Properties and performance of high aluminum containing (Ti,Al)N based supernitride coatings in innovative cutting applications

The development of new materials is always associated with the requirements of low cost manufacturing of parts consisting of these materials. In order to meet the corresponding demands, a range of developments has been brought forward in the area of coating technology. One of the most promising state of the art coatings is the metastable solid solution phase (Ti,Al)N in cubic NaCl (B1) structure. These coatings offer a superior oxidation resistance and hardness as compared to the conventional TiN or TiCN. The oxidation resistance of these coatings increases with increasing Al content in the solution phase. Based on a unique plasma enhanced sputtering technology a novel generation of high performance hard coatings, the supernitrides was developed. Supernitrides comprise a whole family of sputtered films deposited by means of highly ionized plasmas, and they are characterized by a dense, nano-crystalline or nano-layered structure and a high content of oxide forming elements. They show an improved hot hardness, high thermal and chemical stability as well as oxidation resistance. They combine the properties of most modern hard coatings with the chemical and physical properties of typical oxides. In the present article, the frame of the investigations describes a characteristic (Ti,Al)N based supernitride variant, with an AlN content close to the conductivity limit of 65–67 mol.% AlN was deposited on the cemented carbide inserts. The mechanical properties of the film were extracted by means of nano-indentations and impact tests, and compared to the corresponding ones of an effective state of the art (Ti46Al54)N coating. Milling investigations, conducted with both previously mentioned coatings, demonstrated the enhanced cutting performance of the supernitride coating, especially at elevated cutting temperatures.