Rapid discharge sintering of nickel–diamond metal matrix composites

Abstract

Publication information Journal of Materials Processing Technology, 211 (7): 1210-1216Publisher Elsevier Item record/more information http://hdl.handle.net/10197/5260 Publisher's statementThis is the author's version of a work that was accepted for publication in Journal of Materials Processing Technology. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published in Journal of Materials Processing Technology, 211 (7) AbstractThere is considerable interest in processing technologies which can lead to more energy efficient sintering of abrasive metal matrix composites. In this study the use of a novel microwave plasma processing technique called Rapid Discharge Sintering (RDS) for sintering nickel-diamond metal matrix composites (MMCs) is evaluated. Nickel-diamond powder composites (80 -20 % by weight respectively) were uniaxially pressed into 20 mm discs at compaction pressures of 100, 200 and 300 MPa. The discs were sintered using a microwave plasma formed with hydrogen and hydrogen/nitrogen as the discharge gases. For comparison, discs were also sintered using a tube furnace in a gas flow of hydrogen and nitrogen (3:1). Discs pressed to 300 MPa were treated at both 850 and 1000 o C. The properties of the sintered nickel-diamond composites were characterised using density, flexural stress, hardness, wear resistance, SEM and XRD. The RDS samples sintered at 1000 o C achieved the maximum disc strength of approximately 470 MPa within a 20 minute chamber processing time, compared with 6 hours for furnace sintered samples. RDS samples exhibited increased hardness values and a finer nickel matrix over furnace sintered samples. RDS has shown the ability to process nickel-diamond MMCs without oxidation or graphitisation at higher temperatures. As a result, minimal diamond destruction was observed during abrasive wear testing for RDS samples.

Fabrication of Efficient NiO Photocathodes Prepared via RDS with Novel Routes of Substrate Processing for p‐Type Dye‐Sensitized Solar Cells

“…We believe that this is because the charge transfer through the NiO film and the charge collection at the TCS/NiO film interface were the most efficient with this sample. [27,28] Experimental Section provement in the photoelectrochemical performance of p-type electrodes.…”

“…[25,26] Finally, microwave thermal treatments can easily be combined with plasma to achieve the uniform heating of coatings on large-area substrates. [27,28] Experimental Section…”

Influence of Gas Type on the Thermal Efficiency of Microwave Plasmas for the Sintering of Metal Powders

“…Rapid Discharge Sintering process was carried out using a circumferential antenna plasma (CAP) as described in detail previously [9,18]. The system shown in figure Error!…”

“…This may be due to the focal area of the pyrometer, which can detect a large area both on the surface and the surrounding colder regions, which may lead to a small reduction in the recorded temperatures. Overall a balance between the volumetric heating of the microwaves and the convective heating associated with the plasma would lead to an overall homogeneous heating profile, as illustrated by the combined thermocouple and pyrometer readings [9,25].…”

“…The use of plasma treatments such as radio frequency [6] and DC sources [7] both exhibit considerable potential in this regard as they offer a more homogeneous localised treatment for the sintering of metal powders. The microwave plasma technique has also been shown to exhibit considerable potential [8] and we have previously described the sintering process as rapid discharge sintering (RDS) [9]. During the RDS process gas molecules become excited by the microwaves and a plasma is formed, this in turn heats the material placed inside a plasma ball.…”