Process for the production of a surface-coated article

DETAILED DESCRIPTION OF THE INVENTION The inventors have noted a plasma CVD method as a coating method which has an advantage, i.
e.
resulting in a uniformity of a coating film thickness, characteristic of the CVD method, and can lower the coating temperature, have made various studies on means for lowering the coating temperature and consequently, have found that formation of a coating film cannot effectively be accomplished unless the coating temperature and plasma strength, defined by a power introduced into a plasma-forming space, are within constant ranges.
In the plasma CVD method, however, the adhesion between a substrate and coating film is also lowered if the coating temperature is low and increase of the adhesion has thus been desired so as to use the coated substrate as a cutting tool or wear resisting coated part.
Accordingly, the inventors have made various effects to develop a process for surface-coating by the plasma CVD method at a low temperature without lowering the adhesion and have thus achieved the following surprising knowledge.
That is, remarkable improvements of properties can be obtained in, for example, coated steel tools or coated wear resisting steel parts by the plasma CVD method comprising using jointly a high frequency source and a direct current source as a plasma exciting source, holding a steel substrate at a negative potential by the direct current source and adjusting the high frequency power density introduced into a plasma forming space to 0.
01 to 1 W/cm.
sup.
3, the absolute value of the direct current voltage to 1500 V or less, preferably 1-1500 V and the pressure of a gaseous atmosphere to 0.
05 to 5 Torr.
Furthermore, the inventors have noted that a cemented carbide meets with lowering of the strength after coating by the CVD method, have made studies for lowering the coating temperature so as to prevent from the lowering of the strength and consequently, have achieved the following knowledge: (1) If the coating temperature is lowered, the strength of a cemented carbide substrate after coating is lowered to a decreased extent and the breakage resistance is improved