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The oxidation resistance of Hf 0.28 B 0.72 and Hf 0.11 Al 0.20 B 0.69 thin films was investigated comparatively at 700 °C for up to 8 h. Single-phase solid solution thin films were co-sputtered from HfB 2 and AlB 2 compound targets. After oxidation at 700 °C for 8 h an oxide scale thickness of 31  ±  2 nm was formed on Hf 0.11 Al 0.20 B 0.69 which corresponds to 14% of the scale thickness measured on Hf 0.28 B 0.72 . The improved oxidation resistance can be rationalized based on the chemical composition and the morphology of the formed oxide scales. On Hf 0.28 B 0.72 the formation of a porous, O, Hf, and B-containing scale and the formation of crystalline HfO 2 is observed. Whereas on Hf 0.11 Al 0.20 B 0.69 a dense, primarily amorphous scale containing O, Al, B as well as approximately 3 at% of Hf forms, which reduces the oxidation kinetics significantly by passivation. Benchmarking Hf 0.11 Al 0.20 B 0.69 with Ti–Al-based boride and nitride thin films with similar Al concentrations reveals superior oxidation behavior of the Hf-Al-based thin film. The incorporation of few at% of Hf in the oxide scale decelerates oxidation kinetics at 700 °C and leads to a reduction in oxide scale thickness of 21% and 47% compared to Ti 0.12 Al 0.21 B 0.67 and Ti 0.27 Al 0.21 N 0.52 , respectively. Contrary to Ti–Al-based diborides, Hf 0.11 Al 0.20 B 0.69 shows excellent oxidation behavior despite B-richness.

Autonomous health tracking of coated components via electrical resistance measurements requires physical connections between coating and readout. Here, the proof of concept for contactless tracking of decomposition in autonomous self‐reporting Cr‐Al‐B coatings is demonstrated. Contactless‐monitored electrical resistance changes of Cr0.34Al0.31B0.35 coatings reveal decomposition of Cr2AlB2 and Cr3AlB4 to CrB and CrB2. Comparison of contactless‐measured resistance data with in situ and ex situ high‐resolution scanning transmission electron microscopy, as well as ex situ X‐ray diffraction and elastic‐recoil detection analysis, reveals the untapped potential of assessing materials health data in extreme environments. More sustainable materials consumption is enabled by continuous or periodic contactless tracking of materials health data as the individual remaining component lifetime is utilized instead of the much shorter lifetime prediction resulting from safety‐factor‐based design approaches. Proof of concept for contactless tracking of decomposition in self‐reporting ceramic Cr‐Al‐B coatings in extreme environments by contactless resistivity measurements is demonstrated. To verify the results, high resolution in situ and ex situ methods are employed. A more sustainable resource usage is enabled by the contactless tracking of materials health data.

The oxidation resistance of Hf B and Hf Al B thin films was investigated comparatively at 700 °C for up to 8 h. Single-phase solid solution thin films were co-sputtered from HfB and AlB compound targets. After oxidation at 700 °C for 8 h an oxide scale thickness of 31   2 nm was formed on Hf Al B which corresponds to 14% of the scale thickness measured on Hf B . The improved oxidation resistance can be rationalized based on the chemical composition and the morphology of the formed oxide scales. On Hf B the formation of a porous, O, Hf, and B-containing scale and the formation of crystalline HfO is observed. Whereas on Hf Al B a dense, primarily amorphous scale containing O, Al, B as well as approximately 3 at% of Hf forms, which reduces the oxidation kinetics significantly by passivation. Benchmarking Hf Al B with Ti-Al-based boride and nitride thin films with similar Al concentrations reveals superior oxidation behavior of the Hf-Al-based thin film. The incorporation of few at% of Hf in the oxide scale decelerates oxidation kinetics at 700 °C and leads to a reduction in oxide scale thickness of 21% and 47% compared to Ti Al B and Ti Al N , respectively. Contrary to Ti-Al-based diborides, Hf Al B shows excellent oxidation behavior despite B-richness.

Zinc dialkyldithiophosphate (ZDDP), as the most prominent lubrication additive, forms tribofilms consisting primarily of zinc phosphate glasses containing sulfides. As sulfur is linked to environmental concerns, sulfur-free zinc phosphate coatings have been sputtered from a Zn3(PO4)2 target and investigated here. Based on the bridging to non-bridging oxygen ratio, determined by X-ray photoelectron spectroscopy (XPS), the as deposited coatings are classified as metaphosphates. As the annealing temperature is increased, the chain lengths are reduced, as witnessed by XPS data indicated by a loss of phosphorus and oxygen of the coating surface, likely due to hydrolysis with water from the atmosphere. Transmission electron microscopy energy-dispersive X-ray spectroscopy line scans show that the XPS-revealed composition change of the coating surface upon annealing occurs over the whole thickness of the coating. This alteration in composition and chain length reductions causes a rise in hardness, reduced Young's modulus, and wear resistance. Therefore, the properties of the artificial zinc phosphate tribofilms can be tailored via a thermally stimulated composition change, causing an alternation in chain length from meta- to orthophosphate and thereby enabling the design of coatings with desired mechanical properties.