Thermally Sprayed Cr3C2-NiCr Coatings: Improving the Abrasion Resistance

There are many industrial applications in which the surfaces of components are exposed to abrasive wear. Protecting such surfaces against harsh abrasive conditions sets high technical requirements for the materials; typically these materials must combine extreme hardness with adequate toughness. These requirements can usually be satisfied with alloys that consist of hard carbides in the ductile metal matrix, e.g. liquid-phase sintered bulk hardmetals. Large components can often be protected against wear by applying a coating to their surface. The processing of hardmetals into a dense wear-resistant surface layer is achieved solely by thermal spraying technology. In thermal spraying, the hardmetal particles are heated and projected towards the component’s surface by high-pressure combustion. Nowadays for most industrial applications, this thermal spraying is done with a High Velocity Oxy-Fuel (HVOF) torch or, more recently, a High Velocity Air-Fuel (HVAF) torch.Even though tungsten carbide (WC) based hardmetals, e.g. WC-Co and WC-CoCr, serve for the vast majority of abrasion resistant applications, these compositions have technical restrictions. These limitations include rapid oxidation above 500 ◦C and an incommensurate coefficient of thermal expansion with steels. Nevertheless, oxidationresistant compositions that consist of up to 80 wt.% of chromium carbides in a nickelchromium binder, commercially designed as Cr3C2-NiCr, are regularly utilized at high service temperatures. The major disadvantage of Cr3C2-NiCr is its inferior abrasion resistance when compared against WC-Co.This work focuses on the characteristics of the Cr3C2-NiCr composition that influence its abrasion resistance at room temperature and above. A unique high-stress abrasion testing procedure for thermally sprayed coatings was established, wherein the sample was heated-up to the testing temperature by induction heating. Moreover, the coated samples underwent various heat-treatments, aimed at simulating high-temperature service.The commercially available Cr3C2-NiCr coatings under study were varied by selecting different feedstock powders and spray technologies. However, there were only minor variations in their wear resistance after long heat-treatments. This was attributed to the dissolution of the carbides during spraying and the re-precipitation of the excess C and Cr as chromium carbides during the subsequent heat-treatment. The prolonged heat-treatment resulted in coarse carbides with a high degree of coalescence and thus equalized the variations in the as-sprayed microstructures.In order to provide enhanced abrasion resistance at room and elevated temperatures, novel compositions were developed with only 10 wt.% of WC. Both experimental compositions, designated as 70Cr3C2-10WC-20Ni and 80Cr3C2-10WC-10Ni, demonstrated attractive abrasion properties in their as-sprayed state and after heat-treatment. The technical performance of the experimental coatings was attributed to the role of dissolved W as a substitutional solid solution strengthener. Moreover, the high carbide content in 80Cr3C210WC-10Ni was considered essential to provide abrasion resistance at high temperatures.Another major challenge in thermally sprayed coating is the spraying-induced dissolution of the carbides. The dissolved carbides supersaturate the binder of the as-sprayed coating with residual carbide elements, and thus make it brittle. Here, laser post-treatment was used to re-precipitate the residual carbide-forming elements from the brittle as-sprayed binder. This improved the room temperature abrasion resistance of the commercially available 75Cr3C2-25NiCr and 45Cr3C2-37WC-18NiCrCo coatings. In 75Cr3C2-25NiCr the most promising improvement to its abrasion resistance was achieved when relatively low laser fluences were applied, which precipitated small nano-sized particles in the binder. In 45Cr3C2-37WC-18NiCrCo, however, relatively high laser fluences had to be used. This resulted in the formation of hard and wear-resistant (Cr,W)2C grains.<br/

Toward Early-Warning Detection of Gravitational Waves from Compact Binary Coalescence

Rapid detection of compact binary coalescence (CBC) with a network of advanced gravitational-wave detectors will offer a unique opportunity for multi-messenger astronomy. Prompt detection alerts for the astronomical community might make it possible to observe the onset of electromagnetic emission from (CBC). We demonstrate a computationally practical filtering strategy that could produce early-warning triggers before gravitational radiation from the final merger has arrived at the detectors.Comment: 16 pages, 7 figures, published in ApJ. Reformatted preprint with emulateap

Production of He-4 and (4) in Pb-Pb collisions at root(NN)-N-S=2.76 TeV at the LHC

