DLC cold welding prevention films on a Ti6Al4V alloy for space applications

This paper reports on research results from on-going studies in cold welding prevention for space applications. DLC film was tested as a protective coating on devices with texturized Ti6Al4V surfaces to prevent cold welding under conditions of high pressure in a high vacuum environment. Texturized Ti6Al4V surfaces are necessary for the mechanical engagement of movable parts in satellite devices. This kind of application requires very high adherence between the substrate and the film. In this study, the DLC depositions were performed either on smooth or on laser textured Ti6Al4V surfaces. Smooth surfaces were used to measure the friction coefficient on a nanometric scale and the textured surfaces were used to test mechanical engagement. A very thin silicon interlayer was used to improve the DLC adherence to the Ti6Al4V substrates. Both silicon and DLC films were prepared by RF magnetron sputtering with argon as the buffer gas and with an additional DC bias. Raman scattering spectroscopy was used to analyze the existence of sp2 and sp3 chemical bonds of DLC films and the nature of silicon structures in the silicon interlayer. The morphology and roughness were evaluated by SEM and AFM; the LFM was used to measure the friction coefficient in nanoscale and, the micro-indentation technique was used for evaluating film hardness. A new system was developed to measure the friction coefficient in microscale in order to measure the friction value between highly texturized surfaces. This paper presents an in-depth description of the testing process and the results of the cold welding prevention test of textured DLC surfaces in a high vacuum environment.