Tungsten Tantalum Composite Coating on Reduced Activation Ferritic Martensitic Steel

Abstract

The main objective of this study is to impart ductile property in Tungsten (W) thin films at room temperature condition which can be used as a Plasma Facing Material (PFM) in a Tokamak. Along with ductility, the adhesion improvement is also carried out by selecting a suitable interlayer for the developed thin films. Comparatively soft Tantalum (Ta) is used to impart ductile properties in the Tungsten thin films at room temperature condition. RF magnetron sputtering process is used to deposit the films on to the Reduced Activation Ferritic-Martensitic Steel (RAFM). Initially, W is deposited on RAFM substrates with RF sputtering method and behaviour of the thin-film system is studied by analysing for adhesion, morphology and hardness properties. Sputtering parameters are fixed by the initial studies, and further optimisation of parameters to at tain the best adhesion, less hardness and best morphology for the W thin film is carried out using Taguchi L9 orthogonal array. From the optimisation studies of W, parameters are selected and are used for the W-Ta composite film sputtering process. Ta percent age in the composite film is optimised by using Taguchi L9 orthogonal array again in this study with the process parameters selected from W study to attain the best ductil ity, adhesion and morphology. In this study, thin film0 s adhesion is assessed by both qualitatively and quantitatively via indentation test and Nano scratch tests. Hardness and modulus of the films are analysed by nanoindentation analysis and morphology is checked with Field Emission Scanning Electron Microscope (FESEM). The chemical analysis of the developed films is also done by Electron Diffraction Spectroscopy (EDS) method. From this study, it is concluded that addition of 5%Ta improved the plastic deformation by 66% and toughness by 479% of the W film at room temperature condition, implying the composite film is a ductile and tougher film at room temperature condition. Cr as interlayer is found to increase the adhesion strength for W and W-Ta co