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- Hörling, Anders, et al.
(författare)
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Thermal stability, microstructure and mechanical properties of Ti1 − xZrxN thin films
- 2008
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Ingår i: Thin Solid Films. - : Elsevier BV. - 0040-6090 .- 1879-2731. ; 516:18, s. 6421-6431
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Tidskriftsartikel (refereegranskat)abstract
- Single-phase [NaCl]-structure Ti1 − xZrxN thin films (0 < x < 1) have been deposited using cathodic arc plasma deposition. The films were investigated using X-ray diffraction (XRD), transmission electron microscopy, differential scanning calorimetry (DSC), and nanoindentation. Density functional theory calculations on phase stabilities show that the pseudo-binary TiN–ZrN system exhibits a miscibility gap, extending over 0 ≤ x ≤ 0.99 at 1000 °C, with respect to phase transformation from a solid solution into a two-phase mixture of [NaCl]-structure TiN and ZrN components. The films were found to retain their as-deposited single-phase structure during post-deposition annealing at 600 °C (18 h), 700 °C (12 h), 1100 and 1200 °C (2 h), and for as long as 195 h at 600 °C. DSC revealed no heat flow during annealing, similar to TiN, and only the x = 0.53 film exhibited a slight increase in XRD peak broadening after annealing at 1200 °C, consistent with spinodal decomposition. This effective thermal stability of the alloys is explained by the combination of a limited driving force for phase transformation and an insufficient atom diffusivity. In terms of mechanical properties, films with composition deepest within the miscibility gap showed a hardness of ∼ 30 GPa after annealing at 1100–1200 °C; a value only moderately lower than in the as-deposited condition. The principal hardening mechanism for the Ti1 − xZrxN films is proposed to be solid-solution hardening through local lattice strain fields originating from difference in atomic radius of Ti and Zr. The material system is thus promising for cutting tool applications.
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| 2. |
- Sjölén, Jacob, 1977-
(författare)
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Arc evaporated wear-resistant nitride coatings for metal cutting tools
- 2008
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Thesis is dedicated to increase the understanding of arc evaporated PVD coatings as wear resistant layers on metal cutting tools. The approach is to study coatings that have excellent performance in metal cutting applications, specifically (Ti,Al)N and (Ti,Si)N in terms of thermal and mechanical properties, and to correlate this to their microstructure, stress state, and composition. The effect of addition of oxygen into (Ti,Al)N is also evaluated in terms of structure, chemical bonding, and mechanical properties. It is shown that metastable fcc-(Ti,Al)N coatings separate into Ti-rich and Al-rich fcc-(Ti,Al)N zones via spinodal decomposition at 800 - 1000 °C, which acts as a hardening mechanism. This is followed by nucleation and growth into the stable phases fcc-TiN and hex-AlN at T>1000°C, with subsequent loss of hardness. These structural changes are correlated to the cutting performance, showing that the initial spinodal phase separation improves the performance. The success of (Ti,Al)N in metal cutting applications is, hence, due not only to the well documented oxidation resistance, but also to the spinodal decomposition process, which is active at the typical temperatures at the cutting edge of an engaged cutting insert. The potential subsequent renucleation process is, however, detrimental in metal cutting applications. Oxygen is commonly regarded as a contamination in PVD coating processes due to the risk of formation of insulating layers. This study, however, shows that by using arcevaporation, up to 35 at.% O can be incorporated into (Ti,Al)N coatings without altering its NaCl-structure. 1t is inferred that O substitutes for N in the lattice and (Ti,Al)(O,N) is formed. The incorporation of small amounts of oxygen (up to 13 at.%) improves the cutting performance by reducing the risk of chipping. However, at higher oxygen levels, the wear resistant properties are dramatically reduced. Finally, is shown that it is poss ible to replace at least 14 at.% Ti by Si, without altering the NaCl-structure in (Ti,Si)N coatings. The measured hardness of solid solution fcc-(Ti,Si)N is nearly a linear function of Si-content in the coating (from 31 GPa in TiN up to 45 GPa in (Ti0.86Si0.14)N). The hardness is also retained after annealing at 900 oC for 2h.
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