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Mechanical properties of Thin films |
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Contact deformation in TiN hard coatings |
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Multilayers of TiN/AlTiN |
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Benefits of multilayering in crack resistance |
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NiAl bond coats on Super Alloys |
Contact deformation in TiN hard coatings
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Thin columnar hard coatings of TiN accommodate indentation by slipping along their “weak” columnar boundaries. There is little or no transverse shear of the columns! |
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sharing: P=Total P2=supported by expanding cavity in substrate P1=supported by TiN columns before sliding |
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Thick films and soft substrates lead to a new mode of cracking arising out of a strain mismatch between a plastic substrate and a largely elastic film. |
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Domains of cracking /columnar shear Soft substrates cannot support thick films! If a coating on soft substrate performs poorly, making it thicker may make matters worse! |
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Multilayers of TiN/AlTiN
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Varying the substrate rotational speeds and a spatially varying plasma concentration in cathodic arc evaporation can lead to a wide variety of multilayer structures. |
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Schematic of Cathodic arc evaporation with planetary rotation |
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Slow rotation |
Fast rotation |
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Out of focus phase contrast bright field TEM images reveal small fluctuations ~2-4 nm layers which are homogeneously distributed ( fast rotation) or which lie at the boundary between alternating ~20-50nm layers of TiN and AlTiN (slow rotation) |
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How does multilayering influence indentation cracking?
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TiN displays edge and inclined cracking at low loads.
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Multilayering increases the critical load for edge cracking, while inclined cracks becomes discontinuous
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Extent of bending of layers (as opposed to columnar sliding) increases with layer refinement and offers an additional mechanism of strain accommodation |
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Small Scale Fracture testing of bond coated super alloy
Thermal Barrier Coating (TBC) System
Three Point Bending for studying Fracture Properties
FIB Notched Specimen: Depth of the Notch = 15 microns
