Crystalline (Hf,Ta,Ti,V,Zr)N nitride thin films, with a high-entropy metal-sublattice, were synthesized at 440 °C by reactive magnetron sputtering using an equimolar Hf-Ta-Ti-V-Zr-compound target. ...The coatings are single-phase fcc structured mono-nitrides for N2/(Ar + N2) flow-rate-ratios (fN2) between 30 and 45%. For higher fN2 a small fraction of a second phase (next to the fcc matrix) can be detected by X-ray diffraction (XRD) and selected area electron diffraction (SAED). All coatings studied (prepared with fN2 between 30 and 60%) show similar chemical compositions and hardness (H) values between 30.0 and 34.0 GPa with indentation moduli of ~460 GPa. Atom probe tomography (APT) indicates a homogenous distribution of all elements within our fcc-(Hf,Ta,Ti,V,Zr)N even after vacuum-annealing at 1300 °C. While H decreased from 32.5 to 28.1 GPa by this annealing treatment, the coating is still single-phase fcc structured with a defect density (expressed by XRD and SAED features, transmission electron microscopy contrast, and grain sizes) comparable to the as-deposited state. Only after vacuum-annealing at 1500 °C, XRD and APT reveal the formation of hexagonal structured (Ta,V)2N. The onset of nitrogen-loss – detected by thermogravimetric analysis – is ~1350 °C.
Based on our results we can conclude that the sluggish diffusion within our fcc-(Hf,Ta,Ti,V,Zr)N warrants the single-phase fcc structure up to 1300 °C, although ab initio based calculations would suggest the lower-entropy products fcc-(Hf,Zr)N, fcc-(Ta,V)N, and fcc-TiN and fcc-(Hf,Zr)N and fcc-(Ta,Ti,V)N to be energetically more stable up to 1302 K.
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•Single-phase fcc-(Hf,Ta,Ti,V,Zr) nitride coatings•Random distribution of elements up to Ta = 1300 °C•Sluggish diffusion allows for postponed decomposition.•Nitrogen loss causes decomposition of fcc-solid-solution at Ta ≥ 1350 °C.
The concept of Si alloyed transition metal (TM) diborides – well explored for bulk ceramics – is studied for five different physical vapor deposited TM-Si-B2±z (TM = Ti, Cr, Hf, Ta, W) coatings, ...focusing on the oxidation behavior up to 1200 °C. In their as deposited state, all coatings exhibit single phased AlB2 prototype structures, whereby the addition of Si results in dense, refined morphologies with no additional phases visible in the X-ray diffractograms. With already low amounts of Si, the slope of the mass increase during dynamic oxidation flattens, especially for Ti-Si-B2±z, Cr-Si-B2±z, and Hf-Si-B2±z. Above distinct Si contents, the formation of a steady state region exhibiting no further mass increase is promoted (starting at around 1000 to 1100 °C). Best results are obtained for Hf0.21Si0.18B0.61 and Cr0.26Si0.16B0.58 (both around 2.4 μm thick in the as deposited sate), revealing drastically retarded oxidation kinetics forming 400 nm thin oxide scales after 3 h at 1200 °C in ambient air (significantly lower compared to bulk ceramics). This highly protective oxidation mechanism is attributed to the formation of an amorphous Si rich oxide scale. The Si content needed to form these oxide scales largely differs between the TM-Si-B2±z coatings investigated, also diversifying the prevalent oxidation mechanism, especially for Cr-Si-B2±z.
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•The addition of Si enhances the oxidation resistance of transition metal diboride coatings.•Temperature dependent oxide scale formation found for Ti, Hf, W based coatings.•Highly protective silicon rich oxide scale enables strongly retarded growth rates.•Oxide scale thickness of 400 nm observed after 3 h at 1200 °C for Hf0.21Si0.18B0.61.•Cr0.26Si0.16B0.58 exhibits low oxide growth rate from room temperature up to 1400 °C.
