Improvement of press dies used for the production of diamond composites by means of DUPLEX-PVD-coatings

In the machining of hard materials such as glass or stone, cemented carbides have been recently replaced by diamond tools, consisting of a metallic carrier, on to which diamond segments are brazed. One of the most economic ways for the production of diamond segments is the cold compaction of the mixture of a metallic powder and diamond particles. Due to a highly abrasive sliding contact between diamond particles and the die walls, the wear rate of the press dies is very high. As a result of a low lifetime of the press dies, they must be replaced in short time periods. To avoid the costly and time-consuming substitution of the press dies, in this work PVD-coatings were deposited on the inner surface of the pre-plasma nitrided press dies (DUPLEX treatment). Thereby, various high and low alloy tool steels were treated by means of plasma nitriding process. Subsequently, a nanocomposite TiAlN coating (nc-TiAlN) was deposited by means of a high ionization magnetron sputtering device on nitrided and non-nitrided steel substrates. The mechanical and tribological properties of these coating systems were studied by means of several standard tests such as nanoindentation, ball-on-disc and scratch test. The most wear resistant coating system was chosen to employ on the inner surface of the press dies. The wear resistance of the press dies developed in this study was tested under real loading condition during compaction of the mixture of diamond particles and cobalt powder. It was revealed that employing plasma nitrided tool, steels coated with nanocomposite TiAlN decreases the wear rate of the press dies up to 76%.