Electroless Ni-Pon the Bulk Nanocrystalline Ingot Iron
|Course||Physical and chemical|
|Keywords||bulk nanocrystalline ingot iron Ni-P plating crystallization corrosion resistance binding energy|
Bulk nanocrystalline ingot iron (BNII) was produced from conventional polycrystalline ingot iron (CPII) by the severe rolling technique.Electroless nickel-phosphorus (Ni-P) is a technique for solid surface treatment. It has been adopted as representative chemical plating and widely applied in industry. Electroless Ni-P using sodium hypophosphite as a reducing agent, therefore the nickel ion is reduced directly on the catalytic reducting surface of the substrate from Ni-plating solution, and phosphorus is co-deposited simultaneously. Thus chemical Ni-P plating is performed.In this paper, high phosphorus (Pwt% 11%-13%) amorphous plating was obtained by optimum Ni-P electrless plating process at high temperatures of 88℃The acidity of the plating solution was controlled as 4.4-4.5 in pH with a buffer solution. Characterization of nickel-phosphorus plating including the structure and morphology, porosity, hardness, bonding strength, and corrosion resistance properties was made by using scanning electron micrograph, X-ray diffraction analyzer, X-ray photoelectron spectroscopy, metallographic microscope, hardness tester, chi660c electrochemical workstation equipment, respectively. The deposition mechanism of electroless Ni-P on BNII and CPII was studied, and improvement of electroless Ni-P plating on BNII was expected.The experimental results indicated that the prepared Ni-P plating has excellent gloss smoothness, zero porosity, and nice binding force. The thickness of the Ni-P plating was 24±1μm. The hardness was increased from HV 506 at the very beginning of chemical plating to HV 936 after treating at 390℃for 1h. The structure of Ni-P plating is amorphous at room temperature. A crystallized structure with two-phase Ni and Ni3P could be formed at elevated temperatures. The crystallization temperature of the plating on BNII was 340℃, and the melting point was about 883℃. According to the Tafel polarization analysis,in 5% NaCl and in 0.5 mol/L HCl solutions, the corrosion potential Ecorr of BNII with the plating is 216 mV and 197 mV higher than that without plating, respectively; The corrosion potential Ecorr of CPII with the plating is 50 mV and 118 mV higher than that without plating, respectively; Meanwhile, corrosion current density icorr of BNII with the plating (1.303×10-5 A/cm2,4.215×10-5 A/cm2, respectively) are obviously lower than those of BNII without plating (1.303×10-5 A/cm2,1.326×10-4 A/cm2, respectively).According to the X-ray photoelectron spectroscopy, the binding energy of the earlier plating was increased in 0.9 eV for P 2p3; decreaded in 0.1 eV for Ni 2p3 and 0.3 eV for Ni 2p1; decreased in 0.2 eV for Fe 2p3 and 0.4 eV for Fe 2p1, respectively, by comparing the results obtained from BNII plating with those from CPII plating.