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Mechanical properties and machining performance of Ti1−xAlxN-coated cutting tools
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.
Linköping University, Department of Physics, Chemistry and Biology, Thin Film Physics. Linköping University, The Institute of Technology.ORCID iD: 0000-0002-2837-3656
Division of Engineering Materials, The Sirius Laboratory, Luleå University of Technology, Luleå, Sweden.ORCID iD: 0000-0002-2286-5588
SECO Tools AB.
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2005 (English)In: Surface & Coatings Technology, ISSN 0257-8972, E-ISSN 1879-3347, Vol. 191, no 2-3, 384-392 p.Article in journal (Refereed) Published
Abstract [en]

The mechanical properties and machining performance of Ti1−xAlxN-coated cutting tools have been investigated. Processing by arc evaporation using cathodes with a range of compositions was performed to obtain coatings with compositions x=0, x=0.25, x=0.33, x=0.50, x=0.66 and x=0.74. As-deposited coatings with x≤0.66 had metastable cubic structures, whereas x=0.74 yielded two-phase coatings consisting of cubic and hexagonal structures. The as-deposited and isothermally annealed coatings were characterised by nanoindentation, scanning electron microscopy (SEM) and X-ray diffraction (XRD). Cutting tests revealing tool wear mechanisms were also performed. Results show that the Al content, x, promotes a (200) preferred crystallographic orientation and has a large influence on the hardness of as-deposited coatings. The high hardness (∼37 GPa) and texture of the as-deposited Ti1−xAlxN coatings are retained for annealing temperatures up to 950 °C, which indicates a superior stability of this system compared to TiN and Ti(C,N) coatings. We propose that competing mechanisms are responsible for the effectively constant hardness: softening by residual stress relaxation through lattice defect annihilation is balanced by hardening from formation of a coherent nanocomposite structure of c-TiN and c-AlN domains by spinodal decomposition. This example of secondary-phase transformation (age-) hardening is proposed as a new route for advanced surface engineering, and for the development of future generation hard coatings.

Place, publisher, year, edition, pages
2005. Vol. 191, no 2-3, 384-392 p.
Keyword [en]
Hard coatings; TiAlN; Age hardening; Spinodal decomposition; Transition; Metal nitrides
National Category
Condensed Matter Physics
Identifiers
URN: urn:nbn:se:liu:diva-18823DOI: 10.1016/j.surfcoat.2004.04.056OAI: oai:DiVA.org:liu-18823DiVA: diva2:221740
Available from: 2009-06-08 Created: 2009-06-05 Last updated: 2016-08-31Bibliographically approved
In thesis
1. Thermal stability and age hardening of TiN-based thin films
Open this publication in new window or tab >>Thermal stability and age hardening of TiN-based thin films
2005 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The work presented herein is about characterizing phase transformations in cathodic arc plasma-deposited Ti1-xA1xN and Ti1-zZrzN thin films for cutting tool applications, and to investigate how the films' mechanical properties are affected by such transformations during thermal annealing. Post-deposition analyses were carried out using X-ray diffraction (XRD), transmission electron microscopy (TEM), nanoindentation, four-point probe sheet resistance, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and Rutherford backscattering spectrometry (RBS). For Ti1-xA1xN, residual stresses relax through annihilation of depositioninduced lattice defects in the 500-900°C regime. Stress relaxation is a multiple process with activation energies of 2.0-2.9 eV. At ~900°C, phase transformation from the as-deposited metastable single-phase [NaCl] structure into the thermodynamically stable [NaCl]-TiN and [wurtzite]-A1N proceeds through spinodal decomposition, during which [NaCl]-TiN and [NaCl]-A1N domains form from the [NaCl]-Ti1-x,A1xN matrix. Activation energies for the transformation process of 2.9-3.5 eV indicate grain boundary and defect-assisted segregation of Ti and A1. The films age harden during transformation, with an increase in film hardness from the as-deposited condition of ~35 GPa to ~36-37 GPa following post-deposition annealing at 900°C, while pure TiN softens to ~20 GPa. Hardening originates from coherency strains due to lattice-mismatch between [NaCl]-structure TiN and AIN domains formed during initial stages of spinodal decomposition. Ti1-xA1xN-coated cutting tools can therefore be said to 'adapt' to the high temperatures and cutting forces encountered during in-service machining operations. For Ti1-zZrzN, calculations on phase stabilities using density-functional theory (OFT) show that the pseudo-binary system exhibits a miscibility gap. Thus, there is a driving force for transformation from the as-deposited metastable single-phase [NaCl] structure into [NaCl]-structure TiN and ZrN components. For such compositions, an essentially retained film hardness after post-deposition annealing at 1100-1200°C has been observed. The principal hardening mechanism for this particular nitride thin film system is proposed to be solid-solution hardening through localized lattice strain fields originating from difference in atomic radius of Ti and Zr. Finally, single-crystal Ti2A1N thin films belonging to the so-called MAX-phase class of materials have been successfully synthesized by reactive magnetron sputtering. The results are promising for the prospects of synthesizing a range of MAX-phase nitride materials as single-crystal thin films and polycrystalline coatings.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2005. 68 p.
Series
Linköping Studies in Science and Technology. Dissertations, ISSN 0345-7524 ; 922
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-28396 (URN)13532 (Local ID)91-852-9728-3 (ISBN)13532 (Archive number)13532 (OAI)
Public defence
2005-02-25, Planck, Fysikhuset, Campus Valla, Linköpings Universitet, Linköping, 10:15 (English)
Opponent
Available from: 2009-10-09 Created: 2009-10-09 Last updated: 2012-11-27Bibliographically approved
2. Arc evaporated wear-resistant nitride coatings for metal cutting tools
Open this publication in new window or tab >>Arc evaporated wear-resistant nitride coatings for metal cutting tools
2008 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

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.

Place, publisher, year, edition, pages
Linköping: Linköpings universitet, 2008. 33 p.
Series
Linköping Studies in Science and Technology. Thesis, ISSN 0280-7971 ; 1375
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-44911 (URN)78251 (Local ID)978-91-7393-849-5 (ISBN)78251 (Archive number)78251 (OAI)
Available from: 2009-10-10 Created: 2009-10-10 Last updated: 2013-11-22

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Hörling, AndersHultman, LarsOdén, Magnus

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