Comparative evaluation of PVD- and CVD-coated hardmetals

The cutting performance of coated carbides depends on the coating material, the thickness and adhesion of the coating and on the properties of the substrate. The coating temperature is a decisive parameter for the performance. High temperatures affect the properties of the substrate more than low temperatures. This was proved by means of physical investigations and by cutting tests conducted with uncoated and coated carbides. The performance of differently heat treated uncoated carbides drops in interrupted cut turning of quenched and tempered steel according to an increase of the temperature. The maximum tool life is displaced towards higher cutting speed. Titanium based Arc-PVD-coatings deposited at temperatures of about 500 degrees C improve the performance of carbide in interrupted cut turning of quenched and tempered steel, preferably in the range of low cutting speed. Applications like this require tool materials with excellent toughness behaviour. Machining of austenitic stainless steel changes the requirement towards elevated resistance against defoliation of the coating caused by severe adhesion. The cutting tests indicate the necessity for further improvement in order to reduce this type of wear. A comparison of PVD- and differently CVD-coated carbides shows the advantages of the toughness behaviour in accordance with the reduction of coating temperatures.