Pulse-managed plasma method for coating on internal surfaces of workpieces

A method of coating an article with a hard coating, the method comprising:

• selecting a frequency and/or a duty cycle of a power supply as a function of a size of a cavity of the article to coat with the hard coating such that a ratio of a coating thickness at a first region of the hard coating to that at a second region of the hard coating ranges from 0.75 to 1.33, the cavity having a size such that a largest sphere placeable in the cavity has a diameter of less than 7 cm and a sphere having a diameter of 0.5 mm can be placed to occupy any point in the cavity;
• forming a non-equilibrium plasma inside of the cavity of the article in a plasma enhanced chemical vapor deposition (PECVD) chamber;
• introducing one or more gases into the PECVD chamber, the one or more gases including one or more inert gases and one or more precursor gases to start a reaction between the one or more precursor gases;
• and
• pulsing the power supply with the selected frequency and/or the selected duty cycle of the power supply to coat an inner surface delimiting the cavity of the article with the hard coating having a hardness between 18 to 100 GPa.