Abstract The restoration of mandibular bone defects after cancer can be facilitated by computer-assisted preoperative planning. The aim of this study was to assess an in-house manufacturing approach ...to customized cutting guides for use in the reconstruction of the mandible with osteocutaneous free flaps. A retrospective cohort study was performed, involving 18 patients who underwent mandibular reconstruction with a fibula free flap at three institutions during the period July 2012 to March 2015. A single surgeon designed and manufactured fibula and mandible cutting guides using a computer-aided design process and three-dimensional (3D) printing technology. The oncological outcomes, production parameters, and quality of the reconstructions performed for each patient were recorded. Computed tomography scans were acquired after surgery, and these were compared with the preoperative 3D models. Eighteen consecutive patients with squamous cell carcinoma underwent surgery and then reconstruction using this customized in-house surgical approach. The lengths of the fibula bone segments and the angle measurements in the simulations were similar to those of the postoperative volume rendering ( P = 0.61). The ease of access to 3D printing technology has enabled the computer-aided design and manufacturing of customized cutting guides for oral cancer treatment without the need for input from external laboratories.
Reactive high-power impulse magnetron sputtering (R-HiPIMS) is seen as a key-technology for the deposition of future hard and multifunctional coatings. Increased ionisation rates allow for additional ...possibilities in tuning specific coating characteristics based on growth mechanisms varied by surface-diffusion. Especially within the well-established Ti-Al-N system, the Al solubility limit (xmax) of metastable face-centred-cubic (fcc) Ti1−xAlxN is an everlasting scientific topic. Here, we investigate in detail the dependence of xmax on various deposition parameters (i.e. pulse frequency and duration, N2-to-Ar flow rate ratio, and substrate bias potential) during R-HiPIMS of Ti-Al-N coatings using Ti0.6Al0.4, Ti0.5Al0.5 and Ti0.4Al0.6 composite targets. The systematic studies showed that the highest solubility limit of xmax ∼0.55 could be obtained for duty cycles around 3.75 % (peak power densities of ∼1.0 kW/cm2) and a N2-to-Ar flow rate ratio of 0.3. A further decisive fact for the deposition of high Al containing fcc-structured Ti1−xAlxN coatings is surface diffusion controlled by bias potentials (DC as well as modulated pulses) ensuring sufficient intermixing of the arriving film species. Despite the presence of very small amounts of wurtzite-typed phases, excellent hardness values of ∼36 GPa for Ti0.40Al0.60N – which further increased to ∼40 GPa upon annealing for 1 h at 700 °C – could be achieved for a DC bias potential of -50 V, irrespective of all variations conducted. Based on our results we can further conclude, that the ratio and energy of Tin+- and Aln+-ions, simultaneously arriving at the substrate surface, are decisive for stabilising the highly preferred cubic modification. A distinct promotion of specific discharge regimes – selected by synchronised bias pulses – can thus positively influence the cubic phase formation through altered gas-to-metal ion ratios arriving at the film surface.
•R-HiPIMS deposited Ti1-xAlxN (xmax ∼ 0.55) coatings using composite Ti-Al targets.•Optimised discharge conditions at duty cycles of 3.75% and N2/(N2+Ar) = 0.3•Phase stability at c/w boarder is strongly related to bias modulations.•Reduced influence of Me2+ on cubic phase formation through Ti-Al composite targets.•Altered gas-to-metal ion ratios using synchronised US support the fcc-phase.
Abstract Introduction Ameloblastoma is a rare, benign odontogenic tumour associated with a high recurrence rate. It accounts for 1% of all tumours of the jaws. The purpose of this study was to ...compare the ameloblastoma recurrence rate according to the type of treatment: radical or conservative. Patients and methods All patients with a diagnosis of ameloblastoma between 1991 and 2013 were retrospectively identified in order to extract topographic, radiological, and histological data and the type of treatment: conservative (marsupialization, enucleation, curettage) or radical (segmental resection) and to compare the recurrence rate according to the type of treatment. Results Twenty-seven patients were included, managed by conservative treatment (CT) in 22 cases and radical treatment (RT) in 14 cases. The recurrence rate was 90.9% in the CT group and 9.1% in the RT group ( P = 0.025) with a mean follow-up of 56.2 months. Discussion The recurrence rate after conservative treatment was higher than that after radical treatment. These results are similar to those reported in the literature. The choice of treatment must be adapted to the macroscopic and histological characteristics of each tumour and to the patient.
