Diffusion of tungsten in α-iron

Abstract

Tracer diffusion coefficient of ¹⁸¹W in α-iron has been determined in the temperature range between 833 and 1173 K using a serial sputter-microsectioning method. The temperature dependence of the diffusion coefficient, D, over the whole temperature range of α-iron across the Curie temperature (T _C = 1043 K), can be expressed by

where s is the ratio of the spontaneous magnetization at T K to that at 0 K. The factor 0.086 in the above equation is smaller than 0.156 for the self-diffusion, showing that the influence of the magnetic transformation on the diffusion of tungsten in α-iron is smaller than that on the self-diffusion. The activation energy 287 kJ/mol for tungsten diffusion in the paramagnetic iron is much higher than 250.6 kJ/mol for the self-diffusion. Atomic size effect is predominant in the activation energies for diffusion of transition elements in the paramagnetic α-iron.

Acknowledgments

The authors are grateful to Dr S. Ogu of Mitsubishi Heavy Industries, Ltd., for supplying high-purity iron rod and to the staff of the Division of Accelerators at the Laboratory of Nuclear Science and the Cyclotron Radio-Isotope Center, Tohoku University, for accelerator operation. The authors would like to thank Professor Otsuki for production of radioisotope ¹⁸¹W. This work was partly supported by an ISIJ Research Promotion Grant.

Notes

†Present address: Yamaha Motor Co. Ltd., Iwata, Japan.

‡Present address: Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

§Present address: Department of Materials Science and Engineering, Faculty of Engineering, Iwate University, Morioka 020-8551, Japan

Additional information

Notes on contributors

S. Takemoto†

†Present address: Yamaha Motor Co. Ltd., Iwata, Japan.

H. Nitta‡

‡Present address: Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan

Y. Iijima§

§Present address: Department of Materials Science and Engineering, Faculty of Engineering, Iwate University, Morioka 020-8551, Japan