High quality epilayers with a minimum of microstructural features can act as test beds to elucidate intrinsic materials properties and improve the understanding of more complex materials. We report on the growth of epitaxial Ti1-xAlxNy thin films with low aluminium content (x = 0–0.4) on MgO (001) substrates using reactive magnetron co-sputtering from a pure Ti and a compound Ti0.75Al0.25 target. The films are fully strained and display a pronounced (001) orientation with low mosaicity and high lateral coherence. The hardness increases up to 29 GPa because of solid-solution hardening and coherency strains associated with early-stage spinodal decomposition, despite an increase in tensile residual stress with Al content. Electrical resistivity increases as the charge carrier concentration decreases with Al content, because enhanced solute scattering and progressive depletion of the metallic Ti-3d-N-2p hybridized conduction band. Al substitution for Ti introduces lattice distortions that increase disorder, reflected by a decreasing Ioffe-Regel parameter (kFl) with Al content. Mobility shows a non-monotonic trend, first decreasing and then increasing with Al content. The changes in electrical resistivity, carrier density, mobility and Ioffe–Regel parameter imply a shift from metallic to increasingly localized electronic transport with increasing Al incorporation.

Ni-based superalloys components are utilised in some of the most hostile engineering environments. The exceptional high-temperature performance of these alloys presents significant challenges during manufacturing. Machining is a critical process, enabling the precise shaping of forgings into functional components. During material removal, plastic deformation of the workpiece material and friction generate substantial heat and high stresses, which can affect the integrity of both tool and workpiece. CBN (cubic boron nitride) tools are commonly employed for the finish turning of high-value Ni-based superalloy components. High-pressure cooling (HPC) is implemented to prevent premature tool failure by cooling the cutting tool and aiding chip breakage. In the study presented, the influence of HPC - and cutting speed on the resulting workpiece residual stresses were investigated during axial turning of an advanced wrought disk alloy (AD730). It was found that both HPC application and cutting speed influence residual stress depth profiles, which are known to enhance fatigue life and can therefore be optimised to improve in-service performance. Consequently, this research has significant implications for industries such as aerospace and power generation.

Altered and gangue quartz in hydrothermal veins from the Kubi Gold deposit in Dunkwa on Offin in the central region of Ghana are investigated for possible Au-associated indicator minerals and to provide the understanding and increase the knowledge of the mineral hosting and alteration processes in quartz. X-ray diffraction, air annealing furnace, differential scanning calorimetry, energy dispersive X-ray spectroscopy, and transmission electron microscopy have been applied on different quartz types outcropping from surface and bedrocks at the Kubi Gold Mining to reveal the material properties at different temperatures. From the diffraction results of the fresh and annealed quartz samples, we find that the samples contain indicator and the impurity minerals iron disulfide, biotite, titanium oxide, and magnetite. These minerals, under oxidation process between 574 and 1400 degrees C temperatures experienced hematite alterations and a transformation from alpha-quartz to beta-quartz and further to cristobalite as observed from the calorimetry scans for hydrothermally exposed materials. The energy dispersive spectroscopy revealed elemental components of Fe, S, Mg, K, Al, Ti, Na, Si, O, and Ca contained in the samples, and these are attributed to the impurity phase minerals observed in the diffraction. The findings also suggest that during the hydrothermal flow regime, impurity minerals and metals can be trapped by voids and faults. Under favorable temperature conditions, the trapped minerals can be altered to change color at different depositional stages by oxidation and reduction processes leading to hematite alteration which is a useful indicator minerals in mineral exploration.

We report on phase and strain changes in Ti1-xAlxN (0 <= x <= 0.61) coatings on cutting tools during turning recorded in operando by high-energy x-ray diffractometry. Orthogonal cutting of AISI 4140 steel was performed with cutting speeds of 360-370 m/min. Four positions along the tool rake face were investigated as a function of time in cut. Formation of gamma-Fe in the chip reveals that the temperature exceeds 727 degrees C between the tool edge and the middle of the contact area when the feed rate is 0.06 mm/rev. Spinodal decomposition and formation of wurtzite AlN occurs at the positions of the tool with the highest temperature for the x >= 0.48 coatings. The strain evolution in the chip reveals that the mechanical stress is largest closest to the tool edge and that it decreases with time in cut for all analyzed positions on the rake face. The strain evolution in the coating varies between coatings and position on the rake face of the tool and is affected by thermal stress as well as the applied mechanical stress. Amongst others, the strain evolution is influenced by defect annihilation and, for the coatings with highest Al-content (x >= 0.48), phase changes.

