Laser surface polishing of NiCrSiBC – 60WC ceramic-metal matrix composite deposited by laser directed energy deposition process

Deposition of ceramic-metal matrix composite using laser directed energy deposition process presents multi-fold challenges. High melting point ceramic particles often remain partially melted and increase the roughness of the deposit, which essentially requires secondary finishing operation. Besides high surface roughness, the high gradient of thermal and physical properties between ceramic reinforcement and metal matrix introduces cracks in the composite. Therefore, in the present work, the effect of laser surface polishing and substrate heating on improving the surface quality of NiCrSiBC – 60WC ceramic-metal composite deposited by laser directed energy deposition process was investigated. The molten pool thermal history was monitored using an IR pyrometer during laser surface polishing. The effect of rate of heat input on heating rate, cooling rate, molten pool lifetime and peak temperature was investigated and correlated with the surface quality parameters viz. arithmetic surface roughness (Ra) and ten-point height (Rz). A combination of intermediate laser power and scanning speed (600 W and 2000 mm/min) resulted in proper spread of molten pool and rendered better surface finish. The surface roughness (Ra) was found to improve from 19.2 μm ± 1.36 to 1.75 μm ± 0.20. Further, different orientations of laser polishing (0°, 45°and 90°) with respect to the material deposition direction were examined, and 45° was found to yield better surface finish. Surface cracks were observed for all the cases irrespective of process parameters and cooling rates, which were mitigated by substrate pre-heating. © 2020 Elsevier B.V

VapC12 ribonuclease toxin modulates host immune response during Mycobacterium tuberculosis infection

Mechanistic understanding of antibiotic persistence is a prerequisite in controlling the emergence of MDR cases in Tuberculosis (TB). We have reported that the cholesterol-induced activation of VapC12 ribonuclease is critical for disease persistence in TB. In this study, we observed that relative to the wild type, mice infected with ΔvapC12 induced a pro-inflammatory response, had a higher pathogen load, and responded better to the anti-TB treatment. In a high-dose infection model, all the mice infected with ΔvapC12 succumbed early to the disease. Finally, we reported that the above phenotype of ΔvapC12 was dependent on the presence of the TLR4 receptor. Overall, the data suggests that failure of a timely resolution of the early inflammation by the ΔvapC12 infected mice led to hyperinflammation, altered T-cell response and high bacterial load. In conclusion, our findings suggest the role of the VapC12 toxin in modulating the innate immune response of the host in ways that favor the long-term survival of the pathogen inside the host

Performance of additive manufactured Stellite 6 tools in friction stir processing of CuCrZr sheet

In the recent time friction stir welding (FSW), a solid state welding process has rapidly gained attention for joining high melting point materials like Cu, Fe, Ti and their alloys apart from Al alloys due to its several advantages over fusion welding techniques. AISI H13, a versatile chromium–molybdenum hot work hardened steel, has been the most commonly used as a tool material for aluminium alloys. However, low tool life due to plastic deformation and wear at elevated temperatures is limiting its application in welding of high melting point materials. In the present work the performances of as-received, heat treated, laser remelted and Stellite 6 hardfaced H13 steel tools in friction stir processing (FSP) of CuCrZr have been investigated. Stellite 6 hardfaced FSW tools are developed by additive manufacturing (AM) process on H13 steel as a base material. In all these cases except the Stellite 6 hardfaced tool, the shoulder and pin are found to deform plastically with significant wear of shoulder along with the diffusion of CuCrZr into tool from tool pin-shoulder interface. However, tools developed by AM process are found to remain intact without any significant deformation or wear

A study on the influence of substrate pre-heating on mitigation of cracks in direct metal laser deposition of NiCrSiBC-60%WC ceramic coating on Inconel 718

