The grain size of coated cemented carbide tools may significantly affect the tool life by influencing either the coating adhesion to the substrate or the coating growth during deposition. In the ...present study three variously grained cemented carbides were coated with two different PVD films. Various pre‐ and post‐treatments were applied, while their effect on the films' mechanical properties and adhesion was assessed by nanoindentations and inclined impact tests. The coatings deposited on ultra‐fine‐grained substrates exhibited the highest mechanical properties overall. The research revealed elevated adhesive properties for the fine‐grained substrate compared to the normal and ultra‐fine‐grained one. The film adhesion of normal and fine‐grained substrate can be further enhanced through micro‐blasting. Post‐treatments of the coatings were beneficial in all substrate cases, as brushing of the film surface removed droplets while at the same time inducing surface residual stresses at the coating resulting in a hardness increase.
Die Karbidkorngröße von beschichteten Hartmetallwerkzeugen kann die Schichthaftung und das Schichtwachstum maßgeblich beeinflussen und dadurch die Werkzeugstandzeit bestimmen. In der vorliegenden Studie wurden drei Hartmetallsubstrate mit verschiedenen Korngrößen, die mit zwei PVD‐Schichten beschichtet wurden, untersucht. Der Einfluss unterschiedlicher Vor‐ und Nachbehandlungen auf die mechanischen Eigenschaften der Beschichtung sowie auf die Schichthaftung wurde mit Hilfe von Nanoindenter‐Untersuchungen und Impact‐Tests beurteilt. Die Hartstoffschichten die auf Ultrafeinkorn‐Sorten (UF) abgeschieden wurden, wiesen insgesamt die höchsten mechanischen Eigenschaften auf. Darüber hinaus zeigten die Versuchsergebnisse eine verbesserte Schichthaftung bei der Feinstkorn‐Sorte (F) gegenüber den Feinkorn‐ (N) und Ultrafeinkorn‐Sorten. Die Schichthaftung könnte bei fein‐ und feinstkörnigen Hartmetallsubstraten durch eine Mikrostrahlbehandlung mit Festkörpern angepasst werden. Nachbehandlungen der beschichteten Substrate mittels Bürsten waren vorteilhaft für alle unterschiedlichen Substrate. Dies ist sowohl auf die Entfernung von Droplets aus der Schichtoberfläche als auch auf die Induzierung von Druckeigenspannungen zurückzuführen.
Danas je kalcijev karbid, CaC2, sporedni produkt, no u prošlom je stoljeću bio glavni proizvod bazne kemijske industrije. U radu je prikazano njegovo otkriće, početak proizvodnje na prijelazu 19. u ...20. stoljeće te primjene. Poseban je naglasak dan na povijest dviju hrvatskih tvornica za proizvodnju kalcijeva karbida i cijanamida, prve u Dugom Ratu pokraj Splita od 1914. do 1979. i druge, u Skradinu i Šibeniku, od 1897. do 1945. Ukazano je i na svjetske ekološke probleme proizvodnje kalcijeva karbida i drugih proizvoda dobivenih iz kalcijeva karbida, emisiju ugljikova dioksida te onečišćenje okoliša živom (masovno trovanje u zaljevu Minamata, Japan).
Ovo djelo je dano na korištenje pod licencom Creative Commons Imenovanje 4.0 međunarodna .
The formation and dissolution of aluminum carbide is considered the primary factor affecting the life of aluminum electrolysis cells. Herein, the characteristics of sodium-graphite intercalation ...compounds (Na-GICs) were measured and the formation mechanism of Al4C3 during the aluminum electrolysis process was experimentally studied. The Na-GIC characteristics and the products of aluminum and Na-GIC reactions were investigated by Raman spectroscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy. The results showed that graphite can react with the sodium metal to form Na-GICs, which were detectable by Raman spectroscopy. Sodium inserted into the graphite layered structure acted as an intercalation agent to change the original graphite layered structure and increase the volume and specific surface area of graphite. Further, Al4C3 was produced by using sodium-graphite intercalation compounds and aluminum as materials. Thus, the presence of sodium plays an important role in the formation process of Al4C3 in aluminum electrolysis cells.
