The stability of shape memory characteristics in thermal cycling was investigated for Ti-50at.%Ni and Ti-52at.%Ni thin films prepared by r. f. sputtering and annealed for 1h at 773K. The transformation temperatures measured by differential scanning calorimetry indicated less sensitivity to thermal cycling in the Ti-52at.%Ni film than in the Ti-50at.%Ni film. The stability of the shape memory effect was evaluated using a small tensile tester. Under a stress of 120MPa, 100 thermal cycles caused the martensitic and reverse martensitic transformation temperatures of the Ti-50at.%Ni film to decrease by 10 and 20K, respectively. However, the reverse martensitic transformation temperature of the Ti-52at.%Ni film remaind constant, and its martensitic transformation temperature decreased by 5K after the first 20 cycles but then remained constant owing to a training effect. The transformation strains of the films remained constant throughout the thermal cycling. Plastic strain was not observed in the Ti-52at.%Ni film, while in the Ti-50at.%Ni film it varied from 0.4% to 0.03% with thermal cycling. These results, showed that the Ti-52at.%Ni film had highly stable shape memory characteristics against thermal cycling.
The aim of this experiment is to determine the best conditions for spraying WC-Co layers on steel plates (JIS SKD 11) by a Low Pressure Plasma Spray (LPPS). It is found that an appropriate amount of spraying heat at which the compact layers will be coated but the WC in the layers will not be decomposed, is necessary to coat the steel plates with good quality WC-Co layers. The obtained spraying parameters to satisfy the necessary conditions mentioned above are chamber pressure of 6.7×103 Pa, spray current of 500A, spray distance of 400mm, Ar gas flow rate of 50L/min and H2 gas 10L/min. A wear test is carried on samples sprayed under the obtained parameters and compared with untreated steel plate, hard Cr coating, and TD treatment. The wear resistance of the sprayed steel plate is much better than that of the untreated steel plate, and it is found to be superior to hard Cr coating and equivarent to TD treatment in a test of long distance wear.
Polymer/Liquid Crystal (LC) composite films are expected to find application of display materials. Observation and control methods for the morphology of polymer/LC composite films are presented here on the basis of experimental results. Morphology can be controlled by the polymer surface conditions and can be observed by scanning electron micrography (SEM), light scattering and polarizing microscope.
The electrodeposition of chromium from divalent chromium based baths has not been thoroughly investigated, due to the highly transient and unstable nature of Cr (II) ions. The electrodeposition of chromium from a variety of divalent chromium baths was examined to establish conditions suitable for chromium plating. Divalent chromium baths were prepared by electrolytic reduction of aqueous Cr2(SO4)3 solution using a titanium cathode. Lustrous chromium deposition was obtained by electrodeposition at a cathode potential of -1.1V vs SHE, using aqueous 0.8kmol m-3 CrSO4 -2.0kmol m-3 KCl-0.1kmol m-3 HCOOH (pH 1.8). For 30min of deposition, the average current efficiency for chromium deposition was 25.4%. The average deposit thickness was 10.8μm. The HCOOH concentration suitable for chromium deposition from divalent chromium baths, is much lower than that from trivalent chromium bathes. The main role of the organic acid is to control the pH in the vicinity of the cathode surface.
Gold wire bondability of non-cyanide electroless gold plating using disulfiteaurate complex was investigated. Generally, printed wiring boad is fabricated by subtractive or additive process. After fabricate the circuits, contact or terminal areas were usually coated with nickel and gold for maintaing reliability between printed circuit and another electrical functional parts. Usually, diluted palladium solution is adopted to initiate electroless nickel plating on a copper circuits. However, selectivity of nickel deposition on a resin based copper circuits is not good enough by treatment diluted palladium solution as an activator. Selectivity was greatly improved by treatment with strong reducing agents such as SBH, DMAB or TMAB. Bondability was greatly influenced by the contents of phosphorus in the deposited nickel. Gold crystal orientation was also affected by the gold wire bonding, and high bonding strength was obtained with (220), and (311) preferred oriented electroless gold films.
Granular tin pre-coating was applied to improve the weldability of electrolytic chromium coated steel sheet (TFS-CT). Granular tin was easily obtained using a ferrostan bath with no additives and low current density. The size of tin granules was 0.5∼1.0μm in diameter and about 1.0μm in height. The contact resistance of TFS-CT decreased remarkably with pre-coating of granular tin and the range of available welding current was wider than with lightly tin coated steel sheet (LTS). The characteristics of granular tin pre-coated TFS-CT, such as lacquer adhesion, corrosion resistance, sulphur blackening and surface lightness, were the same as for TFS-CT. The lubrication of granular tin particularly reduced the coefficient of dynamic friction, to one half that of TFS-CT, about the same value as for tinplate.
The structure and the formation mechanism of surface oxide films grown on magnesium die cast AZ91D have been studied. The substrate surface after chemical etching shows grains of Mg solid solution matrix of several μm in size with Mg17Al12 compound at grain boundaries, large and small voids, and cavities between the grains. The film surface after chemical conversion coating has a granular structure, with each granule corresponding to a single grain. Direct cross sectional observation revealed that the film was formed by anodic reaction and had a porous cell structure which was separated from the substrate by a thin barrier layer at the film/metal interface. The porous film is composed of cell colonies in the sub-micron range that have branched fine pores, with central holes (mother pores) sized approximately 50nm. Square shaped holes about 300nm in size observed on the film surface are believed to be cathodic sites.
The structure and the growth mechanism of anodic oxide films grown on magnesium die cast AZ91D have been studied by electron microscopy combined with an ultramicrotomy technique. The anodic films are highly uneven in thickness. This may have been caused by film destruction resulting from breakdown accompanied by gas evolution, and also by uneven anodic reaction owing to the presence of cavities and compositional irregularities at the grain boundaries. Porous cell structure with dispersed MgF2 and NaMgF3 crystalline particles is found in the films. It is assumed that anodic film growth proceeds by the formation of MgF2 and magnesium oxyhydroxide at the metal/film interface and the dissolution of the film at the pore bases. The crystallization of MgF2 and the formation of NaMgF3 subsequently proceed in the porous layer.
Noting the rust stabilizing effect of phosphate anions (PO43-) on weathering steels, we developed a rust stabilizing surface treatment that consists of phosphoric acid, iron oxide and polyvinyl butyral resin (PVB). The following results were obtained after long-term atmospheric exposure of weathering steel treated with the technique. (1) Iron ion outflow occurred with vigor in untreated (bare) specimens, but was highly suppressed in treated specimens. The treatment causes significant reduction of rust pollution from weathering steel structures which occurs during initial atmospheric exposure. (2) After long-term exposure in the atmosphere, the treated layer transformed into a mixed layer containing rust. Viewed through a polarizing microscope, an extinction layer (containing Cr, Cu and conspicuous P enrichment) could be clearly observed at the boundary with the steel. (3) Through reaction with the phosphate ions in the treatment agent, the steel interface contained phosphates and the treated film contained a large amount of chromium phosphate and zinc phosphate. It is thought that these phosphates contribute to the suppression of the iron ion outflow and to the growth of the extinction layer (which is thought to be amorphous).