Significant elastic anisotropy in Ti1−x_{1-x}Alx_xN alloys

Strong compositional-dependent elastic properties have been observed theoretically and experimentally in Ti$_{1-x}$Al$_x$ N alloys. The elastic constant, C$_{11}$, changes by more than 50% depending on the Al-content. Increasing the Al-content weakens the average bond strength in the local octahedral arrangements resulting in a more compliant material. On the other hand, it enhances the directional (covalent) nature of the nearest neighbor bonds that results in greater elastic anisotropy and higher sound velocities. The strong dependence of the elastic properties on the Al-content offers new insight into the detailed understanding of the spinodal decomposition and age hardening in Ti$_{1-x}$Al$_x$N alloys.Comment: 3 figures, 3 page

Significant elastic anisotropy in Ti1−x_{1-x}Alx_xN alloys

Strong compositional-dependent elastic properties have been observed theoretically and experimentally in Ti$_{1-x}$Al$_x$ N alloys. The elastic constant, C$_{11}$, changes by more than 50% depending on the Al-content. Increasing the Al-content weakens the average bond strength in the local octahedral arrangements resulting in a more compliant material. On the other hand, it enhances the directional (covalent) nature of the nearest neighbor bonds that results in greater elastic anisotropy and higher sound velocities. The strong dependence of the elastic properties on the Al-content offers new insight into the detailed understanding of the spinodal decomposition and age hardening in Ti$_{1-x}$Al$_x$N alloys.Comment: 3 figures, 3 page

Temperature-dependent elastic properties of Ti_(1−x)Al_xN alloys

Ti_(1−x)Al_xN is a technologically important alloy that undergoes a process of high temperature age-hardening that is strongly influenced by its elastic properties. We have performed first principles calculations of the elastic constants and anisotropy using the symmetry imposed force constant temperature dependent effective potential method, which include lattice vibrations and therefore the effects of temperature, including thermal expansion and intrinsic anharmonicity. These are compared with in situ high temperature x-ray diffraction measurements of the lattice parameter. We show that anharmonic effects are crucial to the recovery of finite temperature elasticity. The effects of thermal expansion and intrinsic anharmonicity on the elastic constants are of the same order, and cannot be considered separately. Furthermore, the effect of thermal expansion on elastic constants is such that the volume change induced by zero point motion has a significant effect. For TiAlN, the elastic constants soften non-uniformly with temperature: C_(11) decreases substantially when the temperature increases for all compositions, resulting in an increased anisotropy. These findings suggest that an increased Al content and annealing at higher temperatures will result in a harder alloy

High temperature behavior of arc evaporated ZrAlN and TiAlN thin films

Hard coatings can extend the life time of a tool substantially and enable higher cutting speeds which increase the productivity in the cutting application. The aim with this thesis is to extend the understanding on how the microstructure and mechanical properties are affected by high temperatures similar to what a cutting tool can reach during operation. Thin films of ZrAlN and TiAlN have been deposited using cathodic arc-evaporation. The microstructure of as-deposited and annealed films has been studied using electron microscopy and x-ray scattering. The thermal stability has been characterized by calorimetry and thermogravity and the mechanical properties have been investigated by  nanoindentation. The microstructure of Zr1−xAlxN thin films was studied as a function of composition, deposition conditions, and annealing temperature. The structure was found to depend on the Al content where a low (x < 0.38) Al-content results in cubic-structured ZrAlN while for x > 0.70 the structure is hexagonal. For intermediate Al contents (0.38 < x < 0.70), a  nanocomposite structure with a mixture of cubic, hexagonal and amorphous phases is obtained. The cubic ZrAlN phase transforms by nucleation and growth of hexagonal AlN when annealed above 900 ◦C. Annealing of hexagonal ZrAlN thin films (x > 0.70) above 900 ◦C causes formation of AlN and ZrN rich domains within the hexagonal lattice. Annealing of nanocomposite ZrAlN thin films results in formation of cubic ZrN and hexagonal AlN. The transformation is initiated by nucleation and growth of cubic ZrN at temperatures of 1100 ◦C while the AlN-rich domains are still amorphous or nanocrystalline. Growth of hexagonal AlN is suppressed by the high nitrogen content of the films and takes place at annealing temperatures of 1400 ◦C. In the more well known TiAlN system, the initial stage of decomposition is spinodal with formation of cubic structured domains enriched in TiN and AlN. By a combination of in-situ xray scattering techniques during annealing and phase field simulations, both the microstructure that evolves during decomposition and the decomposition rate are found to depend on the composition. The results further show that early formation of hexagonal AlN domains during decomposition can cause formation of strains in the cubic TiAlN phase

