With the purpose to produce a hard alumina film on a tool at low temperature, investigations were carried out to improve the arc discharge type high vacuum ion plating (ADIP) system.
As the result of the investigation, following three items can be listed as its main improvement.
(1) To provide a heating mechanism to the ionization electrode.
(2) To apply a negative bias to the cathode filament.
(3) To apply an asymmetrical dc pulse to the substrate in the frequency of 100 kHz.
By this, it was possible to ionize stably alumina vapour and to get a discharge current of 20 A at maximum.
A transparent film was obtained at the deposition rate from 80 to 100 nm/min.
The film structure was decided as amorphous by X-ray diffraction.
The film hardness showed 3600 HK at maximum and increased with the increase of pulse bias voltage.
The surface roughness was also determined as 2.2 nm (rms) from the observation with the atomic force microscope (AFM).