Phase transformation sequence of mixed-structural electroless Ni-19.7Â 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.