Direct metal deposition technology is an emerging laser aided manufacturing technology based on a new additive manufacturing principle, which combines laser cladding with rapid prototyping into a ...solid freeform fabrication process that can be used to manufacture near net shape components from their CAD files. In the present study, direct metal deposition technology was successfully used to fabricate a series of samples of the Ni-based superalloy Inconel 625. A high power CO
2 laser was used to create a molten pool on the Inconel 625 substrate into which an Inconel 625 powder stream was delivered to create a 3D object. The structure and properties of the deposits were investigated using optical and scanning electron microscopy, X-ray diffraction and microhardness test. The microstructure has been found to be columnar dendritic in nature, which grew epitaxially from the substrate. The thermal stability of the dendritic morphology was investigated in the temperature range 800–1200
°C. These studies demonstrate that Inconel 625 is an attractive material for laser deposition as all samples produced in this study are free from relevant defects such as cracks, bonding error and porosity.
Body-center tetragonal (BCT) β-Sn crystals exhibit highly anisotropic properties such as stiffness and thermal expansion, which significantly affect their thermal-mechanical behavior. The homologous ...temperature of β-Sn is relatively high under common applications due to its low melting point, which renders Sn and Sn-based alloys viscoplastic even at room temperature. The orientation-dependent creep behavior of β-Sn specimens have been previously measured by different research groups. A dislocation mechanics based crystal viscoplasticity model is applied in this study to describe this anisotropic steady-state creep behavior of β-Sn single crystals. The model constants are calibrated with single-crystal creep test results available in the literature. The resulting creep behavior of β-Sn single-crystal is also represented with a homogenized continuum-scale finite element approach based on the use of a combined Hill-Norton approach where the creep anisotropy is represented with Hill's anisotropic potential and the creep flow rule is represented with Norton's power-law model. Estimation of the six Hill's constants for β-Sn requires multiple creep tests under specific stress states, for single crystals along crystal principal directions. In this study, these physical creep tests are replaced with ‘virtual tests’ conducted with the developed dislocation-based crystal-viscoplasticity model. To assess the ability of the Hill-Norton finite element approach to represent dislocation creep, the finite element simulation results are compared with results of: (i) physical tests on single crystal specimens reported in the literature; and (ii) crystal-viscoplasticity modeling along many crystal orientations (beyond the fundamental calibration cases conducted along crystal principal directions). In future studies, this approach will be used for anisotropic finite element modeling of creep in polycrystalline specimens.
•A crystal-viscoplasticity (CV) modeling approach was developed for anisotropic creep.•CV prediction for steady-state creep was calibrated with tests on single crystal tin.•A finite element approach is proposed based on Hill-Norton anisotropic model.•Hill-Norton model constants were estimated from CV predictions.
Complicated vascular anomalies have limited therapeutic options and cause significant morbidity and mortality. This Phase II trial enrolled patients with complicated vascular anomalies to determine ...the efficacy and safety of treatment with sirolimus for 12 courses; each course was defined as 28 days.
Treatment consisted of a continuous dosing schedule of oral sirolimus starting at 0.8 mg/m(2) per dose twice daily, with pharmacokinetic-guided target serum trough levels of 10 to 15 ng/mL. The primary outcomes were responsiveness to sirolimus by the end of course 6 (evaluated according to functional impairment score, quality of life, and radiologic assessment) and the incidence of toxicities and/or infection-related deaths.
Sixty-one patients were enrolled; 57 patients were evaluable for efficacy at the end of course 6, and 53 were evaluable at the end of course 12. No patient had a complete response at the end of course 6 or 12 as anticipated. At the end of course 6, a total of 47 patients had a partial response, 3 patients had stable disease, and 7 patients had progressive disease. Two patients were taken off of study medicine secondary to persistent adverse effects. Grade 3 and higher toxicities attributable to sirolimus included blood/bone marrow toxicity in 27% of patients, gastrointestinal toxicity in 3%, and metabolic/laboratory toxicity in 3%. No toxicity-related deaths occurred.
Sirolimus was efficacious and well tolerated in these study patients with complicated vascular anomalies. Clinical activity was reported in the majority of the disorders.
Drug abuse is a worldwide problem. Although commonly abused drugs can be identified during routine urine drug testing, less commonly abused drugs may escape detection. These less commonly abused ...drugs not only include some designer drugs such as synthetic cannabinoid but also include abuse of psychedelic magic mushroom (active ingredients: psilocybin and psilocin), peyote cactus (active ingredient: mescaline), and khat plants (active ingredient: cathinone). Moreover, solvent and glue abuse is gaining popularity among teenagers and young adults which may even cause fatality. Amphetamine/methamphetamine immunoassay has a low cross-reactivity with psilocin. Cathinone, if present in the urine, can be detected by amphetamine/methamphetamine immunoassay due to cross-reactivity of cathinone with assay antibody. Currently there is one commercially available immunoassay which is capable of detecting synthetic cathinone known as bath salts as well as mescaline. However, gas chromatography combined with mass spectrometry as well as liquid chromatography combined with tandem mass spectrometry (LC/MS/MS)-based method is available for confirmation of the active ingredients present in magic mushroom, peyote cactus, and khat plant. Such chromatography-based methods also offer more sensitivity and specificity compared to an immunoassay.
