Deposition Of DLC/Au Coating On Super Smooth Mandrel And Its Demolding Performance

Observing high-energy radiation by space telescopes is a significant way for modern scientists to obtain cosmic information,and X-ray focusing telescope is a kind of widelyused space telescope.In 2018,the Chinese Academy of Sciences started the Enhanced Xray Timing and Polarization(eXTP)mission,in which tackling the processing technology of X-ray focusing mirror is one of the most important topics.In this paper,the deposition of diamond-like carbon(DLC)and Au film in electroforming and replication process of X-ray focusing mirror was studied.Compared with traditional focusing mirror processing technology,adding DLC film as a transition layer for demolding not only improves the surface quality of mandrel,but also improves demolding process.The properties of DLC film and Au film was tested by means of AFM,SEM,peeling tension test and friction test,the process of removing DLC transition layer by oxygen plasma was studied,and the variation of temperature field and stress field during demolding process was analyzed by finite element method.Finally the whole technological process was summarized and the task of manufacturing X-ray focusing mirror was achieved.It was found that the Au film deposited by magnetron sputtering under different parameters appeared to be different in thickness uniformity,surface roughness and filmsubstrate adhesion.With the increase of target-base distance from 150 mm to 200 mm,the uniformity of film thickness increases gradually.With the increase of RF power from 100 W to 400 W,the deposition rate increases,but the surface roughness and thickness inhomogeneity increases.With the increase of substrate bias from 0V to 300 V,the deposition rate decreases,the film thickness uniformity and the adhesion between DLCAu increases,but the surface roughness of central Au film increased.The surface roughness of DLC films deposited on ultra-precision machined surfaces decreased from 4.77 nm to less than 1nm.The friction coefficient of the Ni-P alloy surface of the mandrel is 0.805,and the surface is easy to wear.The DLC film can not only reduce the friction coefficient to less than 0.5,but also effectively avoid the surface wear.With the increase of RF power,the surface roughness of DLC films decreases,the friction coefficient decreases and the wear resistance of DLC films increases.Oxygen plasma reactive etching of DLC films was carried out at different pressure and RF power.The results show that the oxygen plasma etching effect is better at 0.6-0.9 Pa working pressure,while the RF power has little effect on the etching effect.Oxygen plasma etching can produce a dense oxide film on the surface of Ni-P alloy,but it will not obviously reduce the surface roughness of the mandrel and Au film.The finite element simulation result shows that using liquid nitrogen to cool the center of the mandrel can cause a large difference of stress between the mandrel and the nickel shell,with the cooling progress,the stress increases gradually,which leads to the separation of mandrel and nickel shell.Mold-shell separation is most likely to occur at the small diameter end.