Effect of metal ion irradiation on hard coating synthesis by physical vapor deposition
Abstract: The aim of this thesis is to understand and control how the ions in the plasma influence the film growth during thin film deposition processes. Two physical vapor deposition (PVD) techniques are investigated, namely magnetron sputtering and cathodic arc evaporation. For magnetron sputtering, the unconventional hybrid high-power impulse and direct current magnetron cosputtering (HiPIMS/DCMS) configuration is used in this work. By synchronizing the substrate bias pulses with the HiPIMS pulses by a time offset and duration, the metal ions from the target material can be selected to impinge the growing film, whereas the contribution of the working gas ions can be effectively reduced. Two aspects are explored, low-mass ion subplantation and heavy-mass ion irradiation.The thesis begins with establishing the correlation between N2 pressure and plasma properties of the cathodic arc evaporation process using Ti0.5Al0.5 target. The results show Ti ions are the dominant species, followed by Al+. On the other hand, due to the shorter mean free path of the species with increasing N2 pressure, the ion energies and the effective electron temperature decrease while electron density increases. Consequently, comparing the TiAlN coatings grown at lower and higher N2 pressures, the crystallographic textures changes from cubic 220 to 111 along the growth direction, and the residual stress reduces from compressive (-3.4 GPa) to almost stress-free (0.6 GPa).The rest of the thesis addresses the influence of ionized species on microstructures, with a focus on tuning film properties by ions in the plasma. Ti1-x(AlySi1-y)xN coatings (0.38 < x < 0.76 and 0.68 ≤ y ≤ 1.00) were deposited with an AlSi-HiPIMS/Ti-DCMS with synchronized substrate bias setup. The results show that the coatings deposited by this method have higher Al and Si solubilities in NaCl-structured TiN than other PVD techniques due to low mass ion subplantations. Additionally, a range of films with different compositions display a combination of high hardness (~ 30 GPa) and low residual stress (s < 0.5 GPa), which highlights the benefits of minimizing the Ar+ incorporation by synchronizing substrate bias to the Al+/Si+-rich portion of the HiPIMS pulses. The selected TiAlSiN coatings were then studied for the crater wear resistance of high-speed cutting performance on ball bearing steel (100Cr6). The effects of phase contents and microstructures on cutting performance are evaluated.This is further extended by a study of the influence of neutral and ion fluxes overlap and the subplantation range of low-mass ions. This is accomplished by introducing the 1-fold substrate table rotation, different target-to-substrate distances, and substrate bias voltage in a AlSi-HiPIMS/Ti-DCMS hybrid deposition process. The microstructure and phase analysis show the necessity of overlap between HiPIMS and DCMS fluxes to deposit TiAlSiN solid solutions. The compositional variation of the multilayers can be controlled by the applied substrate bias and table rotational speed. Rotation during deposition may yield coatings comparable in hardness to the ones without rotation at the expense of higher compressive stress.The effectiveness of controlling heavy ion irradiation is investigated by replacing external heating with high-mass W+ irradiation to grow dense and hard titanium tungsten carbide (TiWC) coatings by WC-HiPIMS/TiC-DCMS with synchronized bias technique. The ionization degree of W+ are controlled by the peak current density (0.27 ≤ JT ≤ 1.36 A/cm2). The results show that W+ irradiation effectively densified TiWC coatings without external heating. The total energy consumption per hour is reduced by 77% using the HiPIMS/DCMS setup without external heating, yet this TiWC coating is 10 GPa harder than similar coating grown by self-bias DCMS with heating.
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