Multiscale materials design of hard coatings for improved fracture resistance and thermal stability

Physical vapor deposited hard coatings comprised of cubic (c) transition metal (TM)-Al-N, and (TM)-Si-N are the current work horse materials for a large number of metal cutting and wear resistant applicatíons to light against the extreme conditions of temperature and stress simultaneously. In spite of a high degree of sophisticatíon in terms of material choice and microstructural design, a lower fracture resistance and limited thermal stability of the coatings remains a technological challenge in the field. The lower fracture resistance ofthe coating is an inherent material property. Limited thermal stability in the TM-Al-N system is associated with the transformation of metastable c -AIN to its stable wurtzite (w)-AIN phase ata temperature above 900 oC resulting an undesirable hardness drop. The current work shows how to overcome these challenges by manipulaling the coating material at different length scales, i.e. microstructure, crystal and interface structure, and alloy design. The endeavor of multiscale materials design is achieved by converging a deeper material and process knowledge to result specific structural modification over multiple length scales by alloying transition metal nitrides with AIN and SiNxs following. Microstructure variation is achieved in ZrN coating by alloying it with SiNx, where the surface segregated SiNx breaks down the columnar structure and evolves a self-organized nanocomposite structure with a hardness variation from 37 ±2 GPa to 26 ±1 GPa. The indentation induced fracture studies reveal crack deflection for the colum nar coating, likely a long the coiumn boundaries. The crack deflection olfers additional energy dissipative mechanisms that make the columnar structured coating more fracture resistant, which is not the case fur the nanocomposite coating in spite of its lower hardness. Crystal structure of AIN is variad between stable wurtzite structure to metastable cubic structure in the ZrAIN alloy by adapting a mullilayer structure and tuning the layerthickness. The multilayer consisting c-AIN layer shows a hardness of 34 ±1 GPa anda twofold enhancement in the critica! force to cause an indentation induced surface crack compared to the multilayer containing w-AIN in spite of a lower hardness for the later case. The higher fracture resistance is discovered to be ca u sed by stress- induced transformation of /IJN from its metastable cubic structure to its thermodynamically stable wurtzite structure associated with a molar volume expansion of20% that builds up local compressive stress zones delay;ng the onset and propagation of the cracks. This is in fact the first experím en tal data point for the stress-induced transfurmation toughening in a hard coatíng. The current work also demonstrates a concept of im proving the thermal stabilíty ofTM-Al-N by m odifying the interface structure between w-AIN and c-TMN. A popular belief in the field is that AIN in lis stable wurtzite structure is detrimental to coating hardness, and hence the curren! material design strategy Is to force AIN in metas table cubic phase that confines the application temperature (- 900 oC). In contrast, here it is shown that the w-AIN offers a high hardness provided if it is grown (semi-)coherent to c-TMN. This is experimentally shown for lhe multilayer system ofTiN/ZrAIN. The interface structure between the c-TiN, c-ZrN and w-AIN is transformed from incoherent to (semi-)coherent structure bytuning the growth conditions under a favorable crystallographic template. Furthennore, the low energy(semi-) coherent interface structure between w-AIN and c- TiN, c- ZrN display a high thermal stability, causing a high and more stable hardness up to an annealing temperature of 1150 oC with a value of34± 1.5 GPa. This value is 50 % higher comparad to the state-of-the-art monolithic and multilayered Ti-/IJ -N and Zr-Al-N