Abstract
Although α– and κ–Al2O3 hard coatings deposited by chemical vapor deposition are well established in the metal-cutting industry for their ability to increase the performance and lifetime of cutting tools, the literature on their fracture properties is scarce. Thus, within this study, the microstructure and mechanical properties of α– and κ–Al2O3 coatings were investigated and compared to each other. X-ray diffraction and scanning electron microscopy combined with electron backscatter diffraction showed that both coatings exhibited a fiber texture, where the α-Al2O3 coating displayed a (0001) texture and the κ–Al2O3 coating a (001) texture with a certain (013) contribution. Higher hardness and Young’s modulus values of 31.0 ± 0.9 GPa and 474.6 ± 12.5 GPa, respectively, were obtained for the α–Al2O3 coating, compared to 24.2 ± 0.8 GPa and 356.8 ± 7.9 GPa for κ–Al2O3. While the α–Al2O3 coating exhibited a higher fracture stress of 8.1 ± 0.3 GPa (compared to 6.4 ± 0.6 GPa for κ–Al2O3), the κ–Al2O3 coating showed a higher fracture toughness of 4.4 ± 0.3 MPa*m1/2 (compared to 3.2 ± 0.3 MPa*m1/2 for alpha).
Highlights
Wear-resistant coatings deposited by chemical or physical vapor deposition (CVD, PVD) are commonly used in the metal-cutting industry to increase the performance and lifetime of cemented carbide cutting inserts [1]
The unit cell of α–Al2O3 consists of six layers of oxygen anions and six layers of aluminum cations. α–Al2O3 is described by the hexagonal cell, where the oxygen anions are packed in a hexagonal close-packed arrangement with aluminum cations in two thirds of the octahedral sites
Within this study, α–Al2O3 and κ–Al2O3 coatings were synthesized on cemented carbide substrates using thermally activated CVD
Summary
Wear-resistant coatings deposited by chemical or physical vapor deposition (CVD, PVD) are commonly used in the metal-cutting industry to increase the performance and lifetime of cemented carbide cutting inserts [1]. The thermodynamically stable α-Al2O3 and the metastable κ–Al2O3 are used as wear-resistant coatings in order to increase the performance of cutting tools [9,10]. The main disadvantage of the metastable κ–Al2O3 is the phase transformation to the thermodynamically stable α–Al2O3 at elevated temperatures (≥1000 ◦C).
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