The Preparation Of Diamond Films On Stainless Steel Substrate

Diamond films has always been a kind of ideal coating material for its outstanding mechanical properties and chemical inertness,but the complexity of preparation of diamond coatings on various substrate is different.It is difficult to deposit diamond films on stainless steel substrate because of the catalytic activity for graphite from iron and the huge difference of thermal expansion coefficients between the substrate and diamond.The present project aims to deposit diamond films on stainless substrate by hot filament chemical vapor deposition(HFCVD)for the application of diamond films on stainless steel products.In this work,we studied the deposition behavior and the feasibility of diamond films on siliconized stainless steel.Then,we studied the deposition behavior of diamond on stainless substrate with chromium buffer layer and obtained continuous diamond coatings on its surface successfully.Finally,we got the way to deposit uniform diamond films with smooth and compact surface on stainless steel substrate by optimizing process conditions of substrate pretreatment and sputtering of chromium buffer layer.The influences of the distance from hot wires to substrate and the flow rate of acetone on diamond nucleation behavior have been studied.Then we deposited diamond films under the optimized nucleation conditions on siliconized stainless steel substrate.It is beneficial for diamond nucleation when the distance from hot wires to substrate is 15 mm and the flow rate of acetone is 80 sccm.It is found that substrate is bent due to “bimetallic strip effect” when the distance from substrate to hot wires is too small(<10mm).However,diamond nucleation density is reduced and the nucleation uniformity becomes worse when the distance is too large(20 mm).When the flow rate of acetone is small(<70sccm),diamond nucleation is low,and the diamond nucleation uniformity becomes worse when the flow rate is high(90 sccm).Finally,we obtained diamond films on siliconized stainless steel substrate,while a part of films peels from the substrate after cooling in the HFCVD chamber.Chromium buffer layer was prepared by magnetron sputtering on the substrate,while it peeled off from the substrate because of its poor adhesion after ultrasonic pretreatment in diamond dispersion liquid for a period of time.We explored the methods to enhance its adhesion and then we deposited diamond films on stainless steel with chromium buffer layer.The results show that it is difficult to improve the adhesion between buffer layer and substrate by reducing ultrasonic pretreatment time(1~30 min),reducing magnetron sputtering time(10~20 min)or increasing magnetron sputtering power(130~200 W).However,it is effective to improve the adhesion between substrate and buffer layer after annealing for 20 min in HFCVD chamber with acetone gas and hydrogen.As a result,we obtained continuous diamond films with no peeling on the annealed chromium buffer layer after deposition in HFCVD chamber for 2 h.Nanoindentation and electrochemical measurements show that the diamond films are not compact and smooth.The effects of substrate morphology and the thickness of chromium buffer layer on diamond deposition behavior were studied.The results show that it is difficult to enhance the adhesion,smoothness and compactness of diamond films simultaneously only by controlling the surface topography of the substrate.Moreover,it is effective to improve the adhesion between diamond films and substrate by increasing the thickness of chromium buffer layer substantially.Eventually,after the chromium buffer layer was annealed for 20 min,uniform diamond films with smooth and compact surface were deposited on stainless steel substrate polished by 1200# sand paper.