coating containing incoherent w-AIN. Finally, an entropy based alloy design concept is explorad to form a thermodynamicLos recubrimientos duros formados por metales de transición (TM) cúbicos -AlN, y -SiN depositados mediante fase de vapor (CVD) son materiales extensamente utilizados en gran número de aplicaciones de corte y de desgaste bajo condiciones extremas de temperatura y solicitaciones mecánicas. A pesar de un alto grado de sofisticación en cuanto a la selección del material y el diseño microestructural, la baja resistencia a la fractura y la limitada estabilidad térmica sigue siendo un importante reto tecnológico. La variación microestructural en los recubrimientos de ZrN se controla mediante la aleación con SiNx, ya que la segregación superficial de SiNx rompe la estructura columnar y evoluciona a un nanocompuesto autoorganizado con una dureza de entre 37 ±2 GPa y 26 ±1 GPa. Las grietas producidas por indentación muestran la existencia de deflexión de grieta, lo que proporciona un mecanismo de disipación de energía adicional, haciendo de este material más resistente a la generación de grieta.La estructura cristalina del recubrimiento de AlN se varía entre la fase estable wurtzita y la fase cúbica estable ZrAlN mediante el control de la estructura y el espesor de la arquitectura multicapa. El recubrimiento multicapa formado por la fase c-AlN presenta una dureza de 34 ±1 GPa y una resistencia a la generación de grietas por indentación dos veces mayor comparado con el recubrimiento multicapa formado por w-AlN, aunque éste presente una dureza menor. La mayor resistencia a fractura está causada por la transformación inducida por tensión de AlN desde la fase cúbica metaestable a la fase wurtzita termodinámicamente estable acompañada de una expansión molar del 20%, resultando en una generación de tensiones compresivas que retarda la generación y propagación de grietas. Esta es la primera vez que se reporta la existencia de transformación catalizada por tensión en recubrimientos duros. En esta tesis también se demuestra el concepto de mejorar la estabilidad térmica de los recubrimientos basados en TM-Al-N mediante la modificación de la estructura interfacial entre las fases w-AlN y c-TMN. En general la existencia de AlN en su fase estable wurtzita puede ser detrimental para la dureza, y por lo tanto se suele depositar el material en la fase cúbica, lo que limita la temperatura de utilización (~ 900 oC). Esta dureza es un 50%mayor de la dureza reportada para recubrimientos monolíticos y multicapas de Ti-Al-N y Zr-Al-N que contengan fase incoherente de w-AlN. Finalmente, el concepto de aleaciones de alta entropía se utiliza para depositar una solución sólida termodinámicamente estable del sistema TM-Al-N que presenta una entalpía de mezcla positiva. Elementos de aleación multi-principales de (AlTiVCrNb)N se utilizan para formar una solución sólida cúbica . La alta entropía configuracional en la mezcla es mayor que la entalpía, por lo que se espera una formación de solución sólida estabilizada a temperaturas mayores de 1000K. Sin embargo, a temperaturas elevadas, la optimización entre la minimización de la energía de interacción y la maximización del desorden configuracional causa la precipitación de AlN en su estructura wurtzita estable, y la solución sólida cúbica está únicamente confinada entre TiN, CrN , VN y NbN que tienen baja entalpía de mezcla. En resumen, esta tesis presenta soluciones tecnológica a dos retos importantes en el campo. Se consigue una mejora significativa en la resistencia a fractura en los recubrimientos mediante la selección de materiales y el diseño microestructural mediante mecanismos de deflexión de grieta y transformación de fase asistida por tensión. Así mismo, se aumenta la estabilidad térmica de recubrimientos TM-Al-N mediante una nueva microestructura consistente en c-TMN y w-AlN termodinámicamente estable con una estructura interfacial (semi-)coherente de baja energía

