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arXiv · 2411.12624

Columnar grain boundaries are the weakest link in hard coatings: Insights from micro-cantilever testing with bridge notches

Yinxia Zhang·Matthias Bartosik·Steffen Brinckmann·Ujjval Bansal·Subin Lee·Christoph Kirchlechner
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Abstract

The effect of columnar grain boundaries on the fracture toughness was investigated using micro-cantilever fracture testing with a bridge notch, and a unique hard coating consisting of two distinct microstructures: one with columnar grains and another with an epitaxial layer. The bridge-failure sequence qualitatively demonstrated the lower fracture toughness at the columnar-grained structure. Quantitatively, the load drops measured at bridge-failure also revealed a significant decrease in fracture toughness due to grain boundaries. Specifically, the fracture toughness decreased by around 30%, from 4.1 +/- 0.4 MPa m1/2 for epitaxial microstructure to 3.0 +/- 0.3 MPa m1/2 for columnar-grained structure. The fracture toughness of columnar-grained structure is 3.0 +/- 0.2 MPa m1/2 perpendicular to the growth direction higher than 2.7 +/- 0.1 MPa m1/2 along it. These findings suggest that future optimization of hard coatings should focus on grain boundary toughening, and the present toolbox proposes suitable techniques for such microstructure optimization.

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Yinxia Zhang, Matthias Bartosik, Steffen Brinckmann, Ujjval Bansal, Subin Lee, Christoph Kirchlechner. 2024-11-19. Columnar grain boundaries are the weakest link in hard coatings: Insights from micro-cantilever testing with bridge notches. https://arxiv.org/abs/2411.12624

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