X.Y. Sun

Study of γ-ray irradiation effect on permanent magnets

Irradiation damage of FeCrCo, AlNiCo, SmCo, and NdFeB permanent magnets was investigated by using γ-ray irradiation. Results of magnetic property measurement show that FeCrCo and NdFeB have more demagnetization than AlNiCo and SmCo. X-ray diffraction analysis shows that γ-ray irradiation leads to the increase of FeCrCo crystal mismatch and decrease of AlNiCo ordering degree. The investigations by positron annihilation spectroscopy technique show that the defects in AlNiCo and SmCo increase after γ-ray irradiation. The defects induced by γ-ray irradiation in NdFeB magnets are not the main source that leads to partial demagnetization. The irradiation resistances of these magnets are discussed in detail considering the thermal stability, coercivity mechanisms, and defect damage.

Mössbauer Spectrometry Study of Spinodal Decomposition in Fe-25Cr-12Co-1Si Alloy during Step Ageing

The local environment issued from the phase decomposition in Fe-25Cr-12Co-1Si alloy during step ageing has been studied by 57Fe Mössbauer spectrometry. The phase decomposition is influenced by both ageing time and temperature. It processes rapidly when ageing temperature is high. The formation of different kinds of (Fe, Co)-rich, Fe-rich and Cr-rich domains with independent hyperfine parameters during phase decomposition was characterized by hyperfine field distribution. The magnetic hardening of the alloy was discussed basing on single domain particle model.