Hard Coatings to Improve the Machining of Nickel Based Materials

Abstract

Difficult-to-machine materials like nickel based alloys have become a key material in many branches of industry, above all in the aerospace industry. The reasons for this mainly lie in the combination of properties such as high strength at increased temperatures, a high degree of chemical resistance and high wear resistance. However, these advantages are offset by a major disadvantage: the machining, in particular milling, is very difficult. Only relatively low cutting speeds can be used and tool life is usually short. Developing tool and technology solutions aimed at obtaining an enhancement of the machining techniques used for milling of difficult-to-cut materials.The results of research, in particular with regard to the development of hard coatings in conjunction with suitable substrate materials, cutting edge preparation and finishing systems show an improvement in the performance of cutting nickel based alloys. Best results were reached by stable oxynitridic and embedded nanoscale structures. Combinations of these coating structures with optimized coating composition and improved coating adhesion were used to develop coatings with higher strength and hardness as well as an improved stability at higher temperatures. Related to ultra-fine graded solid carbide materials, sharp cutting edges (4 μm) and polished tools, hard coated tools were used for HPC milling of nickel based materials at cutting speeds up to 150 m/min. Various cutting analyses show the applicability of the developed coatings and the corresponding process chain to improve the efficiency of cutting processes.