We investigated the high temperature decomposition behavior of wurtzite phase Ti$_{1-x}$Al$_{x}$N films using experimental methods and first-principles calculations. Single phase metastable wurtzite Ti$_{1-x}$Al$_{x}$N (x = 0.65, 0.75, 085 and 0.95) solid solution films were grown by cathodic arc deposition using low duty cycle pulsed substrate-bias voltage. First-principles calculated elastic constants of the wurtzite Ti$_{1-x}$Al$_{x}$N phase show a strong dependence on alloy composition. The predicted phase diagram shows a miscibility gap with an unstable region. High resolution scanning transmission electron microscopy and chemical mapping demonstrate decomposition of the films after high temperature annealing (950$^{\circ}$C), which resulted in nanoscale chemical compositional modulations containing Ti-rich and Al-rich regions with coherent or semi coherent interfaces. This spinodal decomposition of the wurtzite film causes age hardening of 1-2 GPa.

In this study, we use in-situ synchrotron x-ray diffractometry to monitor the real-time evolution of stress, grain size, and crystallographic orientation during cathodic arc deposition of Titanium-Aluminium-Nitride (Ti1-xAlxN) films with varying Al content (x=0, 0.25, 0.5, and 0.67). We vary the substrate bias voltage and evaluate its effect on the film’s stress and grain size evolution. Our results show that films deposited at a floating potential develop a (111) fiber texture and converged tensile stress, while films formed at a finite negative substrate bias voltage have a compressive stress with an off-axis tilted (200) texture. The biaxial stress and grain size evolution are well described by a power law with an exponent and a pre-factor that have a systematic dependence on substrate bias and Al content. We fit a kinetic model to the stress evolution to extract kinetic parameters of the thin film growth. Under specific growth conditions, cohesive failure occurs in the films, which we have used to determine the fracture toughness to be 3.1 ± 0.1 and 4.8 ± 0.1 MPa·m1/2 for Ti0.75Al0.25N and Ti0.50Al0.50N, respectively.

Understanding the nucleation and growth of polycrystalline thin films is a long-standing goal. Numerous studies have been done to determine the grain size, stress, and the ideal crystallographic orientation in films. The majority of past studies have either employed an ex-situ methodology or only monitor the development of macroscopic stress in real-time. There has never been any research done on the simultaneous changes in crystallographic texture, grain size, and microscopic stress in polycrystalline thin films. In this study, we investigated the generation and temporal evolution of texture, grain size, and internal stress in cathodic arc evaporated Al0.50Ti0.50N thin films using a bespoke deposition apparatus designed for use with 2-dimensional synchrotron x-ray diffraction technique. The influence of the substrate temperature is investigated in terms of the emergence and development of texture, grain size and stress evolution. A dynamic evolution of the crystallographic texture is observed as the overall film thickness varies. We clearly resolved two regime of films growth based on stress evolution. Beyond a threshold grain size (∼ 14 nm), the stress scales inversely to the average grain sizes, and as the film thickness increases, immediate compressive stress relaxation was seen. An extensive ex-situ evaluation of thin films using electron microscopies and electron diffraction was performed to support the in-situ x-ray diffraction results.

Structural changes in Ti1-xAlxN coated tool inserts used for turning in 316L stainless steel were investigated by XANES, EXAFS, EDS, and STEM. For coarse-grained fcc-structured Ti1-xAlxN coatings, with 0 <= x <= 0.62, the XANES spectrum changes with Al-content. XANES Ti 1s line-scans across the rake face of the worn samples reveals that TiN-enriched domains have formed during turning in Ti0.47Al0.53N and Ti0.38Al0.62N samples as a result of spinodal decomposition. The XANES spectra reveal the locations on the tool in which the most TiN-rich domains have formed, indicating which part of the tool-chip contact area that experienced the highest tem-perature during turning. Changes in the pre-edge features in the XANES spectra reveal that structural changes occur also in the w-TiAlN phase in fine-grained Ti0.38Al0.62N during turning. EDS shows that Cr and Fe from the steel adhere to the tool rake face during machining. Cr 1s and Fe 1s XANES show that Cr is oxidized in the end of the contact length while the adhered Fe retains in the same fcc-structure as that of the 316L stainless steel.

