Nano Indentation Response of Various Thin Films Used for Tribological Applications

Introduction

Tribology deals with the study of friction, wear and lubrication of interacting surfaces in relative motion. The word tribology is derived from the Greek word “Tribos” which means rubbing. Until lately, this study was considered as a branch of mechanical engineering, and due to its ever increasing presence in almost every branch of science, it has now turned into an interdisciplinary field. Rapid growth of science and technology has created increased demand for materials with improved performances operated in demanding environment. This has resulted in development of several varieties of materials and more importantly modification of surfaces with different surface and bulk properties.

Surface engineering is one of the most effective ways of enhancing the performance of industrial components to make them suitable for functions that are different from the primary function of the bulk substrate. Although surface engineering has been practiced from the dawn of civilisation, the science and technology of surface modification has been explored only in recent past. Major progress in this direction has been achieved only when a significant gain in performance along with financial benefit is realised by practicing surface modification techniques. Even though surface modification is practiced for several reasons for protection against degradation such as wear, corrosion, fatigue etc. surface engineering for enhanced wear performances is most widely used tools for performance enhancement. Deposition of thin film for monitoring the tribology related surface response has received increased attention in recent days.

Various tribological thin films can be broadly classified under four different heads. The first variety films are hard film with high friction coefficient. These films are used where the wear should be low and high friction coefficient is required. Second variety consists of films with very high nanohardness and low friction coefficient with excellent inertness. These films are used for tribological application under circumstances where corrosion or oxidation resistances plays crucial role. When these films are used as protective coating, wear of mating surface is an important problem. Third varieties films known as self-lubricating film have low nanohardness along with low friction coefficient. Although wear rate of these films are not important from application point of view, the friction coefficients of these films are very low. Finally forth variety is films with reasonable nanohardness but low friction coefficient. These films are used as self-lubricating film where wear is also a concern.

The objective of the present chapter is to critically examine the nano indentation response of selected films pertaining to each variety of films mentioned above. In order to achieve the aforementioned objective, one example of each variety of films is taken. The load vs. displacement curves of each film is analysed. Their nanohardness, elastic modulus, ratio of nanohardness to elastic modulus and elasticity are evaluated. The characteristics features of these properties of each variety of films are ascertained.