Plasma source ion carburizing of steel for improved wear resistance

Abstract

Plasma source ion carburizing is a low-temperature, low-pressure carburizing approach for improved wear resistance of steel with specific advantages over plasma carburizing and plasma source carbon ion implantation. A carburizing apparatus based on an electron cyclotron resonance (ECR) microwave plasma source has been developed. Carbon (as methane and hydrogen) ions are accelerated from the ECR plasma by a low-pulsed negative bias (typically −2 kV), which is applied directly to the sample, implanted, and are finally diffused into the steel at elevated temperatures that are regulated up to 550 °C by an auxiliary heater. Plasma source ion carburizing into pure iron and 35CrMo low alloy steel at a process temperature of 350 °C has been investigated. The carburized samples were characterized using Auger electron spectroscopy, electron probe microanalysis, microhardness measurement, and glancing incidence x-ray diffraction. Significant increases in microhardness have been observed on the carburized pure iron and 35CrMo steel, because of 10 μm thick carburized layers composing a Fe3C phase on the outer surface and a hardened diffusion zone in the matrix that were formed after the carburizing at 350 °C for 8 h. The wear tests were performed on a crank/connecting rod reciprocating tribometer in a flat-on-flat configuration. The test results indicate that the carburized 35CrMo steel improved the abrasive wear resistance and decreased the coefficient of friction in comparison with the uncarburized steel.