The residual stress plays a vital role in determination of the device performance that uses thin films coating and thus the accurate determination of stress and its optimization with process parameters is an ongoing research work for many decades. In line with this, the microscopic origin of the stress at the atomic scale and its development during the thin film deposition is a matter of major scientific interests. The development of stress is a complex phenomenon and has a complex dependence to process parameters, film microstructure and its morphology. In this work, by utilizing a custom-designed cathodic arc deposition system and synchrotron radiation based 2D x-ray diffraction (XRD) technique, we determine the real-time evolution of stress, crystallite sizes and their preferential orientations of Aluminum-Titanium-Nitride (AlxTi1-xN) films with varied Al-content (x=0.0, 0.25, 0.50, and 0.67) on Si-100 substrate. The energies of incoming ions and hence stress in the films is tuned by applying different direct current substrate bias (Vs = floating potential, -20, -40, -60, -80, and -100 V). The instantaneous stress is evaluated by the well-known d vs. sin2ψ technique, while crystallite sizes are determined by analyzing line profiles of x-ray diffractograms. The evolution of stress and crystallite sizes are modelled with multiple numerical models from which kinetic parameters associated with the thin film depositions are extracted. The ex-situ microstructure characterizations of AlxTi1-xN coatings are carried out by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The formation of ex-situ microstructure of the films is discussed considering the results obtained from in-situ XRD data. Finally, we demonstrate that the method utilized here is a powerful approach towards estimation of the fracture toughness of thin film coatings.

The wurtzite phase of TiAlN has been known to form in industrial grade coatings with high Al content; yet, a significant knowledge gap exists regarding its behavior at high temperatures and the impact of defects on its properties. Specifically, its response to high temperatures and the implications of defects on its characteristics are poorly understood. Here, the high-temperature decomposition of nitrogen-deficient epitaxial wurtzite Ti1−xAlxNy (x = 0.79–0.98, y = 0.82–0.86) films prepared by reactive magnetron sputtering was investigated using x-ray diffractometry and high-resolution scanning transmission electron microscopy. The results show that wurtzite Ti1−xAlxNy decomposes by forming intermediary MAX phases, which then segregate into pure c-TiN and w-AlN phases after high-temperature annealing and intermetallic TiAl nanoprecipitates. The semicoherent interfaces between the wurtzite phase and the precipitates cause age hardening of approximately 4−6 GPa, which remains even after annealing at 1200 °C. These findings provide insight into how nitrogen vacancies can influence the decomposition and mechanical properties of wurtzite TiAlN.

The defect structures forming during high-temperature decomposition of Ti1-xAlxNy films were investigated through high-resolution scanning transmission electron microscopy. After annealing to 950 degrees C, misfit edge dislocations and a/6(112){111} partial dislocations permeate the interface between TiN-rich and AlN-rich do-mains to accommodate lattice misfits during spinodal decomposition. The stacking fault energy associated with the partial dislocations decreases with increasing Al content, which facilitates the coherent cubic to wurtzite structure transition of AlN-rich domains. The wurtzite AlN-rich structure is recovered when every third cubic {111} plane is shifted by alpha/root 6 along the [211] direction. After annealing to 1100 degrees C, a temperature where coarsening dominates the microstructure evolution, we observe intersections of stacking faults, which form sessile locks at the interface of the TiN-and AlN-rich domains. These observed defect structures facilitate the formation of semicoherent interfaces and contribute to hardening in Ti1-xAlxNy.

Metastable super-saturated Zr1_xAlxN alloys tend to phase separate into the equilibrium cubic (c) ZrN and wurtzite (w) AlN due to a deep miscibility gap. Transformation is shown here to follow distinctly different paths depending on if Zr1_xAlxN (x = 0.3 and 0.6) is sputter deposited as a single layer or multi-layered with TiN, and further varied by post-deposition annealing. Using in situ high-energy synchrotron wide-angle X-ray scattering and analytical transmission electron microscopy, surface segregation effects are compared to secondary phase transformations occurring in as-deposited layers during thermal annealing up to 1000 degrees C. For the primary phase transformation from the vapor phase, w-AlN nucleates and an AlN-ZrN labyrinthine structure evolves at elevated deposition temperature with semi-coherent interfaces over several nanometers, where the higher Al content narrows the structure in both single and multilayers. Transformation in thinner alloy layers is governed by epitaxial forces which stabilize single-phase c-Zr0.4Al0.6N, which enables c-Zr0.4Al0.6N/TiN superlattice growth at temperatures as low as 350 degrees C. Regardless of the decomposition route, the formation of c-AlN is impeded and w-AlN instantaneously forms during transformation. In contrast, isostructural decomposition into w-AlN and w-Zr (Al)N occurs in w-Zr0.4Al0.6N alloys during annealing.