Results on the production of He-4 and (4) nuclei in Pb-Pb collisions at root(NN)-N-S = 2.76 TeV in the rapidity range vertical bar y vertical bar <1, using the ALICE detector, are presented in this paper. The rapidity densities corresponding to 0-10% central events are found to be dN/dy4(He) = (0.8 +/- 0.4 (stat) +/- 0.3 (syst)) x 10(-6) and dN/dy4 = (1.1 +/- 0.4 (stat) +/- 0.2 (syst)) x 10(-6), respectively. This is in agreement with the statistical thermal model expectation assuming the same chemical freeze-out temperature (T-chem = 156 MeV) as for light hadrons. The measured ratio of (4)/He-4 is 1.4 +/- 0.8 (stat) +/- 0.5 (syst). (C) 2018 Published by Elsevier B.V.Peer reviewe

Thermally Sprayed Cr3C2-NiCr Coatings: Improving the Abrasion Resistance

There are many industrial applications in which the surfaces of components are exposed to abrasive wear. Protecting such surfaces against harsh abrasive conditions sets high technical requirements for the materials; typically these materials must combine extreme hardness with adequate toughness. These requirements can usually be satisfied with alloys that consist of hard carbides in the ductile metal matrix, e.g. liquid-phase sintered bulk hardmetals. Large components can often be protected against wear by applying a coating to their surface. The processing of hardmetals into a dense wear-resistant surface layer is achieved solely by thermal spraying technology. In thermal spraying, the hardmetal particles are heated and projected towards the component’s surface by high-pressure combustion. Nowadays for most industrial applications, this thermal spraying is done with a High Velocity Oxy-Fuel (HVOF) torch or, more recently, a High Velocity Air-Fuel (HVAF) torch.Even though tungsten carbide (WC) based hardmetals, e.g. WC-Co and WC-CoCr, serve for the vast majority of abrasion resistant applications, these compositions have technical restrictions. These limitations include rapid oxidation above 500 ◦C and an incommensurate coefficient of thermal expansion with steels. Nevertheless, oxidationresistant compositions that consist of up to 80 wt.% of chromium carbides in a nickelchromium binder, commercially designed as Cr3C2-NiCr, are regularly utilized at high service temperatures. The major disadvantage of Cr3C2-NiCr is its inferior abrasion resistance when compared against WC-Co.This work focuses on the characteristics of the Cr3C2-NiCr composition that influence its abrasion resistance at room temperature and above. A unique high-stress abrasion testing procedure for thermally sprayed coatings was established, wherein the sample was heated-up to the testing temperature by induction heating. Moreover, the coated samples underwent various heat-treatments, aimed at simulating high-temperature service.The commercially available Cr3C2-NiCr coatings under study were varied by selecting different feedstock powders and spray technologies. However, there were only minor variations in their wear resistance after long heat-treatments. This was attributed to the dissolution of the carbides during spraying and the re-precipitation of the excess C and Cr as chromium carbides during the subsequent heat-treatment. The prolonged heat-treatment resulted in coarse carbides with a high degree of coalescence and thus equalized the variations in the as-sprayed microstructures.In order to provide enhanced abrasion resistance at room and elevated temperatures, novel compositions were developed with only 10 wt.% of WC. Both experimental compositions, designated as 70Cr3C2-10WC-20Ni and 80Cr3C2-10WC-10Ni, demonstrated attractive abrasion properties in their as-sprayed state and after heat-treatment. The technical performance of the experimental coatings was attributed to the role of dissolved W as a substitutional solid solution strengthener. Moreover, the high carbide content in 80Cr3C210WC-10Ni was considered essential to provide abrasion resistance at high temperatures.Another major challenge in thermally sprayed coating is the spraying-induced dissolution of the carbides. The dissolved carbides supersaturate the binder of the as-sprayed coating with residual carbide elements, and thus make it brittle. Here, laser post-treatment was used to re-precipitate the residual carbide-forming elements from the brittle as-sprayed binder. This improved the room temperature abrasion resistance of the commercially available 75Cr3C2-25NiCr and 45Cr3C2-37WC-18NiCrCo coatings. In 75Cr3C2-25NiCr the most promising improvement to its abrasion resistance was achieved when relatively low laser fluences were applied, which precipitated small nano-sized particles in the binder. In 45Cr3C2-37WC-18NiCrCo, however, relatively high laser fluences had to be used. This resulted in the formation of hard and wear-resistant (Cr,W)2C grains.<br/

