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Within this study, we show that single-phase face centered cubic (fcc) Ti0.47Al0.46Ce0.02Si0.05N coatings (sputtered from Ti0.37Al0.57Ce0.02Si0.04 targets plus the addition of Ti) outperform their single-phase fcc Ti0.49Al0.51N counterparts (sputtered from Ti0.40Al0.60 targets plus the same addition of Ti). The deposition rate increases by more than 43% and also the hardness of as-deposited Ti0.47Al0.46Ce0.02Si0.05N coatings is with 39.9 ± 1.2 GPa (on sapphire) 13% higher. Furthermore, this Ce–Si alloyed coating shows a remarkably higher thermal stability, represented by a higher annealing temperature (1200 °C instead of 900 °C) after which hexagonal structured wurtzite-type AlN (w-AlN) can be detected. They also show a more parabolic like oxide growth rate (4.13·10−7 and 1.13·10−5 μm2/s at 850 and 950 °C) during the 10-h-oxidation experiment, whereas that of Ti0.49Al0.51N is close to linear already at 850 °C (especially after ∼2 h). The postponed w-AlN formation guarantees that the hardness of Ti0.47Al0.46Ce0.02Si0.05N is still 40.8 ± 1.6 GPa even after annealing at 1100 °C. Our results clearly demonstrate that the addition of 2 mol% CeSi2 to Ti–Al targets allows to increase the sputter rate and leads to Ce–Si alloyed nitride coatings with improved thermomechanical properties and oxidation resistance.

Recently we showed that Ta as well as Ce significantly increase the thermomechanical properties and oxidation resistance of Ti–Al–N coatings. Here we investigate their synergistic effect by comparing single-phase face centered cubic (fcc) structured Ti0.39Al0.61N, Ti0.40Al0.58Ce0.02N, Ti0.43Al0.51Ta0.06N, Ti0.44Al0.44Ta0.12N, Ti0.43Al0.42Ta0.14Ce0.01N, and Ti0.43Al0.35Ta0.21Ce0.01N coatings, which were prepared by reactive magnetron sputtering of corresponding powder metallurgically prepared composite targets. Especially the Ti0.43Al0.42Ta0.14Ce0.01N coating outperforms the others in hardness, thermal stability and oxidation resistance. This coating is prepared with a Ti0.44Al0.44Ta0.10Ce0.02 target, which allows for a 2.8 times higher deposition rate than the Ti0.50Al0.50 target (for the preparation of a fcc-Ti0.39Al0.61N) under the same deposition parameters (temperature, gas flow, sputtering current, bias potential). The hardness of Ti0.43Al0.42Ta0.14Ce0.01N is 35 GPa in its as-deposited single-phase fcc state, and still 34 GPa after vacuum-annealing at 1200 °C, where only a very small fraction of hexagonal phase-formation can be detected. Ti0.39Al0.61N shows 30 GPa in as-deposited state and 27 GPa after vacuum-annealing at 900 °C (peak-hardness of 32 GPa with Ta = 800 °C), where already hexagonal phases form. But even more striking is the improved oxidation resistance, which outperforms those of the individual Ta or Ce alloyed Ti–Al–N, due to the cumulative effect of Ta and Ce. With a Ta/Ti ratio of ~1/3, Ti0.43Al0.42Ta0.14Ce0.01N provides the optimum Ta content for the formation of a stable and dense TiO2-containing scale, and the additional 1 at.% Ce-metal-fraction enables the growth of a dense and well-adherent protective oxide scale. Based on our results we can conclude, that the combined alloying of Ta and Ce to Ti–Al–N improves the deposition characteristics, thermomechanical properties, as well as thermal stabilities (incl. oxidation resistance), which should provide a better performance of thereby protective machining tools.

TiBx thin films with a B content of 1.43 ≤ x ≤ 2.70 were synthesized using high-power impulse magnetron sputtering (HiPIMS) and direct-current magnetron sputtering (DCMS). HiPIMS allows compositions ranging from understoichiometric to overstoichiometric dense TiBx thin films with a B/Ti ratio between 1.43 and 2.06, while DCMS yields overstoichiometric TiBx films with a B/Ti ratio ranging from 2.20 to 2.70. Excess B in overstoichiometric TiBx thin films from DCMS results in a hardness up to 37.7 ± 0.8 GPa, attributed to the formation of an amorphous B-rich tissue phase interlacing stoichiometric TiB2 columnar structures. We furthermore show that understoichiometric TiB1.43 thin films synthesized by HiPIMS, where the deficiency of B is found to be accommodated by Ti-rich planar defects, exhibit a superior hardness of 43.9 ± 0.9 GPa. The apparent fracture toughness and thermal conductivity of understoichiometric TiB1.43 HiPIMS films are 4.2 ± 0.1 MPa√m and 2.46 ± 0.22 W/(m·K), respectively, as compared to corresponding values for overstoichiometric TiB2.70 DCMS film samples of 3.1 ± 0.1 MPa√m and 4.52 ± 0.45 W/(m·K). This work increases the fundamental understanding of understoichiometric TiBx thin films and their materials properties, and shows that understoichiometric films have properties matching or going beyond those with excess B. Fulltext published under Creative Commons license CC BY 4.0https://creativecommons.org/licenses/by/4.0/Funding agencies: Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [EM16-0004]; Research Infrastructure Fellow program from the Knut and Alice Wallenberg (KAW) Foundation [RIF 14-0074]; KAW; Swedish Government Strategic Research Area

