Microstructure and high temperature mechanical properties of hard TaSiN coatings

Hard nitride coatings are widely used in the cutting tool industry, where coatings are commonly exposed to high temperature under service conditions. The addition of Si into nitride coatings, such as the TaSiN system, has been shown to enhance their oxidation resistance [1], which coupled with its high hardness, make this system of great interest for many engineering applications involving high temperatures. In this study, the room and high temperature mechanical properties of magnetron sputtered TaSiN coatings were measured using nanoindentation (between 25°C and 500°C). Fracture toughness was also evaluated at a similar temperature range using the micro-pillar splitting method (see Figure 1). The effects of N2 flow ratios on the composition, evolving phases and microstructure of the obtained nanocrystalline TaSiN coatings before and after the high temperature testing were examined by RBS, XRD and TEM analysis. Hardness was observed to increase with N content as we approach stoichiometries that allow higher degrees of crystallization of the TaN hard phases, which are embedded in an amorphous matrix. Coatings with an optimal composition of Ta55Si10N35 retain a hardness value of up to 30 GPa at 500°C, being also the toughest. Please click Additional Files below to see the full abstract

Hybrid Cathodic/Anodic Electrosynthesis of Phase Pure Ag4V2O7 Thin Films

Here, we demonstrate a two-step electrosynthesis approach for the preparation of silver pyrovanadate, Ag4V2O7 in thin-film form. In the first, cathodic step, polycrystalline Ag was deposited on fluorine doped tin oxide (FTO) substrate from a non-aqueous bath. Aqueous pyrovanadate species were then generated by aging of a CO2-infused sodium orthovanadate (Na3VO4) solution for three weeks. Silver ions were subsequently generated in situ in this medium using anodic stripping of the Ag/ITO films from the first step. Interfacial precipitation of the Ag+ ions with the pyrovanadate species afforded the targeted product in phase pure form. The various stages of the electrosynthesis were monitored in situ via the combined use of voltammetry, electrochemical quartz crystal nanogravimetry (EQCN), and coulometry. The Ag4V2O7 thin films were characterized by a variety of experimental techniques, including X-ray diffraction, laser Raman spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Surface photovoltage spectroscopy, ambient-pressure photoemission spectroscopy, and Kelvin probe contact potential difference (work function) measurements afforded information on the energy band structure of the p-type Ag4V2O7 semiconductor. Finally, the electrochemical and photoelectrochemical properties of the electrosynthesized Ag4V2O7 thin films were studied in both aqueous and non-aqueous electrolytes

Microstructure and Mechanical Properties of TaN Thin Films Prepared by Reactive Magnetron Sputtering

Reactive magnetron sputtering was used to deposit tantalum nitride (Ta–N) thin films on Si substrate. The effect of varying the N2 percentage in the N2/Ar gas mixture on the Ta–N film characteristics was investigated. Mechanical and tribological properties were studied using nanoindentation and pin-on-disc wear testing. Decreasing the N2 content in the gas mixture was found to change the film structure from face centered cubic (fcc) TaN (from 25% to 10% N2) to highly textured fcc TaN (at 7% N2) to a mixture of fcc TaN1.13 and hexagonal Ta2N (at 5% N2), and finally to hexagonal Ta2N (at 3% N2). A high hardness of about 33 GPa was shown by the films containing the hexagonal Ta2N phase (5% and 3% N2). Decreasing the N2 content below 7% N2 was also found to result in microstructural refinement with grain size 5–15 nm. Besides the highest hardness, the film deposited with 3% N2 content exhibited the highest hardness/modulus ratio (0.13), and elastic recovery (68%), and very low wear rate (3.1 × 10−6 mm3·N−1·m−1)

Microstructure and Mechanical Property Investigation of TaSiN Thin Films Deposited by Reactive Magnetron Sputtering

Tantalum silicon nitride (Ta−Si−N) films were synthesized on Si substrate via magnetron sputtering. The structure and properties of the Ta−Si−N films were investigated as a function of the N2 content in the N2/Ar gas mixture. Increasing the N2 percentage in the gas mixture from 7% to 20% changed the film structure from textured hexagonal (hex) Ta2N to nontextured hex Ta2N to a mixture of face-centered cubic (fcc) TaN and hex Ta2N, and finally to fcc TaN. X-ray photoelectron spectroscopy showed Ta−N and Si−N bonds in the films. The film microstructure was found to change from columnar morphology with visible amorphous boundaries (at 13% N2) to columnar morphology with absence of amorphous boundaries (at 15% N2). Increasing N2 content increased hardness in the films with those deposited with 13−15% N2 displaying the highest hardness of ~40 ± 2 GPa. In addition, the 13% N2 films showed a ratio of H/E* > 0.11, elastic recovery of ~60%, low coefficient of friction of 0.6, reduced wear rate (7.09 × 10−6 mm3/N·m), and remained thermally stable up to 800 °C. The results suggest that the Ta−Si−N films have high potential as hard tribological nanocomposite coatings