HVOF- and HVAF-sprayed Cr3C2-NiCr coatings deposited from feedstock powders of spherical morphology: Microstructure formation and high-stress abrasive wear resistance up to 800 °C

Chromium carbide based coatings are commonly applied to protect surfaces against wear at high temperatures. This work discusses the influence of spray torch and feedstock powder selection on the microstructure and high-stress abrasion resistance of thermally sprayed Cr3C2-NiCr coatings. Four commercial feedstock powders with spherical morphology were deposited by different high-velocity spray processes, namely third generation gas- and liquid fuelled HVOF-torches and by the latest generation HVAF-torch. The microstructures of the coatings were studied in the as-sprayed state and after various heat treatments. The high-stress abrasion resistance of as-sprayed and heat treated coatings was tested at room temperature and at 800 °C. The study reveals that the selection of the spray torch mainly affects the room temperature abrasion resistance of the as-sprayed coatings, which is due to differences in the embrittlement of the binder phase generated by carbide dissolution. At elevated temperatures, precipitation and growth of secondary carbides yields a fast equalization of the various coatings microstructures and wear properties

High<i> iso</i> aldehyde selectivity in the hydroformylation of short-chain alkenes

The hydroformylation of propene to give predominantly iso‐butanal has been achieved; class‐leading selectivity is possible even at higher temperatures that deliver fast conversion. Racemic rhodium complexes of bidentate phospholane phosphites derived from tropos‐biphenols and unusual solvent systems are the key to the selectivity observed

Entwicklung wirtschaftlich effizienter Hartmetallbeschichtungslösungen für Hochtemperaturanwendungen. Teil 2: Einfluss von Wärmebehandlungen und tribologische Untersuchungen

The aim of the present work was to investigate the effect of feedstock powder properties and the spraying process on the performance capabilities and cost-effectiveness of preparation of Cr3C2-NiCr coatings by high velocity oxy-fuel (HVOF) and high velocity air-fuel (HVAF) spray processes. Based on the results specific improvements were targeted. In part two of this study the effect of heat treatment on coating properties and the resistance of the coatings against abrasion and erosion are discussed. To improve the tribological properties it is necessary to minimize the content of dissolved carbides in the binder matrix to avoid embrittlement and corresponding cracking susceptibility. This can be achieved either by decreasing the process temperature and increasing the particle velocity during spraying or by heat-treating the sprayed coatings. The WC-containing compositions were found to exhibit improvements in both performance characteristics and cost-effectiveness of coating preparation and offered considerable potential for further improvement

Improving the high temperature abrasion resistance of thermally sprayed Cr3C2-NiCr coatings by WC addition

Two experimental agglomerated and sintered (a&s) feedstock powders were prepared, in order to reveal the role of WC addition on the microstructure, hardness, and the abrasion resistance of HVOF-sprayed Cr3C2-NiCr coatings. These powders contained 10 wt.% of sub-micron WC, 20 or 10 wt.% of nickel binder, and Cr3C2 as balance. Experimental coatings were deposited by a liquid fueled high velocity oxygen-fuel (HVOF) spray process and subsequently heat treated at 800 C for 8h to simulate elevated temperature service conditions. The microstructures of powders and coatings were studied by SEM and X-ray diraction, and the hardnesses of coatings were probed by means of micro and nanoindentation. In addition, high stress abrasion resistance was tested in a temperature range from room temperature up to 800 C. The microstructural characterization of coatings Displays the presence of WC and core-rim structured Cr3C2 grains, wherein the rim contains tungsten. The coating hardness increases after the heat treatment, which stems from precipitation of secondary carbides and solid solution strengthening of binder by tungsten. In addition, the study reveals that both experimental coatings have high wear resistance at room and elevated temperatures

Underpinning data: High iso aldehyde selectivity in the hydroformylation of short-chain alkenes

NMR data

Inorganic double helices in semiconducting SnIP

Color drawing of Hattiesburg, MS courthouse, featuring Confederate monument; probably produced as promotional material for the Illinois Central Railroad Company\u27s Panama Limited servicehttps://egrove.olemiss.edu/rayburn/1245/thumbnail.jp