Columnar grain boundaries are the weakest link in hard coatings: Insights from micro-cantilever testing with bridge notches
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.
Keywords
Cite
@article{arxiv.2411.12624,
title = {Columnar grain boundaries are the weakest link in hard coatings: Insights from micro-cantilever testing with bridge notches},
author = {Yinxia Zhang and Matthias Bartosik and Steffen Brinckmann and Ujjval Bansal and Subin Lee and Christoph Kirchlechner},
journal= {arXiv preprint arXiv:2411.12624},
year = {2024}
}
Comments
4 figures