Andrew Wells Phelps

Friction induced phase transformation of pulsed laser deposited diamond-like carbon

Structural transformations in the sliding friction of hydrogen-free diamond-like carbon (DLC) films prepared by pulsed laser deposition are investigated. Stainless steel disks were coated with 0.5 μm thick DLC films, and ball-on-disk sliding experiments were performed with steel and sapphire balls in humid air, a nitrogen atmosphere, and under vacuum. Friction coefficients of about 0.1 are reported. The low friction is related to a friction induced transformation of the surface into a graphite-like phase and the formation of an adherent transfer film of this material on the counterface. Surface enhanced micro-Raman studies of the wear tracks, wear debris and the transfer film demonstrated that an sp3 to sp2 phase transition has occurred in the wear tracks on the DLC film surface. The formation of a graphite phase after several thousands of cycles caused a humidity sensitive behavior of the DLC films and an increase in the friction coefficient in high vacuum conditions. A lubricating sp2-rich layer on the surface of the hydrogen-free DLC films is proposed as the reason for their extremely low wear rates in ambient environments.

Type IIb diamond thin films deposited onto near-colorless natural gem diamonds

Abstract Synthetic bluish gray type IIb diamond films were grown by chemical vapor deposition (CVD) on the surface of faceted nonconductive natural diamonds. These electrically conductive synthetic diamond films were made by introducing boron into the diamond growth environment during their formation. The resulting product looks like a very valuable type IIb natural blue diamond—if the starting material has been carefully selected—to a gemologist equipped only with classical gemological observation tools. However, careful microscopy observations, together with UV-visible and IR absorption spectroscopy, can be useful in detecting the presence of the film on a faceted diamond.

Erosion Studies of Infrared Dome Materials

The testing reported in this paper operationalized the material requirement: An infrared transparent dome material must be at least as good as magnesium fluoride in rain tests and substantially better than magnesium fluoride in sand tests. Sand erosion test conclusions, based on changes in midwave infrared transmission, are that CleartranTM with the protective coating system tested is not substantially more resistant to large grain sand erosion damage than magnesium fluoride. ALONTM and spinel are substantially more resistant to large grain sand erosion damage than magnesium fluoride. There is no significant transmission difference due to small grain sand erosion observed between any of the tested coupons. Qualitative analysis of coupon damage after exposure to an artificial rain field on a whirling arm showed that ALONTM and spinel are at least as rain erosion resistant as magnesium fluoride, but the coated CleartranTM coupons delaminated rapidly under the same rain test conditions. Testing coupons exposed sequentially to the milder sand condition followed by the whirling arm rain erosion test demonstrated that magnesium fluoride rain resistance is diminished in the combined test, but that ALONTM and spinel retain their robust resistance. Coated CleartranTM delaminated under the combined conditions as well. It is noteworthy that the results reported for the midwave infrared range also apply to the near infrared region above 1 micron.