On the Novel Biaxial Strain Relaxation Mechanism in Epitaxial Composition Graded La1−xSrxMnO3 Thin Film Synthesized by RF Magnetron Sputtering

We report on a novel method to fabricate composition gradient, epitaxial La1−xSrxMnO3 thin films with the objective to alleviate biaxial film strain. In this work, epitaxial, composition gradient La1−xSrxMnO3, and pure LaMnO3 and La0.67Sr0.33MnO3 thin films were deposited by radio frequency (RF) magnetron sputtering. The crystalline and epitaxy of all films were first studied by symmetric θ–2θ X-ray diffraction (XRD) and low angle XRD experiments. Detailed microstructural characterization across the film thickness was conducted by high-resolution transmission electron microscopy and electron diffraction. Four compositional gradient domains were observed in the La1−xSrxMnO3 film ranging from LaMnO3 rich to La0.67Sr0.33MnO3 at the surface. A continuous reduction in the lattice parameter was observed accompanied by a significant reduction in the out-of-plane strain in the film. Fabrication of the composition gradient La1−xSrxMnO3 thin film was found to be a powerful method to relieve biaxial strain under critical thickness. Besides, the coexistence of domains with a composition variance is opening up various new possibilities of designing new nanoscale structures with unusual cross coupled properties

Mikrostruktura vrstev Hf6B10Si31C2N50 a Hf7B10Si32C2N44 odolných proti oxidaci za vysokých teplot

Amorfní vrstvy Hf6B10Si31C2N50 a Hf7B10Si32C2N44 odolné proti oxidaci za vysokých teplot byly připraveny metodou reaktivního pulzního dc magnetronového naprašování. Tyto vrstvy byly dále vyžíhány ve vzduchu až do 1500 °C z důvodu vyšetřování mechanismu jejich oxidace. Vzniklá mikrostruktura byla zkoumána rentgenovou difrakcí a transmisní elektronovou mikroskopií. Bylo zjištěno, že po vystavení vrstev vysoké teplotě dochází k vytvoření třívrstvé mikrostruktury. Oxidová vrstva, která se nachází na horním povrchu vrstev, je tvořena monoklinickými a/nebo ortorombickými nanočásticemi m-/o-HfO2 rozptýlenými v amorfní matrici na bázi SiOx. Spodní vrstva zůstala po ohřevu amorfní (Hf6B10Si31C2N50) nebo částečně rekrystalizovala a nyní se skládá z h-Si3N4 a HfCxN1−x s t-HfO2 u povrchu této spodní vrstvy (Hf7B10Si32C2N44). Horní a spodní vrstva je v obou případech oddělena částečně zoxidovanou přechodovou vrstvou složenou z nanokrystalického h-Si3N4 a tetragonálního t-HfO2. Proces oxidace začíná na rozhraní spodní/přechodové vrstvy buď oxidací oblastí bohatších na Hf v případě amorfní struktury, nebo oxidací nanočástic HfCxN1−x v případě částečně rekrystalizované struktury vedoucí ke vzniku t-HfO2 oddělených oblastmi Si3N4. Druhá fáze oxidace nastává na hranici oxidové/přechodové vrstvy a je charakterizována těsně uspořádanými strukturami HfO2, Si3N4 a SiO2, které slouží jako bariéra pro difúzi kyslíku. Malé nanočástice t-HfO2 se zde spojují a přetvářejí ve větší m-/o-HfO2, zatímco z h-Si3N4 vzniká amorfní matrice SiOx. Podobný princip oxidace byl navzdory odlišnému vývoji mikrostruktury pozorován v případě obou vyšetřovaných vrstev.High-temperature oxidation resistant amorphous Hf6B10Si31C2N50 and Hf7B10Si32C2N44 films were deposited by reactive pulsed dc magnetron sputtering. To investigate the oxidation mechanism, the films were annealed up to 1500 °C in air. The evolved microstructures were studied by X-ray diffraction and transmission electron microscopy. A three-layered microstructure was developed upon exposure to high temperature. An oxidized layer formed at the top surface for both films consisting of monoclinic and/or orthorhombic m-/o-HfO2 nanoparticles embedded in an amorphous SiOx-based matrix. The as-deposited bottom layer of the films remained amorphous (Hf6B10Si31C2N50) or partially recrystallized (Hf7B10Si32C2N44) exhibiting a h-Si3N4 and HfCxN1−x distribution along with formation of t-HfO2 at its top section. The two layers were separated by a partially oxidized transition layer composed of nanocrystalline h-Si3N4 and tetragonal t-HfO2. The oxidation process initiates at the bottom/transition layer interface with oxidation of Hf-rich domains either in the amorphous structure or in HfCxN1−x nanoparticles resulting in t-HfO2 separated by Si3N4 domains. The second stage occurs at the oxidized/transition layer interface characterized by densely packed HfO2, Si3N4 and quartz SiO2 nanostructures that can act as a barrier for oxygen diffusion. The small t-HfO2 nanoparticles merge and transform into large m-/o-HfO2 while h-Si3N4 forms amorphous SiOx matrix. A similar oxidation mechanism was observed in both films despite the different microstructures developed

