Testing the adhesion between chromium plating and the base metal involves many difficulties, and the conventional test is too inaccurate to permit analysis of adhesion. For this reason an improved adhesion test, based on the drawing method developed by R. A. F. Hammond et al., was used to measure the strength of adhesion of chromium plating to the base metal. As the hydrogen overvoltage on the base metal surface to be plated seems to have a great effect on the mechanism of electrodeposition in chromium plating, it was measured to clarify the chemical characteristics of the surfaces, and the adhesion mechanism was considered. It is considered that the condition of the base metal surface to be plated influences the structure of the metal deposited at the first stage of the electrodeposition, and that the strength of adhesion of the plating to the base metal varies. If the base metal surface is etched by counterelectrolysis in the chromium plating bath just before plating, the base metal surface becomes favorable for plating. This etching process causes stronger adhesion of chromium plating to the base metal.
The adhesion of the hot-dip galvanized coating of high-strength steel sheet was studied in connection with the Al and Pb content of the Zn bath. Coating adhesion, as evaluated by Gardner impact test, 0t-bending test and U-shaped bending test, differed, the Gardner impact test being the most severe. Coating adhesion depended on the structure of the alloy layer formed between the substrate and the coating (η-Zn), which was changed by the Al and Pb contents in the coating bath. In a 0.05% Al-0.20% Pb-Zn bath, an alloy layer consisting of coarsely developed Fe-Zn intermetallic compounds made coating adhesion poor. In a 0.15%Al-0.20%Pb-Zn bath, the poor adhesion of the coating was considered to be due to the alloy layer consisting of fine Al-Fe-Zn intermetallic compounds and locally developed Fe-Zn intermetallic compounds. The addition of Pb to the coating bath facilitated the local formation of Fe-Zn intermetallic compounds.
Electroless nickel plating on silicon wafers were investigated to obtain good adhesion. It was found that complicated micro etch pits ranging from 0.5μm to 1.5μm in depth on the silicon surface produced by etching with potassium hydroxide followed by HF-HNO3-CH3 COOH-H2 O2 etching solution. The micro etch pit formed by this etching sequence showed an interlocking effect with nickel, which permitted mechanical interaction at the nickel-silicon interface.
In order to clarify the suitability of aluminum with hydrated oxide film as a base material for painting, the strength of adhesion of epoxy-phenolic resin to aluminum hydrated using several kinds of baths was evaluated by measurement of the peeling strength, and the mechanism of adhesion for each type of treatment was observed by SEM and ESCA. (1) In every method of treatment, resin adhesion rose in the initial induction stage (a), dropped extremely for a time at the beginning of film growth (b), and then rose again depending on the time of treatment (c). The mechanisms were considered to be as follows: (a) The increase in specific surface area depending on the formation of lumps, (b) The decrease in the adhesion of the lumps to the aluminum base depending on the formation of needle-like or petal-like hydrated oxide film, (c) The increase of specific area depending on the growth of petal-like hydrated oxide film having good adhesion to the aluminum base. (2) The films that were treated in waterglass solution after hydration promoted in sodium hypochlorite solution showed better resin adhesion than did films without waterglass treatment. We considered the cause of the increased resin adhesion to be secondary improvement of the surface of the aluminum base depending on the formation of SiO2-film.
An automatic scratch tester with an acoustic emission (AE) detector has been developed by the CSEM-Centre Suisse d'electronique et de microtechnique S.A.-(former LSRH), it is an automatic device intended to test the mechanical strength-adhesion and intrinsic cohesion-of hard, brittle coatings formed by chemical vapor deposition (CVD) or physical vapor deposition (PVD) on softer, tougher substrates. The test consists in scratching the surface of a coated substrate specimen with a smoothly rounded diamond point. The load applied at the point is increased continuously as the point moves on the surface, and a piezoelectric accelerometer is used to detect the AE produced as the coating is damaged. Preliminary scratch test results are shown using PVD TiN-coated cemented carbide testpieces. The influence on critical load (Lc) of coating thickness, deposition rate and coating pressure is studied. Coating pressure is varied from a lower end of 8×10-4 Torr to 2×10-3 Torr. Coating thickness is changed by the distance of the testpieces from the evaporator crucible. In case of higher coating pressure, critical load increases with coating thickness in the range of 1-4μm, however, coatings thicker than 6μm showed a sudden fall in the critical load value. This suggests that a critical thickness or deposition rate exists for adhesion in PVD TiN coating. In case of lower pressure, reproducibility of the Lc value was rather poor and at thicknesses of 1-8μm there was no apparent difference in the critical load observed.