Phase transformation sequence of mixed-structural electroless Ni-19.7 at.% P deposit

The microstructure and phase transformation sequence of an electroless Ni-19.7 at.% P (Ni-11.5 wt.% P) deposit upon heat treatment are studied in this work. X-ray diffraction and high-resolution transmission electron microscopy analysis show that the deposit has a mixed-structure. A very small volume fraction of nanocrystalline grain with size of approximately 1–5 nm is interspersed in an amorphous matrix. The differential scanning calorimetry curves of the deposit at heating rates ranging from 10 °C/min to 50 °C/min indicate that the apparent activation energy (ΔEx) during the crystallisation process is 178.8 kJ/mol. Upon heating the deposit to 300 °C, the nanocrystalline becomes agglomerated. Upon heating to 400 °C, the Ni and Ni3P phases are precipitated from the retained amorphous matrix and the nanocrystalline is coarsened. The Ni and Ni3P phases mainly exhibit grain growth from 500 °C to 600 °C. Above 880 °C, the deposit undergoes a melting process. A small amount of P is volatilised from the liquated deposit.