TY - THES

T1 - Thermal stability and mechanical properties of arc evaporated Ti-Al-Zr-N hard coatings

AU - Glatz, Stefan

N1 - embargoed until 03-06-2018

PY - 2013

Y1 - 2013

N2 - Over the past years a lot of effort has been driven to develop different coating system for protecting tools against failure and hence to increase their lifetime. A typical protective coating for milling and cutting tool inserts is Ti1-xAlxN, which has a high thermal stability, good wear resistance and oxidation behaviour. Its thermal and mechanical properties are well investigated in respect to e.g. different deposition techniques and various chemical compositions. However, for further increasing machining speeds and tool lifetimes a further development of TiAlN coatings is necessary. One way to fulfil these requested properties can be alloying of TiAlN with e.g. zirconium. This supersaturated Ti1-x-yAlxZryN solid solution is beneficial for high temperature performance, as zirconium is able to enhance the oxidation resistance of the TiAlN coatings. In the present study the effect of substrate biasing and the aluminium content on the coating properties of arc evaporated Ti1-x-yAlxZryN is investigated. Therefore, an industrial scale INNOVA Balzers deposition plant is equipped with two different target types with chemical compositions of Ti0.475Al0.475Zr0.05 and Ti0.375Al0.575Zr0.05. The thin films were deposited at 500°C in 3.5 Pa nitrogen atmosphere on silicon (single crystalline), polycrystalline alumina (Al2O3) and high-speed steel substrate material. Furthermore, a foil of iron was coated, which was chemically removed afterwards to obtain substrate-free coating material. Thereby, any substrate influence during annealing treatments or XRD measurements can be avoided. Coatings obtained from Ti0.475Al0.475Zr0.05 and Ti0.375Al0.575Zr0.05 targets exhibit a chemical composition of Ti0.49Al0.44Zr0.07N and Ti0.39Al0.54Zr0.07N, respectively. Moreover, Ti0.49Al0.44Zr0.07N coatings exhibit a single phase cubic structure whereas a dual phase structure (cubic and wurtzite) was observed for Ti0.39Al0.54Zr0.07N. The BIAS variation between -40, -80 and -120 V leads to decreasing grain size, but does not have an influence on the single or dual phase character of the coatings. Nanoindentation and XRD measurements were used to analyse the hardness and structural development of the thin films after annealing treatments in vacuum with annealing temperatures starting from 600°C up to 1400°C. A pronounced age-hardening effect due to spinodal decomposition cannot be observed. However, Ti0.49Al0.44Zr0.07N coatings still exhibit a hardness of ~35 GPa after annealing to 900°C and more than 24 GPa after annealing to 1200°C. On the other hand, wurtzite phase containing Ti0.39Al0.54Zr0.07N coatings show hardness values of ~22 GPa in as deposited state, which slightly increases to ~25 GPa after annealing to ~900°C, before again a decrease can be observed. However, all single phase cubic thin films exhibit higher hardness values than the dual phase coatings with additional wurtzite phase fractions. Therefore, the oxidation behaviour during thermal treatment for 20h in air at 850°C and 950°C was studied for coatings exhibiting single phase cubic structure in as dep. state. Our observations show that all coatings are protected by an Al2O3/TiO2 oxide layer at 850°C and are fully oxidized if treated at 950°C. In addition, the cross-sectional micrographs studied by scanning electron microscopy and energy dispersive X-ray spectroscopy linescans reveal a layered structure after oxidation treatment at 950°C, which can be a result of repeated cracking and regeneration of the protective Al2O3 oxide scale. We clearly showed that it is possible to deposit single phase cubic Ti0.49Al0.44Zr0.07N in an arc evaporation plant. These coatings show independently from the BIAS voltage far better oxidation resistance than TiAlN, a clearly increased thermal stability and high hardness of even 35 GPa after annealing at 900°C. However, too high Al fractions lead to dual phase structured coatings and hence d