Crystal structure and DNA cleavage properties of a vanadium complex [NH₄][VO(O₂)₂(pm-im)]⋅3H₂O containing 2-(1<i>H</i>-imidazol-2-yl)pyrimidine ligand

A new diperoxovanadium compound, [NH4][VO(O2)2(pm-im)]⋅3H2O (1) (pm-im = 2-(1H-imidazol-2-yl)pyrimidine), has been prepared from aqueous solution and its crystal structure has been determined by single-crystal X-ray diffraction. It belongs to the monoclinic P21/n space group with a = 6.798(4) Å, b = 11.468(6) Å, c = 18.073(9) Å, β = 96.020(6)°, V = 1401.3(13) Å3, and Z = 4. The asymmetric unit of 1 consists of a diperoxovanadium [VO(O2)2(pm-im)]− anion, one free NH4+ counterion, and three lattice water molecules, which are further stacked to form a three-dimensional (3D) supramolecular structure through intra- and intermolecular hydrogen bond interactions. The solution stability of the ion ([VO(O2)2(pm-im)]−) was explored using a combination of multinuclear (1H, 13C, and 51V) magnetic resonance and variable temperature NMR in a 0.15 mol L−1 NaCl/D2O solution that mimics physiological conditions. Additionally, the compound exhibits significant DNA cleavage ability under light, and the electrophoretic result shows that the super helix DNA seems to be directly cleaved into single stranded DNA.</p

Crystal structure, NMR and catalytic properties of a bis-peroxovanadium [NH₄][VO(O₂)₂(mpa)]·H₂O

By reacting NH4VO3 and mpa (mpa = 4-methoxypicolinamide) in the presence of H2O2, a bis-peroxovanadium [NH4][VO(O2)2(mpa)]·H2O (1) was obtained and characterized by X-ray single-crystal diffraction. Structural analyses demonstrate that 1 belongs to the monoclinic space group P21/c and consists of a bis-peroxovanadium [VO(O2)2(mpa)]−, one NH4+ counterion and one free lattice water. Adjacent [VO(O2)2(mpa)]− anions construct a 3D supramolecular framework through intra- and intermolecular hydrogen bonding interactions. The compositions of 1 in solution are investigated by using multinuclear (1H, 13C, and 51V) magnetic resonance, COSY, HSQC, HMBC, and variable temperature NMR in a 0.15 mol L−1 NaCl/D2O solution that mimics the physiological conditions. Comparing the results of single-crystal X-ray and NMR experiments, the VV ion in the undissociated [VO(O2)2(mpa)]− in solution displays a similar seven-coordinate distorted pentagonal bipyramidal geometry with the solid-state crystal. The catalytic activity of the 1 in the oxidative bromination for phenol/aniline-like compounds to mimic bromoperoxidases reactivity was also studied.</p

1,3-Dipolar Cycloaddition of 2,6-Dichlorobenzonitrile Oxide to 2-Methyl-N-confused Porphyrin. Regio- and Stereoselective Synthesis and Structural Characterization of 2-Aza-21-carbabacteriochlorin and Resolution of 2-Aza-21-carbachlorin Enantiomers

The 1,3-dipolar cycloaddition reaction of 2-methyl-N-confused porphyrin with 2,6-dichlorobenzonitrile oxide yielded four isomeric monoadducts of carbachlorin type and one diadduct of carbabacteriochlorin type. Two major carbachlorin products, constituting 82% of the monoadducts, were shown to be structural precursors of the unique 2-aza-21-carbabacteriochlorin. Enantiomers of the most abundant isomer of 2-aza-21-carbachlorin (55% of all carbachlorin products) have been resolved. The crystal structures of 2-aza-21-carbabacteriochlorin and the most abundant isomer of 2-aza-21-carbachlorin were characterized by X-ray diffraction

NMR study on the coordination of diperoxovanadium(V) complexes with 2-hydroxymethyl pyridine derivatives

To understand the substitution effects of 2-hydroxymethyl pyridine on the reaction equilibrium, the interactions between a series of 2-hydroxymethyl pyridine derivatives and diperoxovanadium(V) complex [OV(O2)2(D2O)]−/[OV(O2)2(HOD)]− in solution were explored by the combined use of multinuclear (1H, 13C, and 51V) magnetic resonance together with HSQC in 0.15 mol L−1 NaCl ionic medium for mimicking the physiological conditions. Some direct NMR data are given for the first time. The relative reactivity among the 2-hydroxymethyl pyridine ligands is 2-hydroxymethyl pyridine (1) > 2-methoxymethyl pyridine (2) > 2-ethoxymethyl pyridine (3) > 2-propoxymethyl pyridine (4). The competitive coordination results in the formation of a series of new seven-coordinate diperoxovanadium species [OV(O2)2L]– (L = 1, 2, 3, and 4). The results of density functional calculations indicated that steric effects play an important role in these reactions, providing a reasonable explanation on the relative reactivity of the 2-hydroxymethyl pyridine derivative.</p

