High Temperature Thermal Stability of Innovative Nanostructured Thin Coatings for Advanced Tooling

Abstract

Tools for machining are made of hard steels and cemented carbide (WC-Co). For specialized applications, such as aluminium machining, diamond or polycrystalline cubic boron nitride are also used. The main problem with steel, isthat itexhibits a relatively low hardness (below 10 GPa) which strongly decreases upon annealing above about 600 K.Thus, the majority of modern tools are nowadays coated with hard coatings that increase the hardness, decrease the coefficient of friction and protect the tools against oxidation. A similar approach has been recently used to obtain a longer duration of the dies for aluminium die-casting.

Investigation of the Temperature-Related Wear Performance of Hard Nanostructured Coatings Deposited on a S600 High Speed Steel

“…Previous studies performed on the same samples by some of the authors in the present study [64,78] showed that upon thermal cycling at 873 K, the superlattice CrN/NbN coating showed oxidation and hardness decay, while the multilayer AlTiCrN coating showed high oxidation resistance with a stable high degree of hardness. The mechanical properties (hardness and elastic modulus) of the coatings were also investigated by nanoindentation in previous papers published by some of the authors in the present study [64,78]. According to these results, the resistance to plastic deformation, which is described by the ratio H 3 /E 2 [79], resulted in~0.146 for the CrN/NbN coating and~0.153 for the AlTiCrN at RT.…”

“…The peculiar architectures of the chosen coatings make them suitable for technologically challenging applications and since coatings for cutting tools typically need to withstand mechanical and thermal loads, tribology tests (tribotests) were performed at room temperature (RT, 293 K) and high temperature (HT, 873 K). Given the results reported on the thermal stability of these two coatings published by some of the authors in the present study [64], where the superlattice coating showed degradation of its mechanical properties at around 873 K, this temperature was chosen as the highest to be set in order to evaluate the tribological performance of the two commercially available coatings. The results of the dry sliding tests were discussed and analyzed using coupling optical profilometry, field emission gun scanning electron microscopy (FEGSEM), and energy dispersive spectroscopy (EDS) techniques.…”

Constitutive analysis for the quantification of hardness decay in a superlattice CrN/NbN hard-coating

“…The present coating showed a significant thickness reduction, which more than halved, reaching a mean thickness of 1.2-1.4 μm after thermal cycling according to the C1 scheme at 900°C [75]. A non negligible fraction of the heavy metals (Nb and Cr) of which the coating is made diffused into the substrate.…”