After nickel plating on copper substrates and tin plating on top of that, the effects of heat treatment on crystal structure, contact resistance and hardness of the double plating films were investigated. X-ray diffraction measurements showed that heating the tin/nickel double plating films at 180°C for one hour resulted in the formation of tin-nickel intermetallic compounds. The contact resistance of the double plating films increased with increasing heat treatment time at 180°C, and showed higher contact resistance than bright nickel films. In a humidity cabinet test at 60°C and 90 percent relative humidity, double plating films after heat treatment at 180°C for four hours showed lower contact resistance than did bright nickel films. The hardness of the double plating films was enhanced by heat treatment, and was greater than that of bright nickel films. The double plating films after heat treatment were similar in appearance to stainless steel, with a slightly pink color.
Soft magnetic films useful in computer memory application as the undercoating of perpendicular recording madia were prepared by electroless Ni-Fe-P plating, and optimum plating conditions were investigated in terms of the relation of plating conditions to solution stability and the composition and magnetic properties of the films. Stable conditions for electroless Ni-Fe-P plating were obtained in caustic alkaline solutions including ammonium sulfate. Fe-rich films (about 20wt% Fe) with low coercive force (Hc) could be plated from these solutions at relatively high rate.
Pit morphology under potentiostatic conditions was investigated for aluminum with (100) crystal orientation in 1.0mol dm-3 hydrochloric acid solution at 363K. The potential is considered to be an important factor in determining pit morphology. Increases in anodic potential led to an increase in the number of pits and in tunnel length, and to a decrease in pit diameter within 20C·cm-2. The transition of pit sites indicated that many pits were formed at an early stage of etching, and then deepened until a limiting length was reached. New pits did not form but the walls of ordinary pits were dissolved as a second step at a higher anodic charge, corresponding to the point of inflection of current density with time. The phenomenon in which tunnel growth stops abruptly at a limiting length seems to be associated with the increase of Al3+in the tunnel. It is considered that tunnel growth stops because the aluminum chloride at the tunnel tips saturates, causing the pitting potential to become more noble.
An effort has been made to improve the properties and specifically the permeability μ, of CoB soft magnetic films produced by electroless plating by application of heat treatment in a 2 kOe magnetic field. The optimum treatment conditions were found to be 150°C for 30min with the field applied along the hard magnetization axis of the film, and this treatment increased μ to 2000. The magnetic anisotropy field Hk decreased from 40 Oe to 8 Oe. The microstructure of films treated at various temperatures was also investigated. As-plated films consisted of fine hcp crystallite grains about 100Å in diameter, and this was retained with treatment up to 300°C. At above 350°C, fine, uniform grains grew locally and the formation of an fcc phase was detected. It is suggested that the improvement in permeability was due to an appropriately low value of Hk for the conditions at which the fine crystal grains were retained.
The crystal structure and properties of electrodeposited Pd-Ni-P alloy films were investigated. The alloy films obtained were made up of a Pd-Ni solid-solution phase and a Pd-Ni-P amorphous phase. With phosphorus codeposition, the films were found to undergo orientation transformations into the closed-packed facet of the fcc lattice and a decrease in the crystallite size of the Pd-Ni solid-solution phase. The hardness of the films increased with an increase in phosphorus content, reaching a maximum of over 1500Hv for alloys containing 60mol% Pd-32mol% Ni-8 mol% P after heat treatment at 350°C, and resulting in precipitation hardening of the Pd-Ni-P phase. The electric contact resistance of the films was less than 1.5mΩ at a load of 50g. Based on these experimental results on hardness and electric contact resistance, it is suggested that electrodeposited Pd-Ni-P alloys may be used as an alternative to electrodeposited rhodium for high-load electrical contacts.
Adhesion is one of the most important properties in the field of ceramics coating. To evaluate adhesion, the scratch test is widely used because of its easy operation. Adhesion is generally evaluated by measuring the critical load Lc, but it is well known that Lc depends on many factors such as substrate hardness. However, the dynamical meaning of Lc and the mechanism of coating failure have not been sufficiently clarified. In this study, scratch tests were carried out on TiN films applied to SKH 51 by ion plating to clarify the relationship between the modes of coating failure and the frictional force, and also some factors that influence the critical load were investigated from the point of plastic deformation. The experimental results obtained were as follows: (1) In the scratch channel, three types of cracks, partial coating loss, and overall coating loss were observed with the increase of vertical load. Partial coating failure involved oblique cracks extending from the edge of the channel. (2) Frictional force changed similar to vibration corresponding to the partial coating loss and increased rapidly corresponding to the overall coating loss. These changes of frictional force enabled the determination of critical load (the load at which partial coating loss starts to develop: Lc1, and the overall loss load: Lc2). Lc1 and Lc2 depended on the substrate hardness, while the widths of channels Wc1, Wc2 were almost same regardless of the substrate hardness. (3) Lc1 depended on coating thickness, while the critical contact angle θci, was almost same regardless of coating thickness. Furthermore, Lc1 depended on stylus tip radius R and was proportional to R1.4, while the critical contact angle θci was almost same.