Cutting tools with hard coatings have been successfully employed in the industry for almost 50 years. Nowadays, 85% of all cemented carbide tools are coated. There is an increasing demand for ever more efficient tools driven by the use of new workpiece materials as well as the demand for increased productivity of manufacturing processes. A historical review of the development of CVD and PVD processes shows a continuous improvement of successful coating materials through adjustments of the chemical composition and the coating architecture. Especially nanostructured PVD coatings managed to establish themselves on the market surprisingly quickly. Cutting tools are an excellent example for how the development of coated products is traced methodologically by means of a holistic view over the application. The demand for innovative tooling concepts will continue to exist in the future, as will the high potential for this aim to be achieved through high-performance coatings on improved cutting materials with adjusted tool design.

High-performance coatings for cutting tools

Multilayer (TiN, TiAlN) ceramic coatings for nuclear fuel cladding

Toughness, besides hardness, is one of the most important properties of wear-resistant coatings. We use ab initio density-functional theory calculations to investigate the mechanical properties of ...

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Electronic mechanism for toughness enhancement in Ti x M 1 − x N ( M = Mo and W)

Coating used for radioactive fuel or a structural component in radioactive fuel reactors, e.g., nuclear fuel cladding alloys, can include a ternary monolithic coating or multiple layers of one or more layers of TiAlN TiZrN, TiCrN, TiNbN and/or CrN, ZrN, NbN, TiN, TaN, HfN. TiHfN, TaHfN, TaNbN, or mixed combinations and/or CrN, ZrN, NbN, TiN, TaN, Si3N4, and/or HfN. In addition, one or more layers can be comprised of a nitride, oxide, or carbide or mixed combination (i.e., carbonides, oxynitrides, oxycarbides, etc.) from Ti, Al, Zr, Cr, Si, Nb, Hf, or mixed combination (i.e., TiAlC 1-x N x ). The multilayer coating can be doped with a dopant.

Ceramic coating for corrosion resistance of nuclear fuel cladding

Coatings like TiN or TiAlN are well established as hard and wear resistant tool coatings. These coatings often are prepared by PVD techniques like arc evaporation or d.c. magnetron sputtering. Typical micro hardness values of such hard coatings are in the range of 30 GPa. Compared to d.c. magnetron sputtering processes the pulsed magnetron sputter deposition technique could be shown as a clear advancement. Furthermore pure TiAlN hard coatings as well as TiAlN coatings modified by addition of elements like Si and Cr were prepared in order to improve the coating properties using the pulsed magnetron sputter technique in a batch coater equipped with 4 targets. Coatings prepared with the pulsed sputter process showed both high hardness and high wear resistance. The application potential of pulsed sputtered TiAlN coatings is demonstrated by turning test results of coated cemented carbide cutting inserts. Beside hardness and wear, other properties like adhesion or high temperature stability were determined. Cross sectional SEM images revealed the growth structure in dependence of the applied substrate bias and of the added elements. The chemical composition of the coatings was investigated by electron microprobe analysis and the phase and crystal size were determined by X-ray diffraction. Using the pulsed magnetron sputter process the coating properties, especially the hardness and the morphology, could be significantly improved. With indentation hardness values in the range of 40 GPa the region of super hard materials could be reached.

Modified TiAlN coatings prepared by d.c. pulsed magnetron sputtering

It is recognized that the quality and performance of PVD coatings on tungsten carbide based cutting tools are strongly affected by the level of residual stress as it may cause the coatings to delaminate from the substrate and affect the tool life. Here we report on the substrate bias as an important parameter to affect the compressive stress and the texture in TiAlN PVD coatings on WC/Co cutting inserts as analyzed by X-ray diffraction. Approximately 3 μm TiAlN coatings were deposited by arc evaporation with constant process parameters except for the negative substrate bias, which was varied between 40, 70, 100, 140 and 200 V. The residual stress was analyzed using X-ray diffraction and the sin 2 ψ method was used to evaluate the data. The compressive stress increased with increasing bias from − 1.7 GPa for the coating deposited at 40 V to about − 5 GPa for the 70–200 V coatings. As seen in SEM-images, the coatings prepared at higher bias (140 and 200 V) showed a glassy-like type of structure, with {111} texture and with a lattice parameter close to TiN. For the 40 V coating, a columnar type of structure with pronounced {200} texture was observed. Nano-indentation measurements show an increase in hardness by 15% in the bias range studied. Cutting tests show a correlation between the increase of the substrate bias and the edge line coating delamination, and also give an indication of a critical residual stress level for these coatings.

M. Ahlgren

Papers

Influence of bias variation on residual stress and texture in TiAlN PVD coatings