Protective coatings of nanophase diamond prepared by a laser plasma discharge source

Nanophase diamond films are prepared at room temperature with a laser plasma discharge source without the use of any catalyst. The beam from a pulsed Nd:YAG laser operating with a repetition rate of 10 Hz is focused on graphite in an ultrahigh vacuum chamber. At laser intensities near 5 x 10{dollar}sp{lcub}11{rcub}{dollar} W cm{dollar}sp{lcub}-2{rcub}{dollar}, an ablation plasma of multiply charged carbon ions carrying energies of about 1 keV is produced. It expands through a discharge space and condenses on a substrate to be coated. Composed of packed nanophase nodules in which the carbon atoms are linked with the tetrahedral bonding of diamond, the resulting noncrystalline films adhere readily to materials for which there are important applications as protective coatings. The high energies of condensation cause the deep penetration of carbon atoms into the substrates where they form significant interfacial layers helping to bond the nanophase diamond film to the item being coated.; In this research, a detailed study of the bonding and properties realized with the direct deposition of nanophase diamond on the II-VI compounds of zinc sulfide and zinc selenide was performed. It was shown that adhesion and mechanical properties of the films could be correlated with the amounts of defects and impurities in the substrates. Significant interfacial layers relating to the amount of zinc hydride impurities were confirmed by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM). To compensate for the adverse influence of substrate impurities, extensive surface preparation procedures were implemented which resulted in excellent film adhesions. Resistances to wear were estimated with a modified sandblaster, and results indicated that only 1 {dollar}mu{dollar}m coating of nanophase diamond increased lifetimes of the zinc sulfide and zinc selenide samples by a factor better than 5. The protection afforded by the nanophase diamond under harsh environmental conditions of rain impacts was also extensively studied.; In addition, erosion resistances and tribological behaviors of the nanophase diamond films deposited directly on steel substrates were examined. Resistances to wear from particles with diameters larger than the film thicknesses were estimated with devices simulating high and low impact conditions. Test results indicated that a 1-3 {dollar}mu{dollar}m coating of nanophase diamond could protect the steel substrates and increase lifetimes by considerable amount. The results of other mechanical measurements, such as those obtained by friction tests, are also reported. The combination of long lifetime against abrasive wear and a low coefficient of friction about 0.1 from a diamond film that can be deposited directly onto steel substrates suggests many practical applications.