Ti–Al–N thin films are well established due to their outstanding thermo-mechanical properties. Nevertheless, this system is still a subject of many research activities to further enhance their oxidation resistance and thermal stability. The addition of reactive elements, such as Cerium, can significantly improve especially the oxidation resistance of various materials. Therefore, we study in detail the impact of Ce (2 at.% alloyed to powder metallurgically prepared Ti 0.50 Al 0.50 targets) on growth processes, structure, mechanical properties, thermal stability, and oxidation resistance of magnetron sputtered Ti 1 − x − y Al x Ce y N coatings prepared with DC bias potentials of U bias = − 25, − 50, − 75, and − 100 V. The deposition rate is significantly increased by a factor of ~ 1.75 (U bias = − 25 V) to 1.45 (U bias = − 100 V) when using Ti 0.49 Al 0.49 Ce 0.02 instead of Ti 0.50 Al 0.50 targets. Furthermore, also the hardness of the resulting single phase face centered cubic Ti 0.43 Al 0.55 Ce 0.02 N is with ~ 35 GPa above that of Ti 0.42 Al 0.58 N with ~ 34 GPa, for coatings on polycrystalline Al 2 O 3 and U bias = − 50 V. All temperature dependent characteristics of Ti 0.42 Al 0.58 N are improved significantly by the addition of Cerium. Wurtzite-structured AlN formation within Ti 0.43 Al 0.55 Ce 0.02 N can only be detected at T a = 1100 °C, about 200 °C higher as for Ti 0.42 Al 0.58 N. Their peak-hardness, due to spinodal decomposition of the supersaturated cubic phase is ~ 37.0 GPa with T a = 900 °C, as compared to 34.6 GPa with T a = 800 °C for Ti 0.42 Al 0.58 N. Additionally, even after exposure to ambient air at 950 °C for 3 h, still > 50% of the Ti 0.43 Al 0.55 Ce 0.02 N coating is intact (below the ~ 1.2 μm thin oxide scale), whereas Ti 0.42 Al 0.58 N is already fully oxidized. Based on our results we can conclude, that Ce-doping improves the deposition characteristics and mechanical properties as well as thermal stabilities (incl. oxidation resistance) of Ti–Al–N, to be used as protective coatings for a wide range of high-demanding applications.

CrB x thin films with 1.90 < x < 2.08 have been deposited by direct-current magnetron sputtering (DCMS) from a stoichiometric CrB 2 target at 5 and 20 mTorr (0.67 and 2.67 Pa) Ar pressure onto sapphire (0 0 01) substrates. All films, irrespective of deposition conditions, exhibit a (0 0 01) texture. Attesting to the achievement of close-to-stoichiometric composition, epitaxial film growth is observed at 900 ?C, while film growth at 500 ?C yields (0001) fiber texture. Film composition does not depend on substrate temperature but exhibits slightly reduced B content with increasing pressure for samples deposited at 900 ?C. Excess B in the overstoichiometric epitaxial CrB 2.08 films segregates to form B-rich inclusions. Understoichiometry in CrB 1.90 films is accommodated by Cr-rich stacking faults on { 1 1? 00 } prismatic planes. ? 2021 The Author(s). Published by Elsevier Ltd on behalf of Acta Materialia Inc. This is an open access article under the CC BY license ( http://creativecommons.org/licenses/by/4.0/ ) Funding Agencies|Swedish Foundation for Strategic Research (SSF)Swedish Foundation for Strategic Research [EM16-0004, RIF 14-0074]; Knut and Alice Wallenberg (KAW) FoundationKnut & Alice Wallenberg Foundation [KAW 2015.0043]; Swedish Government Strategic Research Area in Materials Science on Functional Materials at Linkoping University [200900971]; KAW

Face-centred cubic (fcc-) Mo N and Ta N exhibit an inherent driving force for vacancy formation. To study their interaction and effects on structural evolution and mechanical properties, we synthesised Mo–Ta–N coatings by reactive magnetron sputtering using nitrogen-to-total pressure ratios, pN2/pT, of 0.32 and 0.69. Low pN2/pT results in high concentration of N vacancies, which stabilise single-phase fcc-Mo1-xTaxNy up to x = 0.76. These solid solutions follow the MoN0.5–Ta0.875N0.875 quasi-binary tie line. Compressive residual stresses, σ, indentation hardness, H, and toughness, KC, increase with Ta content, reaching their maxima of (on average) -2.0 GPa, 28 GPa, and 7.0 MPa√m, respectively, within the x range 0.38–0.69. Higher Ta contents favour higher concentration of metal vacancies deteriorating the properties. High pN2/pT favours the formation of fcc-Mo1-xTaxNy rich in metal vacancies, which however always coexists with a hexagonal phase. Within the x range 0.33–0.66, the fraction of the hexagonal phase is negligible, and σ, H, and KC deviate from −1.0 GPa, 28 GPa, and 2.9 MPa√m, respectively, within the error of measurements. The combination of experimental and theoretical studies demonstrates the power of point defects in stabilising desired crystal structures and improving mechanical properties through the thereby tuned atomic configuration.