Phase transformations in nanocomposite ZrAlN thin films during annealing

Nanocomposite Zr0.52Al0.48N1.11 thin films consisting of crystalline grains surrounded by an amorphous matrix were deposited using cathodic arc evaporation. The structure evolution after annealing of the films was studied using high-energy x-ray scattering and transmission electron microscopy. The mechanical properties were characterized by nanoindentation on as-deposited and annealed films. After annealing in temperatures of 1050-1400 ◦C nucleation and grain growth of cubic ZrN takes place in the film. This increases the hardness, which reaches a maximum while parts of the film remain amorphous. Grain growth of the hexagonal AlN phase occurs above 1400 ◦C.funding agencies|Swedish Research Council (VR)||VINNEX center of Excellence on Functional Nanoscale Materials (FunMat)||U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences|DE-AC02-06CH11357|Linnaeus Grants||</p

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Wear behavior of ZrAlN coated cutting tools during turning

In this study we explore the cutting performance of ZrAlN coatings. WC:Co cutting inserts coated by cathodic arc evaporated Zr1-xAlxN coatings with x between 0 and 0.83 were testeciin a longitudinal turning operation. The progress of wear was studied by optical microscopy and the used inserts were studied by electron microscopy. The cutting performance was correlated to the coating composition and the best performance was found for the coating with highest Al-content consisting of a wurtzite ZrAlN phase which is assigned to its high thermal stability. Material from the work piece was observed to adhere to the inserts during turning and the amount of adhered material and its chemical composition is independent on the Al-content of the coating. (C) 2015 Elsevier B.V. All rights reserved.Funding Agencies|Vinnova (Swedish Governmental Agency for Innovation Systems) through the VINN Excellence Center on Functional Nanoscale Materials (Fun Mat)</p

Formation of block-copolymer-templated mesoporous silica

In situ attenuated total reflectance Fourier transform infrared spectroscopy is used to monitor the chemical evolution of the mesoporous silica SBA-15 from hydrolysis of the silica precursor to final silica condensation after the particle formation. Two silica precursors, tetraethyl orthosilicate (TEOS) or sodium metasilicate (SMS) were used, and the effects of additive (heptane and NH4F) concentrations were studied. Five formation stages are identified when TEOS is used as the precursor. The fourth stage correlates with the appearance and evolution of diffraction peaks recorded using in situ small angle X-ray diffraction. Details of the formed silica matrix are observed, e.g. the ratio between six-fold cyclic silica rings and linear bonding increases with the NH4F concentration. The TEOS hydrolysis time is independent of the NH4F concentration for small amounts of heptane, but is affected by the size of the emulsion droplets when the heptane amount increases. Polymerization and condensation rates of both silica precursors are affected by the salt concentration. Materials synthesized using SMS form significantly faster compared to TEOS-materials due to the pre-hydrolysis of the precursor. The study provides detailed insights into how the composition of the synthesis solution affects the chemical evolution and micellar aggregation during formation of mesoporous silica. (C) 2018 Elsevier Inc. All rights reserved.Funding Agencies|Swedish Research Council [2015-00624]; Vinnova [2016-05156]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University (Faculty Grant SFO-Mat-LiU) [2009-00971]; Knut and Alice Wallenberg Foundation [KAW 2012.0083]; EUs Erasmus-Mundus program DocMASE; Nanolith Sverige AB</p

In-situ x-ray scattering study of the cubic to hexagonal transformation of AlN in Ti1-xAlxN

In the present work, we have studied the decomposition of arc evaporated Ti0.55Al0.45N and Ti0.36Al0.64N during heat treatment in vacuum by in-situ synchrotron wide angle x-ray scattering primarily to characterize the kinetics of the phase transformation of AlN from the cubic NaCl-structure to the hexagonal wurtzite-structure. In addition, in-situ small angle x-ray scattering measurements were conducted to explore details of the wavelength evolution of the spinodal decomposition, thus providing information about the critical size of the c-AlN rich domains prior to the onset of the h-AlN transformation. We report the fractional cubic to hexagonal transformation of AlN in Ti1-xAlxN as a function of time and extract activation energies between 320 and 350 kJ/mol dependent on alloy composition. The onset of the hexagonal transformation occurs at about 50 K lower temperature in Ti0.36Al0.64N compared to Ti0.55Al0.45N where the high Al content alloy also has a significantly higher transformation rate. A critical wavelength for the cubic domains of about 13 nm was observed for both alloys. Scanning transmission electron microscopy shows a c-TiN/h-AlN microstructure with a striking morphology resemblance to the c-TiN/c-AlN microstructure present prior to the hexagonal transformation.On the day of the defence date of the thesis the status of this article was Manuscript.</p