EFFECT OF TEMPERATURE AND SUBSTRATE ROUGHNESS ON THE ADHESION OF COATINGS OF Ni ALLOY DEPOSITED BY FLAME SPRAY

Abstract

The temperature and roughness at which the adhesion occurs among an oxy-fuel thermally sprayed coating from a nickel-alloy powder and AISI 1020  carbon steel substrate is reported. The coatings were obtained using a modified Castolin Eutectic-Terodyn 2000 torch coupled to an electromechanical chamber, which allows to control the parameters of process. In order to establish the effect of the substrate roughness on the adhesion of coatings, these  surfaces are prepared with SiC abrasive paper and abrasive blasting of corundum particles. The average roughness (Ra) obtained varies between 0,027±0,012 and 4,9±0,77 μm. The effect of substrate preheating temperature was evaluated for each test varying the speed of the torch and the preheating number passes, while the spraying distance and the oxidizing flame were kept constant. The spraying distance was 150 mm, while the flame  used was obtained by mixing 21.8 L/min of acetylene and 59.5 L/min of oxygen. The torch speed was increased from 0.63 to 0.77 cm/s. The results indicate that the adhesion begins from an Ra value of 0,079±0,077 µm and a substrate preheating temperature of 180°C. From these values, as the roughness and temperature of the substrate increases, adhesion improves. Such studies contribute to the understanding of the mechanisms of adhesion between the coating and the substrate when flame spray is used.