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Maliska, A.M.; Egert, Paola; Souza, A. R. de; Speller, C. V.; Klein, Aloı́sio Nelmo

doi:10.1023/a:1018670001929

Cited by 14 publications

(3 citation statements)

References 8 publications

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“…Here, the role of oxygen in the plasma ionization should be also considered. Being the oxygen a strong negative ion former [16,54], and hence an electron receptor, it tends to decrease the electron current density and the plasma ionization, causing an effect of temperature decrease [16,55]. Note that such effect is evidenced for the AS1 heating from ∼800 °C, and it is confirmed by the variation of electrical discharge parameters through the characteristics of the hollow cathode discharges, when compared to AS2 and AS3 (see figures 7-10 results).…”

Section: Electrical Discharge Parameters Variation and Hollow Cathode...mentioning

confidence: 62%

Surface state change influence’s theoretical approach of pressed iron on hollow cathode discharge characteristics: first results of plasma heating reproducibility for sintering purposes

Brunatto¹

2022

Surf. Topogr.: Metrol. Prop.

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In this work first results of the plasma heating process reproducibility for sintering purposes of pressed iron powder sample was investigated analyzing changes on the current-voltage characteristics of pulsed direct current (dc) Ar + H2 hollow cathode discharges sequentially carried out. For this purpose, the temperature of a sample acting as central cathode was varied by changing the switched-on time (duty cycle) of the pulse, via plasma species bombardment (ions and fast neutrals), which typically occurs in both cathode cylindrical surfaces that constitute the annular (hollow cathode) glow discharge, and measured by a thermocouple inserted in the central cathode sample holder. After two sequential plasma heating experiments, the third one practically reproduced the measured plasma parameters evidenced in the second heating, and the respective heating curves as a function of the time have led to similar current-voltage characteristics suggesting the iron sample sintering in non-isothermal way. Principles comprising plasma-surface interface and metallurgical-physical-chemical reactions, powder surface aspects, thermodynamic properties, metallurgical transformation of the pressed sample, and hollow cathode discharge properties are presented and discussed. The main points considered in the present approach are related to plasma (oxygen-affected plasma ionization, high ionization and excitation rate, and the intense light radiation of the annular glow discharge), thermodynamics (oxidation-reduction reactions, electron work function, sintering driving force, and surface energy), and powder (particle size distribution, morphology, specific surface, and iron recrystallization). To the best of the author's knowledge, it is the first time that it is brought to the light the changes on hollow cathode discharge characteristics while an iron sample acting as the central cathode of an annular glow discharge is subjected to distinct heating steps on the temperature range of 20 to ~1250 °C, leading it to have its sintering initiated.

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Section: Electrical Discharge Parameters Variation and Hollow Cathode...mentioning

confidence: 62%

Surface state change influence’s theoretical approach of pressed iron on hollow cathode discharge characteristics: first results of plasma heating reproducibility for sintering purposes

Brunatto¹

2022

Surf. Topogr.: Metrol. Prop.

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“…Moreover, the reduction of oxide phases and organic compound vaporization caused by both the ion bombardment and the presence of hydrogen reactive species tends to increase the amount of oxygen atoms of the plasma at the beginning of the heating process. Oxygen being a strong former of negative ions (Amemiya and Ogawa 1997), and hence an electron receptor, it tends to decrease the electron current density and the plasma ionization, causing an effect of temperature decrease (Maliska et al 1997). This partially explains why the sample heating efficiency dropped when the lowest flow was used.…”

Section: Evolution Of the Electrical Discharge Parameters In The Sint...mentioning

confidence: 99%

Influence of the gas mixture flow on the processing parameters of hollow cathode discharge iron sintering

Brunatto¹,

Muzart²

2007

J. Phys. D: Appl. Phys.

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A study was made to verify the influence of the gas mixture flow on the iron sintering process with simultaneous surface enrichment of alloying elements by hollow cathode discharge. In this process, two independent cathodes formed an annular discharge: (1) a pressed cylindrical sample of iron powder, acting as the central cathode, was placed concentrically inside an external (hollow) cathode; (2) the external cathode, machined from a AISI 310 steel bar, acted both to confine the geometry of the plasma and as a source of alloying elements (Cr and Ni). The sintering was carried out at 1423 K, for a period of 7.2 × 103 s, under a gas mixture of 80% Ar + 20% H2 and a pressure of 399 Pa, at flow rates of 2 × 10−6, 5 × 10−6, and 8 × 10−6 m3 s−1, with an inter-cathode radial space of 5.8 mm. The discharge was generated using a pulsed voltage power source with a 200 µs period. The gas mixture flow plays an important role both in the cleanliness of the sintering atmosphere (reflected in the electric power utilized to maintain the sample's temperature) and in the amount of metallic atoms deposited on the sample's surface (as a result of the sputtering and the oxidation/reduction process on the cathode surfaces).

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“…In addition to its environmental acceptability, plasma processes also make it possible to produce layers with specific structure and properties, which is a consequence of the large number of freely adjustable treatment parameters. [14][15][16] Besides nitriding duration and temperature, it is possible to independently adjust gas composition and pressure and various electrical parameters, such as current, voltage and pulse ratio. In the last few years, plasma treatments have been widely used for industrial applications.…”

Section: Introductionmentioning

confidence: 99%

Effect of nature of nitride phases on microabrasion of plasma nitrided sintered iron

Mello

Binder

et al. 2010

Tribology - Materials, Surfaces & Interfaces

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In the present investigation, the effect of plasma nitriding on the microabrasion behaviour of sintered unalloyed iron is investigated. Plasma nitriding was carried using two different sets of operative parameters in order to produce microstructures composed of different dominants iron nitrides, e.g. Fe 4 N (c9) and Fe 2-3 N (e), phases. Microabrasive wear tests were carried out in a 'free ball' microabrasion tester using SiC slurries. The tribological parameters were kept constant during the tests. The microstructures constituted of e-(Fe 2-3 N) phase presented a superior abrasion resistance.

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Untitled

Cited by 14 publications

References 8 publications

Surface state change influence’s theoretical approach of pressed iron on hollow cathode discharge characteristics: first results of plasma heating reproducibility for sintering purposes

Surface state change influence’s theoretical approach of pressed iron on hollow cathode discharge characteristics: first results of plasma heating reproducibility for sintering purposes

Influence of the gas mixture flow on the processing parameters of hollow cathode discharge iron sintering

Effect of nature of nitride phases on microabrasion of plasma nitrided sintered iron

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