Influence of the radial spacing between cathodes on the surface composition of iron samples sintered by hollow cathode electric discharge

Abstract

The present work reports an investigation of the influence of the radial spacing between cathodes on the iron sintering process by hollow cathode electrical discharge, with surface enrichment of the alloying elements Cr and Ni. Pressed cylindrical samples of 9.5 mm diameter and density of 7.0 ± 0.1 g/cm³ were prepared by compaction of Ancorsteel 1000C iron powder. These samples, constituting the central cathode, were positioned concentrically in the interior of an external cathode machined from a tube of stainless steel AISI 310 (containing: 25% Cr, 16% Ni, 1.5% Mn, 1.5% Si, 0.03% C and the remainder Fe). Sintering was done at 1150 °C, for 120 min, utilizing radial spacings between the central and hollow cathodes of 3, 6 and 9 mm and a gas mixture of 80% Ar and 20% H2, with a flow rate of 5 cm³/s at a pressure of 3 Torr. The electric discharge was generated using a pulsed voltage power source, with a period of 200 mus. The radial spacing had only a slight influence on the quantity of atoms of alloying elements deposited and diffused on the surface of the sample. Analysis with a microprobe showed the presence of chrome (up to 4.0%) and nickel (up to 3.0%, in at. %) at the surface of the samples. This surface enrichment can be attributed to the mechanism of sputtering of the metallic atoms present in the external cathode, with the deposition of these elements on the sample surface and consequent diffusion within the sample

Hollow cathode discharge: application of a deposition treatment in the iron sintering

“…Based on the characteristics of the hollow cathode (annular) discharge, two alternatives proved viable: (a) sintering metallic samples placed in the central cathode, and (b) altering their chemical ABCM surface composition using an outer hollow cathode with a different chemical composition (Brunatto et al, 2001).…”

“…The plasma-sintering chamber, comprising the anode, consisted of a stainless steel cylinder 350 mm in diameter and 380 mm in height. Detailed representation of the experimental apparatus is available in the earlier reports (Brunatto et al, 2001;2005).…”

Plasma assisted parts' manufacturing: sintering and surface texturing - part II - influence of inter-cathode distance and gas pressure

“…Two aspects were studied: a) the superficial pores' morphology modification in pressed samples processed by HCD, which could be explored as a new way to perform sintering and surface texturing treatments in cylindrical parts like axles, pins, and pivots presenting small diameters (the study of the chemical composition modification of the iron sample's surface is not considered here, since it is presented in previous work, Brunatto et al, 2001); and b) in the internal surface of the external cathode, which acts as a pipe (see Fig. 1), the mechanism of the metallic atoms deposition, altering its start chemical composition and the surface morphology via HCD, which could be explored as a new way to perform deposition and surface texturing treatments in pipes presenting small internal diameters.…”

“…Figure 1 shows an "in situ" view of the plant in use showing the hollow cathode discharge and both the cathodes. Detailed representation of the experimental apparatus is available in the earlier reports (Brunatto et al, 2001;. The discharge chamber consisted of a 350 mm diameter, 380 mm high stainless steel cylinder attached to steel plates and sealed with o-rings at both ends.…”

Study Of Erosion Rates And Surface Effects of Different Hollow Cathode Materials During Vacuum Microarc Discharge

“…Among the different fields of applications using plasma are: light sources, surface treatments, production of new materials, thin film technology, plasmochemistry, lasers, fuel for nuclear fusion, sintering of ceramic materials, fast switches and charged particle accelerators [1][2][3][4][5][6][7]. Among the different fields of applications using plasma are: light sources, surface treatments, production of new materials, thin film technology, plasmochemistry, lasers, fuel for nuclear fusion, sintering of ceramic materials, fast switches and charged particle accelerators [1][2][3][4][5][6][7].…”