AB - Over the past years a lot of effort has been driven to develop different coating system for protecting tools against failure and hence to increase their lifetime. A typical protective coating for milling and cutting tool inserts is Ti1-xAlxN, which has a high thermal stability, good wear resistance and oxidation behaviour. Its thermal and mechanical properties are well investigated in respect to e.g. different deposition techniques and various chemical compositions. However, for further increasing machining speeds and tool lifetimes a further development of TiAlN coatings is necessary. One way to fulfil these requested properties can be alloying of TiAlN with e.g. zirconium. This supersaturated Ti1-x-yAlxZryN solid solution is beneficial for high temperature performance, as zirconium is able to enhance the oxidation resistance of the TiAlN coatings. In the present study the effect of substrate biasing and the aluminium content on the coating properties of arc evaporated Ti1-x-yAlxZryN is investigated. Therefore, an industrial scale INNOVA Balzers deposition plant is equipped with two different target types with chemical compositions of Ti0.475Al0.475Zr0.05 and Ti0.375Al0.575Zr0.05. The thin films were deposited at 500°C in 3.5 Pa nitrogen atmosphere on silicon (single crystalline), polycrystalline alumina (Al2O3) and high-speed steel substrate material. Furthermore, a foil of iron was coated, which was chemically removed afterwards to obtain substrate-free coating material. Thereby, any substrate influence during annealing treatments or XRD measurements can be avoided. Coatings obtained from Ti0.475Al0.475Zr0.05 and Ti0.375Al0.575Zr0.05 targets exhibit a chemical composition of Ti0.49Al0.44Zr0.07N and Ti0.39Al0.54Zr0.07N, respectively. Moreover, Ti0.49Al0.44Zr0.07N coatings exhibit a single phase cubic structure whereas a dual phase structure (cubic and wurtzite) was observed for Ti0.39Al0.54Zr0.07N. The BIAS variation between -40, -80 and -120 V leads to decreasing grain size, but does not have an influence on the single or dual phase character of the coatings. Nanoindentation and XRD measurements were used to analyse the hardness and structural development of the thin films after annealing treatments in vacuum with annealing temperatures starting from 600°C up to 1400°C. A pronounced age-hardening effect due to spinodal decomposition cannot be observed. However, Ti0.49Al0.44Zr0.07N coatings still exhibit a hardness of ~35 GPa after annealing to 900°C and more than 24 GPa after annealing to 1200°C. On the other hand, wurtzite phase containing Ti0.39Al0.54Zr0.07N coatings show hardness values of ~22 GPa in as deposited state, which slightly increases to ~25 GPa after annealing to ~900°C, before again a decrease can be observed. However, all single phase cubic thin films exhibit higher hardness values than the dual phase coatings with additional wurtzite phase fractions. Therefore, the oxidation behaviour during thermal treatment for 20h in air at 850°C and 950°C was studied for coatings exhibiting single phase cubic structure in as dep. state. Our observations show that all coatings are protected by an Al2O3/TiO2 oxide layer at 850°C and are fully oxidized if treated at 950°C. In addition, the cross-sectional micrographs studied by scanning electron microscopy and energy dispersive X-ray spectroscopy linescans reveal a layered structure after oxidation treatment at 950°C, which can be a result of repeated cracking and regeneration of the protective Al2O3 oxide scale. We clearly showed that it is possible to deposit single phase cubic Ti0.49Al0.44Zr0.07N in an arc evaporation plant. These coatings show independently from the BIAS voltage far better oxidation resistance than TiAlN, a clearly increased thermal stability and high hardness of even 35 GPa after annealing at 900°C. However, too high Al fractions lead to dual phase structured coatings and hence d

KW - TiAlN

KW - ZrAlN

KW - thermische Stabilität

KW - Oxidationswiderstand

KW - PVD

KW - Lichtbogenverdampfen

KW - physikalische Dampfphasenabscheidung

KW - Härtesteigerung

KW - TiAlN

KW - ZrAlN

KW - thermal stability

KW - oxidation resistance

KW - age-hardening

KW - PVD

KW - physical vapour deposition

KW - arc evaporation

M3 - Diploma Thesis

ER -