A new technique with carburization followed by magnetic separation is presented for the preparation of high-grade iron carbide from pyrite cinder to promote the high value-added utilization of pyrite ...cinder. The effects of carburizing temperature, carburizing time and Na2SO4 dosage on carburized pellets were investigated, and the effects of Na2SO4 dosage and grinding fineness on magnetic concentrate were carried out. The optimized process parameters were proposed as follows: carburizing at 650?C for 180 minutes in CO-CO2-H2 gas mixtures, Na2SO4 dosage of 9%, magnetic field intensity of 130 mT, and grinding fineness of 92.25% powder passing 0.025mm. The iron content, total carbon content, total iron and carbon content of magnetic concentrate were 82.62%, 5.60%, and 88.22%, respectively. The recovery rate of iron reached 88.67%. The behaviors and mechanisms of carburization, separation, and Na2SO4, were ascertained with optical microscopy, X-ray powder diffraction (XRD), and scanning electron microscope (SEM).
nema
Analysis of the tool work and refusals when heavy machines cutting shows the necessity to use methods of bulk modification for improving structural strength and fracture resistance of cemented ...carbide cutting plates. It is suggested to test cutting plates to assess the structural strength limit. The accelerated method to estimate theresistancetoscatteredcontactdamage and chipping resistance is developed.It is obtained that the pulsed magnetic field treatment(PMNF) of cutting plates (85% WoC,5% TiC, 10% Co) leads to a dependent on treatment regime increase in structural bending strength limit under static load. The PMTF allows increasing theresistancetoscatteredcontactdamage and chipping resistancefor cutting plates (92% WoC, 8% Co).It is shown thatphysical method of pulsed magnetic field treatment is promising for modification of tool materials
Stähle wie X40CrMnN18-18 mit ≈ 0,6 Masse-% Stickstoff erreichen eine hohe Streckgrenze und Kaltverfestigung, neigen aber in dickeren Bauteilen zu unerwünschten Karbid- oder Nitridausscheidungen beim ...Abschrecken von Lösungsglühtemperatur. Durch Berechnung eines optimalen Verhältnisses (C/N)
gelingt es, das Phasenfeld des homogenen Austenits zu tieferer Temperatur T
zu erweitern, wodurch die Ausscheidung in einen kälteren Bereich verschoben und damit verzögert wird. Durch Zusatz von Kupfer steigt T
deutlich an, während Molybdän diese Temperatur kaum beeinflusst. Seinem Gehalt sind aber Grenzen durch die Stabilisierung der σ-Phase gesetzt. Von 0,85 Masse-% (C+N) bis 1,07 Masse-% (C+N) nimmt die 0,2 % Dehngrenze von 561 MPa auf 604 MPa zu und die wahre Bruchspannung von 2020 MPa auf 2545 MPa bei einer Bruchdehnung von 67% bis 74%. Die Berechnung der Konstitution legt nahe, wegen möglicher Ausscheidungen beim Abschrecken den (C+N)-Gehalt und damit die erzielbare Festigkeit zu senken, wenn die Bauteildicke steigt.
Metal dusting of iron proceeds via the formation and disintegration of the metastable carbide Fe3C, and the resulting fine Fe particles in the coke further catalyse carbon deposition. By contrast, ...nickel disintegrates directly, and larger grains are released. As revealed by TEM and AEM techniques, in both cases the disintegration proceeds by inward growth of thin graphite filaments, the atomic basal planes of which being oriented perpendicular to the surface thus effecting a high reactivity at the growth front.
Consequently, successive alloying of iron with nickel should lead to a change over from one disintegration mechanism to the other, and, in fact, we could evidence that the carbide formation takes place only up to a nickel content of about 5 wt.%. Already at a Ni concentration of 10 wt.% a direct disintegration of the metal proceeds, as it is typical for pure nickel. Furthermore, in all investigated Ni‐Fe alloys a surface‐near enrichment of Ni was observed which indicates a selective corrosion of Fe, decreasing with increasing Ni content of the basic alloy.
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