β-type titanium alloys are a kind of age hardened alloys and are well known for easy working as well as for high specific strength and corrosion resistance. To take advantage of these properties, a large number of β-type alloys have been investigated and many are in practical use today. Titanium alloys, however, are inferior in terms of wear, abrasion and galling, and it is hoped that these problems may improved by surface hardening. In this investigation, Ti-15Mo-5Zr-3Al alloy, a β-type titanium alloy was ion-nitrided during solution treatment, and then aged. This method resulted in increased surface hardness due to the nitriding, and increased hardness in the bulk due to the aging. A TiN phase, not more than 2μm was observed by optical microscopy, and was comfirmed by X-ray diffractometry.
Studies were made on the growth of nitride layers produced by ion nitriding of aluminum at pressures of 1.4∼3.8Torr and temperatures of 400∼550°C. It was found that the formation of nitride layers and the sputtering of the formed layers by nitrogen ion bombardment proceeded simultaneously. This sputtering effect was more marked at lower nitrogen gas pressures and temperatures, and therefore the nitrogen gas pressure and nitriding temperature influenced the growth rate and morphology of the nitride layers. The growth rate increased at higher temperatures and lower nitrogen gas pressures. The reaction kinetics on the growth of the layers was represented by a linear relationship.
Effects of anion species and the pH of Ni salt solution on the microstructure and electric resistivity of an Ni film prepared by an electroless plating method were examined by SEM, XRD, Hg porosimetory, BET surface analyses and resistometory. Because they were made up of uniform microparticles, Ni films prepared from NiSO4 solutions gave the largest specific surface area, the lowest pore radius and the lowest specific resistivity, while those prepared from NiCl2 and Ni(NO3)2 did not give good results due to the fact that their Ni particles were segregated and large, and had low crystallinity. Ni films prepared from a pH 5 solution of NiSO4 gave the largest specific surface area and the lowest specific resistivity, owing to the uniformly grown Ni particles. Ni films prepared from NiSO4 at pH 5 were thought to be the most suitable material for electrodes.
The effects of asymmetric sine-wave current plating on gold deposition have been studied using electrographic tests for porosity and accelerated environment tests. Comparison of the porosity of the deposit with that of a plate deposited under DC current indicated that an asymmetric sine-wave decreased porosity by more than 50%. A salt spray test showed that salt water resistance was improved. Frequencies of 1kHz or less were effective in decreasing porosity and improving resistance, the anodic current of the sine-wave increased the porosity and enlarged the crystal size of the deposits. The implications of these observations relating to the porosity-decreasing mechanism are discussed and compared to those of pulsed current plating.
The orientation and microstructure of nickel electrodeposits are affected by the conditions of electrolysis. This study considers the effects of hydrogen on crystal structure and hardness of electrodeposited dull nickel. Dull nickel films were electrodeposited from a Watt's bath under excess current density such that hydrogen generates positively, and their crystal structure, hardness and hydrogen content were investigated. The results are summarized as follows. (1) The preferential orientation changed from (200) to (220) under excess current density. (2) The hardness of the nickel films changed with current density, and a correlation was found between hardness and morphology. (3) The hydrogen content of the nickel films increased with current density, but no correlation was found between hydrogen content and hardness.
The hydrogen permeation current of steels was measured during zinc electroplating using baths of zincate, zinc chloride-ammonium chloride and zinc sulfate. Shortly after the start of electroplating, the zinc chloride-ammonium chloride bath showed higher hydrogen permeation current than the other baths because of its low pH due to a large amount of NH4Cl, but after 40 minutes it showed lower permeation current than the zincate bath, because there were few pin holes. The zinc sulfate bath showed lower hydrogen permeation current than the other baths. With 40 minutes of electroplating using the zinc chloride-ammonium chloride bath, the quantity of permeated hydrogen was lower than with the zincate bath. The quantity of permeated hydrogen in the zinc sulfate bath was almost the same as in the zinc chloride-ammonium chloride bath.
To elucidate the mechanism of corrosion inhibition of mild steel by polyphenol compounds (gallic acid, tannic acid, etc.), the action of gallic acid (GA) in neutral solution was investigated by physicochemical methods. While GA had a corrosion inhibiting efficiency of about 99% in air, it had no such action in an oxygen-free atmosphere. Electrochemical measurements showed that GA was a cathodic inhibitor and various other methods demonstrated that it was an absorption (type II) inhibitor rather than an oxygen scavenger (type I) inhibitor. As for the mechanism of GA corrosion inhibition, it is thought that i) GA molecules are electrostatically attracted to the steel surface by the φ-potential theory, ii) GA molecules adsorb physically and chemically on the surface, and iii) an adsorption layer like a membrane forms on the surface to inhibit the corrosion of steel.
The effect of Ca hardness on the pitting corrosion of copper in open cooling systems that contain an inhibitor in the cooling water such as nitrilotris methylene triphosphonic acid (ATMP), benzotriazole (BTA), or sulfate of zinc (ZnSO4) has been investigated by immersion tests and electrochemical measurement. It was found that pitting corrosion occurred with difficulty when Ca hardness increased from 10 to 100. There was a close relationship between the electrochemical properties of corrosion potential after immersion for 420h ECORR/breakdown potential Eb and the occurrence of pitting corrosion in copper, such that occurred with difficulty when Eb≥ECORR.
The average thickness of the diffusion layer in composite deposition was studied by means of atomic absorption analysis of the cadmium content of deposits obtained as zinc-cadmium alloy from a zinc sulfate solution containing both suspended α-alumina particles and 10-3mol/dm3 cadmium sulfate. Plating was performed using a circular coplanar concentric cell consisting of a copper cathode 36cm2 in surface area around a columnar zinc anode, under stirred conditions. Use of this cell resulted in superior reproducibility of the α-alumina particle content of the deposits and in uniformity in their appearance. Average diffusion layer thickness decreased with increasing stirring velocity until the solution began a whirlpool flow, and was independent of the concentration of the α-alumina particles suspended in the plating solution at constant stirring velocity.
The effects of two kinds of nickel substrate on the average strain in a substrate that has been self-deformed by hydrogen absorbed during hydrogen evolution in a sulfuric acid solution, and on the average strain in a chromium film plated from a conventional chromium plating bath were investigated by an electric resistance wire type strain gauge setup on the reverse side of the substrate. One substrate was a nickel sheet with a preferred (220) orientation as received and the other was a nickel film with a preferred (200) orientation deposited on a copper sheet from a Watts bath. It was found that: (1) In the cathodic electrolysis of the sulfuric acid solution, the overpotential for hydrogen evolution on the commercially available nickel sheet was always smaller than that on the nickel film deposited from the Watts bath, and the compressive strain deformation of the substrate by absorption of hydrogen was larger in the commercially available nickel sheet than in the substrate with the deposited nickel film. (2) For the commercially available nickel sheet, the time variation in the strain deformation of the substrate in cathodic electrolysis of sulfuric acid solution was quite similar to that of the substrate in chromium plating. (3) For the nickel film substrate as deposited, the time variation in the strain deformation of the substrate in cathodic electrolysis of sulfuric acid solution was different from that of the substrate in chromium plating. As a substrate for chromium plating, the nickel film deposited from the Watts bath was superior in current efficiency to the commercially available nickel sheet.