Reduction of wear at hot forging dies by using coating systems containing boron
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The near surface area of forging dies is exposed to high mechanical loads. Additionally thermal and chemical stresses appear during the hot forging process. Depending on the number of forged parts, several kinds of stresses occur in the near surface area, which lead to the initial failures of forging dies. Wear is the main reason for production downtimes with a ratio of 70%. Furthermore, thermal and mechanical cracks are typical causes for failures causes as well as plastic deformation. In order to reduce wear, the abrasion resistance of the forging die surface has to be increased. Hence, different methods like plasma nitriding and optional additional thin hard coatings (TiN, TiCN, TiC, TiBN and TiB2) were successfully examined. Recently developed Ti–B–N coatings in specific multilayer designs are thermally stable, wear-resistant and anti-adhesive regarding the sticking of work piece material. This paper presents the wear reduction possibilities of boron-containing multilayer coating systems applied to forging dies by using the plasma enhanced chemical vapor deposition treatment. A basic mechanical and analytical characterization of different coating systems is realized in the first stage of the project. Best qualified multilayer coating variants were applied to forging dies for experimental investigations. As a result of the tests, wear can be reduced significantly by using thermally stable boron multilayer coatings. To receive realistic wear values under production conditions, an automated forging process was used for testing. After 3,000 forged parts, the coatings were examined by tactile measurement, SEM and EDX analyses to characterize the occurring wear.
KeywordsPACVD Coating design Multilayer Hot forging Wear resistance Cracks
The presented investigations were carried out within the “Industrielle Gemeinschaftsförderung” (IGF) project No. AiF 15759 N “Increase of Tool Life by Boron Containing PACVD-Multilayer Coatings on Forging Dies”, sponsored by the Federal Ministry of Economics and Technology (BMWI) via the AiF. We are thankful for the assistance provided. The authors would also like to thank Dr. Stueber and Dr. Ziebert of the Karlsruhe Institute of Technology KIT, Institute for Materials Research I, Karlsruhe, Germany, and Dr. Mayrhofer of the Department of Physical Metallurgy and Materials Testing at Montanuniversität Leoben, Austria, for carrying out investigations on the nanostructural characterization of the coatings.
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