Direct metal laser deposition of ceramic-metal composite coatings has received much attention in the recent past over other conventional methods due to a large number of advantages. However, formation of cracks due to large thermal gradients and rapid cooling rates limits its application. Therefore, in the present study the influence of cooling rate on crack mitigation in multilayer direct metal laser deposition of NiCrSiBC-60%WC on Inconel 718 substrate has been investigated by monitoring the thermal history of the molten pool using an IR pyrometer. Cracks could not be mitigated by varying the cooling rate through changing the scan speed within the present experimental range of 300 mm/min to 700 mm/min, possibly due to the large thermal gradients build up between the substrate and the deposited clad track. Therefore, in order to decrease the cooling rate and the thermal gradient, and study their effect on crack mitigation pre-heating of the substrates at two different temperatures, 300 °C and 500 °C was employed during the deposition process. Crack-free coatings could be obtained with substrate pre-heating, except at the lower pre-heating temperature of 300 °C and the highest scan speed of 700 mm/min which had yielded a relatively fast cooling rate. Also, at the higher pre-heating temperature of 500 °C and the lowest scan speed of 300 mm/min scan speed micro-cracks were observed inside the coating due to severe dissolution of WC particles making the matrix brittle. Further, residual stresses, hardness and wear resistance of the deposited coating under above experimental conditions were determined and correlated with the cooling rate and the microstructure. © 2020 Elsevier B.V

Pathophysiology of thromboembolism in patients with COVID-19

Introduction and aim. A small number of critically ill patients with coronavirus disease (COVID-19) develop thromboembolism (arterial or venous), both micro- and macrovascular complications such as deep vein thrombosis, pulmonary embolism, and pulmonary arterial thrombosis. The objective of the study is to describe the pathophysiology of venous thromboembolism in patients with COVID-19. Material and methods. In this article a narrative review regarding pathophysiology of thromboembolism in patients with COVID-19. Analysis of the literature. The development of coagulopathy is a consequence of the intense inflammatory response associated with hypercoagulability, platelet activation, and endothelial dysfunction. The pathophysiology that relates pulmonary thromboembolism (PTE) with COVID-19 is associated with a hypercoagulable state. PTE is suspected in hospitalized patients presenting dyspnea, decreased oxygen requirement, hemodynamic instability, and dissociation between hemodynamic and respiratory changes. In COVID-19-associated coagulopathy, initially, patients present with elevated levels of fibrinogen and D-dimer, with minimal changes in prothrombin time and platelet count. The main risk factor for the development of pulmonary embolism is the increase in D-dimer that is associated with the development of PTE. The administration of iodine-based contrast agent to patients with COVID-19 would affect P-creatinine and renal function, where Ultrasound is viewed as cost-effective and highly portable, can be performed at the bedside. Conclusion. Acute respiratory distress syndrome severity in patients with COVID-19 can explain PTE as a consequence of an exaggerated immune response

Linear and nonlinear optical properties of Tellurium Vanadate (Te2V2O9)

We report here the structure property correlation of Tellurium Vanadate (Te2V2O9) through various optical and vibrational spectroscopic investigations. Pure phase polycrystalline powder of Te2V2O9 was prepared by solid state reaction technique. Phase purity of the sample was confirmed by Powder X-Ray diffraction and the microstructural investigation was analyzed using Scanning Electron Microscopy. Raman microscopy was employed to validate the molecular structure. Diffused Reflectance and Photoluminescence spectroscopy were employed to study the optical properties. Because of non-centrosymmetry, we also observed second harmonic generation in tellurium vanadate. Subsequently, third order nonlinear optical response of Te2V2O9 was probed using open-aperture Z-scan technique estimating the nonlinear absorption coefficient to be 1e-10 mW(-1). The mechanism of nonlinear absorption was deduced to be a two-photon absorption process. This was ascertained through existence of excited states predicted from electronic structure of Te2V2O9 using Density Functional Theory. It is also noteworthy to highlight that Te2V2O9 possess higher nonlinear optical coefficient than other vanadate compounds reported in literature. (C) 2017 Elsevier B.V. All rights reserved