Simultaneous Enhancement of Mechanical and Magnetic Properties in Extremely-Fine Nanograined Ni-P Alloys

Exploring structural effects that influence both the mechanics and magnetism in nanocrystalline materials, particularly extremely-fine nanograined ones with grain sizes down to several nanometers, is of high interest for developing multifunctional materials combining superior mechanical and magnetic performances. We found in this work that electrodeposited extremely-fine nanograined Ni-P alloys exhibit a significant enhancement of magnetization, simultaneously along with an increase in hardness, after low-temperature annealing. The relaxation of non-equilibrium structures, precipitation of the second phase and the segregation of P atoms to grain boundaries (GBs) during annealing have then been sequentially evidenced. By systematically comparing the variations in macroscopic and microstructural investigation results among several Ni-P alloys with different P contents, we suggest that the second phase has little effect on magnetization enhancement, and essentially both the structural relaxation and GB segregation can play important roles in hardening by governing GB stability, and in the improvement of magnetization by enhancing Ni-Ni atom exchange interactions.