Nano layers give toughest finish to tools

By depositing alternate layers of very hard and hard plus tough layers of nitrided materials onto a steel, it is possible to achieve extraordinary durabilities, plus low friction. Best of all results are achieved by starting with a carbo nitrided steel, and laying down hundreds of layers, each only a few nm thick, to achieve in one case, a 25 fold improvement in tool life. The technologies are the latest developments to be made available by Nitrotec Services, a company with long experience of nitrocarburising the surfaces of steel components for the automotive, construction equipment and small arms industries. Nitrocarburising started out at the end of the WWII, as a means of putting the surfaces of plain carbon steels into compression by immersion in baths of molten cyanide salts. This later gave way to processes based on heat treatment in an ammonia atmosphere, followed by a small and carefully controlled amount of oxidation, processes that the company still provides as environmentally friendly alternatives to hard chrome electroplating with tailored and often superior mechanical properties. The firm, however, now offers the additional ability to plasma nitride using a gas discharge in a vacuum furnace and then to use physical vapour deposition to lay down thin layers of other materials. One such coating is titanium carbo nitride, which has a hardness of 3500 {{plusminus}}500 HV, and a dry coefficient of friction against steel of about 0.15 to 0.2. Unfortunately, it is so highly stressed, that it would spall off if laid down on its own. Hence, it is best laid down only in thin layers, each containing more carbon, with interleaving layers of titanium nitride, to achieve a total of six layers about 4.6 microns thick. In another process, given the name 'Variantic' by its inventors, the German Eifeler company, 24 layers of titanium aluminium nitride are laid down with interleaving layers of titanium nitride. The top of the range treatment involves laying down hundreds of layers of titanium aluminium carbo nitride and titanium nitride, each only nm thick. Used on machining tools, nanolayer treatments are able to roughly double the lives of tools coated with micron thick layers, which are in turn, about 50% better than monolithic coatings. In one case a cropping tool was able to make 25,000 parts instead of 1,000. Other applications include drilling, machining all types of steel under dry and wet conditions, aluminium die-casting and metal forming. TTI Group web site Contact Nitrotec Services Pointers * Multi layer wear resistant physical vapour deposited coatings achieve extreme hardnesses and low coefficients of friction on cutting and forming tools * Nano layers achieve around twice the tool lives of multiple micron thick layers which are in turn around 50% better than monolayers