to 80 u03bcm 2 1 a grinding treatment was performed on the mold surface such that a roughness of the mold surface achieved ra 0 8 u03bcm 2 2 a cleaning treatment was conducted on the mold surface with alcohol or acetone to remove greasy dirt on the mold surface and 2 3 the mold surface was subjected to a sandblasting treatment wherein a brown corundum having a particle size less than 700 u03bcm was selected to be a material for the sandblasting a sandblasting air pressure was 0 7 mpa a sandblasting angle was 45 u00b0 and a distance from the spraying gun to the mold surface was 0 15 m 3 1 a supersonic plasma spraying gun was used as the spraying equipment the primary gas for spraying was argon with a gas flow rate of 38l u00b7 min u2212 1 the secondary gas for spraying was hydrogen with a gas flow rate of 16 l u00b7 min u2212 1 the powder feeding gas was argon and the spraying distance was 125mm the powder feeding amount was 40 g u00b7 min u2212 1 the spraying power was 46 kw and the spraying current was 540a 3 2 with the spraying parameters a workpiece surface was sprayed by using a supersonic plasma spraying gun wherein a scanning process was performed in a form of u201c tic tac toe u201d with a scanning speed of 1 25 m min and 3 2 scanning in the.