Various compound layers composed of nitride (Fe-N, Cr-N), carbide (V-C, Cr-C) and boride (Fe-B) were formed on the surface of steels by surface hardening treatments. Influence of temperature on the hardness of various surface compound layers has been investigated in the present paper. A low carbon steel (S 15C) and an alloy tool steel (SKD61) were used. The following conclusions have been obtained. The values of hardness of the compound layers were about Hv 800 for Fe-N (Fe_3.2N, Fe₄N), about Hv 1200 for Cr-N[(Mn, Cr)₃N], about Hv 1600 for Fe-B (Fe₂B), about Hv 2600 for Cr-C (Cr₇C₃, Cr₂₇C₆) and about Hv 3200 for V-C (VC), respectively. The values of hardness of compound layers of Fe-N and Cr-N at 400°C were about Hv 550 for Fe-N and about Hv 900 for Cr-N. However, the hardness values rapidly decreased at elevated temperatures over 400°C and coincided with those (about Hv 50 for S15C, about Hv 200 for SKD61) of the steels at 800°C. Compound layers of Fe-B, Cr-N and V-C kept comparatively higher hardness values even at elevated temperature. For example, the hardness values at 800°C were about Hv 700 for Fe-B, about Hv 1200 for Cr-C and about Hv 800 for V-C. The hardness of a Cr-C compound layer at elevated temperature had much higher values than those of the other compound layers.

抄録全体を表示

Electrolytic coloring of anodized aluminum is attained by electrodeposition of Cu, Ni and Sn etc. on the surface of micropores of anodic oxide films in an appropriate aqueous solution. The deposition of the metals requires an electronic current to flow across the barrier layer. A method useful for detecting the electronic current through the barrier layer is to employ an Al-Mn (1%) alloy as the base metal on which thin Al₂O₃: Mn phosphors have been formed by anodization, and the anodic films emitt yellow electroluminescence (EL) due to the collision excitation of Mn activator by accelerated electrons in the films. The EL intensity has been almost proportional to the electronic current which plays an important role on the metal deposition. The electronic current, however, occupy only a small portion of the total current applied. The Al-Mn (1%) alloy was anodized in 1mol/l sulfuric acid bath at 18°C, and 300A/m² for 12min., and then transferred to a coloring bath containing 0.12mol/l CuSO₄+0.31mol/l H₂SO₄ and electrolysed with rectangular AC current of varying frequencies (10-1000 Hz). From the frequency dependence of the EL intensity, 100 Hz gave the maximum EL intensity, while the best frequency for the electrolytic coloring was found to be ca. 1000 Hz at which spalling was markdly suppressed. Under applied voltages less than 8V, neither EL nor coloration occurred for the specimens. From 8 to 17V, EL appeared with slight gas evolution and reddish brown coloration. The deepness in color shade was proportional to the EL intensity. In applied voltages over 17V, many bright spots appeared and local break-down of the oxide films so called “spalling” occurred.

抄録全体を表示

Effects of small amounts of copper and oxygen in water on the local cell polarization curve of high purity zinc were studied. Further, the formation of local cells was examined as functions of degree of heterogeneity of the metal surface, and the amounts of dissolved copper and oxygen, especially by observing the microscopic structure of deposited copper. When water is deaerated, corrosion of zinc is controlled by the rate of supply of copper ions which act as oxidizing agent, and copper deposits are observed to occur at the surrounding areas of the surface defects. When not deaerated, the corrosion rate of zinc appears to be determined by the reduction of dissolved oxygen on the copper deposits, and copper deposits directly on the surface defects. This was observed for a copper concentration of 5mg/l. It was found that dissolved oxygen accelerates the corrosion when the copper concentration is below 0.5mg/l but acts to inhibit the corrosion at copper concentrations above 5mg/l.

抄録全体を表示

Crack-free iron-molybdenum alloy coating having a micro-vickers hardness of a bout 450 and a light black hue has been electroplated onto mild steel substrates at cathodic current densities of 1-1.5A/dm² and at 35°C. The optimum electrolyte composition was found to be 0.26mol/l Na₃C₆H₅O₇, 0.12mol/l Na₂MoO₄, and 0.14mol/l of FeSO₄ at pH 4.0 adjusted with dilute H₂SO₄. The alloy composition exactly corresponds to Fe₃Mo. Transmission and reflection electron diffraction patterns of the alloy showed an amorphous structure but the surface was found to be crystallized. Three kinds of the alloy plating baths in which sodium or potassium concentration is kept constant at two different levels have been prepared for the analysis of the current-potential characteristics. In addition, the catholyte pH was directly measured by using an antimony microelectrode. It was found that the electrodeposition involves a cycle of electrolytic reduction-reoxidation by the sodium, potassium and molybdenum ions. It was also revealed that sodium and potassium atoms form a layer on the electrode to protect the electrode surface from the reoxidation of electrolytically formed lower oxide of molybdenum. This provides a good explanations for the previously reported characteristics of the induced molybdenum codposition.

抄録全体を表示

An electroless nickel deposit on glass has been studied to use as a micro-pattern. For this purpose, metal to glass adhesion and the surface smoothness is substantially important. Good adhesion strength between glass and the deposited nickel obtained by immersing the glass in a the conventional chromic-sulfuric acid etching solution and by treating with sodium hydroxide solution. A high levelling nickel deposit was also obtained by using sodium citrate or ammonium citrate as a condition complexing agent in the electroless nickel bath. The optimum etching composition and operating for the production of micro-patterns were found to be 8% HNO₃-70% H₃PO₄-22% H₂O, temperature: 25°C, etching time: 5-7min.

抄録全体を表示