Tensile Stress-Strain Properties of a-C:H (Diamond-Like Carbon) thin Films
- PDF / 1,181,488 Bytes
- 6 Pages / 420.48 x 639 pts Page_size
- 2 Downloads / 204 Views
TENSILE STRESS-STRAIN PROPERTIES OF a-C:H (DIAMOND-LIKE CARBON) THIN FILMS PAUL D. GARRETT* AND BRIAN K. DANIELS** *Physical and Analytical Science Center, Monsanto Chemical Co., 730 Worcester
St., Springfield, MA 01151 "**Advanced Performance Materials, Monsanto Chemical Co., 400 N. Lindbergh St., St. Louis, MO 63167 ABSTRACT Fundamental mechanical properties of a-C:H (amorphous or "diamond-like" carbon, DLC) thin film coatings have been investigated. Coatings were deposited by a methane-argon RF plasma on polycarbonate films. Tensile stress-strain behavior of the coated polymer was studied using an extensometer to monitor strain. The differences in moduli between uncoated and coated samples were used to calculate apparent coating moduli, which varied from 1 GPA to 82 GPa. The mode of failure was observed via in-situ optical microscopy during deformation. Intrinsic bond strength of the coating/substrate interface was estimated from crack spacings in the deformed coating.
INTRODUCTION Amorphous hydrocarbon (a-C:H) materials, often called "diamond-like" carbon (DLC), are an interesting new class of materials that have been developed as an outgrowth of efforts to produce crystalline diamond by vapor deposition techniques [11. Produced in the form of films on a variety of substrates, the materials show no crystalline order and may contain up to 50% hydrogen [2-41. Although their properties are not nearly those of true diamond, the films are still valuable as hard coatings for scratch resistance. They may also have utility in electronics applications for their unique optical and insulating properties. This paper describes methods for measuring the mechanical properties of DLC films through the behavior of the film/substrate composite. Also described is the application to DLC films of techniques for measuring interfacial adhesion through analysis of the periodic pattern of cracks that develops when the film/substrate composite is strained in tension [5-9]. Characterization of these properties is thought to give insight into factors controlling performance properties such as abrasion resistance. The methods described here may also be used in characterization of other systems where thin film and interface phenomena are important. EXPERIMENTAL The materials under study were polycarbonate (PC) sheets coated with DLC using a methane-argon RF plasma. Coating thickness was measured on fractured crossections by SEM and ranged from 0.2 to 4 microns* Mechanical testing was carried out using rectangular strips 1 cm wide and 6 cm long, or on dog-bone shaped specimens with a gauge length of 12.7 mm, by 2.54 mm wide. Both Mat. Res. Soc. Symp. Proc. Vol. 239. 01992 Materials Research Society
660
coated and uncoated PC was tested, with PC orientation held constant to eliminate variations due to any substrate anisotropy. Tensile testing was carried out using an Instron 4202 tensile tester, and also a Polymer Laboratories Minimat miniature tensile tester. The Minimat was used in order to make real-time observations of deformation du
Data Loading...