In this study, the effects of the microstructural properties on the deformation and damage mechanism of CrN/TiN multilayer coatings deposited on Custom 450 steel using the unbalanced reactive magnetron sputtering PVD process were studied. All coatings were fabricated with an overall thickness of 1.5 &micro, m, but different bilayer periods (&Lambda, ). Structural and mechanical properties of coatings were investigated by XRD analysis and nanoindentation experiment, respectively. Indentation tests at three loads of 100, 300, and 450 mN were performed on the coatings&rsquo, surface and then, cross-sections of fractured imprints were analyzed with SEM and TEM. Measuring the length of the cracks induced by indentation loads and analyzing the load-displacement curves, apparent fracture energy values of multilayer coatings were calculated. We observed that multilayer systems with bilayer periods of 4.5&ndash, 15 nm possess superlattice structure, which also results in higher values for Young&rsquo, s modulus and hardness as well as higher fracture energy. Comparison of cross-sectional SEM and TEM observations showed that coatings with smaller bilayer periods tend to deform by shear sliding mechanism due to the existence of the long-grown columns, while short dispersed grains&mdash, growing in the coatings with a larger bilayer period&mdash, led to deformation via local grain boundary sliding and grain rotation.

We studied the growth-morphology, structure, mechanical and tribological properties of Ti0.43Cr0.57N0.92, Ti0.35Cr0.65N0.78/Ni0.003, and Ti0.13Cr0.74Mo0.13N0.71/Ni0.025 coatings synthesized by cathodic arc evaporation. The Ni-free and low-Ni-containing coatings, Ti0.43Cr0.57N0.92 and Ti0.35Cr0.65N0.78/Ni0.003, are characterized by a dense columnar growth-morphology and coherent growth of Ti-rich and Cr-rich layers (due to the two-fold substrate rotation). The addition of only 0.3 at% Ni to the growing film results in a significant grain refinement, increased compressive stresses (from −6.7 to −9.7 GPa), and increased hardness (from 25 to 43 GPa). These two coatings show a high cohesive strength with crack formation during scratch tests for loads above 75 N. The Ni-richer and Mo-containing coating, Ti0.13Cr0.74Mo0.13N0.71/Ni0.025, also exhibits a dense growth-morphology with a layered structure. The higher Ni content of 2.5 at% leads to metallic Ni formation, allowing the growth of films with low compressive stresses of only −0.6 GPa and still a comparably high hardness of 30 GPa. The Ni segregated to grain and column boundaries weakens their cohesive strength (allowing to relax the growth induced stresses), and crack formation can already be observed for loads of 25 N during the scratch tests. However, their performance during pin-on-disk tests at 550 °C is superior – with a lower coefficient of friction of 0.45 and lower wear rate of 0.4 · 10−6 mm3/(N·m) – to the other two coatings.

State-of-the-art machining applications require new developments in the field of protective coatings, to guarantee for excellent dimensional accuracy and effective processes. Recently, we showed an enormous enhancement in deposition rate, mechanical strength, and thermal stability of Ti–Al–N when using Ce-alloyed Ti–Al composite targets. Within this study, we further follow the concept of alloying lanthanides to nitride-based coatings, by sputtering Ti0.5Al0.5 composite targets alloyed with 2 mol% LaB6 in mixed Ar/N2 atmospheres. This allowed us to produce coatings that outperform not only Ti–Al–N (significantly) but also Ce-alloyed Ti–Al–N coatings. Compared with coatings prepared from non-alloyed Ti0.5Al0.5 composite targets (Ti0.43Al0.57N), we achieved an impressive increase in deposition rate from 77 to 139 nm/min. Furthermore, we observed an increase in hardness from 34 to 40 GPa (on polished polycrystalline Al2O3 substrates) in the as-deposited state, accompanied by a delayed spinodal decomposition, and an additional TiB2 precipitation, allowing for still 40 GPa after annealing at 1100 °C. Also the oxidation resistance could be significantly improved through the addition of LaB6. After exposure to ambient air at 850 °C for 10 h or 950 °C for 1 h, the oxide scale thickness is only 500 nm for the LaB6 alloyed coatings, whereas the Ti0.43Al0.57N counterpart was already fully oxidized after 10 h at 850 °C or 1 h at 950 °C.