Autocatalytic electroless plating of tin-lead alloy film has been achieved for the first time using titanium trichloride as a reducing agent. It was possible to form bright, highly dense films with excellent solderability directly on alumina and nickel, the former with activation by palladium and the latter without. Deposition proceeded under moderate conditions of pH 7.0 and 40-70°C, employing sodium carbonate as a pH controller. Basic bath composition was [stannous chloride+lead chloride] 0.08M, disodium EDTA 0.09M, trisodium citrate 0.24M, NTA 0.10M, titanium trichloride 0.04M, and sodium carbonate for pH adjustment. The lead content of the films was arbitrarily controlled in the range of 3.0-28.0at.% by varying the lead chloride concentration between 0.001 and 0.01M. It was also observed that bath renewal and the addition of titanium trichloride to baths were effective in forming thick tin-lead alloy films.
In order to improve the abrasion resistance of thermal sprayed Ni-base self-fluxing alloy coatings, plasma-carburizing was carried out in the temperature range of the fusing treatment. The following results were obtained. 1) As a result of the fusing treatment, the pores observed in the as-sprayed coatings almost entirely disappeared and fine, uniform coatings were obtained. 2) The results of X-ray diffraction and EPMA analysis indicated that the carbide produced near the surface of the coatings by plasma-carburizing was Cr3C2 containing small amounts of Mo and Fe. 3) In abrasion wheel wear tests, the plasma-carburized coatings showed excellent abrasion resistance, almost equal to that of Cr3C2 coatings formed by high velocity flame spraying.
In the scratch test, the most commonly used method for evaluating the adhesion of thin surface coatings, the coated surface is scratched by a conical diamond indenter as load is gradually increased to the critical value Lc, at which the coating fails. As local deformation and failure occur in the material, some of the energy stored in the coating is released as acoustic emission. This paper analyzed the acoustic emissions while scratch testing high-speed tool steel (SKH 51) that was TiN-coated by PVD method. It was found that acoustic emissions were detected as an event rate signal when cracking of the coating occured, and that the average amplitude of the signals suddenly increased when chipping or spalling failure occured. It was concluded that the analysis of the average amplitude of signals was an effective means of estimating Lc, the value of which depended on the thickness both of the TiN coating and of the Ti undercoating.
Zn-7wt%Cr alloy was electrodeposited from an acidic sulfate bath consisting of Zn, Cr and organic additives. Studies of the structure of the plating layer by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and transmission electron spectroscopy (TEM) indicated that it consisted of metallic Zn, Cr, a small amount of Cr oxide and 0.015 wt% of carbon. XRD pattern obtained from the plating layer showed a broad peak around 2θ=40 degrees. The crystallite size as determined by TEM was 5-20nm. It is concluded that the plating layer consisted of fine crystallites of Zn-Cr alloy phase, whose structure was uncertain. This alloy recrystallized at 195°C and changed into a regular crystal structure 20-50nm in size. The melting point of the alloy was 452°C, which is not same as the melting point of θ-phase Zn-4.7wt%Cr alloy in the Zn-Cr alloy phase diagram.
Steels electroplated with Pb-Sn alloys are generally used as a solderable outer package materials for electrical machinery. Solderable electrogalvanized steels have been developed as a replacement of such steels. This paper reports various post-treatments for electrogalvanized steel that resulted in both good solderability and good corrosion resistance, and the soldering mechanism is discussed. A large number of post-treatment solutions containing surfactants, waxes and corrosion inhibitors were prepared and coated on the steel. The addition of a styrene-maleic acid copolymer and a wax to a post-treatment solution that contained a phosphoric acid ester and CrO3 increased corrosion resistance without decreasing solderability. In terms of the soldering mechanism, it is assumed that the Zn layer elutes into the soldering bath so that while small amount of zinc remains in the layer, the major portion is concentrated on the solder surface.
Investigations were conducted to determine optimum bath compositions for the anodizing of aluminum, and the properties of the coatings obtained were investigated using organic (choline-fluoride base) alkaline baths containing ammonium fluoride and organic acid salts. In the anodizing of aluminum in baths containing organic acid salts ((NH4)2C2O4, (NH4)2C4H4O6 and (NH4)3C6H5O7) uniform films were obtained, but in baths without these additives and with added ammonium acetate, non-uniform films were formed. The thickest films (about 15μm) were formed by anodizing for 30min at 20°C at a current density of 2A/dm2 in 0.2mol/L cholins solution containing 0.2mol/L ammonium fluoride and 0.1mol/L ammonium tartrate or in 0.2mol/L choline solution containing 0.1mol/L ammonium fluoride and 0.2mol/L ammonium citrate. The film formed in 0.2mol/L choline solution containing 0.3mol/L ammonium fluoride and 0.1mol/L ammonium oxalate showed a high hardness (about 28 in Marten's scratch hardness test, load 50gf) and high corrosion resistance. It was found by SEM observation that pores of films prepared in baths containing ammonium citrate were about 50∼100nm in diameter, while those prepared in baths containing ammonium oxalate measured only about 40nm.
Plasma-carburizing treatment of powder metallurgy chromium was carried out and the following results were obtained. 1) X-ray diffraction analysis showed the formation of Cr3C2, Cr7C3 and Cr23C6. 2) Cr23C6 was formed in the surface at the early stages of the carburizing process, but Cr7C3 and Cr3C2 were formed as treatment proceeded. 3) The thickness of the carbide layer was proportional to the square root of treatment time