The wear behavior of TiAlN coatings during turning of stainless steel 316L at low cutting speeds (60-120 m/min) was investigated using scanning electron microscopy. In this speed range, the coatings fail by fracture due to an adhesive wear mechanism. The fracture of the coating is described in detail, including the strong influence of Alcontent and cutting speed on the rate of wear. Low Al-content (x <= 0.23) coatings showed worse wear resistance than high Al-content (x >= 0.53) samples. Less substrate is exposed when the cutting speed is increased, because of reduced adhesive wear. The TiN and Ti0.77Al0.23N coatings are severely worn for all cutting speeds while Ti0.47Al0.53N and Ti0.38Al0.62N remain essentially unaffected at the highest speed. The difference in wear behavior is interpreted as a difference in the fracture toughness of the coatings.

This study investigates the wear of W- and Mo-alloyed Ti1-x-yAlxMeyN coatings (Me = W, Mo) with x asymptotic to 0.55 and y asymptotic to 0.10 during high-speed turning of stainless steel 316L. A difference in the crater wear rate was observed between TiAlN and Ti1-x-yAlxMeyN coatings. The wear behavior in the sliding area is characterized in detail for two different regions by scanning and transmission electron microscopy and energy dispersive X-ray spectroscopy. A thin adhered layer constituted of elements from the workpiece material is observed on the top of all coatings, followed by diffusion of species from the stainless steel 316L into the coatings. Co from the cemented carbide substrate also diffuses through column boundaries of the coating. The temperature varies in the sliding area. The presence of Mo or W retards the spinodal decomposition and the formation of h-AlN as compared to TiAlN coatings, leading to lower crater wear rate in alloyed coatings.

Although titanium nitride (TiN) is among the most extensively studied and thoroughly characterized thin-film ceramic materials, detailed knowledge of relevant dislocation core structures is lacking. By high-resolution scanning transmission electron microscopy (STEM) of epitaxial single crystal (001)-oriented TiN films, we identify different dislocation types and their core structures. These include, besides the expected primary a/2{110}< 1 (1) over bar0 > dislocation, Shockley partial dislocations a/6{111}< 11 (2) over bar > and sessile Lomer edge dislocations a/2{100}< 011 >. Density-functional theory and classical interatomic potential simulations complement STEM observations by recovering the atomic structure of the different dislocation types, estimating Peierls stresses, and providing insights on the chemical bonding nature at the core. The generated models of the dislocation cores suggest locally enhanced metal-metal bonding, weakened Ti-N bonds, and N vacancy-pinning that effectively reduces the mobilities of {110}< 1 (1) over bar0 > and {111}< 11 (2) over bar > dislocations. Our findings underscore that the presence of different dislocation types and their effects on chemical bonding should be considered in the design and interpretations of nanoscale and macroscopic properties of TiN. (c) 2022 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

Although titanium nitride (TiN) is among the most extensively studied and thoroughly characterized thin-film ceramic materials, detailed knowledge of relevant dislocation core structures is lacking. By high-resolution scanning transmission electron microscopy (STEM) of epitaxial single crystal (001)-oriented TiN films, we identify different dislocation types and their core structures. These include, besides the expected primary full a/2<1$\bar{1}$0>{110} dislocation, Shockley partial dislocations a/6<11$\bar{2}$>{111} and sessile Lomer edge dislocations a/2<1$\bar{1}$0>{001}. Density-functional theory and classical interatomic potential simulations complement STEM observations by recovering the atomic structure of the different dislocation types, estimating Peierls stresses, and providing insights on the chemical bonding nature at the core. We underline that a variety of dislocation types should be considered in interpretations of observed nanoscale and macroscopic properties of TiN.

