DLC (Diamond like carbon) films are deposited by bend type filtered cathodic vacuum arc (FCVA) technique with argon gas and a graphite target. Mechanical properties, such as nanoindentation hardness and nanowear resistance dependence on bias voltage, are evaluated by atomic force microscopy (AFM). The bend type FCVA is efficient for depositing low surface roughness DLC films free of microparticles. Ion energy, controlled by the substrate bias, is an important parameter in determining the mechanical properties of films deposited by FCVA. The substrate was subjected to DC or pulse bias voltage for film deposition. The modulus of dissipation and E/H decreases as nanoindentation hardness increases. In nanoindentation tests, property deposited FCVA films showed a higher hardness, a lower modulus of dissipation energy and a lower material factor of plastic index E/H, than those of sputtered and ion planting DLC films. The maximum hardness and Young's modulus values for DLC film deposited at a bias voltage of −50V DC were observed. According to the nanowear tests by AFM (atomic force microscope), the atomic scale wear was evaluated, and the correlation between microwear, hardness, modulus of dissipation and E/H are verified. The hardest DLC film shows the lowest wear; therefore, fewer dissipated permanent deformations such as cracks or dislocations were caused by nanoindentation and microwear. FCVA DLC films deposited at a proper bias voltage, like −50V DC bias voltage, show excellent nanometerscale mechanical properties.
Cerium conversion coatings of 20-70nm in thickness, have been deposited onto electroless nickel-phosphorus substrate by immersion into a simple 0.01mol/L cerium(III) chloride aqueous solution in the temperature range of 298 to 353K. Cerium-rich film was formed by the dissolution of nickel substrate at the anodic sites and the reduction of dissolved oxygen at the cathodic sites on Ni-P substrate. X-ray diffraction(XRD) and X-ray photoelectron spectroscopy(XPS) have been used to characterize the cerium conversion coatings. It was found that the cerium-rich films were crystalline cerium (hydr)oxide with CeO2-fluoride structure. The high-temperature oxidation resistance of Ni-P films in air has been studied after cerium conversion treatment. It was found that the cerium oxide layer on the Ni-P alloy improved the oxidation resistance in the temperature range of 673 to 973K. After oxidation tests, XPS depth profiles revealed the cerium concentration maximum in the oxide scale. The good oxidation resistance of cerium-treated Ni-P was attributed to the low ionic mobility of nickel ion in the cerium-rich oxide layer.
Anodic dissolution mechanisms of zinc in citric acid/sodium hydroxide buffer solutions (pH2-5) and sodium carbonate/sodium hydrogen carbonate buffer solutions (pH9-10) have been investigated using electrochemical techniques. The reaction parameters were obtained from the polarization curves of zinc, and the following dissolution mechanism was proposed. Zn+OH−=ZnOHads+e− Zn+ZnOHads+OH−→ZnOHads+ZnOH++2e− ZnOH+=Zn2++OH− An electrochemical quartz crystal microbalance (EQCM) was applied, and the mass change of zinc electrode was determined simultaneously with the measurement of polarization curve. Furthermore, the influences of chloride and sulfate ions on the anodic behavior of zinc were discussed.
We have succeeded in preparating an Fe-Cr alloy film with a compositionally graded structure on an Al substrate using the electroplating method. By controlling the current density with time during the electroplating process, the ratio of Cr changes gradually with the depth of the electroplated Fe-Cr coating, so that the Cr content grows proportionally upwards. Thus prepared Fe-Cr alloy coating has two distinct sets of properties, first, a high abrasion resistance and high hardness on its top surface, due to the higher Cr ratio, and secondly, a high adhesion strength and low hardness nearer the substrate, due to the lower Cr ratio in the Fe-Cr layer adjacent to the substrate.