Laser melting of Al–Si alloys has been investigated extensively, however, little work on the microstructural evolution of laser deposited Al–Si alloys has been reported to date. This paper presents a ...detailed microstructural investigation of laser deposited Al–11.28Si alloy. Laser aided direct metal deposition (DMD) process has been used to build up solid thin wall samples using Al 4047 prealloyed powder. The evolution of macro- and microstructures of laser deposited Al–Si samples was investigated using X-ray diffraction, optical microscopy, scanning electron microscopy and electron backscattered diffraction techniques. Microstructural observation revealed that the morphology and the length scale of the microstructures are different at different locations of the sample. A periodic transition of microstructural morphology from columnar dendrite to microcellular structure was observed in each layer. The observed difference in the microstructure was correlated with the thermal history of the deposit.
► This paper presents microstructural evolution in eutectic Al–Si alloy. ► Microstructural morphology varies with the location of the deposit. ► Microstructural anisotropy was correlated with the thermal history of the deposit. ► Microstructure of the deposit can be controlled by appropriate deposition pattern.
Mycophenolic acid (MPA) is an immunosuppressant requiring therapeutic drug monitoring. Although immunoassays are commercially available, there is significant positive bias using this approach when ...compared to high-performance liquid chromatography or LC combined with mass spectrometry (LC/MS) or tandem mass spectrometry (LC/MS/MS). Positive bias is due to variable cross-reactivity of MPA acyl glucuronide with antibodies traditionally used in immunoassay formats. As can be expected, the magnitude of bias varies considerably. MPA strongly binds albumin and, as a result, disproportionate increases in free MPA occur in patients with uremia, hypoalbuminemia, and hepatic dysfunction. As such, monitoring free MPA poses additional challenges. Because MPA inhibits inosine monophosphate dehydrogenase, monitoring this enzyme may provide an alternative approach.
•A multiscale Crystal Viscoplasticity (CV) model is developed for SAC crystals•Creep resistance can be quantified as a function of microstructural features•The continuum formulation with Hill ...potential allows 3D computational analysis•Numerical simulations provide estimates of the variability of failure analysis
Creep can have a significant impact on the reliability of Sn-based solder alloys even at room temperature because of their relatively low melting temperatures. SnAgCu (SAC) solder joints used in electronic packaging typically consist of only a few highly anisotropic grains, which consist of Sn dendrites embedded in a near-eutectic Sn-Ag component. The unique grain structure of each joint leads to stochastic variations in the thermomechanical response of such joint. Therefore, grain-scale testing and modeling are recommended to better characterize the anisotropic behavior and to estimate the influence of stochastic variability of grain structure on the viscoplastic response of the joint. This work aims to investigate the anisotropic steady-state creep behavior of single-crystal SAC solder joints. The orientation-dependent viscoplastic behavior of individual SAC grains is modeled with a multi-scale crystal-viscoplasticity approach for representing the relevant dislocation mechanics. The response predicted by the crystal viscoplasticity model is then captured in an equivalent homogenized continuous-scale constitutive model (Hill-Garofalo formulation).
This modeling strategy was implemented in numerical simulations, as an illustrative example, to analyze the behavior of single-grain solder joints subjected to combined steady compression (from heat-sink clamping force) and thermal cyclic loading. The cyclic ratcheting in the presence of the steady compressive force causes: (i) transverse expansion of the solder ball, potentially leading to eventual short circuits; and (ii) cyclic fatigue damage leading to eventual failure of the solder joint. The proposed grain-scale modeling approach is shown to be able to address the stochastic variability of both these damage mechanisms, as a function of grain orientation. The present methodology can be used to predict the realistic behavior of solder joints, based on their microstructure, and provide valuable insights for their reliability analysis.
▶ 4340 steel was successfully deposited using diode laser DMD system on mild steel. ▶ Ferrite, martensite and cementite microstructural phases were identified in the clad. ▶ Lattice parameters of ...identified phases are shorter than reported lattice parameters. ▶ Microhardness of the clad decreases down the clad layers. ▶ Decrease in microhardness corresponds to degree of tempering of martensite phase.
In the current investigation AISI 4340 steel was laser deposited on a rolled mild steel substrate by Direct Metal Deposition (DMD) technology. The microstructural investigation of the clad was performed using optical and electron microscopes and X-ray diffraction techniques. The microstructure consisted of ferrite, martensite and cementite phases. Two types of martensite, lathe-type and plate-type, were observed in the microstructure. Decrease in microhardness values from the top layer to the alloy layer proves that the degree of tempering of the martensite phase increases in the same direction. The lattice parameters of the identified phases were found to be shorter than those reported in literature. The reported parameters in literature are from samples processed under equilibrium conditions.
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