This paper deals with the outline of gas boronizing methods and oxidation behavior, wear characteristics, and fatigue test of the boride layers. Formation of the double acicular boride layer consisting of FeB and Fe₂B has been achieved by use of the mixture of BCl₃ and H₂ as a boronizing reagent and by heating the specimens in a high frequency induction furnace; for the formation of the single boride layer of Fe₂B a mixture of B₂H₆ and H₂ was suitable. The eutectic structure layer of α-Fe-Fe₂B was obtained either by coating powdered boron compounds on the surface of the specimens or by producing acicular boride layers using gas boronizing method, prior to the heat treatment at the temperatures above eutectic transformation point. Infrared spectroscopic examination on the oxidation behavior of boride layers showed that the B₂O₃ phase was produced principally on the surface due to preferential oxidation of boron in the boride layer. These data show that the oxidation resistance of the boride layer at high temperatures can not be expected. The wear characteristic curves for FeB and Fe₂B layers gave similar patterns, and the wear conditions for the maximum wear rates were 0.30m/sec in sliding velocity for FeB layer and 0.50m/sec for Fe₂B layer. From the results of fatigue test, increasing tendency of fatigue strength was seen, when a transition zone was present on the matrix at the inner part of the boride layer. It was considered that the fatigue strength was affected by the microstructures of the matrix.

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SUS 304 under stress easily cracks within hours in a boiling, relatively concentrated MgCl₂ solution that is hydrolyzed to be slightly acidic. In order to improve the resistivity against stress corrosion cracking (S.C.C.) of SUS 304, the effect of surface treatments, i.e., Al hot-dipping and Al diffusion-coating on S.C.C. was studied in a boiling 42% MgCl₂ solution. The mechanism of corrosion protection was also suggested by measuring the galvanic potential and galvanic current between the surface-treated specimens and SUS 304. The resistance to S.C.C, of SUS304 was remarkably improved by the surface treatments above mentioned, and no cracks were observed for 1050 hours under the applied stress of 20kg/mm². This effect seems to be related to the following experimental facts; (1) The corrosion potential of SUS304 shifts to a less noble direction than the critical potential for S.C.C. of SUS 304 by coupling it with the Al coated specimen, (2) SUS304 is cathodically protected against corrosion as Al coating layer serves as a sacrificed anode.

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An electrolytic process of recovering metals from sludges, which are supplied to the anode compartment of an diaphragm cell and are dissolved with acids liberated at an insoluble anode, will be successfully carried out when the concentration of the metal ions in the cathode compartment is kept at reasonable values during electrolysis. For the establishment of the basic principles required for the cell design, mass transfer through the diaphragm was investigated, both theoretically and experimentally. Difference in metal ion concentration on each side of a diaphragm increased with the increase in cell current and cell depth, and with the decrease in permeability of diaphragm. A satisfactory agreement was observed between theory and experiments with a soluble anode. Consideration must be taken about the plugging of pores of the diaphragm with sludge particles in practical electrolysis. The pH control problem at the cathode compartment was also discussed.

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Some mechanical properties of titanium carbonitride films were investigated. The carbonitride films 30-120μm thick were formed on carbon steel (0.2C%) substrate in an ultrasonic field by CVD with a mixture of the reactant gases of TiCl₄, C₃H₈ (or CH₄), N₂, and H₂. Vickers microhardness (100g/load) of the TiC_xN_1-x (0≤x≤1) film surface increases linearly with the value of x in the range of 1850 (TiN) to 3600 (TiC). The TiC_xN_1-x film obtained in an ultrasonic field has an adherence strength to the substrate more than 110kg/cm², while the film obtained by the ordinary CVD tends to be peeled off by thermal shock in the cooling treatment of the specimens. Neither crack nor peeling-off of the film was observed when an impact less than 0.2kg·m was given onto the deposited surface by a falling weight of 1kg. The wear resistance of the film was measured with Ohgoshi's abration test machine and Roberts jet abrader. The TiC_xN_1-x films with the composition of x≥0.7 was found to have a strong resistance to both sliding abration by the rotary disk and jet abration by alumina powders.

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The effects of process parameters on the formation of titanium nitride and the properties of the coatings (such as hardness, morphology, crystal structure and wear resistance) have been investigated. Titanium nitride coatings were deposited on high speed steel substrates by a reactive ion-plating technique using a probe biased to positive potential. By means of charging positive potential to the probe, a reactive zone was produced above the molten titanium pool and the reaction between titanium and nitrogen was accelerated. Knoop hardness of the titanium nitride coatings formed under the condition such as probe current of 150mA, nitrogen partial pressure of 9.3×10^-2Pa and substrate temperature of 500°C, was approximately Hk 1750 with 10g load for 5μm film thickness. Titanium coatings on high speed steel showed an excellent wear resistance as compared with uncoated materials as-heat treated.

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