mater., 335(2004)515.

[2] H. Plank, W. Eckstein, Nucl. Instr. and Meth B, 124(1997)23.

[3] C. Bjorkas, K. Vortler, K. Nordlund, Phy. Rev. B, 74(2006)140103(R).