THIN-LAYER CERAMIC COAT: METHOD OF MAKING SUCH COAT; FRICTION SURFACE ON BASE OF THIN-LAYER CERAMIC COAT AND METHOD OF MAKING SUCH SURFACE Russian patent published in 2001 - IPC

FIELD: electroplating; forming wear-resistant coats on surfaces of metals by micro-arc oxidizing. SUBSTANCE: thin-layer ceramic coat consists of crystals of alpha-Al₂O₃, having filamentary shape which are contained in finely crystalline matrix of gamma-Al₂O₃ and mullite 3 Al₂O₃·2SiO₂.. Coat is characterized by intensive wear I = 10^-10-10^-12, friction coefficient f = 0.010 - 0.035, microhardness H = 15-19 HPa and critical cracking load P= 2.7-3/5 N. Proposed method includes oxidizing of aluminum-containing metal composition including copper in the amount of 4 to 10 % in anode- cathode mode at I_c/I_a=1.0-1.15 in electrolyte in form of aqueous alkaline solution 1-6 g/l with addition of water glass 5-10 g/l and mixture of powder consisting of SiO₂ and Al₂O₃ at ratio of 70 and 30% respectively, dispersivity 1-10 mkm and concentration 0.5-2.0 g/l. Friction surface on base of ceramic coat is formed by free ends of filamentary crystals alpha- Al₂O₃ extending beyond finely crystalline matrix of gamma-Al₂O₃ and mullite 3 Al₂O₃·2SiO₂ which forms backing of friction surface. Proposed method includes treatment of coat by means of abrasive whose strength is higher than that of backing of friction surface. EFFECT: enhanced microhardness, wear resistance and crack resistance of coat and friction surface. 5 cl