The influence of pulsed substrate bias duty cycle on the growth, microstructure, and defects of Ti1-xAlxN coatings grown by cathodic arc deposition was investigated. Ti1-xAlxN coatings of varying compositions (x = 0.56, 0.38, 0.23) were deposited on cemented carbide substrates with 10, 25, 50, and 95% duty cycles of 50 V pulsed-bias under 10 Pa of pure N-2 gas. Coatings grown at low duty cycles (10 and 25%) showed strongly textured, underdense coatings with facetted columns and low amount of lattice defects. Applying higher duty cycles (50 and 95%) produced coatings that have denser microstructures, less preferred orientation, increasing compressive stresses and increased lattice defect densities. Our study elucidates how duty cycle variation not only changes the overall average energy supplied at the growth front but also kinetically influences the coating growth and thus microstructure and defect structure.

In this research, a fundamental study was conducted on damage behavior of cathodic arc evaporated TiN and Ti0.44Al0.56N coatings, in terms of oxidation and cracking/spallation, when they were exposed to single-pulse laser treatment in a temperature range of 1200-2100 degrees C. Moreover, a multiple-pulse laser treatment was designed to apply thermo-mechanical loads on the coatings in order to evaluate their thermal degradation during rapid heating/cooling cycles between 200 and 1200 degrees C. Single-pulse treatment of TiN up to 1500 degrees C led to the intercolumnar cracking and formation of ultrafine TiO grains. An increase in temperature up to 2100 degrees C resulted in a notable bulging of the surface, and formation of TiO2 of various morphologies such as grainy structure, dense molten and re-solidified structure, droplets from melt expulsion and, more interestingly, nanofibers. Multiplepulse treatment of TiN was accompanied by a severe cracking and spallation, which divided the surface into two layers: a heavily cracked top layer composed of dense TiO2 grains, and a bottom layer having porous TiO2 grains indicating incomplete oxidation. Conversely, Ti0.44Al0.56N did not show any visible cracking and oxidation after single-pulse treatment. Multiple-pulse treatment did not also yield cracking and spallation for Ti0.44Al0.56N, and its ablated region consisted of TiO2 grains combined with thin Al2O3 platelets. An excellent combination of properties including higher oxidation resistance and greater fracture toughness at high temperatures led to a higher thermal damage resistance for Ti0.44Al0.56N coating compared to TiN when undergoing single- and multiple-pulse laser treatments.

The influence of the aluminium content (x) on crater wear mechanisms of Ti1-xAlxN coated WC-Co inserts in highspeed turning of 316L stainless steel was investigated. Electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the wear behaviour. Ti1-xAlxN coatings with x <= 0.53 showed, after 1/3 of the tool life, a thick adhered layer composed of oxides and metallic species from the steel, and no diffusion of workpiece material into the coating. These coatings presented the best wear resistance and least abrasive wear. The high aluminium content Ti0.38Al0.62N coating showed the worst crater wear resistance. This is assigned to interdiffusion of workpiece elements and oxygen into the coating as a consequence of spinodal decomposition of the cubic TiAlN-phase, resulting in more severe abrasive wear.

The influence of the microstructure on the thermal behavior of cathodic arc deposited TiAlN coatings was studied as a function of isothermal annealing. Two compositionally similar but structurally different coatings were compared, a Ti0.34Al0.66N0.96 coating with a fine-grain structure consisting of a mixture of cubic (c) and hexagonal (h) phases, and a Ti0.40Al0.60N0.94 coating with a coarse-grain structure of cubic phase. By in situ wide-angle synchrotron x-ray scattering, spinodal decomposition was confirmed in both coatings. The increased amount of internal interfaces lowered the decomposition temperature by 50 degrees C for the dual-phase coating. During the subsequent isothermal anneal at 1000 degrees C, a transformation from c-AlN to h-AlN took place in both coatings. After 50 min of isothermal annealing, atom probe tomography detected small amounts of Al (similar to 2 at.%) in the c-TiN rich domains and small amounts of Ti (similar to 1 at.%) in the h-AlN rich domains of the coarse-grained single-phase Ti0.40Al0.60N0.94 coating. Similarly, at the same conditions, the fine-grained dual-phase Ti0.34Al0.66N0.96 coating exhibits a higher Al content (similar to 5 at.%) in the c-TiN rich domains and higher Ti content (similar to 15 at.%) in the h-AlN rich domains. The study shows that the thermal stability of TiAlN is affected by the microstructure and that it can be used to tune the reaction pathway of decomposition favorably. (C) 2020 The Authors. Published by Elsevier B.V.