Hybrid Cathodic/Anodic Electrosynthesis of Phase Pure Ag4V2O7 Thin Films

Here, we demonstrate a two-step electrosynthesis approach for the preparation of silver pyrovanadate, Ag4V2O7 in thin-film form. In the first, cathodic step, polycrystalline Ag was deposited on fluorine doped tin oxide (FTO) substrate from a non-aqueous bath. Aqueous pyrovanadate species were then generated by aging of a CO2-infused sodium orthovanadate (Na3VO4) solution for three weeks. Silver ions were subsequently generated in situ in this medium using anodic stripping of the Ag/ITO films from the first step. Interfacial precipitation of the Ag+ ions with the pyrovanadate species afforded the targeted product in phase pure form. The various stages of the electrosynthesis were monitored in situ via the combined use of voltammetry, electrochemical quartz crystal nanogravimetry (EQCN), and coulometry. The Ag4V2O7 thin films were characterized by a variety of experimental techniques, including X-ray diffraction, laser Raman spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy. Surface photovoltage spectroscopy, ambient-pressure photoemission spectroscopy, and Kelvin probe contact potential difference (work function) measurements afforded information on the energy band structure of the p-type Ag4V2O7 semiconductor. Finally, the electrochemical and photoelectrochemical properties of the electrosynthesized Ag4V2O7 thin films were studied in both aqueous and non-aqueous electrolytes

Mimořádné vysokoteplotní chování elektricky vodivé keramické vrstvy Hf7B23Si22C6N40

V této práci bylo systematicky vyšetřováno vysokoteplotní chování keramické vrstvy Hf7B23Si22C6N40 ve vzduchu do teploty 1700 °C a v inertních plynech do teploty 1600 °C. Vrstva je v nadeponovaném stavu elektricky vodivá, neprůhledná, tvrdá a vykazuje amorfní strukturu. Byla připravena pomocí reaktivního pulzního dc magnetronového naprašování ve směsi Ar+N2. Studie se soustředí na oxidační odolnost této vrstvy a na vývoj struktury, mikrostruktury a prvkového složení po ohřevu ve vzduchu a v argonu. Dále se soustředí na teplotní stabilitu tvrdosti a elektrické vodivosti po ohřevu v heliu. Vrstva vykazuje výbornou oxidační odolnost až do teploty 1600 °C díky kompaktní ochranné oxidové vrstvě, která se vytváří na povrchu během ohřevu a která vykazuje nankompozitní strukturu tvořenou z monoklinických a tetragonálních/orthorombických krystalitů HfO2 obklopených amorfní matricí na bázi SiO2. Z amorfní struktury vzniká během ohřevu několik fází, např. HfB2, HfC0.5N0.5 and α-Si3N4, avšak prvkové složení vrstvy zůstává nezměněné až do teploty 1600 °C. Teplotní stabilita tvrdosti i elektrické vodivosti této vrstvy je velmi vysoká.The high-temperature behavior of an electrically conductive, opaque and hard Hf7B23Si22C6N40 ceramic film with an amorphous structure was systematically investigated in air up to 1700 °C and inert gases up to 1600 °C. The film was prepared by reactive pulsed dc magnetron sputter deposition in an argon-nitrogen gas mixture. The study is focused on the oxidation resistance of the film and the evolution of the structure, microstructure and elemental composition upon annealing in air and argon, and on the thermal stability of its hardness and electrical resistivity upon annealing in helium. The film exhibits an excellent oxidation resistance up to 1600 °C due to the formation of a compact protective oxide surface layer with a nanocomposite structure consisting of monoclinic and tetragonal/orthorhombic HfO2 nanocrystallites surrounded by a SiO2-based amorphous matrix. The film itself crystallizes into several phases such as HfB2, HfC0.5N0.5 and α-Si3N4 upon annealing but its elemental composition remains unaffected up to 1600 °C. In addition, the hardness and electrical resistivity exhibit also very high thermal stability