Transition-metal disilicides (TMSi2) based thin films are suggested as promising, novel protective coating materials used in various high-temperature applications. In this study, we investigate the ...phase formation, microstructure, and mechanical properties (i.e. H, E, and KIC) of sputter-deposited TMSix films (TM = Mo, Ta, Nb) in correlation with the varied bias potential. The as-deposited TaSix and MoSix coatings show Si sub-stoichiometries with Si/Me (x)< 2, while all the NbSix coatings are overstoichiometric in Si. All TaSix and NbSix coatings are stabilized in their preferred hexagonal structure, whereas the MoSix coatings exhibit small fractions of T1-Mo5Si3 next to the dominant metastable hexagonal β-phase. The oxidation behaviour of the coatings was examined up to 1400 °C. MoSix based films are distinguished by an outstanding oxidation resistance, forming dense and protective silica scales of only 650 nm after 100 h at 1200 °C – also obtaining an extremely high interfacial stability. In contrast, TaSix suffers accelerated oxidation at 1200 °C due to the formation of mixed, non-protective scales consisting of Ta2O5 and SiO2. Moreover, NbSix coatings show retarded oxidation kinetics up to 60 h at 1200 °C, forming a dense and uniform SiO2 scale of only 533 ± 131 nm. Micro-cantilever bending experiments reveal that TaSi1.7 coating exhibit the highest fracture toughness, KIC, of 2.7 ± 0.2 MPa∙m1/2 compared to 2.3 ± 0.1 and 1.7 ± 0.1 MPa∙m1/2 for NbSi2.4 and MoSi1.9, respectively.
•Mechanical properties of TaSix and NbSix exhibit dependency on varied bias potential.•TaSi1.7 shows the highest KIC of 2.7 ± 0.2 MPa∙m1/2.•Thin Si-based Oxide scale of only 650 nm after 100 h at 1200 °C for MoSi2.•Retarded oxidation kinetics of NbSi2 at 1200 °C up to 60 h.•Accelerated oxidation for TaSi2 over 850 °C by forming mixed oxides.
Ternary W1−xTaxB2−z is a promising protective coating material possessing enhanced ductile character and phase stability compared to closely related binaries. Here, the oxidation resistance of ...W1−xTaxB2−z thin films was experimentally investigated at temperatures up to 700 °C. Ta alloying in sputter deposited WB2−z coatings led to decelerated oxide scale growth and a changed growth mode from paralinear to a more linear (but retarded) behavior with increasing Ta content. The corresponding rate constants decrease from kp* = 6.3 ⋅ 10−4 µm2/s for WB2−z, to kp* = 1.1 ⋅ 10−4 µm2/s for W0.66Ta0.34B2−z as well as kl = 2.6 ⋅ 10−5 µm/s for TaB2−z, underlined by decreasing scale thicknesses ranging from 1170 nm (WB2−z), over 610 nm (W0.66Ta0.34B2−z) to 320 nm (TaB2−z) after 10 min at 700 °C. Dense and adherent scales exhibit an increased tantalum content (columnar oxides), which suppresses the volatile character of tungsten-rich as well as boron oxides, hence being a key-factor for enhanced oxidation resistance. Thus, adding Ta (in the range of x = 0.2–0.3) to α-structured WB2−z does not only positively influence the ductile character and thermal stability but also drastically increases the oxidation resistance.
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•Ta positively influences the oxidation behavior of α-WB2−z.•Oxide growth mode changes from paralinear to linear with increasing Ta content.•Decelerating oxidation kinetics (rate constant) by one order of magnitude.•Addition of Ta decreases the oxide scale thickness drastically.