Synthesis of N-Confused Porphyrin Derivatives with a Substituted 3-C Position

Active methylene compounds such as 5,5-dimethylcyclohexane-1,3-dione, cyclohexane-1,3-dione, 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one, 1,3-dimethyl-1H-pyrazol-5(4H)-one, and 3-methylisoxazol-5(4H)-one react with the 3-C position of N-confused porphyrin in THF for 5 min to afford a novel type of N-confused porphyrin derivatives in good yield without the need of any catalyst

High-Capacity Gas Storage by a Microporous Oxalamide-Functionalized NbO-Type Metal–Organic Framework

A microporous oxalamide-functionalized NbO-type metal–organic framework, HNUST-3, has been designed and synthesized by self-assembling [Cu₂(COO)₄] paddlewheel SBUs and a novel tetracarboxylate ligand with linking oxalamide groups. HNUST-3 represents the first example of a porous oxalamide-functionalized MOF, which exhibits a high BET surface area of 2412 m²·g^–1, large H₂ uptake (unsaturated total capacity of 6.1 wt % at 20 bar and 77 K), and excellent CH₄ storage (135.8 cm³(STP)­cm^–3 at 20 bar and 298 K) as well as high CO₂ adsorption capacity (20.2 mmol·g^–1 at 20 bar and 298 K) with good selectivity for CO₂ over CH₄ (7.9) and N₂ (26.1) at 298 K

High-Capacity Gas Storage by a Microporous Oxalamide-Functionalized NbO-Type Metal–Organic Framework

A microporous oxalamide-functionalized NbO-type metal–organic framework, HNUST-3, has been designed and synthesized by self-assembling [Cu₂(COO)₄] paddlewheel SBUs and a novel tetracarboxylate ligand with linking oxalamide groups. HNUST-3 represents the first example of a porous oxalamide-functionalized MOF, which exhibits a high BET surface area of 2412 m²·g^–1, large H₂ uptake (unsaturated total capacity of 6.1 wt % at 20 bar and 77 K), and excellent CH₄ storage (135.8 cm³(STP)­cm^–3 at 20 bar and 298 K) as well as high CO₂ adsorption capacity (20.2 mmol·g^–1 at 20 bar and 298 K) with good selectivity for CO₂ over CH₄ (7.9) and N₂ (26.1) at 298 K

Synthesis and Characterization of Novel Reversible Photoswitchable Fluorescent Polymeric Nanoparticles via One-Step Miniemulsion Polymerization

In the present study, novel polymeric nanoparticles of ca. 55 nm in diameter with reversibly photoswitchable fluorescence properties were synthesized using a facile one-step miniemulsion polymerization, in which the donor of fluorescence resonance energy transfer (FRET), 4-methamino-9-allyl-1,8-naphthalimide (MANI), and the acceptor, spiropyran-linked methacrylate (SPMA), were covalently incorporated into a polymeric matrix during the polymerization process. The fluorescence emission of MANI dye in nanoparticles can be reversibly switched using the alternating irradiation of UV and visible light, which can induce the structural interconversion between the SP form and MC form of spiropyran moieties inside nanoparticles and thus reversibly switch on and switch off the FRET process. The prepared photoswitchable fluorescent polymer nanoparticles not only show a high load capacity of dyes, controllable amount and ratio of the two dyes, and tunable FRET efficiency but also exhibit higher spectral stability because of covalent linkage between dye molecules and the particle, relatively fast photoresponsibility, and better photoreversibility compared to some previously reported systems