Crack Free Tungsten Carbide Reinforced Ni(Cr) Layers obtained by Laser Cladding

[EN] The development of hardfacing coatings has become technologically significant in many industries A common approach is the production of metal matrix composites (MMC) layers. In this work NiCr-WC MMC hardfacing layers are deposited on C25 steel by means of laser cladding. Spheroidal fused tungsten carbides is used as reinforcement phase. Three different NiCr alloys with different Cr content were tested. Optimum conditions to obtain dense, uniform carbide distribution and hardness close to nominal values were defined. The effect of Cr content respect to the microstructure, susceptibility for cracking and the wear rate of the resulting coating will also be discussed. © 2011 Published by Elsevier Ltd.This works has been done under the financial support of Xunta de Galicia, project reference 08DPI024CT, Programa de Diseno y Produccion Industrial.Amado Paz, JM.; Tobar Vidal, MJ.; Yañez Casal, AJ.; Amigó Borrás, V.; Candel Bou, JJ. (2011). Crack Free Tungsten Carbide Reinforced Ni(Cr) Layers obtained by Laser Cladding. Physics Procedia. 12(1):338-344. https://doi.org/10.1016/j.phpro.2011.03.043S33834412

Low frequency view of GRB 190114C reveals time varying shock micro-physics

We present radio and optical afterglow observations of the TeV-bright long Gamma Ray Burst (GRB) 190114C at a redshift of $z=0.425$, which was detected by the MAGIC telescope. Our observations with ALMA, ATCA, and uGMRT were obtained by our low frequency observing campaign and range from $\sim1$ to $\sim140$ days after the burst and the optical observations were done with three optical telescopes spanning up to $\sim25$ days after the burst. Long term radio/mm observations reveal the complex nature of the afterglow, which does not follow the spectral and temporal closure relations expected from the standard afterglow model. We find that the microphysical parameters of the external forward shock, representing the share of shock-created energy in the non-thermal electron population and magnetic field, are evolving with time. The inferred kinetic energy in the blast-wave depends strongly on the assumed ambient medium density profile, with a constant density medium demanding almost an order of magnitude higher energy than in the prompt emission, while a stellar wind-driven medium requires approximately the same amount energy as in prompt emission.Comment: MNRAS, in press, expanded after referee report, 19 pages, 15 figures, 6 table

Low frequency view of GRB 190114C reveals time varying shock micro-physics

We present radio and optical afterglow observations of the TeV-bright long gamma-ray burst 190114C at a redshift of z = 0.425, which was detected by the Major Atmospheric Gamma Imaging Cherenkov telescope. Our observations with Atacama Large Millimeter/submillitmeter Array, Australia Telescope Compact Array, and upgraded Giant Metre-wave Radio Telescope were obtained by our low frequency observing campaign and range from ∼1 to ∼140 d after the burst and the optical observations were done with three optical telescopes spanning up to ∼25 d after the burst. Long-term radio/mm observations reveal the complex nature of the afterglow, which does not follow the spectral and temporal closure relations expected from the standard afterglow model. We find that the microphysical parameters of the external forward shock, representing the share of shock-created energy in the non-thermal electron population and magnetic field, are evolving with time. The inferred kinetic energy in the blast-wave depends strongly on the assumed ambient medium density profile, with a constant density medium demanding almost an order of magnitude higher energy than in the prompt emission, while a stellar wind-driven medium requires approximately the same amount energy as in prompt emission

Low frequency view of GRB 190114C reveals time varying shock micro-physics

We present radio and optical afterglow observations of the TeV-bright long gamma-ray burst 190114C at a redshift of z = 0.425, which was detected by the Major Atmospheric Gamma Imaging Cherenkov telescope. Our observations with Atacama Large Millimeter/submillitmeter Array, Australia Telescope Compact Array, and upgraded Giant Metre-wave Radio Telescope were obtained by our low frequency observing campaign and range from ∼1 to ∼140 d after the burst and the optical observations were done with three optical telescopes spanning up to ∼25 d after the burst. Long-term radio/mm observations reveal the complex nature of the afterglow, which does not follow the spectral and temporal closure relations expected from the standard afterglow model. We find that the microphysical parameters of the external forward shock, representing the share of shock-created energy in the non-thermal electron population and magnetic field, are evolving with time. The inferred kinetic energy in the blast-wave depends strongly on the assumed ambient medium density profile, with a constant density medium demanding almost an order of magnitude higher energy than in the prompt emission, while a stellar wind-driven medium requires approximately the same amount energy as in prompt emission

Observation of inverse Compton emission from a long γ-ray burst.

Long-duration γ-ray bursts (GRBs) originate from ultra-relativistic jets launched from the collapsing cores of dying massive stars. They are characterized by an initial phase of bright and highly variable radiation in the kiloelectronvolt-to-megaelectronvolt band, which is probably produced within the jet and lasts from milliseconds to minutes, known as the prompt emission1,2. Subsequently, the interaction of the jet with the surrounding medium generates shock waves that are responsible for the afterglow emission, which lasts from days to months and occurs over a broad energy range from the radio to the gigaelectronvolt bands1-6. The afterglow emission is generally well explained as synchrotron radiation emitted by electrons accelerated by the external shock7-9. Recently, intense long-lasting emission between 0.2 and 1 teraelectronvolts was observed from GRB 190114C10,11. Here we report multi-frequency observations of GRB 190114C, and study the evolution in time of the GRB emission across 17 orders of magnitude in energy, from 5 × 10-6 to 1012 electronvolts. We find that the broadband spectral energy distribution is double-peaked, with the teraelectronvolt emission constituting a distinct spectral component with power comparable to the synchrotron component. This component is associated with the afterglow and is satisfactorily explained by inverse Compton up-scattering of synchrotron photons by high-energy electrons. We find that the conditions required to account for the observed teraelectronvolt component are typical for GRBs, supporting the possibility that inverse Compton emission is commonly produced in GRBs

Preparation of TEM Foils from Nb-10 a/o Si

Ductile phase toughened composites contain phases with significantly different physical properties. Consequently, these phases thin at different rates depending on the sample preparation procedure. A new TEM foil preparation method for the ductile phase toughened Nb-10 a/o Si material has been developed. The method involves chemical thinning in a 70% nitric acid/ 30% hydrofluoric acid solution followed by electropolishing in a 12.5% sulfuric acid/87.5% methanol electrolyte at −40°C. This procedure for making TEM foils results in large thin areas with the minimum of artifacts. Mechanical grinding of a sample followed by either ion milling, dimpling, or electropolishing produced foils with large electron transparent areas, but with uncharacteristic features of the original Nb-10 a/o Si alloy microstructure. These artifacts were identified as dislocations, surface mottling, and antiphase domains. © 1992 Wiley-Liss, Inc

Preparation of TEM Foils from Nb-10 a/o Si

Ductile phase toughened composites contain phases with significantly different physical properties. Consequently, these phases thin at different rates depending on the sample preparation procedure. A new TEM foil preparation method for the ductile phase toughened Nb-10 a/o Si material has been developed. The method involves chemical thinning in a 70% nitric acid/ 30% hydrofluoric acid solution followed by electropolishing in a 12.5% sulfuric acid/87.5% methanol electrolyte at −40°C. This procedure for making TEM foils results in large thin areas with the minimum of artifacts. Mechanical grinding of a sample followed by either ion milling, dimpling, or electropolishing produced foils with large electron transparent areas, but with uncharacteristic features of the original Nb-10 a/o Si alloy microstructure. These artifacts were identified as dislocations, surface mottling, and antiphase domains. © 1992 Wiley-Liss, Inc