Identifier

etd-04202005-161203

Degree

Doctor of Philosophy (PhD)

Department

Mechanical Engineering

Document Type

Dissertation

Abstract

A detailed examination of the intrinsic stress development and mechanical properties of titanium-containing hydrogenated amorphous carbon (Ti-C:H) and W-C:H coatings, deposited in an inductively coupled plasma (ICP) assisted hybrid chemical/physical vapor deposition (CVD/PVD) environment was carried out. Intrinsic stresses within those coatings were found to be compressive and dependent on compositions. The intrinsic compression within Ti-C:H was further shown to be significantly influenced by the energy of ionic species bombarding the substrate during growth. The results suggested that ion bombardment played a significant role in intrinsic stress generation within Ti-C:H, and was likely to influence stress development in other low temperature deposited amorphous hydrocarbon (a-C:H) based ceramic nanocomposite coatings. A higher deposition temperature, ~600C, promoted TiC precipitation and resulted in little Ti dissolution within the a-C:H matrix. High-temperature deposited Ti-C:H specimens were found to possess lower modulus and hardness values as compared to those deposited at low temperature, ~250C, especially at low Ti compositions. This is rationalized by electron microscopy evidence of increased short and medium range graphitic order within the a-C:H matrix of high-temperature deposited Ti-C:H, and supported by additional Raman spectroscopic observations. Annealing treatment at 600C combined with Raman scattering measurements showed that the a-C:H matrix in high temperature deposited Ti-C:H specimens appears to be less structurally sensitive to additional high temperature annealing. The effective coefficients of thermal expansion (CTE) of Ti-C:H coatings were measured through temperature induced changes in the curvature of film/substrate assemblies. Measured effective CTE values for Ti-C:H are consistent with previous measurements on a-C:H thin films, and show little dependence on the Ti composition. Highly hydrogenated carbon coatings with hydrogen content approaching 60 atomic percent were deposited with a modified ICP-assisted CVD technique. The hydrogen release temperature was found to be above 500C, which was 150C higher than findings in previous experiments. Plasma diagnostics suggested that a decreased ratio of ionic species flux to activated neutral species flux at the substrate during deposition was responsible for the increased hydrogen incorporation into the film.

Date

2005

Document Availability at the Time of Submission

Release the entire work immediately for access worldwide.

Committee Chair

Wen Jin Meng

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