Temperature of nanocrystallisation of magnetically soft alloys for high-temperature applications

The newest class of magnetically soft materials are the nanocrystalline iron alloys obtained by partial crystallisation of metallic glasses. Within this group, FINEMET (Fe-Si-Nb-Cu-B) and NANOPERM (Fe-Zr-Cu-B) alloys exhibit the unique combination of interesting magnetic properties. These materials may be used at temperature below 230 °C. For high-temperature applications, the HITPERM alloys (Fe-Co-Zr-Cu-B) are used. Their optimisation should lead to good (i) magnetic properties at working temperature and (ii) thermal stability of structure and properties. The alloys' properties are the function of chemical composition and heat treatment. This work is related to the optimisation of heat treatment conditions of HITPERM alloys. High operating temperature may induce further crystallisation of amorphous matrix. It is suggested that the nanocrystallisation temperature should be as high as possible, and the optimisation of HITPERM-type alloys should focus on their chemical composition.