Magnetothermal study of nanocrystalline particle formation in amorphous electroless Ni-P and Ni-Me-P alloys

The microstructure of amorphous Ni-P and Ni-Me-P materials and especially i ts change during the heat treatment is of great importance for their magnet ic, mechanical and corrosion behavior. A new magnetic phase analysis method (magneto thermal) is presented that reveals the precipitation of nanoparti cles with strong magnetic properties during phase transformation upon heat treatment. It is applied to electroless Ni-P, Ni-Cu-P and Ni-Sn-P amorphous alloys. The results acquired by this method are compared with data obtaine d by differential scanning calorimetry, as well as by microhardness measure ments using identical heat treatment in all three cases. Due to the high se nsitivity of the magnetothermal method a more detailed picture of the preci pitation processes in Ni-P alloys is obtained and the new information is di scussed. Magnetothermal measurements reveal several stages of precipitation of a phase with strong magnetic properties. This phase is Ni in the Ni-P a lloy, and Ni(Me) solid solution in the Ni-Me-P alloys. Though Sn has a stro nger effect on the Ni magnetization, Cu is more effective in preventing the appearance of high magnetization in a thermally treated Ni-Cu-P alloy. Thi s is due to Cu incorporation in Ni particles in a quantity above four times larger than Sn. (C) 2001 Elsevier Science Ltd. All rights reserved.