Tomoya Minegishi

Surface modification of electrodeposited chromium films by ion implantation

Abstract Electrodeposited chromium films implanted with nitrogen and argon ions were characterized by surface analysis, surface hardness, wear, and corrosion. Depth profiles were examined by Auger electron spectroscopy and the chemical bonding state was estimated by X-ray photoelectron spectroscopy. The near-surface hardness of nitrogen-implanted chromium was measured with a Vickers microhardness tester and a dynamic ultramicrohardness tester. Wear tests were carried out using an Ohgoshi rapid wear-testing machine and a Taber abrasion test apparatus. The corrosion resistance was investigated by the electrochemical method of cyclic voltammetry in 0.05 M H 2 SO 4 . The following results were obtained. 1. (1) Nitrogen implantation caused the surface hardness to increase. 2. (2)NNitrogen-implanted chromium showed a remarkable wear resistance. 3. (3) The corrosion resistance of chromium was improved markedly by nitrogen implantation. 4. (4) Nitrogen depth profiles showed definitely that there were two peaks. 5. (5) Depth profiles and measurement of chemical bonding showed that the implanted nitrogen combined with chromium to form Cr 2 N.

Structure and mechanical properties of internally hydrided Mg-IIIa transition metal alloys

Magnesium alloys containing IIIa transition metals, such as Sc, Y and Ho, respectively, were hydrogenated at 773 K and examined for microstructure, X-ray diffraction pattern, micro-Vickers hardness, and tensile properties at room and high temperatures. Results obtained are as follows:1.The alloys, respectively, have been internally hydrided and have precipitated hydrides of the IIIa transition metals as small flake-like particles in the matrix and at grain boundaries, as well as twin boundaries.2.The dispersed hydride particles do not necessarily contribute to further hardening of the alloys at room temperature and up to near 673 K.3.However, the dispersed particles are very stable and seem to improve mechanical properties of the alloys above 673 K.4.Presumed relationships of crystallographic coincidence between the matrix and hydrides have been obtained.

Electric field-assisted and field-depressed segregation of reactive metals to the bonding interface in braze alloy joining

Segregation of reactive metals at the bonding interface has been observed in various ceramic and/or metal joints bonded with reactive metal-bearing braze alloys. When a d.c. of 20 mAcm−2 is applied to the ceramic/braze/ceramic system at a brazing temperature of, say, 1373 K, the electric field assists the segregation at the braze-ceramic interface on the cathode side and suppresses the segregation at the interface on the anode side. This may imply that reactive metal atoms in the braze can migrate as a cation. E.m.f. measurement on the ceramic (AIN or ZrB2)-metal foil systems with increasing temperature shows that a negative e.m.f. to the ceramic pole appears from about 900 K for AIN and from 500 K for ZrB2, as does the thermally stimulated current in polymers. These temperatures coincide well with those where the electrical conductivity of AIN and ZrB2, respectively, begins to increase with increasing temperature. Therefore, it is considered that the polarization of the ceramics may take place and assist the migration, and consequently segregation, of reactive metals in braze alloys to the braze-ceramic interface during brazing.

Special issue "Magnesium and magnesium alloys". Preparation of porous sintered compacts by mixing magnesium powder in the green state.

Being mixed with magnesium powder by up to 50%, 304 stainless steel and titanium powders were compacted under various compacting loads, respectively, and then the green compacts were sintered in a vacuum of 10-2Pa, finally at 1375K where magnesium can be vaporized completely. The sintered compacts were examined as to density, compressive strength and structure. The density and compressive strength decreased with increase in the amount of magnesium powder added to the green compacts, as well as decrease in the compacting load. The process was applied to make sintered ZrNi compacts capsulated with porous sintered stainless steel compacts. Sintered titanium and nickel compacts with a graded porosity distribution were also prepared, respectively.

Experiments on Chromium Plating Bath of Fluosilicates

A chromium plating bath principally composed of chromic anhydride with a large content of fluosilicate (K2SiF6 of 3-55g/l) was studied with respect to the current density.The following results were obtained:(1) The solubility of potassium fluosilicate in chromic acid solution was increased by means of preliminary electrolysis.(2) In the electrolysis for an extremely short time, the current efficiency was always higher than that of the Sargent Bath. However, the efficiency was above 50% on the side of higher temperature and higher current density.When the time for electrolysis was longer, it was difficult to maintain such a high current efficiency, but the efficiency was likely to be higher than that of the Sargent Bath.(3) This plating had a wider range of brightness than the Sargent Bath. Burnt deposits were not produced in this plating even under a high current density as 200amp./dm2.