電析Ni-P合金の加熱にともなう構造変化

抄録

The thermal behavior of electrodeposited Ni-P alloys containing 3.2 to 15.8 wt%P (5.9∼26.2 at%P) and the structural transformation or crystalline products associated with the exotherms were investigated by differential scanning carolimetry (DSC), X-ray diffraction and transmission electron microscopy. Moreover, in order to reveal the chemical bonding of phosphorus in the alloys, the P-K_β soft X-ray emission spectra from the alloys, nickel phosphides (Ni₃P and Ni₂P) and pure red phosphorus were measured by an electron probe microanalyzer. In the alloys with 3.2≤P≤11.2 wt%, the supersaturated solid solution of P in the fcc Ni structure is transformed into a structure consisting of an aggregate mixture of Ni and Ni₃P at 340∼430°C. In the alloys with 12.7≤P≤15.8 wt%, the amorphous solid converts into the metastable single phase at 280∼360°C, and upon further heating this phase is transformed into three different stable phases such as Ni₃P plus Ni, Ni₃P and Ni₃P plus Ni₅P₂ according to P contents at 430∼460°C. It has been found that the microhardness increases remarkably when the heat treatment of the alloys results in the formation of Ni₃P crystals. The P-K_β X-ray emission spectra of the alloys are quite different in both shape and peak position from those of pure P and resemble gradually those of Ni₃P with increasing P content. This fact suggests that phosphorus in the alloys is bonded to nickel by metallic bonds.