TY - JOUR
T1 - Precipitation-based grain boundary design alters Inter- to Trans-granular Fracture in AlCrN Thin Films
AU - Meindlhumer, Michael
AU - Ziegelwanger, Tobias
AU - Zalesak, Jakub
AU - Hans, Marcus
AU - Löfler, Lukas
AU - Spor, Stefan
AU - Jäger, Nikolaus
AU - Stark, Andreas
AU - Hruby, Hynek
AU - Daniel, Rostislav
AU - Holec, David
AU - Schneider, Jochen M.
AU - Mitterer, Christian
AU - Keckes, Jozef
N1 - https://doi.org/10.1016/j.actamat.2022.118156
PY - 2022/9/15
Y1 - 2022/9/15
N2 - Despite their high hardness and indentation modulus, nanostructured crystalline ceramic thin films produced by physical vapour deposition usually lack sufficient fracture strength and toughness. This brittleness is often caused by underdense columnar grain boundaries of low cohesive energy, which serve as preferential paths for crack propagation. In this study, mechanical and structural properties of arc-evaporated Al0.9Cr0.1N thin films were analyzed using micromechanical tests, electron microscopy, atom probe tomography and in situ high-energy high-temperature grazing incidence transmission X-ray diffraction. Vacuum annealing at 1100°C resulted in the formation of regularly-distributed globular cubic Cr(Al)N and elongated cubic CrN precipitates at intracrystalline Cr-enriched sublayers and at columnar grain boundaries with sizes of ∼5 and ∼30 nm, respectively. Consequently, in situ micromechanical testing before and after the heat treatment revealed simultaneous enhancement of Young's modulus, fracture stress and fracture toughness by ∼35, 60 and 10%, respectively. The annealing-induced concomitant improvement of toughness and strength was inferred to precipitations observed within grains as well as at grain boundaries enhancing the cohesive energy of the grain boundaries and thereby altering the crack propagation pathway from inter- to transcrystalline. The here reported experimental data unveil the hitherto untapped potential of precipitation-based grain boundary design for the improvement of mechanical properties of transition metal nitride thin films.
AB - Despite their high hardness and indentation modulus, nanostructured crystalline ceramic thin films produced by physical vapour deposition usually lack sufficient fracture strength and toughness. This brittleness is often caused by underdense columnar grain boundaries of low cohesive energy, which serve as preferential paths for crack propagation. In this study, mechanical and structural properties of arc-evaporated Al0.9Cr0.1N thin films were analyzed using micromechanical tests, electron microscopy, atom probe tomography and in situ high-energy high-temperature grazing incidence transmission X-ray diffraction. Vacuum annealing at 1100°C resulted in the formation of regularly-distributed globular cubic Cr(Al)N and elongated cubic CrN precipitates at intracrystalline Cr-enriched sublayers and at columnar grain boundaries with sizes of ∼5 and ∼30 nm, respectively. Consequently, in situ micromechanical testing before and after the heat treatment revealed simultaneous enhancement of Young's modulus, fracture stress and fracture toughness by ∼35, 60 and 10%, respectively. The annealing-induced concomitant improvement of toughness and strength was inferred to precipitations observed within grains as well as at grain boundaries enhancing the cohesive energy of the grain boundaries and thereby altering the crack propagation pathway from inter- to transcrystalline. The here reported experimental data unveil the hitherto untapped potential of precipitation-based grain boundary design for the improvement of mechanical properties of transition metal nitride thin films.
KW - AlCrN
KW - Heat treatment
KW - Grain-boundary segregation engineering
KW - Micromechanics
U2 - 10.1016/j.actamat.2022.118156
DO - 10.1016/j.actamat.2022.118156
M3 - Article
SN - 1359-6454
VL - 237.2022
JO - Acta materialia
JF - Acta materialia
IS - 15 September
M1 - 118156
ER -