The metastable phases formed in amorphous Ni–P alloys during crystallization

It is shown by electron diffraction and microscopy that the first stage in the crystallization of chemically and electrolytically deposited amorphous Ni–P alloys on heating to 250°C is an f.c.c. metastable phase α with a=0·55 nm. In the second stage of crystallization, at 270–400°C, metastable hexagonal phases α1, α2 and α3 are formed. These phases have the same a=0·672 nm but different c parameters, the latter being in the ratio 2:3:8 with c(α1)=0·952 nm. They originate from the f.c.c. α phase with (001)hex parallel to {111}α and ⟨210⟩hex parallel to ⟨110⟩α. The growth habit of α1 exhibits a dendrite-like morphology consisting of 90° rotation twins about [001]α. Above 400°C, these hexagonal metastable phases transform into stable phases Ni3P, Ni12P5 and the nickel solid solution. The three ‘new’ metastable Ni3P phases reported by Vafaei-Makhsoos (1980) have not been confirmed; on the contrary, all the electron diffraction patterns of these phases can be indexed quite easily as those of Ni12P5.