In the field of hard protective coatings, nano-crystalline Ti-B-N films are of great importance due to the adjustable microstructure and mechanical properties through their B content. Here, we ...systematically study this influence of B on Ti-B-N during reactive as well as non-reactive DC magnetron sputtering. The different deposition routes allow for an additional, very effective key parameter to modify bond characteristics and microstructure. Plasma analysis by mass spectroscopy reveals that for comparable amounts of Ti+, Ti2+, Ar+, and Ar2+ ions, the count of N+ ions is about 2 orders of magnitude lower during non-reactive sputtering. But for the latter, the N+/N2+ ratio is close to 1, whereas during reactive sputtering this ratio is only 0.1. This may explain why during reactive deposition of Ti-B-N, the BN bonds dominate (as suggested by X-ray photoelectron spectroscopy), whereas the BB and TiB bonds dominate for non-reactively prepared Ti-B-N. Chemically, reactively versus non-reactively sputtered Ti-B-N coatings follow the TiN-BN versus TiN-TiB2 tie line, respectively. Detailed X-ray diffraction and transmission electron microscopy studies reveal, that up to 10 at.% B can be dissolved in the fcc-TiN lattice when prepared by non-reactive sputtering, whereas already for a B content of 4 at.% a BN-rich boundary phase forms when reactively sputtered. Thus, we could not only observe a higher hardness (35 GPa instead of 25 GPa) as well as a higher indentation modulus (480 GPa instead of 260 GPa), but also a higher fracture energy (0.016 instead of 0.009 J/m during cube-corner indentations) for Ti-B-N coatings with 10 at.% B, when prepared non-reactively.
•Major differences in plasma species between reactive and non-reactive sputtering•The elemental composition also varies with the deposition route.•Significant differences in mechanical properties at higher boron contents
Mandibular reconstruction using fibula free flap has been improved in the last decade with computer-aided design and computer-aided manufacturing (CAD/CAM) but any functional and aesthetic evaluation ...of their reattempts has been realized. Aim of this retrospective study is to compare functional and morphologic outcomes after mandibular reconstruction with fibula free flap using CAD/CAM or conventional peroperative shaping for mandible reconstruction. Moreover, we compared quality of life, patient and surgery characteristics in the two groups.
We realized a monocentric retrospective analyzed of 25 cases of unilateral mandibular reconstruction divided in two groups, using CAD/CAM (12 patient) or conventional approach (13 patients) between April 2012 and March. Functional and aesthetic measurements were performed postoperatively.
Mouth opening, laterotrusion and protrusion of the mandible seemed to be improved in CAD/CAM group compared with conventional group but did not differ significantly. Quality of life, bite force, masticatory ability, eating and chewing satisfaction, appearance and social activity satisfaction did not differ significantly in the two groups.
Even if no superiority has been established for CAD/CAM group regarding functional and aesthetic outcomes, a prospective design of future studies and transdisciplinary approach should improve our data and their interpretations. Thus, the integration of virtual planning and guided surgery is definitely of significant value and must be considered in complex maxillofacial reconstructions.
Diffusion driven high-temperature oxidation is one of the most important failure mechanisms of protective thin films in industrial applications. Within this study, we investigated the diffusion of ...oxygen at 800 to 1100 °C through nano-laminated crystalline Ti-Al-N and amorphous Mo-Si-B based multilayer coatings. The most prominent oxygen diffusion pathways, and hence the weakest points for oxidation, were identified by combining 18O tracer diffusion and atom probe tomography. An oxygen inward diffusion along column boundaries within Ti-Al-N layers in front of a visually prevalent oxidation front could be proven, highlighting the importance of these fast diffusion pathways. Furthermore, the amorphous Mo-Si-B layers act as barriers and therefore mitigate the migration of oxygen by accumulating reactive O species at a nanoscale range. Preventing oxygen diffusion along column boundaries – through the implementation of amorphous interlayers – lead to paralinear oxidation behavior and stable scales even after 7 h at 1100 °C. Our results provide a detailed insight on the importance of morphological features such as grain and column boundaries during high-temperature oxidation of protective thin films, in addition to their chemistry.
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•Ultra high oxidation resistance•Blocking fast diffusion pathways through amorphous interlayers•18O tracer diffusion for highly resolved diffusion pathway analysis using atom probe tomography•Identification of fast diffusion pathways in fcc-(Ti,Al)N protective coatings•Atom probe tomography of nano-scaled (Ti,Al)N/Mo-Si-B multilayer coating.
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