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Abstract

Electroless nickel-phosphorus deposits with 5-8 wt% P and 3-5 wt% P were analysed for the effects of continuous heating on the crystallization kinetics and phase transformation behaviour of the deposits. The as-deposited coatings consist of a mixture of amorphous and microcrystalline nickel phases, featuring in their X-ray diffraction patterns. Continuous heating processes to 300• C-800• C at 20• C/min were carried out on the deposits in a differential scanning calorimetric apparatus. The subsequent X-ray diffraction analyses show that the sequence of phase transformation process was: amorphous phase + microcrystalline nickel → f.c.c. nickel + Ni 3 P stable phases. Preferred orientation of nickel {200} plane developed in the deposits after the heating processes. Differential scanning calorimetry of the deposits indicates that the crystallization temperatures increased with decreasing phosphorus content, and increasing heating rate. Crystallization activation energies of the deposits (230 and 322 kJ/mol, respectively) were calculated using the peak temperatures of crystallization process, from the differential scanning calorimetric curves at the heating rates ranging from 5 to 50• C/min. It was found that the deposit with lower phosphorus content has higher activation energy. C 2002 Kluwer Academic Publishers

Enhancement of Corrosion Resistance of NiCrFeBSi Coatings Obtained by Flame Thermal Spray Process Adding an Electroless Nickel Coating Ni-P

“…Figure 5 confirms that the electroless nickel deposit follows the contour of the flame thermal spray coating, thereby enabling a "sealant" action which undoubtedly is effective, resulting in a decrease in the effect of porosity and helps to reduce the risk of corrosion. Figure 6 shows a sample of one of the spectra obtained from electroless nickel deposits in which it can be seen that in these coatings the P content is above 9% by weight, which would be in agreement with the approach that would be expected to be amorphous, and which has been reported in other works [16] [17] [18] [19]. Figure 7 shows a EDS spectrum of one of the coatings generated by flame thermal spray process of the NiCrFeBSi combination.…”

“…It should also be noted that of the coated parts, those coated with the NiCrFeBSi layer are the ones with the highest corrosion rate (2.65 mm/year), which is considered associated with the porosity of the coating. Re-lated to the electroless nickel plated sample, results (0.86 mm/year) confirm its good qualities as a corrosion resistant coating, which is linked to its predominant amorphous condition as a function of the P content, as reported in other studies [16] [17] [18] [19]. Corrosion rate is higher than found in other papers such as [16] in which an aluminum alloy was coated with an electroless NiP coating (11% P) and evaluated by electrochemical tests in a solution such as the one used in this work, where a corrosion rate of 0.08 mm/year is reported.…”

“…This due to the possible variation of the microstructural condition of the electroless nickel deposit, which initially, depending on its content of P, could be expected to be amorphous and that the heating associated with the flame thermal spray process could modify, to some degree, towards a partial or total crystallinecondition, and as result less corrosion resistance, as stated in [16] [17] [18] [19].…”

Effect of laser‐induced nanocrystallisation on the properties of electroless Ni‐P/Ni‐W‐P duplex coatings

“…The incomplete crystallisation was also reported in Ref. [22,23] for an electroless Ni-P (3∼16 wt.%) deposits treated by continuously heating at the rates of 5…”

“…The maximum load applied was 50 mN, and the distance between any two neighboring indentations was 5 μm and counting 10 indentations along the cross section. The unlubricated friction and wear experiments for individual Ni-P and Ni-W-P coatings before and after laser treatment were performed under the ambient laboratory condition (22 • C, 45% relative humidity) using a pin-on-disk tester with a high carbon -high chromium steel ball of 4 mm in diameter and 65 HRC in hardness as a counterpart. Duration of the wear test was limited for 30 min at a normal load of 20 N and a rotational speed of 200 rpm (with the circular track of diameter of 5 mm).…”