1. Columnar grain boundaries are the weakest link in hard coatings: Insights from micro-cantilever testing with bridge notches
- Author
-
Zhang, Yinxia, Bartosik, Matthias, Brinckmann, Steffen, Bansal, Ujjval, Lee, Subin, and Kirchlechner, Christoph
- Subjects
Physics - Applied Physics ,Condensed Matter - Materials Science - 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., Comment: 4 figures
- Published
- 2024