Structural and Tribological Properties of Molybdenum Disulfide/Metal Multilayered Films Deposited by Pulsed Laser Deposi
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STRUCTURAL AND TRIBOLOGICAL PROPERTIES OF MOLYBDENUM DISULFIDE/ METAL MULTILAYERED FILMS DEPOSITED BY PULSED LASER DEPOSITION A.R. Phani, J.E. Krzanowski, Dept of Mechanical Engineering, University of New Hampshire, Durham, NH; J.J. Nainaparampil, MBLT/WPAFB, OH ABSTRACT The structural, mechanical and tribological properties of MoS2/metal and MoS2/carbide multilayer thin films have been examined in this study. The films were deposited by pulsed laser deposition of sequential layers of MoS2 and either Ti, Cr or TiC. The compositions of the films were analyzed by wavelength dispersive spectroscopy (WDS) and confirmed the presence of the deposited elements. X-ray diffraction and crosssection SEM methods were employed to characterize the films. The XRD results did not reveal the presence of separate Ti, Cr or TiC phases, and the SEM did not show any multilayer structures. From these results, it was concluded that the added metal or carbide elements are present as either a dispersed nano-structured phase or in solid Nonetheless, friction and wear testing showed dramatic solution with the MoS2. improvements over MoS2 films when tested in a humid (45% r/h) environment. INTRODUCTION Significant advances have recently been made in the field of solid lubricants. Graphite-type materials, such as highly ordered pyrolytic graphite (HOPG) and intercalated graphite have been extensively studied [1]. Other solid lubricants include layered-hexagonal transition metal dichalcogenides (LTMDs) such as MoS2, NbS2 and TeSe2, and lubricious oxides such as TiO2-x (rutile polymorph). Among these, MoS2 has found to be particularly useful, and is widely used in vacuum environment applications. The natural lubricious properties of MoS2 have led to numerous investigations aimed at depositing it as a coating material. The early work of Spalvins [2] used sputtering methods to deposit films of MoS2. Since then, d.c., r.f., magnetron and reactive sputtering methods have been used [3-5], in addition to ion beam enhanced deposition [6], pulsed laser deposition [7] and chemical vapor deposition [8]. The primary issues that have been investigated are the effects of chemical purity, crystallographic texture, operating environment, and types of dopant elements on tribological properties. The texture of MoS2 is an important factor in determining the tribological properties. Films can have texture that results in the basal planes parallel to the substrate, perpendicular to the substrate (known as edge growth), as random polycrystalline films, or in an amorphous state. Films with parallel texture have been reported to exhibit reduced friction [9], as well as improved resistance to degradation in humid air. However, edge growth seems to be the more common growth mode. In this mode, the edges are susceptible to degradation by oxidation of the plane edges resulting in the formation of MoO3. Zhang et al. [9] detected MoO3 and SO42- in fretting wear tracks and debris of random-oriented MoS2. They also found that basal-plane oriented MoS2 was less sensitiv
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