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

Multivisceral IgG4-related disease presenting as recurrent massive gastrointestinal bleeding: a case report and literature review

Abstract Background IgG4-related disease (IgG4-RD) is a newly recognized autoimmune systemic disorder characterized by elevated levels of serum IgG4 and abundant infiltration of IgG4-positive plasmacytes in the affected organs. The liver, biliary system and pancreas are the most commonly affected organs. However, involvement of the digestive tract is very rare. To date, only a few cases of isolated gastric IgG4-RD have been reported. Case presentation We present a case of IgG4-RD of the liver, gallbladder, pancreas and duodenum, which was clinically misinterpreted and thereafter over-treated. A 52-year-old male presented with obstructive jaundice for 3 years, melena for 5 months and hematemesis for 10 days. Three years prior, the patient had undergone biopsies of pancreatic lesions, liver lesions, cholecystectomy and choledochojejunostomy. Histopathology showed chronic inflammatory changes. Endoscopy at admission revealed a duodenal ulcer with active bleeding. Despite medical management, the patient presented with repeated gastrointestinal bleeding. Upon evaluation, serum IgG4 levels were found to be elevated. Histopathology of the duodenal ulcer biopsy and repeated examination of the gallbladder and pancreatic and liver biopsies confirmed IgG4 positive plasma cell infiltration. A definitive diagnosis of IgG4-RD was made and steroid administration was initiated. At last follow up, 11 months to-the-day after initiating steroid treatment, the patient was asymptomatic. Conclusions Notably, IgG4-RD of multiple digestive organs is still very rare. As a systemic disease, it is characterized by the infiltration of IgG4-bearing plasma cells and raised IgG4 levels. Histopathology findings remain the diagnostic gold standard for this disorder

Chelator Iminodisuccinic Acid Regulates Reactive Oxygen Species Accumulation and Improves Maize (Zea mays L.) Seed Germination under Pb Stress

To explore the effects of iminodisuccinic acid (a chelating agent) on maize (Zea mays L.) seed germination under lead (Pb) stress, we comparatively analyzed the effects of applying different concentrations of iminodisuccinic acid (0, 5, 20, and 100 mmol·dm−3) and combined an addition of exogenous substances regulating reactive oxygen species production on maize seed germination, seedling growth, H2O2 content, NADPH oxidase activity, and antioxidant enzyme activities under Pb-stressed and Pb-free conditions. Iminodisuccinic acid (100 mmol·dm−3) significantly delayed seed germination under normal germination conditions and alleviated the inhibitory effects of Pb stress (20 mmol·dm−3) on seed germination. Under normal conditions (without Pb stress), the iminodisuccinic acid-induced inhibition of seed germination was enhanced by treatment with dimethylthiourea (a specific scavenger of reactive oxygen species) or diphenyleneiodonium chloride (a specific inhibitor of NADPH oxidase), but diminished by treatment with H2O2, CaCl2, diethyldithiocarbamic acid (a specific inhibitor of superoxide dismutase), or aminotriazole (a specific inhibitor of catalase). Under Pb stress, iminodisuccinic acid partially eliminated the excessive H2O2 accumulation, improved superoxide dismutase and catalase activity, and weakened the high NADPH oxidase activity. In addition, Ca2+ chelation may be essential for maintaining the reactive oxygen species’ balance and improving seed germination and seedling growth by iminodisuccinic acid supplementation in maize under Pb stress. The proposed iminodisuccinic acid supplementation-based method improved maize seed germination in Pb-polluted soil

Genome-wide identification and expression analysis of the NAC transcription factor family in Saccharum spontaneum under different stresses

The NAC (NAM, ATAF1/2, and CUC2) transcription factor family is one of the largest families unique to plants and is involved in plant growth and development, organs, morphogenesis, and stress responses. The NAC family has been identified in many plants. As the main source of resistance genes for sugarcane breeding, the NAC gene family in the wild species Saccharum spontaneum has not been systematically studied. In this study, 115 SsNAC genes were identified in the S. spontaneum genome, and these genes were heterogeneously distributed on 25 chromosomes. Phylogenetic analysis divided the SsNAC family members into 18 subgroups, and the gene structure and conserved motif analysis further supported the phylogenetic classification. Four groups of tandemly duplicated genes and nine pairs of segmentally duplicated genes were detected. The SsNAC gene has different expression patterns at different developmental stages of stems and leaves. Further qRT–PCR analysis showed that drought, low-temperature, salinity, pathogenic fungi, and other stresses as well as abscisic acid (ABA) and methyl jasmonate (MeJA) treatments significantly induced the expression of 12 SsNAC genes, indicating that these genes may play a key role in the resistance of S. spontaneum to biotic and abiotic stresses. In summary, the results from this study provide comprehensive information on the NAC transcription factor family, providing a reference for further functional studies of the SsNAC gene

Genome-Wide Identification, Evolution, and Expression Analyses of AP2/ERF Family Transcription Factors in <i>Erianthus fulvus</i>

The AP2/ERF transcription factor family is one of the most important gene families in plants and plays a vital role in plant abiotic stress responses. Although Erianthus fulvus is very important in the genetic improvement of sugarcane, there are few studies concerning AP2/ERF genes in E. fulvus. Here, we identified 145 AP2/ERF genes in the E. fulvus genome. Phylogenetic analysis classified them into five subfamilies. Evolutionary analysis showed that tandem and segmental duplication contributed to the expansion of the EfAP2/ERF family. Protein interaction analysis showed that twenty-eight EfAP2/ERF proteins and five other proteins had potential interaction relationships. Multiple cis-acting elements present in the EfAP2/ERF promoter were related to abiotic stress response, suggesting that EfAP2/ERF may contribute to adaptation to environmental changes. Transcriptomic and RT-qPCR analyses revealed that EfDREB10, EfDREB11, EfDREB39, EfDREB42, EfDREB44, EfERF43, and EfAP2-13 responded to cold stress, EfDREB5 and EfDREB42 responded to drought stress, and EfDREB5, EfDREB11, EfDREB39, EfERF43, and EfAP2-13 responded to ABA treatment. These results will be helpful for better understanding the molecular features and biological role of the E. fulvus AP2/ERF genes and lay a foundation for further research on the function of EfAP2/ERF genes and the regulatory mechanism of the abiotic stress response