Pulsed Laser Deposition of Functionally Graded Diamond-Like Carbon Films with Designed Gradient Profiles

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Pulsed Laser Deposition of Functionally Graded Diamond-Like Carbon Films with Designed Gradient Profiles
Won, Yoo Jai
Ki, Hyungson
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Graduate school of UNIST
This thesis contains three sections; the first section is about fabrication of functionally graded diamond-like carbon (FGDLC) films, the second section is about the characteristics of functionally graded diamond-like carbon films and the final section is about the adhesion characteristics and residual stress of diamond-like carbon films with various deposition parameters. In the first section, FGDLC films are deposited with pulsed laser deposition (PLD) technique with two different target materials, 316L stainless steel and graphite. From the stainless steel substrate, which is same material as one of target materials, the content is gradually changing from stainless steel to diamond-like carbon (DLC,) and then additional pure DLC is deposited onto the gradient layer. With deposition data of DLC and stainless steel films, power profiles are obtained from given target content profiles. Intended thicknesses of FGDLC films are 600 nm with 450 nm of gradient layer. Deposition errors of content are less than 3 % for both DLC and stainless steel and errors on thickness are less than 2 %. In the second section, adhesion strengths, compressive residual stresses and effective hardness of FGDLC films are examined. Five polynomials are selected for content profiles of FGDLC films. With a Rockwell C type indenter, three different indentation loads are employed to induce interfacial cracks. In this thesis, adhesion strengths of FGDLC films are compared to one from the relation between crack radius and indentation loads. Residual stresses are calculated with Stoney’s equation from difference in radius of curvature of (100) silicon substrate before and after film deposition. With existence of gradient layer in the film, adhesion strength is improved and compressive residual stress is largely reduced. The effective hardness of FGDLC films are measured with nano-indentation technique. In the last section, sp3 contents, residual stresses, and adhesive characteristics of DLC films deposited with different deposition parameters are examined. Two important deposition factors — power of laser and temperature of substrate — are selected for this section. Residual stresses of DLC films show the same trend as sp3 content of films; however, adhesion strengths of films behave exactly in opposite way as sp3 content. The optimal point for the highest sp3 content of DLC is found at higher power of laser and lower temperature of substrate.
Department of Mechanical Engineering
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