Microstructure and plastic deformation of textured CVD alumina coatings
The microstructures of three different CVD α-Al2O3 layers deposited onto a Ti(C,N,O) bonding layer were studied. Grain boundary diffusion of heavy elements from the substrate to the bonding layer/α-Al2O3 interface was observed. This may be the cause of a disturbance in the early growth of α-Al2O3. Additionally, it was found that the number of interfacial pores at the bonding layer/α-Al2O3 interface increased by introducing the H2S gas. The H2S gas also promoted an earlier development of the (0001) texture. The orientation of the grains was developed to the desired texture both as a gradual change over several grains and as an abrupt transformation from one grain to another.
The probability of plastic deformation in different wear zones on the rake face of a cutting tool was investigated theoretically and experimentally by analyzing Schmid factors for textured α-Al2O3 coatings. Schmid factor diagrams were constructed using MATLAB/MTEX and used to extract frequency distributions for different slip systems and textures. The results were compared with lateral distribution maps of Schmid factors obtained from experimental coatings. It was observed that basal slip is most easily activated in the transition zone, followed by prismatic slip systems 1 and 2 in coatings with an (0001)-texture. The homogeneous plastic deformation behavior observed in this coating is also connected to mostly high Schmid factors in the m-value distribution. The differences between the m-value distributions for the three slip systems are not that pronounced in the (01-12) and (11-20) textures, and the distributions are relatively wide. The low wear rate and more homogeneous deformation of the coating with (0001) texture compared to the other coating textures may be the result of the high plasticity, offered by the easy activation of basal slip and prismatic 1 slip, and the low spread of Schmid factor values at the transition zone.
In conclusion, the results presented in this thesis form a knowledge platform that can be used to understand the microstructure and wear mechanisms of textured CVD α-alumina coatings.
Chalmers, Fysik, Mikrostrukturfysik
Microstructure investigation of textured CVD alumina coatings
INTERNATIONAL JOURNAL OF REFRACTORY METALS & HARD MATERIALS,; Vol. 87(2020)
Paper i proceeding
Shoja, S, Alm, O, Norgren, S, Andrén, H.O, Halvarsson, M. Calculated and experimental Schmid factors for chip flow deformation of textured CVD α-alumina coatings
Nedbrytningsmekanismer för CVD-skikt vid metallbearbetning
Stiftelsen för Strategisk forskning (SSF), 2017-01-01 -- 2021-12-31.
Bearbetnings-, yt- och fogningsteknik
Metallurgi och metalliska material
Chalmers tekniska högskola
PJ hall and Zoom
Opponent: Staffan Jacobson