Studies on the bulk nanocrystalline Ni–Fe–Co alloy prepared by mechanical alloying–sintering–hot rolling route

Abstract

Nanocrystalline Ni–Fe alloys have emerged as a promising soft magnetic material for high frequency applications where low hysteresis loss is the prime requirement. Nanocrystalline 80Ni–20Fe (wt.%) alloys synthesized by mechanical alloying have shown improved magnetic properties as compared to conventional 80Ni Permalloy due to formation of nanocrystalline Ni 3Fe as major phase during mechanical alloying. However, retaining nanocrystallinity during consolidation to prepare bulk material is a key issue. The present paper describes preparation of bulk nanocrystalline 80Ni–15Fe–5Co (wt.%) alloy by a powder metallurgy route involving mechanical alloying of elemental powder mixture followed by sintering and hot rolling. The average grain size of the mechanically alloyed powder was approximately 10 nm after milling for 46 h. A multi-step sintering–hot rolling route was developed to prepare a crack-free strip having an average grain size 32 ± 2 nm and 99% theoretical density. The bulk nanocrystalline 80Ni–15Fe–5Co strip resulted in a very narrow hysteresis loop indicating a very small hysteresis loss. The present study shows that mechanical alloying–sintering–hot rolling route can be a promising method for producing bulk nanocrystalline materials.