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Remanufacturing and Advanced Machining
strength and the oxide layer improves chemical resistance. Each layer is commonly
ca. 500 nm thick, providing an overall coating thickness of 5–10 μm.
Among superhard materials, TiN/VN multilayer coating can be named as one of
the best examples, with hardness up to 56 GPa and nanoscale thickness of 5.2 nm.
However, this coating exhibits susceptibility to oxidation, which poses some limitations to its applications. ZrN/TiN multilayer coatings of 1.5 μm thickness demonstrate 30% longer tool life in difficult milling conditions, compared with uncoated
tools or tools coated with single ZrN layer.
Mechanical properties of multilayer coatings can be also improved by introduction of layers of new nanocrystalline or amorphous materials. For instance, TiN/
MoN coatings exhibit high hardness of ca. 30 GPa, which is 25% higher than that of
single-layer coatings, while their thickness is 25 nm (Pogrebnjak et al., 2019).
However, Łępicka et al. (2019) draw attention to the fact that even though TiN
is considered an almost all-purpose coating, examples of adverse effects and wear
intensification after TiN deposition have been reported, too. When a titanium nitride
coating is placed on mild or low-alloy steels, TiAl intermetallics, or aluminum 1000
series, wear resistance becomes ambiguous and dependent on the applied load. The
authors conclude that wear performance of metallic substrates coated with TiN
depends on friction conditions and material properties, especially the elastic modulus mismatch between an outer coating and an underlying substrate. They also suggest that other factors should be taken into consideration, such as differences in
chemical reactivity of the substrate and coating materials.
Remanufacturing and Advanced Machining
strength and the oxide layer improves chemical resistance. Each layer is commonly
ca. 500 nm thick, providing an overall coating thickness of 5–10 μm.
Among superhard materials, TiN/VN multilayer coating can be named as one of
the best examples, with hardness up to 56 GPa and nanoscale thickness of 5.2 nm.
However, this coating exhibits susceptibility to oxidation, which poses some limitations to its applications. ZrN/TiN multilayer coatings of 1.5 μm thickness demonstrate 30% longer tool life in difficult milling conditions, compared with uncoated
tools or tools coated with single ZrN layer.
Mechanical properties of multilayer coatings can be also improved by introduction of layers of new nanocrystalline or amorphous materials. For instance, TiN/
MoN coatings exhibit high hardness of ca. 30 GPa, which is 25% higher than that of
single-layer coatings, while their thickness is 25 nm (Pogrebnjak et al., 2019).
However, Łępicka et al. (2019) draw attention to the fact that even though TiN
is considered an almost all-purpose coating, examples of adverse effects and wear
intensification after TiN deposition have been reported, too. When a titanium nitride
coating is placed on mild or low-alloy steels, TiAl intermetallics, or aluminum 1000
series, wear resistance becomes ambiguous and dependent on the applied load. The
authors conclude that wear performance of metallic substrates coated with TiN
depends on friction conditions and material properties, especially the elastic modulus mismatch between an outer coating and an underlying substrate. They also suggest that other factors should be taken into consideration, such as differences in
chemical reactivity of the substrate and coating materials.