Ni-B Coatings Research Articles

無電解Ｎｉ‐Ｂ‐Ｇｒａｐｈｉｔｅ複合めっき皮膜の作製とその特性

Composite coatings of graphite particles codeposited to an electroless Ni-B matrix obtained from the bath using dimethylamine borane (DMAB) as the reducing agent were produced, and the physical properties of the coatings were studied. It was possible to obtain composites containing up to 5.5wt% of graphite particles. The hardness of the coatings decreased with increasing graphite content. Ni-B-graphite composite coatings were found to have good self-lubricating properties and their contact resistance was as low as that of Ni-B coatings.

Laser-induced prenucleation of alumina for electroless plating

This paper deals with the deposition of palladium from decomposition of a thin palladium acetate layer on rough and porous alumina ceramic surfaces by irradiating it with a UV excimer laser. The palladium acetate layer was formed from a combination of propyl glycol methyl ether acetate solvent and photoresist, and the undecomposed material was removed with the photoresist remover. The discontinuous palladium cluster film formed by the technique was used as seed for electroless coatings. Different patterns were obtained using point focus as well as projection pattering method and subsequently plated with adhesive layers of electroless Ni-B coatings.

Three-dimensional quantification of wear tracks on amorphous NiB coatings

The early stage of the wear process can be best investigated by means of three-dimensional profilometry. This allows not only maps to be made but also wear rates to be quantified. Linear, surface and volumetric parameters are given. An application to the wear resistance of amorphous NiB coatings (thickness, 10 μm; 26 at.% B) on iron substrates was performed. Dry sliding friction tests are carried out using a pin-on-disc system. Two specific types of behaviour (viscoplastic and plastic) are exhibited before seizure occurs.

The oxidation of electroless Ni-B and Ni-P coatings in air at 800 to 1000�C

The oxidation of electroless Ni-B coatings in air at 800 to 1000°C has been determined by kinetic, X-ray diffraction, and microscopical methods. Some data have also been obtained on the oxidation of Ni-P coatings, the oxidation of nickel, and the effect of Na2SO4 on the oxidation process. All kinetics followed the parabolic oxidation law and the rate increased in the order spectrographically pure nickel, commercially pure nickel, Ni-B, and Ni-P, with the Ni-P oxidizing approximately 1000 times faster than the spectrographically pure nickel. Fine surface deposits of Na2SO4 greatly increase the oxidation rate of all materials except the Ni-P coatings which appear to be immune to hot-corrosion. The nature of the oxidation processes are discussed.

Passivation and pitting of electroless nickel surface coatings

Commercial electroless nickel coatings containing nominally Ni-0.25%B, Ni-10%P and Ni-11.5%P-1%Cu were tested potentiodynamically and examined with a microscope to determine the effect of heat treatment and chloride ion concentration on the passivation and pitting behaviour in 10 vol.% H 2SO 4. All the electroless nickel coatings had inferior corrosion and pitting resistance compared with commercial nickel. Precipitation hardening or chloride ion concentrations up to 0.005 M did not significantly influence the corrosion. Combined precipitation hardening and the presence of chloride ions greatly increased the corrosion and pitting. The Ni-B coatings had a much higher resistance to corrosion and pitting than the Ni-P coatings had.

ジメチルアミンボランを用いる化学ニッケルめっき浴におけるモノカルボン酸塩ならびに硝酸タリウムの効果

The mode of action of monocarboxylates and thallous nitrate in the chemical nickel bath was investigated. The monocarboxylates act as a buffer in the bath, and the buffering action increases in the following order; Propionate>Acetate>Formate. On the other hand, the internal stress of Ni-B coatings was decreased with the co-deposition of Tl, and the deposits gave rise to crack-free bright surface. The deposition rate of Ni-B coatings wasconfirmed to be about 5μm h-1 for formate bath and 10μm h-1 for acetate and propionate baths. The anodic oxidation of dimethylamine borane is inhibited strongly in the presence of formate to give the smaller deposition rate in the former bath. The fact that the lower pH gave the slower deposition rate of Ni-B coating and the higher rate of hydrogen evolution was fully explained by the analysis of partial cathodic and anodic polarization curves on the basis of the mixed potential theory.

Some data on the mechanism of the liberation of hydrogen and the microstructure of chemically reduced Ni-B-H alloys

1. The hydrogen content in chemically reduced Ni-B coatings is ≈0.02%, regardless of the amount of boron in the alloy. 2. The rate of evolution of hydrogen during the heating of the coatings is related to the structural-phase transformations that occur in them. 3. A comparison of the data on the evolution of hydrogen with thermographic data gives a basis for believing that the hydrogen contained in the coatings is partially present in the atomic state, partially in a protonated state. 4. The laminarity detected for certain coatings is considered as a consequence of a periodic variation in the ratio of the rates of reduction of nickel and boron, which are inversely dependent on the acidity of the medium.